Hemodynamic response to the upright posture

Facilitating ambulatory heart rate variability analysis using accelerometry-based classifications of body position and self-reported sleep

Objective.This study aimed to examine differences in heart rate variability (HRV) across accelerometer-derived position, self-reported sleep, and different summary measures (sleep, 24 h HRV) in free-living settings using open-source methodology.Approach.HRV is a biomarker of autonomic activity. As it is strongly affected by factors such as physical behaviour, stress, and sleep, ambulatory HRV analysis is challenging. Beat-to-beat heart rate (HR) and accelerometry data were collected using single-lead electrocardiography and trunk- and thigh-worn accelerometers among 160 adults participating in the SCREENS trial. HR files were processed and analysed in the RHRV R package. Start time and duration spent in physical behaviours were extracted, and time and frequency analysis for each episode was performed. Differences in HRV estimates across activities were compared using linear mixed models adjusted for age and sex with subject ID as random effect. Next, repeated-measures Bland-Altman analysis was used to compare 24 h RMSSD estimates to HRV during self-reported sleep. Sensitivity analyses evaluated the accuracy of the methodology, and the approach of employing accelerometer-determined episodes to examine activity-independent HRV was described.Main results.HRV was estimated for 31 289 episodes in 160 individuals (53.1% female) at a mean age of 41.4 years. Significant differences in HR and most markers of HRV were found across positions [Mean differences RMSSD: Sitting (Reference) - Standing (-2.63 ms) or Lying (4.53 ms)]. Moreover, ambulatory HRV differed significantly across sleep status, and poor agreement between 24 h estimates compared to sleep HRV was detected. Sensitivity analyses confirmed that removing the first and last 30 s of accelerometry-determined HR episodes was an accurate strategy to account for orthostatic effects.Significance.Ambulatory HRV differed significantly across accelerometry-assigned positions and sleep. The proposed approach for free-living HRV analysis may be an effective strategy to remove confounding by physical activity when the aim is to monitor general autonomic stress.

Heart Rate Variability and Pulse Rate Variability: Do Anatomical Location and Sampling Rate Matter?

Wearable technology and neuroimaging equipment using photoplethysmography (PPG) have become increasingly popularized in recent years. Several investigations deriving pulse rate variability (PRV) from PPG have demonstrated that a slight bias exists compared to concurrent heart rate variability (HRV) estimates. PPG devices commonly sample at ~20-100 Hz, where the minimum sampling frequency to derive valid PRV metrics is unknown. Further, due to different autonomic innervation, it is unknown if PRV metrics are harmonious between the cerebral and peripheral vasculature. Cardiac activity via electrocardiography (ECG) and PPG were obtained concurrently in 54 participants (29 females) in an upright orthostatic position. PPG data were collected at three anatomical locations: left third phalanx, middle cerebral artery, and posterior cerebral artery using a Finapres NOVA device and transcranial Doppler ultrasound. Data were sampled for five minutes at 1000 Hz and downsampled to frequencies ranging from 20 to 500 Hz. HRV (via ECG) and PRV (via PPG) were quantified and compared at 1000 Hz using Bland-Altman plots and coefficient of variation (CoV). A sampling frequency of ~100-200 Hz was required to produce PRV metrics with a bias of less than 2%, while a sampling rate of ~40-50 Hz elicited a bias smaller than 20%. At 1000 Hz, time- and frequency-domain PRV measures were slightly elevated compared to those derived from HRV (mean bias: ~1-8%). In conjunction with previous reports, PRV and HRV were not surrogate biomarkers due to the different nature of the collected waveforms. Nevertheless, PRV estimates displayed greater validity at a lower sampling rate compared to HRV estimates.

Influence of age on the relation between body position and noninvasively acquired intracranial pulse waves

The capacitive measurement of the head's dielectric properties has been recently proposed as a noninvasive method for deriving surrogates of craniospinal compliance (CC), a parameter used in the evaluation of space-occupying neurological disorders. With the higher prevalence of such disorders in the older compared to the younger population, data on the head's dielectric properties of older healthy individuals would be of particularly high value before assessing pathologic changes. However, so far only measurements on young volunteers (< 30 years) were reported. In the present study, we have investigated the capacitively obtained electric signal known as W in older healthy individuals. Thirteen healthy subjects aged > 60 years were included in the study. W was acquired in the resting state (supine horizontal position), and during head-up and head-down tilting. AMP, the peak-to-valley amplitude of W related to cardiac action, was extracted from W. AMP was higher in this older cohort compared to the previously investigated younger one (0°: 5965 ± 1677 arbitrary units (au)). During head-up tilting, AMP decreased (+ 60°: 4446 ± 1620 au, P < 0.001), whereas it increased during head-down tilting (- 30°: 7600 ± 2123 au, P < 0.001), as also observed in the younger cohort. Our observation that AMP, a metric potentially reflective of CC, is higher in the older compared to the younger cohort aligns with the expected decrease of CC with age. Furthermore, the robustness of AMP is reinforced by the consistent relative changes observed during tilt testing in both cohorts.

Orthostatic Hypotension in Adults With Hypertension: A Scientific Statement From the American Heart Association

Although orthostatic hypotension (OH) has long been recognized as a manifestation of autonomic dysfunction, a growing body of literature has identified OH as a common comorbidity of hypertension. This connection is complex, related to pathophysiology in blood pressure regulation and the manner by which OH is derived as the difference between 2 blood pressure measurements. While traditional therapeutic approaches to OH among patients with neurodegenerative disorders focus on increasing upright blood pressure to prevent cerebral hypoperfusion, the management of OH among patients with hypertension is more nuanced; resting hypertension is itself associated with adverse outcomes among these patients. Although there is substantial evidence that intensive blood pressure treatment does not cause OH in the majority of patients with essential hypertension, some classes of antihypertensive agents may unmask OH in patients with an underlying autonomic impairment. Practical steps to manage OH among adults with hypertension start with (1) a thorough characterization of its patterns, triggers, and cause; (2) review and removal of aggravating factors (often pharmacological agents not related to hypertension treatment); (3) optimization of an antihypertensive regimen; and (4) adoption of a tailored treatment strategy that avoids exacerbating hypertension. These strategies include countermaneuvers and short-acting vasoactive agents (midodrine, droxidopa). Ultimately, further research is needed on the epidemiology of OH, the impact of hypertension treatment on OH, approaches to the screening and diagnosis of OH, and OH treatment among adults with hypertension to improve the care of these patients and their complex blood pressure pathophysiology.

Haemodynamic Parameters Underlying the Relationship between Sarcopenia and Blood Pressure Recovery on Standing

BACKGROUND

Sarcopenia, delayed blood pressure (BP) recovery following standing, and orthostatic hypotension (OH) pose significant clinical challenges associated with ageing. While prior studies have established a link between sarcopenia and impaired BP recovery and OH, the underlying haemodynamic mechanisms remain unclear.

METHODS

We enrolled 107 participants aged 50 and above from a falls and syncope clinic, conducting an active stand test with continuous non-invasive haemodynamic measurements. Hand grip strength and five-chair stand time were evaluated, and muscle mass was estimated using bioelectrical impedance analysis. Participants were categorised as non-sarcopenic or sarcopenic. Employing mixed-effects linear regression, we modelled the effect of sarcopenia on mean arterial pressure and heart rate after standing, as well as Modelflow®-derived parameters such as cardiac output, total peripheral resistance, and stroke volume, while adjusting for potential confounders.

RESULTS

Sarcopenia was associated with diminished recovery of mean arterial pressure during the 10-20 s period post-standing (β -0.67, p < 0.001). It also resulted in a reduced ascent to peak (0-10 s) and recovery from peak (10-20 s) of cardiac output (β -0.05, p < 0.001; β 0.06, p < 0.001). Furthermore, sarcopenia was associated with attenuated recovery (10-20 s) of total peripheral resistance from nadir (β -0.02, p < 0.001) and diminished recovery from peak (10-20 s) of stroke volume (β 0.54, p < 0.001). Notably, heart rate did not exhibit a significant association with sarcopenia status at any time interval post-standing.

CONCLUSION

The compromised BP recovery observed in sarcopenia appears to be driven by an initial reduction in the peak of cardiac output, followed by attenuated recovery of cardiac output from its peak and total peripheral resistance from its nadir. This cardiac output finding seems to be influenced by stroke volume rather than heart rate. Possible mechanisms for these findings include cardio-sarcopenia, the impact of sarcopenia on the autonomic nervous system, and/or the skeletal muscle pump.

Influence of sex on the reliability of cerebral blood velocity regulation during lower body negative pressure and supine cycling with considerations of the menstrual cycle

Objective.To evaluate sex differences in the reliability of absolute and relative cerebral blood velocity (CBv) during concurrent supine cycling with lower body negative pressure (LBNP).Approach. A total of 19 participants (11 females; aged 20-33 years) completed five testing sessions, occurring on 7 d intervals. Visit 1 was a maximal-ramp-cycle test to ascertain peak CBv wattage. During visits 2-5, supine cycling protocol occurred at individualized peak CBv wattages with progressive decreases in LBNP from 0 to -20, -40, -60, -70, and -80 Torr. Menstrual cycle day was self-reported via the Rhinessa Women's Questionnaire. Transcranial Doppler ultrasound insonated bilateral middle cerebral artery velocity (MCAv). Two-way ANOVA assessed potential day- and sex-differences at each LBNP stage. Reliability was determined using intraclass correlation coefficients (ICC) and coefficient of variation (CoV).Main results. For all physiological measures, no main-effects were present for day- or interaction-terms (p> 0.067; negligible-to-small effect sizes), while sex differences were noted for MCAv, blood pressure, and heart rate (p< 0.046). Across visits, males and females displayed excellent and good-to-excellent levels of reliability for MCAv metrics, respectively (ICC range: 0.745-0.999; CoV range: 0.33%-9.90%).Significance. During the current investigation, both relative and absolute CBv demonstrated high reliability in both male and female participants during a supine LBNP cycling protocol. An exploratory analysis revealed increased variance was found in female participants dependent on contraceptive use. Despite this, results indicate future LBNP studies may include females at any menstrual cycle stage.

Preclinical Orthostatic Abnormalities May Predict Early Increase in Vascular Stiffness in Different Age Groups: A Pilot Study

Clinical orthostatic hypotension (OH) and hypertension (OHT) are risk factors for arterial hypertension (AH) and cardiovascular diseases (CVD) and are associated with increased vascular stiffness. Preclinical OH and OHT are poorly understood. The main objective was to investigate preclinical orthostatic abnormalities and their association with increased vascular stiffness in different age groups of adults. A specially designed head-up tilt test standardized for hydrostatic column height was used to detect them. Three age groups of clinically healthy subjects were examined. In the group of young adults up to 30 years old, a significant predominance of orthostatic normotension (ONT) and an insignificant number of subjects with preclinical OH and OHT were found. In the age group over 45 years, compared to the group under 30 years, there was a twofold decrease in the proportion of individuals with ONT and a significant increase with preclinical OH and OHT. In all age groups, there was a significant orthostatic increase in vascular stiffness (as measured by the brachial-ankle pulse wave velocity (baPWV), which was recovered to the baseline level when returning to the supine position. Overall, subjects with preclinical OH and OHT had significantly higher baPWV values compared to those with ONT (p = 0.001 and p = 0.002, respectively), with all subjects having vascular stiffness values within normal age-related values.

Cardiovascular Autonomic Function and Incident Chronic Obstructive Pulmonary Disease Hospitalizations in Atherosclerosis Risk in Communities

Rationale: The autonomic nervous system extensively innervates the lungs, but its role in chronic obstructive pulmonary disease (COPD) outcomes has not been well studied. Objective: We assessed relationships between cardiovascular autonomic nervous system measures (heart rate variability [HRV] and orthostatic hypotension [OH]) and incident COPD hospitalization in the multicenter ARIC (Atherosclerosis Risk In Communities) study. Methods: We used Cox proportional hazards regression models to estimate hazard ratios and 95% confidence intervals between baseline (1987-1989) autonomic function measures (HRV measures from 2-minute electrocardiograms and OH variables) and incident COPD hospitalizations through 2019. Adjusted analyses included demographic data, smoking status, lung function, comorbidities, and physical activity. We also performed analyses stratified by baseline airflow obstruction. Results: Of the 11,625 participants, (mean age, 53.8 yr), 56.5% were female and 26.3% identified as Black. Baseline mean percentage predicted forced expiratory volume in 1 second was 94 ± 17% (standard deviation), and 2,599 participants (22.4%) had airflow obstruction. During a median follow-up time of 26.9 years, there were 2,406 incident COPD hospitalizations. Higher HRV (i.e., better autonomic function) was associated with a lower risk of incident COPD hospitalization. Markers of worse autonomic function (OH and greater orthostatic changes in systolic and diastolic blood pressure) were associated with a higher risk of incident COPD hospitalization (hazard ratio for the presence of OH, 1.5; 95% confidence interval, 1.25-1.92). In stratified analyses, results were more robust in participants without airflow obstruction at baseline. Conclusions: In this large multicenter prospective community cohort, better cardiovascular autonomic function at baseline was associated with a lower risk of subsequent hospitalization for COPD, particularly among participants without evidence of lung disease at baseline.

Influence of head-over-body and body-over-head posture on craniospinal, vascular, and abdominal pressures in an acute ovine in-vivo model

INTRODUCTION

Optimal shunt-based hydrocephalus treatments are heavily influenced by dynamic pressure behaviors between proximal and distal ends of shunt catheters. Posture-dependent craniospinal, arterial, venous, and abdominal dynamics thereby play an essential role.

METHODS

An in-vivo ovine trial (n = 6) was conducted to evaluate communication between craniospinal, arterial, venous, and abdominal dynamics. Tilt-testing was performed between -13° and + 13° at 10-min intervals starting and ending at 0° prone position. Mean pressure, pulse pressure, and Pearson correlation (r) to the respective angle were calculated. Correlations are defined as strong: |r|≥ 0.7, mild: 0.3 <|r|< 0.7, and weak: |r|≤ 0.3. Transfer functions (TFs) between the arterial and adjacent compartments were derived.

RESULTS

Strong correlations were observed between posture and: mean carotid/femoral arterial (r = - 0.97, r = - 0.87), intracranial, intrathecal (r = - 0.98, r = 0.94), jugular (r = - 0.95), abdominal cranial, dorsal, caudal, and intravesical pressure (r = - 0.83, r = 0.84, r = - 0.73, r = 0.99) while mildly positive correlation exists between tilt and central venous pressure (r = 0.65). Only dorsal abdominal pulse pressure yielded a significant correlation to tilt (r = 0.21). TFs followed general lowpass behaviors with resonant peaks at 4.2 ± 0.4 and 11.5 ± 1.5 Hz followed by a mean roll-off of - 15.9 ± 6.0 dB/decade.

CONCLUSIONS

Tilt-tests with multi-compartmental recordings help elucidate craniospinal, arterial, venous, and abdominal dynamics, which is essential to optimize shunt-based therapy. Results motivate hydrostatic influences on mean pressure, with all pressures correlating to posture, with little influence on pulse pressure. TF results quantify the craniospinal, arterial, venous, and abdominal compartments as compliant systems and help pave the road for better quantitative models of the interaction between the craniospinal and adjacent spaces.

The impact of upright posture on left ventricular deformation in athletes

Besides LV ejection fraction (LVEF), global longitudinal strain (GLS) and global myocardial work index (GWI) are increasingly important for the echocardiographic assessment of left ventricular (LV) function in athletes. Since exercise testing is frequently performed on a treadmill, we investigated the impact of upright posture on GLS and GWI. In 50 male athletes (mean age 25.7 ± 7.3 years) transthoracic echocardiography (TTE) and simultaneous blood pressure measurements were performed in upright and left lateral position. LVEF (59.7 ± 5.3% vs. 61.1 ± 5.5%; P = 0.197) was not affected by athletes' position, whereas GLS (- 11.9 ± 2.3% vs. - 18.1 ± 2.1%; P < 0.001) and GWI (1284 ± 283 mmHg% vs. 1882 ± 247 mmHg%; P < 0.001) were lower in upright posture. Longitudinal strain was most frequently reduced in upright posture in the mid-basal inferior, and/or posterolateral segments. Upright posture has a significant impact on LV deformation with lower GLS, GWI and regional LV strain in upright position. These findings need to be considered when performing echocardiography in athletes.

Adverse childhood experiences are associated with altered cardiovascular reactivity to head-up tilt in young adults

Adverse childhood experiences (ACEs) are associated with greater prevalence of cardiovascular disease and altered acute stress reactivity. The current study investigated the effect of ACEs on hemodynamic and autonomic responses to orthostatic stress imposed by 60° head-up tilt (HUT) in young adults. Two-hundred twenty-six healthy young adults (age = 22.6 ± 1.5 yr; n = 116 females) without cardiovascular disease participated and had complete data. Participants underwent supine blood pressure (BP), R-R interval (RRI), cardiac output (CO), total peripheral resistance (TPR), and cardiovagal baroreflex sensitivity (cvBRS) testing followed by a transition to 60° HUT where measures were reassessed. Childhood adversity exposures were assessed based on categorical exposure and nonexposure to childhood household dysfunction and maltreatment, and <4 and ≥4 types of ACEs. Significantly greater increases in SBP (P < 0.05), DBP, MAP, and TPR (P < 0.01; all) following 60° HUT were observed in individuals with ≥4 compared with those with <4 types of ACEs. Attenuated decreases in RRI and cvBRS were observed in those with ≥4 types of ACEs (P < 0.05). Experiencing ≥4 types of ACEs was associated with augmented BP and TPR reactivity and a blunted decrease in cvBRS in response to 60° HUT in young adults. Results suggest that a reduced vagal response to orthostatic stress is present in those who have experienced ≥4 types of ACEs that may promote autonomic dysfunction. Future research examining the sympathetic and vagal baroreflex branches is warranted.

Validity and reliability of capillary vs. Venous blood for the assessment of haemoglobin mass and intravascular volumes

Objectives: Haemoglobin mass (Hbmass) assessment with the carbon monoxide rebreathing method is a more accurate estimate than other measures of oxygen-carrying capacity. Blood may be collected by several means and differences in the measured variables may exist as a result. The present study assessed the validity and reliability of calculated Hbmass and intravascular volumes obtained from capillary blood (CAP) when compared to venous blood (VEN) draws. Methods: Twenty-two adults performed a carbon monoxide rebreathing procedure with paired VEN and CAP draws at baseline, pre-rebreathing and post-rebreathing (POST). Thirteen of these participants performed this protocol on two occasions to assess the data reliability from both blood sampling sites. In a second experiment, 14 adults performed a 20-min seated and a 20-min supine rest to assess for the effect of posture on haematological parameters. Results: Haemoglobin mass (CAP = 948.8 ± 156.8 g; VEN = 943.4 ± 157.3 g, p = 0.108) and intravascular volume (CAP = 6.5 ± 1 L; VEN = 6.5 ± 0.9 L, p = 0.752) were statistically indifferent, had low bias (Hbmass bias = 14.45 ± 40.42 g, LoA -64.78 g-93.67 g) and were highly correlated between sampling techniques. Reliability analysis demonstrated no difference in the mean change in variables calculated from both sampling sites and good to excellent intraclass correlation coefficients (>0.700), however, typical measurement error was larger in variables measured using CAP (VEN Hbmass TE% = 2.1%, CAP Hbmass TE% = 5.5%). The results indicate that a supine rest prior to the rebreathing protocol would have a significant effect on haemoglobin concentration and haematocrit values compared to a seated rest, with no effect on carboxyhaemoglobin %. Conclusion: The present study demonstrates that CAP and VEN were comparable for the calculation of Hbmass and intravascular volumes in terms of accuracy. However, reduced reliability and increased error in the CAP variables indicates that there are methodological considerations to address when deciding which blood drawing technique to utilise. To reduce this CAP error, increased replicate analyses are required.

Awareness of postural orthostatic tachycardia syndrome is required in adolescent syncope

We investigated head-up tilt test (HUTT) results across age-groups in syncope/presyncope patients to establish pediatric postural orthostatic tachycardia syndrome (POTS) characteristics. We retrospectively reviewed syncope patients' medical records. Adolescents were defined as 10 to 19 years old, adults as 20 to 59 years old, and older individuals as ≥60 years old. From HUTT results, we determined POTS prevalence and differences among the age-groups. We included 147 adolescents, 269 adults, and 123 older patients. Seventy (13.0%) patients (61.4% females; median age: 20 [17-25] years) were diagnosed with POTS. The syndrome was more prevalent among adolescents (33 [22.4%]) than adults (37 [13.8%]), and was absent among older individuals. Affected adolescents had significantly lower resting diastolic blood pressure (DBP) and heart rate (HR), and converted to maximum HR more rapidly than adolescents without the syndrome during the passive phase. Adolescents with POTS demonstrated several unique characteristics compared to adults with and adolescents without this syndrome. POTS may be underrecognized among syncope and presyncope patients, among which 22.4% of adolescents were diagnosed with the syndrome. POTS should be considered when evaluating syncope patients.

Relations of postural change in blood pressure with hypertension-mediated organ damage in middle-aged adults of the Framingham heart study: A cross-sectional study

Background

Dysregulation of compensatory mechanisms to regulate blood pressure (BP) upon postural change is a phenotype of BP variability and an emerging risk factor for cardiovascular outcomes.

Materials and methods

We assessed postural change in BP (starting 2 min after standing from a supine position), carotid-femoral pulse wave velocity (cfPWV), and markers of hypertension-mediated organ damage (HMOD) in the heart, kidney, and brain in Framingham Third Generation, Omni-2, and New Offspring Spouse Cohort participants. We related vascular measures (postural change in BP measures and cfPWV) with HMOD in 3,495 participants (mean age 47 years, 53% women) using multivariable logistic and linear regression models.

Results

In multivariable-adjusted models, we did not observe significant associations of vascular measures with presence of left ventricular hypertrophy, albuminuria, covert brain infarcts, or white matter hyperintensities (Bonferroni-adjusted P-values > 0.05/20 > 0.0025). In multivariable models, greater cfPWV (est. β = 0.11 ± 0.03; P < 0.001), but not postural change in BP measures (Bonferroni-adjusted P-values > 0.05/20 > 0.0025), was associated with higher white matter free water using brain magnetic resonance imaging. In multivariable models, greater postural change in pulse pressure was associated with higher urinary albumin-creatinine ratio (est. β = 0.07 ± 0.02; P < 0.001). No other postural change in BP measure was associated with urinary albumin-creatinine ratio (Bonferroni-adjusted P-values > 0.05/20 > 0.0025). In sex-specific analyses, higher cfPWV was associated with higher urinary albumin-creatinine ratio in men (est. β: 0.11 ± 0.04; P = 0.002) but not in women (est. β: 0.03 ± 0.03; P = 0.44). We also observed marginal to strong effect modification by above vs. at/below median postural change in BP for the association of cfPWV with urinary albumin-creatinine ratio (Bonferroni-adjusted interaction P < 0.001-0.01). Vascular measures were not related to left ventricular mass index or fractional anisotropy (Bonferroni-adjusted P-values > 0.05/20 > 0.0025).

Conclusion

Baroreflex dysfunction is associated with greater subclinical kidney damage. Additionally, relations of higher aortic stiffness with greater kidney damage may be modified by associated baroreflex dysregulation.

Association of general and abdominal adiposity with postural changes in systolic blood pressure: results from the NAKO pretest and MetScan studies

The association between anthropometric measurements and postural changes in systolic blood pressure (SBP) has not been frequently reported. This study aimed to investigate the association of body mass index (BMI) and waist circumference (WC) with postural changes in SBP in two German cross-sectional studies. Data were derived from 506 participants of the population-based German National Cohort (NAKO) pretest and from 511 participants of the convenience sample-based MetScan studies. Linear regression models were used to estimate the association between BMI and WC with the difference between standing and sitting SBP (dSBP). Odds ratios (ORs) for an increase (dSBP > 10 mmHg) or decrease (dSBP ≤ -10 mmHg) in dSBP were calculated using logistic regression. The results were pooled by meta-analysis using an inverse variance model. In pooled analysis, a 5 kg/m² higher BMI was associated with a 1.46 mmHg (95% confidence interval (CI) 0.98-1.94) higher dSBP, while a 5 cm higher WC was associated with a 0.51 mmHg (95% CI 0.32-0.69) higher dSBP. BMI or WC were associated with a higher odds of an increase in dSBP (adjusted OR, 1.71; 95% CI 1.36-2.14 per 5 kg/m² higher BMI and 1.22; 95% CI 1.05-1.40 per 5 cm higher WC) but with a reduced odds of a decline in dSBP (adjusted OR, 0.67; 95% CI 0.44-1.00 per 5 kg/m² higher BMI and 0.84; 95% CI 0.72-0.99 per 5 cm higher WC). The associations between WC and dSBP were no longer statistically significant after BMI adjustments. In conclusion, higher BMI and higher WC were associated with higher postural increases in SBP; however, WC was not related to postural changes in SBP once adjusted for BMI.

Effect of intraoperative operating table rotation on lower limb perfusion index in patients in the lithotomy position

We focused on "returning to the horizontal position," one of the measures for preventing well leg compartment syndrome implemented at our hospital, and aimed to clarify the effect of intraoperative positional changes by operating table rotation on blood perfusion in the lower extremities during lithotomy in patients under general anesthesia. This prospective observational study examined 64 patients scheduled to undergo general anesthesia in the lithotomy position from March 2021 to May 2022. The primary endpoint was the perfusion index (PI) of the lower limb before and after operating table rotation. The baseline lower limb PI before the operating table rotation was 2.376 (1.591), and the lower limb PI after the change from Trendelenburg to the horizontal position was as follows: immediately after, 2.123 (1.405); 5 minutes, 1.894 (1.138); 10 minutes, 1.915 (1.167); and 15 minutes, 1.993 (1.218). Compared with the baseline, no significant difference was noted in the change in the lower limb PI due to the Trendelenburg to horizontal positional change. The baseline lower leg pressure before the operating table rotation was 51.4 (13.4) mm Hg, and the lower leg pressure after the change from the Trendelenburg to the horizontal position was as follows: immediately after, 36.6 (10.3) mm Hg; 5 minutes, 36.5 (10.2) mm Hg; 10 minutes, 36.4 (10.0) mm Hg; and 15 minutes, 36.5 (10.2) mm Hg. Compared with the baseline, the change in lower leg pressure due to the Trendelenburg to horizontal positional change showed a significant decrease immediately afterward (P < .001). After operating table rotation from the Trendelenburg to the horizontal position, the lower limb PI did not change significantly after 15 min. However, lower leg pressure showed a significant decrease immediately after returning to the horizontal position. This result provides evidence for operating table rotation as a preventive measure for well leg compartment syndrome.

Detection of Preclinical Orthostatic Disorders in Young African and European Adults Using the Head-Up Tilt Test with a Standardized Hydrostatic Column Height: A Pilot Study

Arterial hypertension (AH) remains the most common disease. One possible way to improve the effectiveness of the primary prevention of AH is to identify and control the preclinical orthostatic disturbances that precede the development of AH. The aim of the study was to determine the feasibility of a new protocol for the head-up tilt test (HUTT) with a standardized hydrostatic column height for the detection of asymptomatic orthostatic circulatory disorders and their racial differences in young African and European adults. Methods. In total, 80 young healthy adults (40 African and 40 European) aged 20–23 years performed the HUTT with a standardized hydrostatic column height of 133 cm. The hemodynamic parameters were recorded using a Task Force Monitor (3040i). The cardio-ankle vascular index (CAVI) was measured using a VaSera VS-2000 volumetric sphygmograph. Results. The baseline and orthostatic hemodynamic changes in both racial groups were within normal limits. Orthostatic circulatory disturbances were not detected in 70% of the European participants and 65% of the African participants; however, preclinical orthostatic hypertension, which precedes AH, was detected using the new HUTT protocol in 32.5% of the African participants and 20% of the European participants. The baseline CAVI was higher in the European group compared to the African group. Conclusion. The results of this study showed the feasibility of the detection of preclinical orthostatic disturbances in young adults and the detection of their racial differences using the HUTT protocol, providing the use of a standard gravity load. Further study on the evolution of preclinical orthostatic disturbances and their relation to increased vascular stiffness is necessary among large samples.

Orthostatic stress response in pediatric Fontan patients and the effect of ACE inhibition

Background

Many cardiocirculatory mechanisms are involved in the adaptation to orthostatic stress. While these mechanisms may be impaired in Fontan patients. However, it is yet unclear how Fontan patients, who exhibit a critical fluid balance, respond to orthostatic stress. Angiotensin converting enzyme inhibitors are often prescribed to Fontan patients, but they may negatively influence orthostatic tolerance. Therefore, we evaluated the response to orthostatic stress in pediatric Fontan patients before and after treatment with enalapril.

Methods

Thirty-five Fontan patients (aged 14 years) with moderate-good systolic ventricular function without pre-existent enalapril treatment were included. Before and after a three-month enalapril treatment period, the hemodynamic response to head-up tilt test was evaluated by various parameters including cardiac index, blood pressure, cerebral blood flow, aortic stiffness and cardiac autonomous nervous activity. Thirty-four healthy subjects (aged 13 years) served as controls.

Results

Fontan patients had a decreased cerebral blood flow and increased aortic stiffness in the supine position compared to controls, while all other factors did not differ. Patients and controls showed a comparable response to head-up tilt test for most parameters. Twenty-seven patients completed the enalapril study with a mean dosage of 0.3±0.1mg/kg/day. Most parameters were unaffected by enalapril, only the percent decrease in cardiac index to tilt was higher after treatment, but the cardiac index during tilt was not lower (3.0L/min/m2 pre-enalapril versus 2.8L/min/m2 after treatment; P = 0.15).

Conclusion

Pediatric Fontan patients adequately respond to orthostasis with maintenance of blood pressure and cerebral blood flow and sufficient autonomic response. Enalapril treatment did not alter the response.

Clinical trial information

Scientific title: ACE inhibition in Fontan patients: its effect on body fluid regulation (sAFE-study).

The Netherlands National Trial Register: Trail NL6415. Registered 2017-07-20.

Trial information: https://www.trialregister.nl/trial/6415

Mechanical deconditioning of the heart due to long-term bed rest as observed on seismocardiogram morphology

During head-down tilt bed rest (HDT) the cardiovascular system is subject to headward fluid shifts. The fluid shift phenomenon is analogous to weightlessness experienced during spaceflight microgravity. The purpose of this study was to investigate the effect of prolonged 60-day bed rest on the mechanical performance of the heart using the morphology of seismocardiography (SCG). Three-lead electrocardiogram (ECG), SCG and blood pressure recordings were collected simultaneously from 20 males in a 60-day HDT study (MEDES, Toulouse, France). The study was divided into two campaigns of ten participants. The first commenced in January, and the second in September. Signals were recorded in the supine position during the baseline data collection (BDC) before bed rest, during 6° HDT bed rest and during recovery (R), post-bed rest. Using SCG and blood pressure at the finger, the following were determined: Pulse Transit Time (PTT); and left-ventricular ejection time (LVET). SCG morphology was analyzed using functional data analysis (FDA). The coefficients of the model were estimated over 20 cycles of SCG recordings of BDC12 and HDT52. SCG fiducial morphology AO (aortic valve opening) and AC (aortic valve closing) amplitudes showed significant decrease between BDC12 and HDT52 (p < 0.03). PTT and LVET were also found to decrease through HDT bed rest (p < 0.01). Furthermore, PTT and LVET magnitude of response to bed rest was found to be different between campaigns (p < 0.001) possibly due to seasonal effects on of the cardiovascular system. Correlations between FDA and cardiac timing intervals PTT and LVET using SCG suggests decreases in mechanical strength of the heart and increased arterial stiffness due to fluid shifts associated with the prolonged bed rest.

Type and intensity distribution of structured and incidental lifestyle physical activity of students and office workers: a retrospective content analysis

Background

Physical activity (PA) guidelines acknowledge the health benefits of regular moderate-to-vigorous physical activity (MVPA) regardless of bout duration. However, little knowledge exists concerning the type and intensity distribution of structured and incidental lifestyle PA of students and office workers. The present study aimed to i) assess the duration and distribution of intensity of MVPAs during waking hours ≥50% of heart rate reserve (HRR), ii) to identify the type of PA through diary assessment, iii) to assign these activities into structured and lifestyle incidental PA, and iv) to compare this information between students and office workers.

Methods

Twenty-three healthy participants (11 students, 12 office workers) recorded heart rate (HR) with a wrist-worn HR monitor (Polar M600) and filled out a PA diary throughout seven consecutive days (i.e. ≥ 8 waking h/day). Relative HR zones were calculated, and PA diary information was coded using the Compendium of PA. We matched HR data with the reported PA and identified PA bouts during waking time ≥ 50% HRR concerning duration, HRR zone, type of PA, and assigned each activity to incidental and structured PA. Descriptive measures for time spend in different HRR zones and differences between students and office workers were calculated.

Results

In total, we analyzed 276.894 s (76 h 54 min 54 s) of waking time in HRR zones ≥50% and identified 169 different types of PA. The participants spend 31.9 ± 27.1 min/day or 3.9 ± 3.2% of their waking time in zones of ≥50% HRR with no difference between students and office workers (p > 0.01). The proportion of assigned incidental lifestyle PA was 76.9 ± 22.5%.

Conclusions

The present study provides initial insights regarding the type, amount, and distribution of intensity of structured and incidental lifestyle PA ≥ 50% HRR. Findings show a substantial amount of incidental lifestyle PA during waking hours and display the importance of promoting a physically active lifestyle. Future research could employ ambulatory assessments with integrated electronic diaries to detect information on the type and context of MVPA during the day.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-022-12999-z.

Risk factors of sitting-induced tachycardia syndrome in children and adolescents

Background

The study was designed to explore the risk factors for sitting-induced tachycardia syndrome (STS) in children and adolescents.

Methods and results

In this case-control study, 46 children with STS and 184 healthy children and adolescents were recruited. Demographic characteristics, lifestyle habits, allergy history, and family history were investigated using a questionnaire. The changes in heart rate and blood pressure from supine to sitting were monitored using a sitting test. The possible differences between STS patients and healthy children were analyzed using univariate analysis. Logistic regression analysis was used to explore the independent risk factors for STS. Univariate analysis showed that the daily sleeping time of the STS children were significantly shorter than that of the control group [(8.8 ± 1.2) hours/day vs. (9.3 ± 1.0) hours/day, P = 0.009], and the proportion of positive family history of syncope in the STS patients was higher than the controls (4/42 vs. 3/181, P = 0.044). Multivariate logistic regression studies showed that reduced daily sleeping time was an independent risk factor of STS in children (P = 0.006). Furthermore, when daily sleeping time was prolonged by 1 h, the risk of STS was decreased by 37.3%.

Conclusion

Reduced daily sleeping was an independent risk factor for STS in children and adolescents.

Orthostatic Hypotension: Management of a Complex, But Common, Medical Problem

Orthostatic hypotension (OH), a common, often overlooked, disorder with many causes, is associated with debilitating symptoms, falls, syncope, cognitive impairment, and risk of death. Chronic OH, a cardinal sign of autonomic dysfunction, increases with advancing age and is commonly associated with neurodegenerative and autoimmune diseases, diabetes, hypertension, heart failure, and kidney failure. Management typically involves a multidisciplinary, patient-centered, approach to arrive at an appropriate underlying diagnosis that is causing OH, treating accompanying conditions, and providing individually tailored pharmacological and nonpharmacological treatment. We propose a novel streamlined pathophysiological classification of OH; review the relationship between the cardiovascular disease continuum and OH; discuss OH-mediated end-organ damage; provide diagnostic and therapeutic algorithms to guide clinical decision making and patient care; identify current gaps in knowledge and try to define future research directions. Using a case-based learning approach, specific clinical scenarios are presented highlighting various presentations of OH to provide a practical guide to evaluate and manage patients who have OH.

Association between orthostatic blood pressure dysregulation and geriatric syndromes: a cross-sectional study

Background

Orthostatic blood pressure dysregulation, including orthostatic hypotension (OH) and orthostatic hypertension (OHT), is common in the elderly. The association between OH and, to a lesser extent, OHT with geriatric syndromes is controversial and little investigated.

Our objective was to assess the association between orthostatic blood pressure dysregulation and geriatric syndromes in an ambulatory outpatient population.

Methods

This observational study included all outpatients for whom a one-visit comprehensive geriatric assessment was performed during a year. OH was defined as a decrease of at least 20 mmHg in systolic blood pressure (SBP) and/or 10 mmHg in diastolic blood pressure (DBP) after 1 or 3 min of standing. OHT was defined as an increase of more than 20 mmHg in SBP after 1 or 3 min of standing. Comorbidities, drugs regimen, a history of previous falls, nutritional, frailty, functional and cognitive status were compared between patients with OHT or OH and controls (NOR).

Results

Five hundred thirty patients (mean age: 82.9 ± 5.1 years) were included. 19.6% had an OH and 22.3% an OHT. OHT patients were more frequently female, had more diabetes and a lower resting SBP than patients with NOR. OH patients had a higher resting SBP than NOR. After adjusting for age, sex, resting SBP and diabetes, OHT was associated with a low walking speed (OR = 1.332[1.009–1.758]; p = 0.043) and severe cognitive impairment at MMSe score (OR = 1.629[1.070–1.956]; p = 0.016) compared to NOR. Conversely, OH was associated with a lower grip strength (p = 0.016) than NOR.

Conclusion

OHT and OH are common in elderly but associated with different geriatric phenotypes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12877-022-02844-8.

Cardiovascular Response to Posture Changes: Multiscale Modeling and in vivo Validation During Head-Up Tilt

In spite of cardiovascular system (CVS) response to posture changes have been widely studied, a number of mechanisms and their interplay in regulating central blood pressure and organs perfusion upon orthostatic stress are not yet clear. We propose a novel multiscale 1D-0D mathematical model of the human CVS to investigate the effects of passive (i.e., through head-up tilt without muscular intervention) posture changes. The model includes the main short-term regulation mechanisms and is carefully validated against literature data and in vivo measures here carried out. The model is used to study the transient and steady-state response of the CVS to tilting, the effects of the tilting rate, and the differences between tilt-up and tilt-down. Passive upright tilt led to an increase of mean arterial pressure and heart rate, and a decrease of stroke volume and cardiac output, in agreement with literature data and present in vivo experiments. Pressure and flow rate waveform analysis along the arterial tree together with mechano-energetic and oxygen consumption parameters highlighted that the whole system approaches a less stressed condition at passive upright posture than supine, with a slight unbalance of the energy supply-demand ratio. The transient dynamics is not symmetric in tilt-up and tilt-down testing, and is non-linearly affected by the tilting rate, with stronger under- and overshoots of the hemodynamic parameters as the duration of tilt is reduced. By enriching the CVS response to posture changes, the present modeling approach shows promise in a number of applications, ranging from autonomic system disorders to spaceflight deconditioning.

Vestibular-autonomic interactions: beyond orthostatic dizziness

PURPOSE OF REVIEW

This review aims to summarize the current literature describing vestibular-autonomic interactions and to describe their putative role in various disorders' clinical presentations, including orthostatic dizziness and motion sensitivity.

RECENT FINDINGS

The vestibular-autonomic reflexes have long been described as they relate to cardiovascular and respiratory function. Although orthostatic dizziness may be in part related to impaired vestibulo-sympathetic reflex (orthostatic hypotension), there are various conditions that may present similarly. A recent clinical classification aims to improve identification of individuals with hemodynamic orthostatic dizziness so that appropriate recommendations and management can be efficiently addressed. Researchers continue to improve understanding of the underlying vestibular-autonomic reflexes with recent studies noting the insular cortex as a cortical site for vestibular sensation and autonomic integration and modulation. Work has further expanded our understanding of the clinical presentation of abnormal vestibular-autonomic interactions that may occur in various conditions, such as aging, peripheral vestibular hypofunction, traumatic brain injury, and motion sensitivity.

SUMMARY

The vestibular-autonomic reflexes affect various sympathetic and parasympathetic functions. Understanding these relationships will provide improved identification of underlying etiology and drive improved patient management.

Influence of Acute Water Ingestion and Prolonged Standing on Raw Bioimpedance and Subsequent Body Fluid and Composition Estimates

This study evaluated the influence of acute water ingestion and maintaining an upright posture on raw bioimpedance and subsequent estimates of body fluids and composition. Twenty healthy adults participated in a randomized crossover study. In both conditions, an overnight food and fluid fast was followed by an initial multi-frequency bioimpedance assessment (InBody 770). Participants then ingested 11 mL/kg of water (water condition) or did not (control condition) during a 5-minute period. Thereafter, bioimpedance assessments were performed every 10 minutes for one hour with participants remaining upright throughout. Linear mixed effects models were used to examine the influence of condition and time on raw bioimpedance, body fluids, and body composition. Water consumption increased impedance of the arms but not trunk or legs. However, drift in leg impedance was observed, with decreasing values over time in both conditions. No effects of condition on body fluids were detected, but total body water and intracellular water decreased by ~0.5 kg over time in both conditions. Correspondingly, lean body mass did not differ between conditions but decreased over the measurement duration. The increase in body mass in the water condition was detected exclusively as fat mass, with final fat mass values ~1.3 kg higher than baseline and also higher than the control condition. Acute water ingestion and prolonged standing exert practically meaningful effects on relevant bioimpedance variables quantified by a modern, vertical multi-frequency analyzer. These findings have implications for pre-assessment standardization, methodological reporting, and interpretation of assessments.

Orthostatic Challenge Causes Distinctive Symptomatic, Hemodynamic and Cognitive Responses in Long COVID and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome

Background

Some patients with acute COVID-19 are left with persistent, debilitating fatigue, cognitive impairment ("brain fog"), orthostatic intolerance (OI) and other symptoms ("Long COVID"). Many of the symptoms are like those of other post-infectious fatigue syndromes and may meet criteria for myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Common diagnostic laboratory tests are often unrevealing.

Methods

We evaluated whether a simple, standardized, office-based test of OI, the 10-min NASA Lean Test (NLT), would aggravate symptoms and produce objective hemodynamic and cognitive abnormalities, the latter being evaluated by a simple smart phone-based app.

Participants

People with Long COVID (N = 42), ME/CFS (N = 26) and healthy control subjects (N = 20) were studied just before, during, immediately after, 2 and 7 days following completion of the NLT.

Results

The NLT provoked a worsening of symptoms in the two patient groups but not in healthy control subjects, and the severity of all symptoms was similar and significantly worse in the two patient groups than in the control subjects (p < 0.001). In the two patient groups, particularly those with Long COVID, the NLT provoked a marked and progressive narrowing in the pulse pressure. All three cognitive measures of reaction time worsened in the two patient groups immediately following the NLT, compared to the healthy control subjects, particularly in the Procedural Reaction Time (p < 0.01).

Conclusions

A test of orthostatic stress easily performed in an office setting reveals different symptomatic, hemodynamic and cognitive abnormalities in people with Long COVID and ME/CFS, compared to healthy control subjects. Thus, an orthostatic challenge easily performed in an office setting, and the use of a smart phone app to assess cognition, can provide objective confirmation of the orthostatic intolerance and brain fog reported by patients with Long COVID and ME/CFS.

Insufficient sampling frequencies skew heart rate variability estimates: Implications for extracting heart rate metrics from neuroimaging and physiological data

BACKGROUND

While cardiac pulsations are widely present within physiological and neuroimaging data, it is unknown the extent this information can provide valid and reliable heart rate and heart rate variability (HRV) estimates. The objective of this study was to demonstrate how a slight temporal shift due to an insufficient sampling frequency can impact the validity/accuracy of deriving cardiac metrics.

METHODS

Twenty-two participants were instrumented with valid/reliable industry-standard or open-source electrocardiograms. Five-minute lead II recordings were collected at 1000 Hz in an upright orthostatic position. Following artifact removal, the 1000 Hz recording for each participant was downsampled to frequencies ranging 2-500 Hz. The validity of each participant's downsampled recording was compared against their 1000 Hz recording ("reference-standard") using Bland-Altman plots with 95 % limits of agreement (LOA), coefficient of variation (CoV), intraclass correlation coefficients, and adjusted r-squared values.

RESULTS

Downsampled frequencies of ≥ 50 and ≥ 90 Hz produced highly robust measures with narrow log-transformed 95 % LOA (<±0.01) and low CoV values (≤3.5 %) for heart rate and HRV metrics, respectively. Below these thresholds, the log-transformed 95 % LOA became wider (LOA range: ±0.1-1.9) and more variable (CoV range: 1.5-111.6 %).

CONCLUSION

These results provide an important consideration for obtaining cardiac information from physiological data. Compared to the "reference-standard" ECG, a seemingly negligible temporal shift of the systolic contraction (R wave) greater than 11-milliseconds (90 Hz) away from its true value, lessened the validity of the HRV. Further research is warranted to determine the minimum sampling frequency required to obtain valid heart rate/HRV metrics from pulsatile waveforms.

Menstrual cycle effects on sympathetic neural burst amplitude distribution during orthostasis in young women

PURPOSE

Fluctuations in ovarian hormones during the menstrual cycle impact muscle sympathetic nerve activity burst frequency and burst incidence at rest. The purpose of this study was to investigate menstrual cycle effects on sympathetic neural burst amplitude distribution during an orthostatic challenge in young women.

METHODS

This study included 11 healthy women (33 ± 10 years [mean ± standard deviation]). Muscle sympathetic nerve activity was measured in the supine position as baseline measurement and during 5 min of 60° upright tilting, during the early follicular phase (low estrogen and progesterone) and mid-luteal phase (high estrogen and progesterone) of the menstrual cycle. Relative burst amplitude distribution of muscle sympathetic nerve activity was characterized by the mean, median, skewness, and kurtosis.

RESULTS

From the supine to upright position, mean and median values of relative burst amplitude increased (both P < 0.05), regardless of phases of the menstrual cycle (P = 0.5 and P = 0.7, respectively). In comparison, during the early follicular phase, skewness and kurtosis remained unchanged (P =  0.6 and P =   0.3, respectively) and kurtosis decreased (1.25 ± 1.11 supine vs. - 0.03 ± 0.73 upright; P = 0.02); there was no change in skewness during the mid-luteal phase (P = 0.4).

CONCLUSIONS

In response to orthostasis, while the symmetry and tailedness/peakness of burst amplitude distribution do not change during the early follicular phase, the distribution during the mid-luteal phase becomes flatter with a lower but broader peak. The latter result suggests that the firing probability of large axon action potentials in response to orthostatic challenge is higher when estrogen and progesterone levels are elevated. The role of changes in sympathetic neural burst amplitude distribution in orthostatic tolerance remains to be determined.

Ultrasound-guided interscalene block anesthesia performed by an orthopedic surgeon: a study of 1322 cases of shoulder surgery

Background

Interscalene blocks are becoming increasingly common for shoulder surgeries. This study primarily aimed to demonstrate the efficacy and complications and the secondarily to investigate the anesthesia-related time and patient satisfaction of an ultrasound-guided interscalene block performed by an orthopedic surgeon.

Methods

We retrospectively reviewed the medical records of 1322 consecutive patients (arthroscopic, 1225 cases; open, 97 cases) with a mean age of 64.2 years, who underwent shoulder surgery (arthroscopic or opensurgery) under an ultrasound-guided interscalene block performed by an orthopedic surgeon at a single institution between December 2012 and December 2019. We investigated patient satisfaction, block success rates, and complications and also compared the anesthesia-related time of an interscalene block with that of general anesthesia (428 cases, arthroscopic, 257 cases; open, 171 cases) for shoulder surgery with patients in the beach chair position during the same period. Difference between total anesthesia time and surgical time was defined as anesthesia-related time.

Results

Approximately 98.3% of patients were satisfied with an interscalene block, and the block success rate on the first attempt was 99.9%. Total complication incidence was 2.3%, with no recorded life-threatening complications. Anesthesia-related times were significantly shorter in the interscalene block group than those in the general anesthesia group (45 ± 14 min vs. 100 ± 26 min, P < .001).

Conclusion

An ultrasound-guided interscalene block performed by an orthopedic surgeon for shoulder surgery is effective and safe, requires less time, and has a high patient acceptance rate, making it a feasible and alternative to the block performed by anesthesiologists.

Postural orthostatic tachycardia syndrome (POTS) occurring during treatment for breast cancer

Postural orthostatic tachycardia syndrome (POTS) is a common condition of orthostatic intolerance in response to changes in position. We report a case of a middle-aged woman presenting with a new onset of POTS likely due to chemotherapy for treatment of breast cancer. She was started on a trial of a beta blocker, which was effective in controlling her symptoms and heart rate. The objective of this report was to encourage clinicians to consider POTS as a differential diagnosis, while managing patients with symptoms of orthostatic intolerance.

Evaluation of gravity effect on inferior vena cava and abdominal aortic flow using multi-posture MRI

BACKGROUND

Inferior vena cava flow (IVCF) and abdominal aortic flow (AAF) are essential components of the systemic circulation. Although postural changes might alter IVCF and AAF by the gravity effect, the exact details are unknown.

PURPOSE

To evaluate the effect of gravity on IVCF and AAF using a novel magnetic resonance imaging (MRI) system that can image in any position.

MATERIAL AND METHODS

Caval velocity-mapped images were obtained using the cine phase-contrast technique in the upright and supine positions with multi-posture MRI (n = 12). The mean IVCF/AAF velocity, maximum IVCF/AAF velocity, cross-sectional area of IVC/AA, mean IVCF/AAF, maximum IVCF/AAF, and heart rate in the two positions were assessed.

RESULTS

The mean IVCF velocity, maximum IVCF velocity, cross-sectional area of IVC, mean IVCF, maximum IVCF, mean AAF velocity, maximum AAF velocity, mean AAF, and maximum AAF were significantly lower in the upright position compared with the supine position (P < 0.05 for all), with differences of 52% ± 33%, 36% ± 19%, 56% ± 18%, 26% ± 18%, 19% ± 11%, 33% ± 13%, 33% ± 22%, 42% ± 21%, and 37% ± 28%, respectively. Heart rate was significantly higher in the upright position compared with the supine position (116% ± 9.2%; P = 0.003). There were no differences in cross-sectional area of AA between the two positions (108% ± 22%; P = 0.583).

CONCLUSION

The effect of gravity decreases IVCF and AAF. Clarifying the effect of gravity on IVCF and AAF during a postural change may help to improve the management of patients with circulatory disease.

Cardiac baroreflex dysfunction in patients with pulmonary arterial hypertension at rest and during orthostatic stress: role of the peripheral chemoreflex

The baroreflex integrity in early-stage pulmonary arterial hypertension (PAH) remains uninvestigated. A potential baroreflex impairment could be functionally relevant and possibly mediated by enhanced peripheral chemoreflex activity. Thus, we investigated 1) the cardiac baroreflex in nonhypoxemic PAH; 2) the association between baroreflex indexes and peak aerobic capacity [i.e., peak oxygen consumption (V̇o_2peak)]; and 3) the peripheral chemoreflex contribution to the cardiac baroreflex. Nineteen patients and 13 age- and sex-matched healthy adults (HA) randomly inhaled either 100% O₂ (peripheral chemoreceptor inhibition) or 21% O₂ (control session) while at rest and during a repeated sit-to-stand maneuver. Beat-by-beat analysis of R-R intervals and systolic blood pressure provided indexes of cardiac baroreflex sensitivity (cBRS) and effectiveness (cBEI). The PAH group had lower cBEI for all sequences (cBEI_ALL) at rest [means ± SD: PAH = 0.5 ± 0.2 vs. HA = 0.7 ± 0.1 arbitrary units (a.u.), P = 0.02] and lower cBRS_ALL (PAH = 6.8 ± 7.0 vs. HA = 9.7 ± 5.0 ms·mmHg^-1, P < 0.01) and cBEI_ALL (PAH = 0.4 ± 0.2 vs. HA= 0.6 ± 0.1 a.u., P < 0.01) during the sit-to-stand maneuver versus the HA group. The cBEI during the sit-to-stand maneuver was independently correlated to V̇o_2peak (partial r = 0.45, P < 0.01). Hyperoxia increased cBRS and cBEI similarly in both groups at rest and during the sit-to-stand maneuver. Therefore, cardiac baroreflex dysfunction was observed under spontaneous and, most notably, provoked blood pressure fluctuations in nonhypoxemic PAH, was not influenced by the peripheral chemoreflex, and was associated with lower V̇o_2peak, suggesting that it could be functionally relevant.NEW & NOTEWORTHY Does the peripheral chemoreflex play a role in cardiac baroreflex dysfunction in patients with pulmonary arterial hypertension (PAH)? Here we provide new evidence of cardiac baroreflex dysfunction under spontaneous and, most notably, provoked blood pressure fluctuations in patients with nonhypoxemic PAH. Importantly, impaired cardiac baroreflex effectiveness during provoked blood pressure fluctuations was independently associated with poorer functional capacity. Finally, our results indicated that the peripheral chemoreflex did not mediate cardiac baroreflex dysfunction among those patients.

Spectral Cerebral Blood Volume Accounting for Noninvasive Estimation of Changes in Cerebral Perfusion Pressure in Patients with Traumatic Brain Injury

We present the application of a new method for non-invasive cerebral perfusion pressure estimation (spectral nCPP or nCPP_s) accounting for changes in transcranial Doppler-derived pulsatile cerebral blood volume. Primarily, we analysed cases in which CPP was changing (delta [∆],magnitude of changes]): (1) rise during vasopressor-induced augmentation of ABP (N = 16); and (2) spontaneous changes in intracranial pressure (ICP) during plateau waves (N = 14). Secondarily, we assessed nCPP_s in a larger cohort in which CPP presented a wider range of values. The average correlation in the time domain between CPP and nCPP_s for patients undergoing an induced rise in arterial blood pressure (ABP) was 0.95 ± 0.07. For the greater traumatic brain injury (TBI) cohort, this correlation was 0.63 ± 0.37. ∆ correlations between mean values of CPP and nCPP_s were 0.73 (p = 0.002) and 0.78 (p < 0.001) respectively for induced rise in ABP and ICP plateau wave cohorts. The area under the curve (AUC) for ∆CPP was of 0.71 with a 95% confidence interval of 0.54-0.88. To detect low CPP, AUC was 0.817 with a 95% confidence interval of 0.79-0.85. nCPP_s can reliably identify changes in direct CPP across time and the magnitude of these changes in absolute values. The ability to detect changes in CPP is reasonable but stronger for detecting low CPP, ≤70 mmHg.

Gravity Threshold and Dose Response Relationships: Health Benefits Using a Short Arm Human Centrifuge

Purpose

Increasing the level of gravity passively on a centrifuge, should be equal to or even more beneficial not only to astronauts living in a microgravity environment but also to patients confined to bed. Gravity therapy (GT) may have beneficial effects on numerous conditions, such as immobility due to neuromuscular disorders, balance disorders, stroke, sports injuries. However, the appropriate configuration for administering the Gz load remains to be determined.

Methods

To address these issues, we studied graded G-loads from 0.5 to 2.0g in 24 young healthy, male and female participants, trained on a short arm human centrifuge (SAHC) combined with mild activity exercise within 40–59% MHR, provided by an onboard bicycle ergometer. Hemodynamic parameters, as cardiac output (CO), stroke volume (SV), mean arterial pressure (MAP), systolic blood pressure (SBP), diastolic blood pressure (DBP), and heart rate (HR) were analyzed, as well as blood gas analysis. A one-way repeated measures ANOVA and pairwise comparisons were conducted with a level of significance p < 0.05.

Results

Significant changes in heart rate variability (HRV) and its spectral components (Class, Fmax, and VHF) were found in all g loads when compared to standing (p < 0.001), except in 1.7 and 2.0g. There were significant changes in CO, cardiac index (CI), and cardiac power (CP) (p < 0.001), and in MAP (p = 0.003) at different artificial gravity (AG) levels. Dose-response curves were determined based on statistically significant changes in cardiovascular parameters, as well as in identifying the optimal G level for training, as well as the optimal G level for training. There were statistically significant gender differences in Cardiac Output/CO (p = 0.002) and Cardiac Power/CP (p = 0.016) during the AG training as compared to standing. More specifically, these cardiovascular parameters were significantly higher for male than female participants. Also, there was a statistically significant (p = 0.022) gender by experimental condition interaction, since the high-frequency parameter of the heart rate variability was attenuated during AG training as compared to standing but only for the female participants (p = 0.004).

Conclusion

The comprehensive cardiovascular evaluation of the response to a range of graded AG loads, as compared to standing, in male and female subjects provides the dose-response framework that enables us to explore and validate the usefulness of the centrifuge as a medical device. It further allows its use in precisely selecting personalized gravity therapy (GT) as needed for treatment or rehabilitation of individuals confined to bed.

The validity and reliability of ultra-short-term heart rate variability parameters and the influence of physiological covariates

Ultra-short-term (UST) heart rate variability (HRV) metrics have increasingly been proposed as surrogates for short-term HRV metrics. However, the concurrent validity, within-day reliability, and between-day reliability of UST HRV have yet to be comprehensively documented. Thirty-six adults (18 males, age: 26 ± 5 yr, BMI: 24 ± 3 kg/m²) were recruited. Measures of HRV were quantified in a quiet-stance upright orthostatic position via three-lead electrocardiogram (ADInstruments, FE232 BioAmp). All short-term data recordings were 300 s in length and five UST time points (i.e., 30 s, 60 s, 120 s, 180 s, and 240 s) were extracted from the original 300-s recording. Bland-Altman plots with 95% limits of agreement, repeated measures ANOVA and two-tailed paired t tests demarcated differences between UST and short-term recordings. Linear regressions, coefficient of variation, intraclass correlation coefficients, and other tests examined the validity and reliability in both time- and frequency domains. No group differences were noted between all short-term and UST measures, for either time- (all P > 0.202) or frequency-domain metrics (all P > 0.086). A longer recording duration was associated with augmented validity and reliability, which was less impacted by confounding influences from physiological variables (e.g., respiration rate, carbon dioxide end-tidals, and blood pressure). Conclusively, heart rate, time-domain, and relative frequency-domain HRV metrics were acceptable with recordings greater or equal to 60 s, 240 s, and 300 s, respectively. Future studies employing UST HRV metrics should thoroughly understand the methodological requirements to obtain accurate results. Moreover, a conservative approach should be utilized regarding the minimum acceptable recording duration, which ensures valid/reliable HRV estimates are obtained.NEW & NOTEWORTHY A one size fits all methodological approach to quantify HRV metrics appears to be inappropriate, where study design considerations need to be conducted upon a variable-by-variable basis. The present results found 60 s (heart rate), 240 s (time-domain parameters), and 300 s (relative frequency-domain parameters) were required to obtain accurate and reproducible metrics. The lower validity/reliability of the ultra-short-term metrics was attributable to measurement error and/or confounding from extraneous physiological influences (i.e., respiratory and hemodynamic variables).

Longitudinal agreement of four bioimpedance analyzers for detecting changes in raw bioimpedance during purposeful weight gain with resistance training

BACKGROUND

Due to inherent errors involved in the transformation of raw bioelectrical variables to body fluids or composition estimates, the sole use of resistance (R), reactance (Xc), and phase angle (φ) has been advocated when quantifying longitudinal changes. The aim of this investigation was to assess the ability of four bioimpedance analyzers to detect raw bioimpedance changes induced by purposeful weight gain with resistance training.

METHODS

Twenty-one resistance trained males completed a 6-week lifestyle intervention with the aim of purposeful weight gain. Bioimpedance analysis was performed before and after the intervention using four different analyzers (MFBIA_InBody: InBody 770; MFBIA_SECA: Seca mBCA 515/514; BIS: ImpediMed SFB7; SFBIA: RJL Quantum V) for the quantification of R, Xc, and φ at the 50-kHz frequency. Repeated measures ANOVA and follow up tests were performed.

RESULTS

Analysis revealed main effects of time and method for R, Xc, and φ (p ≤ 0.02), without significant time x method interactions (p ≥ 0.07). Follow up for time main effects indicated that, on average, R decreased by 4.5-5.8%, Xc decreased by 2.3-4.0%, and φ increased by 1.8-2.6% across time for all analyzers combined. However, varying levels of disagreement in absolute values were observed for each bioelectrical variable.

CONCLUSIONS

The differences in absolute bioelectrical values suggests that analyzers should not be used interchangeably, which holds particular importance when reference values are utilized. Despite absolute differences, analyzers with varying characteristics demonstrated similar abilities to detect changes in R, Xc, and φ over time.

Systemic and cerebral circulatory adjustment within the first 60 s after active standing: An integrative physiological view

Transient cardiovascular and cerebrovascular responses within the first minute of active standing provide the means to assess autonomic, cardiovascular and cerebrovascular regulation using a real-world everyday stimulus. Traditionally, these responses have been used to detect autonomic dysfunction, and to identify the hemodynamic correlates of patient symptoms and attributable causes of (pre)syncope and falls. This review addresses the physiology of systemic and cerebrovascular adjustment within the first 60 s after active standing. Mechanical factors induced by standing up cause a temporal mismatch between cardiac output and vascular conductance which leads to an initial blood pressure drops with a nadir around 10 s. The arterial baroreflex counteracts these initial blood pressure drops, but needs 2-3 s to be initiated with a maximal effect occurring at 10 s after standing while, in parallel, cerebral autoregulation buffers these changes within 10 s to maintain adequate cerebral perfusion. Interestingly, both the magnitude of the initial drop and these compensatory mechanisms are thought to be quite well-preserved in healthy aging. It is hoped that the present review serves as a reference for future pathophysiological investigations and epidemiological studies. Further experimental research is needed to unravel the causal mechanisms underlying the emergence of symptoms and relationship with aging and adverse outcomes in variants of orthostatic hypotension.

Linking the hemodynamic consequences of adverse childhood experiences to an altered HPA axis and acute stress response

Adverse childhood experiences (ACEs), such as maltreatment and severe household dysfunction, represent a significant threat to public health as ACEs are associated with increased prevalence of several chronic diseases. Biological embedding, believed to be rooted in dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis, is the prevailing theory by which chronic diseases become imprinted in individuals following childhood adversity. A shift towards HPA axis hypoactivity occurs in response to ACEs exposure and is proposed to contribute towards altered cortisol secretion, chronic low-grade inflammation, and dysregulated hemodynamic and autonomic function. This shift in HPA axis activity may be a long-term effect of glucocorticoid receptor methylation with downstream effects on hemodynamic and autonomic function. Emerging evidence suggests syncopal tendencies are increased among those with ACEs and coincides with altered neuroimmune function. Similarly, chronic low-grade inflammation may contribute towards arterial baroreceptor desensitization through increased arterial stiffness, negatively impacting autonomic regulation following posture change and increasing rates of syncope in later life, as has been previously highlighted in the literature. Although speculative, baroreceptor desensitization may be secondary to increased arterial stiffness and changes in expression of glucocorticoid receptors and arginine vasopressin, which are chronically altered by ACEs. Several research gaps and opportunities exist in this field and represent prospective areas for future investigation. Here, we synthesize current findings in the areas of acute psychosocial stress reactivity pertaining to HPA axis function, inflammation, and hemodynamic function while suggesting ideas for future research emphasizing systemic interactions and postural stress assessments among those with ACEs. This review aims to identify specific pathways which may contribute towards orthostatic intolerance in populations with history of childhood adversity.

Agreement of bioelectrical resistance, reactance, and phase angle values from supine and standing bioimpedance analyzers

OBJECTIVE

Bioimpedance devices are commonly used to assess health parameters and track changes in body composition. However, the cross-sectional agreement between different devices has not been conclusively established. Thus, the objective of this investigation was to examine the agreement between raw bioelectrical variables (resistance, reactance, and phase angle at the 50-kHz frequency) obtained from three bioimpedance analyzers.

APPROACH

Healthy male (n=76, Mean±SD; 33.8±14.5 years; 83.9±15.1 kg; 179.4±6.9 cm) and female (n=103, Mean±SD; 33.4±15.9 years; 65.6±12.1 kg; 164.9±6.4 cm) participants completed assessments using three bioimpedance devices: supine bioimpedance spectroscopy (BIS), supine single-frequency bioelectrical impedance analysis (SFBIA), and standing multi-frequency bioelectrical impedance analysis (MFBIA). Differences in raw bioelectrical variables between the devices were quantified via one-way analysis of variance for the total sample and for each sex. Equivalence testing was used to determine equivalence between methods.

MAIN RESULTS

Significant differences in all bioelectrical variables were observed between the three devices when examining the total sample and males only. The devices appeared to exhibit slightly better agreement when analyzing female participants only. Equivalence testing using the total sample as well as males and females separately revealed that resistance and phase angle were equivalent between the supine devices (BIS, SFBIA), but not with the standing analyzer (MFBIA).

SIGNIFICANCE

The present study demonstrated disagreement between different bioimpedance analyzers for quantifying raw bioelectrical variables, with the poorest agreement between devices that employed different body positions during testing. These results suggest that researchers and clinicians should employ device-specific reference values to classify participants based on raw bioelectrical variables, such as phase angle. If reference values are needed but are unavailable for a particular bioimpedance analyzer, the set of reference values produced using the most similar analyzer and reference population should be selected.

Drug-Related Orthostatic Hypotension: Beyond Anti-Hypertensive Medications

Orthostatic hypotension (OH) is an abnormal blood pressure response to standing, which is associated with an increased risk of adverse outcomes such as syncope, falls, cognitive impairment, and mortality. Medical therapy is one the most common causes of OH, since numerous cardiovascular and psychoactive medications may interfere with the blood pressure response to standing, leading to drug-related OH. Additionally, hypotensive medications frequently overlap with other OH risk factors (e.g., advanced age, neurogenic autonomic dysfunction, and comorbidities), thus increasing the risk of symptoms and complications. Consequently, a medication review is recommended as a first-line approach in the diagnostic and therapeutic work-up of OH, with a view to minimizing the risk of drug-related orthostatic blood pressure impairment. If symptoms persist after the review of hypotensive medications, despite adherence to non-pharmacological interventions, specific drug treatment for OH can be considered. In this narrative review we present an overview of drugs acting on the cardiovascular and central nervous system that may potentially impair the orthostatic blood pressure response and we provide practical suggestions that may be helpful to guide medical therapy optimization in patients with OH. In addition, we summarize the available strategies for drug treatment of OH in patients with persistent symptoms despite non-pharmacological interventions.

Severe orthostatic hypotension in otherwise uncomplicated Plasmodium vivax infection

Impaired autonomic control of postural homeostasis resulting in orthostatic hypotension has been described in falciparum malaria. However, severe orthostatic intolerance in Plasmodium vivax has been rarely reported. A case of non-immune previously healthy Thai woman presenting with P. vivax infection with well-documented orthostatic hypotension is described. In addition to oral chloroquine and intravenous artesunate, the patient was treated with fluid resuscitation and norepinephrine. During hospitalization, her haemodynamic profile revealed orthostatic hypotension persisting for another three days after microscopic and polymerase chain reaction confirmed parasite clearance. Potential causes are discussed.

Electrodiagnostic assessment of the autonomic nervous system: A consensus statement endorsed by the American Autonomic Society, American Academy of Neurology, and the International Federation of Clinical Neurophysiology

Evaluation of disorders of the autonomic nervous system is both an art and a science, calling upon the physician's most astute clinical skills as well as knowledge of autonomic neurology and physiology. Over the last three decades, the development of noninvasive clinical tests that assess the function of autonomic nerves, the validation and standardization of these tests, and the growth of a large body of literature characterizing test results in patients with autonomic disorders have equipped clinical practice further with a valuable set of objective tools to assist diagnosis and prognosis. This review, based on current evidence, outlines an international expert consensus set of recommendations to guide clinical electrodiagnostic autonomic testing. Grading and localization of autonomic deficits incorporates scores from sympathetic cardiovascular adrenergic, parasympathetic cardiovagal, and sudomotor testing, as no single test alone is sufficient to diagnose the degree or distribution of autonomic failure. The composite autonomic severity score (CASS) is a useful score of autonomic failure that is normalized for age and gender. Valid indications for autonomic testing include generalized autonomic failure, regional or selective system syndromes of autonomic impairment, peripheral autonomic neuropathy and ganglionopathy, small fiber neuropathy, orthostatic hypotension, orthostatic intolerance, syncope, neurodegenerative disorders, autonomic hyperactivity, and anhidrosis.

Impaired Cerebral Autoregulation in Alzheimer's Disease: A Transcranial Doppler Study

BACKGROUND

Vasculature changes have been observed in Alzheimer's disease (AD). AD-related vascular pathology might impair cerebral autoregulation (CA).

OBJECTIVE

This study was designed to evaluate CA of AD patients by using transcranial doppler (TCD).

METHODS

A total of 61 participants were included in the study, including 31 AD patients and 30 controls. The trend curves of cerebral blood flow velocities (CBFV), pulsatility index, and resistance index were obtained using TCD during supine-to-standing posture changes. CA was measured by the changes of CBFV curves during supine-to-standing test.

RESULTS

There were two spikes named X spike and W spike that appeared in the CBFV curve when the subjects stood abruptly. The slope of the X spike descending branch, the slope of the W spike ascending branch, and the angle between X and W spikes (α angle), showed significant differences between the experimental and control groups (2.34±0.99 versus 3.15±1.61 cm/s2, p = 0.021; 2.31±0.81 versus 3.38±1.18 cm/s2, p < 0.001; and 52.71±20.26 versus 41.4±12.87 degrees, p = 0.012, respectively). ROC analysis showed that AUCαangle is 0.664 (p = 0.028) and that AUCSAB and AUCadjustedSAB are 0.775 and 0.738, respectively (both p < 0.001).

CONCLUSIONS

Our study demonstrated that supine-to-standing TCD test is a valuable tool for the evaluation of CA in AD patients. Impaired CA in AD patients manifested as decreased efficiency of changes in the CBFV curve. Neurovascular units were involved in the pathogenesis of AD.

Mathematical modeling of the cardiovascular autonomic control in healthy subjects during a passive head-up tilt test

A mathematical model is proposed for the autonomic control of cardiovascular system, which takes into account two separated self-exciting sympathetic control loops of heart rate and peripheral vascular tone. The control loops are represented by self-exciting time-delay systems and their tone depends on activity of the aortic, carotid, and lower-body baroreceptors. The model is used to study the dynamics of the adaptive processes that manifest in a healthy cardiovascular system during the passive head-up tilt test. Computer simulation provides continuous observation of the dynamics of the indexes and variables that cannot be measured in the direct experiment, including the noradrenaline concentration in vessel wall and heart muscle, tone of the sympathetic and parasympathetic control, peripheral vascular resistance, and blood pressure. In the supine and upright positions, we estimated the spectral characteristics of the model variables, especially in the low-frequency band, and the original index of total percent of phase synchronization between the low-frequency oscillations in heart rate and blood pressure signals. The model demonstrates good quantitative agreement with the dynamics of the experimentally observed indexes of cardiovascular system that were averaged for 50 healthy subjects.