Impact of changes in respiratory frequency and posture on power spectral analysis of heart rate and systolic blood pressure variability in normal subjects and patients with heart failure

Does Exercise Training Improve Cardiac-Parasympathetic Nervous System Activity in Sedentary People? A Systematic Review with Meta-Analysis

The aim of this study was to investigate the training-induced effect on cardiac parasympathetic nervous system (PNS) activity, assessed by resting heart rate variability (HRV) and post-exercise heart rate recovery (HRR), in sedentary healthy people. Electronic searches were carried out in PubMed, Embase, and Web of Science. Random-effects models of between-group standardised mean difference (SMD) were estimated. Heterogeneity analyses were performed by means of the chi-square test and I² index. Subgroup analyses and meta-regressions were performed to investigate the influence of potential moderator variables on the training-induced effect. The results showed a small increase in RMSSD (SMD₊ = 0.57 [95% confidence interval (CI) = 0.23, 0.91]) and high frequency (HF) (SMD₊ = 0.21 [95% CI = 0.01, 0.42]) in favour of the intervention group. Heterogeneity tests reached statistical significance for RMSSD and HF (p ≤ 0.001), and the inconsistency was moderate (I² = 68% and 60%, respectively). We found higher training-induced effects on HF in studies that performed a shorter intervention or lower number of exercise sessions (p ≤ 0.001). Data were insufficient to investigate the effect of exercise training on HRR. Exercise training increases cardiac PNS modulation in sedentary people, while its effect on PNS tone requires future study.

Effects of trunk posture on cardiovascular and autonomic nervous systems: A pilot study

Objective: Although regular and moderate physical activity has been shown to improve the cardiovascular and autonomic nervous systems, little has been done to study the effects of postural changes in the movement on the heart and autonomic nervous system. To uncover changes in cardiac function and autonomic nerves induced by different underlying posture transitions and explore which trunk postures lead to chronic sympathetic activation. Therefore, this study investigated the effects of trunk posture on the cardiovascular and autonomic nervous systems. Methods: Twelve male subjects (age 24.7 ± 1.3) underwent this study. The non-invasive cardiac output NICOM monitoring equipment and the FIRSTBEAT system are used to dynamically monitor seven trunk postures in the sitting position simultaneously (neutral position, posterior extension, forward flexion, left lateral flexion, right lateral flexion, left rotation, right rotation). Each posture was maintained for 3 min, and the interval between each movement was 3 min to ensure that each index returned to the baseline level. Repeated analysis of variance test was used to compare and analyze the differences in human cardiac function, heart rate variability index, and respiratory rate under different postures. Results: Compared with the related indicators of cardiac output in a neutral trunk position: the cardiac index (CI) was significantly reduced in forwarding flexion and left rotation (3.48 ± 0.34 vs. 3.21 ± 0.50; 3.48 ± 0.34 vs. 3.21 ± 0.46, Δ L/(min/m2)) (p = 0.016, p = 0.013), cardiac output decreased significantly (6.49 ± 0.78 vs. 5.93 ± 0.90; 6.49 ± 0.78 vs. 6.00 ± 0.96, Δ L/min) (p = 0.006, p = 0.014), the stroke volume (stroke volume)decreased significantly (87.90 ± 15.10 vs. 81.04 ± 16.35; 87.90 ± 15.10 vs. 79.24 ± 16.83, Δ ml/beat) (p = 0.017, p = 0.0003); heart rate increased significantly in posterior extension (75.08 ± 10.43 vs. 78.42 ± 10.18, Δ beat/min) (p = 0.001); left rotation stroke volume index (SVI) decreased significantly (47.28 ± 7.97 vs. 46.14 ± 8.06, Δ ml/m2) (p = 0.0003); in the analysis of HRV-related indicators, compared with the neutral trunk position, the LF/HF of the posterior extension was significantly increased (1.90 ± 1.38 vs. 3.00 ± 1.17, p = 0.037), and the LF/HF of the forward flexion was significantly increased (1.90 ± 1.38 vs. 2.85 ± 1.41, p = 0.041), and the frequency-domain index LF/HF of right rotation was significantly increased (1.90 ± 1.38 vs. 4.06 ± 2.19, p = 0.008). There was no significant difference in respiratory rate (p > 0.05). Conclusion: A neutral trunk is the best resting position, and deviations from a neutral trunk position can affect the cardiovascular and autonomic nervous systems, resulting in decreased stroke volume, increased heart rate, and relative activation of sympathetic tone.

Autonomic nervous system activity in primary Raynaud's phenomenon: Heart rate variability, plasma catecholamines and [123 I]MIBG heart scintigraphy

Background and Aim

Primary Raynaud's phenomenon (pRP) is characterized by an exaggerated response to cold, resulting in the whitening typically of the fingers and toes. The patients are generally perceived as healthy individuals with a benign condition. However, the condition has been associated with increased cardiovascular mortality and changes in autonomic nervous system activity. This study aimed to investigate whether pRP is associated with pervasive changes in autonomic nervous activity. The hypothesis was that patients with pRP have increased sympathetic nervous activity.

Methods

The autonomic nervous activity of 22 patients with pRP was investigated by means of heart rate variability (HRV) and the plasma catecholamine response to head‐up tilt and compared with 22 age‐ and gender‐matched controls. In addition, the patients were examined with a [¹²³I]metaiodobenzylguanidine heart scintigraphy and compared with an external control group.

Results

The plasma norepinephrine response to head‐up tilt was significantly lower in the patient group than in the control group. Similarly, the heart scintigraphy revealed a lower heart‐to‐mediastinum ratio in the patient group than in the control group. HRV analysis did not reveal significant differences between the groups.

Conclusion

The findings of the study showed that the autonomic nervous activity of patients with pRP was altered compared with the activity of healthy individuals. This was observed both during rest and after positional stress, but the findings did not uniformly concur with our initial hypothesis.

Wearable Device for Yogic Breathing with Real-Time Heart Rate and Posture Monitoring

Background:

Yogic breathing also called as “Pranayama” is practiced with inhalation (Pooraka), holding the breath for some time (Kumbhaka) and then exhalation (Rechaka). The effective methods of yogic breathing keep oneself healthy and also improves immunity power. The yogic breathing can be practiced irrespective of one's age and gender and even in the office which helps to reduce the stress. To get the best results through yoga, a person has to follow certain timings and sit in a correct posture. Although many devices are existing in the market to monitor heart rate, posture and breathing during physical activity, there is a need of a device which is simple, cheap, and easy to use without an additional requirement of a smartphone. Moreover, the proposed device is able to evaluate the breathing data by transmitting it to a webpage through a Wi-Fi hotspot of the Microcontroller.

Methods:

The developed device has two subsystems: (i) A wrist subsystem to measure the heart rate, visual aid of breathing and vibration feedback for kapalabhati. (ii) A waist subsystem to monitor the posture with help of flex sensor and the results are displayed on the display of the wrist device. It also provides vibration feedback. The inertial measurement unit is used for breath detection. The subsystems are communicated through SPI communication. The breathing data are transmitted to a webpage through a Wi-Fi hotspot of the microcontroller.

Results:

The various yogic breathing and normal breathing exercises are tested on different normal subjects using the developed device and analyzed. The heart rate and beats per minute are evaluated. The heart rate sensor is validated using a standard medical device and it is observed that there was a 97.4% accuracy.

Conclusion:

The results show that the device is able to accurately monitor different kinds of breathing and additionally provide heart rate and posture information while performing the breathing exercises.

What will we ask to artificial intelligence for cardiovascular medicine in the next decade?

Artificial intelligence (AI) comprises a wide range of technologies and methods with heterogeneous degrees of complexity, applications and abilities. In the cardiovascular field, AI holds the potential to fulfil many unsolved challenges, eventually translating into improved patient care. In particular, AI appears as the most promising tool to overcome the gap between ever-increasing data-rich technologies and their practical implementation in cardiovascular research, in the cardiologist routine, in the patient daily life and at the healthcare-policy level. A multiplicity of AI technologies is progressively pervading several aspects of precision cardiovascular medicine including early diagnosis, automated imaging processing and interpretation, disease sub-phenotyping, risk prediction and remote monitoring systems. Several methodological, logistical, educational and ethical challenges are emerging by integrating AI systems at any stage of cardiovascular medicine. This review will discuss the basics of AI methods, the growing body of evidence supporting the role of AI in the cardiovascular field and the challenges to overcome for an effective AI-integrated cardiovascular medicine.

Heart rate-based indices to detect parasympathetic hyperactivity in functionally overreached athletes. A meta-analysis

Investigations into the sensitivity of heart rate-(HR) derived indices for tracking parasympathetic nervous system (PNS) changes in functionally overreached (F-OR) endurance-trained athletes have produced equivocal findings. Lack of clarity may be a result of methodological inconsistencies. Therefore, the aims of this systematic review and meta-analysis were (a) to determine the sensitivity of resting and post-exercise vagal-related HR variability (HRV) and HR recovery (HRR) indices to detect PNS modulation in F-OR and non-overreached (non-OR) athletes, and (b) to investigate the influence of methodological factors on the sensitivity of HR-based indices to detect PNS hyperactivity in F-OR athletes. We searched CENTRAL, Scopus, PubMed, Embase, and Web of Science up to May 2020 for the following terms: male and female endurance-trained athletes, controlled and uncontrolled studies that carried out an overload training period, and PNS modulation measured in resting and post-exercise, pre- and post-overload training period. A random-effects model of standardized mean difference (SMD) was estimated for each outcome measure based on the training-induced fatigue status (F-OR vs non-OR athletes), and the influence of methodological issues to detect PNS hyperactivity in F-OR was assessed by subgroup analyses. Pooled analysis showed that resting vagal-related HRV indices did not detect PNS hyperactivity in F-OR athletes (SMD₊ = -0.01; 95% confidence interval [CI] = -0.51, 0.50), and no statistical difference (P = .600) was found with non-OR athletes (SMD₊ = 0.15; 95% CI = -0.14, 0.45). However, subgroup analysis based on HRV parameter showed a moderate statistical increase in weekly averaged HRV in F-OR athletes (SMD₊ = 0.81; 95% CI = 0.35, 1.26), while isolated HRV values did not reach statistical significance (SMD₊ = -0.45; 95% CI = -0.96, 0.06). We observed a moderate and statistically significant increase in HRR indices among F-OR athletes (SMD₊ = 0.65; 95% CI = 0.44, 0.87), no changes for non-OR athletes (SMD₊ = 0.10; 95% CI = -0.15, 0.34), and statistically significant differences between F-OR and non-OR athletes (P < .001). Insufficient data prevented meta-analysis for post-exercise vagal-related HRV indices. Our findings show that when methodological factors are considered, HR-based indices are sensitive to increased PNS modulation in F-OR.

Haemodynamic effects of hyperventilation on healthy men with different levels of autonomic tone

The topicality of the research is stipulated by insufficient study of the correlation between the functional state of the cardiorespiratory system and autonomic tone. The goal of the research was to analyze the changes of central haemodynamics with 10-minute regulated breathing at the rate of 30 cycles per minute and within 40 minutes of recovery after the test in healthy young men with different levels of autonomic tone. Records of the chest rheoplethysmogram were recorded on a rheograph KhAI-medica standard (KhAI-medica, Kharkiv, Ukraine), a capnogram - in a lateral flow on a infrared capnograph (Datex, Finland), and the duration of R-R intervals was determined by a Polar WIND Link in the program of Polar Protrainer 5.0 (Polar Electro OY, Finland). Systolic and diastolic blood pressure were measured by Korotkov’s auscultatory method by mercury tonometer (Riester, Germany). The indicator of the normalized power of the spectrum in the range of 0.15–0.40 Hz was evaluated by 5-minute records; three groups of persons were distinguished according to its distribution at rest by the method of signal deviation, namely, sympathicotonic, normotonic and parasympathicotonic. The initial level of autonomic tone was found to impact the dynamics of СО2 level in alveolar air during hyperventilation and during recovery thereafter. Thus, PetCО2 was higher (41.3 mm Hg) in parasympathicotonic than in sympathicotonic (39.3 mm Hg) and normotonic (39.5 mm Hg) persons. During the test, R-R interval duration decreased being more expressed in normotonic persons. At the same time, the heart index was found to increase in three groups, and general peripheral resistance – to decrease mostly in normo- and parasympathicotonic persons. In addition, the reliable increase of stroke index and heart index was found in these groups. In the recovery period after hyperventilation, the decrease of tension index and ejection speed was found in normo- and, particularly, parasympathicotonic compared with sympathicotonic men and the increase of tension phase and ejection phase duration.

TESTING THE VAGAL WITHDRAWAL HYPOTHESIS DURING LIGHT EXERCISE UNDER AUTONOMIC BLOCKADE: A HEART RATE VARIABILITY STUDY

INTRODUCTION

We performed the first analysis of heart rate variability (HRV) at rest and exercise under full autonomic blockade on the same subjects, to test the conjecture that vagal tone withdrawal occurs at exercise onset. We hypothesized that, between rest and exercise: i) no differences in total power (PTOT) under parasympathetic blockade; ii) a PTOT fall under β1-sympathetic blockade; iii) no differences in Ptot under blockade of both ANS branches.

METHODS

7 males (24±3 years) performed 5-min cycling (80W) supine, preceded by 5-min rest during control and with administration of atropine, metoprolol and atropine+metoprolol (double blockade). Heart rate and arterial blood pressure were continuously recorded. HRV and blood pressure variability were determined by power spectral analysis, and baroreflex sensitivity (BRS) by the sequence method.

RESULTS

At rest, PTOT and the powers of low (LF) and high (HF) frequency components of HRV were dramatically decreased in atropine and double blockade compared to control and metoprolol, with no effects on LF/HF ratio and on the normalised LF (LFnu) and HF (HFnu). At exercise, patterns were the same as at rest. Comparing exercise to rest, PTOT varied as hypothesized. For SAP and DAP, resting P_TOT was the same in all conditions. At exercise, in all conditions, P_TOT was lower than in control. BRS decreased under atropine and double blockade at rest, under control and metoprolol during exercise.

CONCLUSIONS

The results support the hypothesis that vagal suppression determined disappearance of HRV during exercise.

A Portable Wireless Communication Platform Based on a Multi-Material Fiber Sensor for Real-Time Breath Detection

In this paper, we present a new mobile wireless communication platform for real-time monitoring of an individual's breathing rate. The platform takes the form of a wearable stretching T-shirt featuring a sensor and a detection base station. The sensor is formed by a spiral-shaped antenna made from a multi-material fiber connected to a compact transmitter. Based on the resonance frequency of the antenna at approximately 2.4 GHz, the breathing sensor relies on its Bluetooth transmitter. The contactless and non-invasive sensor is designed without compromising the user's comfort. The sensing mechanism of the system is based on the detection of the signal amplitude transmitted wirelessly by the sensor, which is found to be sensitive to strain. We demonstrate the capability of the platform to detect the breathing rates of four male volunteers who are not in movement. The breathing pattern is obtained through the received signal strength indicator (RSSI) which is filtered and analyzed with home-made algorithms in the portable system. Numerical simulations of human breath are performed to support the experimental detection, and both results are in a good agreement. Slow, fast, regular, irregular, and shallow breathing types are successfully recorded within a frequency interval of 0.16-1.2 Hz, leading to a breathing rate varying from 10 to 72 breaths per minute.

Cerebral ischemia during hemodialysis-finding the signal in the noise

Hemodialysis patients have multiple risk factors for small vessel cerebrovascular disease and cognitive dysfunction. Hemodialysis itself may cause clinically significant neurological injury through repetitive cerebral ischemia. However, supporting evidence to date consists of epidemiological associations, expert opinion, and small, single-centre studies of variable methodological quality. Isolating the impact of intra-dialytic hemodynamic instability from underlying renal and vascular disease on clinically relevant functional outcomes would require very large, controlled studies, given the heterogeneity and confounding comorbidities of the population, and the complex relationship between blood pressure and cerebral oxygen delivery. There has been an increase in complementary physiological studies looking directly at intra-dialytic cerebral oxygen balance, which have provided supporting evidence for the occurrence of cerebral ischemia, often independently of hemodynamics. Data suggesting a relationship between these measures of oxygen balance and functional outcomes is only hypothesis-generating at this stage. We advocate the testing of interventions that aim to reduce intra-dialytic cerebral hypoxia (rather than hypotension) in sufficiently powered studies, followed by correlation with validated, longitudinal assessment of clinically relevant neurological damage.

Reduced cardiac autonomic response to deep breathing: A heritable vulnerability trait in patients with schizophrenia and their healthy first-degree relatives

Reduced resting heart rate variability (HRV) has been observed in patients with schizophrenia and their relatives, suggesting genetic predispositions. However, findings have not been consistent. We assessed cardiac autonomic response to deep breathing in first-degree relatives of patients with schizophrenia (n=45; 26 female; aged 39.69±14.82 years). Data were compared to healthy controls (n=45; 26 female; aged 38.27±9.79 years) matched for age, gender, body mass index and physical activity as well as to unmedicated patients with acute schizophrenia (n=45; 25 female; aged 37.31±12.65 years). Electrocardiograms were recorded under supine resting and deep-breathing conditions (10-12breaths/min). We measured HRV components including variance, low-frequency (LF) power, which may reflect baroreflex function, high-frequency (HF) power, which reflects cardiac parasympathetic activity, and LF/HF ratio, which may reflect sympatho-vagal balance. Patients rather than relatives exhibited lower resting-state HRV (variance, LF, and HF) than controls. As expected, deep breathing induced an increase in variance and HF-HRV in controls. However, such a response was significantly reduced in both patients and their relatives. In conclusion, the diminished cardiac autonomic reactivity to deep breathing seen in patients and their unaffected relatives indicates that this pattern of cardiac autonomic dysregulation may be regarded as a genetic trait marker for schizophrenia.

Weight-of-evidence evaluation of short-term ozone exposure and cardiovascular effects

There is a relatively large body of research on the potential cardiovascular (CV) effects associated with short-term ozone exposure (defined by EPA as less than 30 days in duration). We conducted a weight-of-evidence (WoE) analysis to assess whether it supports a causal relationship using a novel WoE framework adapted from the US EPA's National Ambient Air Quality Standards causality framework. Specifically, we synthesized and critically evaluated the relevant epidemiology, controlled human exposure, and experimental animal data and made a causal determination using the same categories proposed by the Institute of Medicine report Improving the Presumptive Disability Decision-making Process for Veterans ( IOM 2008). We found that the totality of the data indicates that the results for CV effects are largely null across human and experimental animal studies. The few statistically significant associations reported in epidemiology studies of CV morbidity and mortality are very small in magnitude and likely attributable to confounding, bias, or chance. In experimental animal studies, the reported statistically significant effects at high exposures are not observed at lower exposures and thus not likely relevant to current ambient ozone exposures in humans. The available data also do not support a biologically plausible mechanism for CV effects of ozone. Overall, the current WoE provides no convincing case for a causal relationship between short-term exposure to ambient ozone and adverse effects on the CV system in humans, but the limitations of the available studies preclude definitive conclusions regarding a lack of causation. Thus, we categorize the strength of evidence for a causal relationship between short-term exposure to ozone and CV effects as "below equipoise."

Two separable mechanisms are responsible for mental stress effects on high frequency heart rate variability: an intra-individual approach in a healthy and a diabetic sample

Central withdrawal of parasympathetic cardiac control and increased respiratory frequency represent two important determinants of reduced respiratory-related heart rate variability (HRV). However, studies are missing to disentangle their relative contribution during mental stress. Healthy subjects (n=10) and type 2 diabetic patients (n=8), the latter with evidence of cardiac autonomic neuropathy, participated in this study. Using an intra-individual approach, high-frequency (hf) HRV was assessed for spontaneous (during rest and mental stress) and paced breathing (0.15, 0.2, 0.25, 0.3, 0.35, 0.4 and 0.45 Hz; randomized sequence). Mental stress was induced by a challenging reaction time task. Effects of respiratory frequency on hf HRV were individually predicted by paced breathing data. Mental stress decreased hf HRV (p<.001), and increased respiratory frequency (p=.01). Individual prediction of hf HRV by stress respiratory frequency resulted in lower values (p=.02) than observed during rest, indicating that respiratory stress effects were sufficient to reduce hf HRV. However, observed hf HRV values during stress were even lower (p<.001). These results indicate that hf HRV reductions during stress can only partly be explained by concomitant respiratory frequency changes. This effect is detectable in healthy subjects and in patients with evidence of diabetic cardiac autonomic neuropathy.

Acupuncture--deep pain with an autonomic dimension?

Stimulation of acupuncture point Pc6, located above the median nerve, has been shown to be effective in treating nausea and vomiting. It has also frequently been reported to cause a heart rate reduction. The mechanism behind this autonomic reaction has not been clarified, so far. We combined brainstem-sensitive functional magnetic resonance imaging with heart rate recording and time-resolved rating of the needling sensation to measure neuronal correlates of sensations and autonomic reactions during acupuncture. On the cortical level, needling sensation activated typical pain-related areas, of which the ventromedial and dorsolateral prefrontal cortex and perigenual anterior cingulate cortex were further involved in mediating the heart rate response. In the brainstem, needling sensation activated nuclei of the descending pain control system, in which a network of hypothalamus, periaqueductal gray, rostral ventromedial medulla, and ventrolateral medulla was identified as the source of the heart rate changes. Our findings indicate that acupuncture may be a special pain stimulus, whose autonomic concomitants could explain its non-analgesic effects and in some cases even have a therapeutic potential.

Metabolic energy correlates of heart rate variability spectral power associated with a 900-calorie challenge

We studied healthy males challenged with a 900 Cal test beverage and correlated EE with the raw (ms²) and normalized units (nu) of total power (TP), low frequency/high frequency (LF/HF) and VLF spectral power of heart rate variability (HRV). The correlations were evaluated during 20 min of normal breathing (NB, control) and 20 min of paced breathing (PB) at 12 breaths·min⁻¹ (0.2 Hz). EE was not significantly correlated with any of the HRV variables before the metabolic challenge. After the challenge, EE was positively correlated with LF/HF and with VLF; VLF was also positively correlated with LF/HF during both NB and PB. These findings suggest that EE may be a correlate of LF/HF and of VLF spectral power of HRV in healthy adolescent/young adult males. The association of lower resting energy expenditure with lower amounts of VLF spectral power may occur in individuals with predilections for obese phenotypes.

Effects of prolonged expiration breathing on cardiopulmonary responses during incremental exercise

This study was designed to clarify the effects of breathing with prolonged expiration on cardiopulmonary responses and autonomic nervous activity during incremental exercise. Eleven healthy men were randomly assigned to breathing mode: a prolonged expiration breathing with a 2-s inspired time and 4-s expired time and a spontaneous breathing without any constraints. Oxygen uptake (V(O2)), ventilation efficiency (V(E)/V(CO2)) and rate pressure product were measured. Low- (LF) and high-frequency (HF) components of blood pressure and heart rate variability were analyzed to assess sympathetic and parasympathetic nervous activities, respectively. V(E)/V(CO2), rate pressure product and LF were significantly lower, and [Formula: see text] and HF were significantly higher during exercise with prolonged expiration than with spontaneous breathing. Striking effects of prolonged expiration breathing included the improvement of ventilation efficiency, the suppression of sympathetic nervous activity and the activation of parasympathetic one during incremental exercise. Furthermore, prolonged expiration breathing may have suppressed the exercise-induced increase in myocardial V(O2).

Association of body fat percentage and heart rate variability measures of sympathovagal balance

AIMS

We tested the hypothesis that body fat percentage determines cardiac sympathovagal balance in healthy subjects.

MAIN METHODS

Heart rate variability (HRV) measurements were made of the standard deviation of the normal-normal RR intervals (SDNN) and the low frequency/high frequency (LF/HF) ratio, from time domain and fast Fourier transform spectral analysis of electrocardiogram RR intervals during trials of uncontrolled and controlled (paced) breathing at 0.2Hz. Body fat percentage was measured by dual energy x-ray absorptiometric (DEXA) scanning. Significance of differences between uncontrolled and controlled (paced) breathing was determined by analysis of variance and correlations between body fat percentage and HRV measurements by Pearson's coefficient at P<0.05.

KEY FINDINGS

Percent body fat was negatively correlated with LF/HF during the uncontrolled breathing (r=-0.56, two-tailed P<0.05, one-tailed P<0.01) but not during the paced breathing trial (r=-0.34, (P>0.1).

SIGNIFICANCE

We conclude that sympathetic activity produced by paced breathing at 0.2Hz can obscure the relationship between body fat percentage and sympathovagal balance and that high body fat percentage may be associated with low sympathetic modulation of the heart rate in healthy adolescent/young adult males.

Effect of different breathing patterns on nonlinearity of heart rate variability

We studied the effects of different respiratory patterns, namely, spontaneous breathing, paced breathing (at a rate of 10 breaths/min and at their mean spontaneous breathing frequency) and breath holding, on the nonlinear characteristics of heart rate variability (HRV). The results showed that paced breathing at both rates significantly diminished the nonlinearity of HRV detected by the Volterra-Wiener series method in comparison with spontaneous breathing, while breath holding increased it. These findings indicate spontaneous breathing rate is probably optimum to maintain cardiopulmonary coupling nonlinearly, and thus to minimize the influence on cardiovascular variabilities.

Indirect measures of human vagal withdrawal during head-up tilt with and without a respiratory acidosis

Human ECG records were analyzed during supine (SUP) rest and whole body 80 degrees head-up tilt (HUT), with a respiratory acidosis (5%CO(2)) and breathing room air (RA). HUT increased heart rate in both conditions (RA(SUP) 60 +/- 13 vs. RA(HUT) 79 +/- 16; 5%CO(2SUP) 63 +/- 12 vs. 5%CO(2HUT) 79 +/- 14 beats min(-1)) and decreased mean R-R interval, with no changes in the R-R interval standard deviation. When corrected for changes in frequency spectrum total power (NU), the high frequency (0.15-0.4 Hz) component (HF(NU)) of heart rate variability decreased (RA(SUP) 44.01 +/- 21.57 vs. RA(HUT) 24.05 +/- 13.09; 5%CO(2SUP) 69.23 +/- 15.37 vs. 5%CO(2HUT) 47.64 +/- 21.11) without accompanying changes in the low frequency (0.04-0.15 Hz) component (LF(NU)) (RA(SUP) 52.36 +/- 21.93 vs. RA(HUT) 66.58 +/- 19.49; 5%CO(2SUP) 22.97 +/- 11.54 vs. 5%CO(2HUT) 40.45 +/- 21.41). Positive linear relations between the tilt-induced changes (Delta) in HF(NU) and R-R interval were recorded for RA (DeltaHF(NU) = 0.0787(DeltaR-R) - 11.3, R (2) = 0.79, P < 0.05), and for 5%CO(2) (DeltaHF(NU) = 0.0334(DeltaR-R) + 1.1, R (2) = 0.82, P < 0.05). The decreased HF component suggested withdrawal of vagal activity during HUT. For both RA and 5%CO(2), the positive linear relations between DeltaHF(NU) and DeltaR-R suggested that the greater the increase in heart rate with HUT, the greater the vagal withdrawal. However, a reduced range of DeltaHF during HUT with respiratory acidosis suggested vagal withdrawal was lower with a respiratory acidosis.

Cardiac vagal control and respiratory sinus arrhythmia during hypercapnia in humans

Normoxic hypercapnia may increase high-frequency (HF) power in heart rate variability (HRV) and also increase respiratory sinus arrhythmia (RSA). Low-frequency (LF) power may remain unchanged. In this study, 5-min ECG recordings (N = 10) were analyzed in time and frequency domains while human subjects breathed normoxic 5% CO2 (5%CO2) or room air (RA). Tidal volume (VT), inhalatory (TI), and exhalatory (TE) times of breaths in the final minute were measured. ECG time domain measures were unaffected by CO2 inhalation (P > 0.05). Following natural logarithmic transformation (LN), LFLN was unaltered (RA: 7.14 +/- 0.95 vs. 5%CO2: 7.35 +/- 1.12, P > 0.05), and HFLN increased (RA: 7.65 +/- 1.37 vs. 5%CO2: 8.58 +/- 1.11, P < 0.05) with CO2 inhalation. When changes in total power (NU) were corrected, LF(NU) decreased (RA: 34.4 +/- 22.9 vs. 5%CO2: 23.8 +/- 23.1, P < 0.01), and HFNU increased (RA: 56.5 +/- 22.3 vs. 5%CO2: 66.8 +/- 22.9, P < 0.01) with CO2 inhalation. TI (RA: 2.0 +/- 1.0 vs. 5%CO2: 1.9 +/- 0.8 s) and TE (RA: 2.5 +/- 1.1 vs. 5%CO2: 2.4 +/- 0.9 s) remained unchanged, but VT increased with CO2 inhalation (RA: 1.1 +/- 0.3 vs. 5%CO2: 2.0 +/- 0.8 L, P < 0.001). Heart rates during inhalation (RA: 35.2 +/- 4.4, 5%CO2: 34.5 +/- 4.8 beats min(-1)) were different from heart rates during exhalation (RA: 28.8 +/- 4.4, 5%CO2: 29.1 +/- 3.1 beats min(-1)). Hypercapnia did not increase the clustering of heart beats during inhalation, and we suggest that the HF component may not adequately reflect RSA.

Sample entropy of electrocardiographic RR and QT time-series data during rest and exercise

Sample entropy (SampEn) is a measure of the complexity of data. Few studies have compared the SampEn of electrocardiographic cardiac interval (RR) data (SampEn-RR) during differing physiological states, and none have examined SampEn for the corresponding QT interval (SampEn-QT). The aim of this study was to quantify SampEn-RR and SampEn-QT during rest and for a range of exercise workloads. Specific objectives were to assess both the utility of SampEn for discriminating between physiological states and the relationship of SampEn-RR with traditional measures of heart rate variability (HRV). Twelve males of similar age, mass and aerobic fitness participated. A three-lead ECG was recorded continuously during pre-exercise, progressive bicycle exercise and recovery, and beat-to-beat RR and QT intervals were quantified for sinus beats. SampEn and HRV were calculated within consecutive 1 min periods throughout. Consistent estimation of SampEn-RR and SampEn-QT was possible with an appropriate choice of SampEn parameters. SampEn-RR was sensitive to differing physiological conditions, but its discriminating ability was poorer than that of linear HRV indices. SampEn-RR was also negatively correlated with normalized LF and LF/HF parameters. We interpret changes in SampEn for RR and QT data in terms of the altered autonomic nervous system (ANS) control of either the atrial or the ventricular myocardium (or both) during discrete physiological states. We speculate that greater complexity in QT data might be explained by a direct ANS influence on the ventricular myocardium.

The periaqueductal grey area and the cardiovascular system

In this chapter, we report that blood pressure can be increased or decreased depending on whether an electrode is in ventral or dorsal PAG. We also describe that it is theoretically possible to treat orthostatic hypotension. These are exciting developments not only because they provide an example of direct translational research from animal research to humans but also because they highlight a potential for future clinical therapies. The control of essential hypertension without drugs is attractive because of the side effects of medication such as precipitation of heart failure [10]. Similarly, drug treatment of orthostatic hypotension cannot differentiate between the supine and standing positions and can therefore lead to nocturnal hypertension [22, 29]. A stimulator could be turned off at night or contain a mercury switch that reacts to posture.

Autonomic neurosurgery: from microvascular decompression to image guided stimulation

The paper reviews mechanisms underlying autonomic disorders, with a focus on cardiovascular dysfunction. Neurosurgical approaches are described for medically refractory hypertension and orthostatic hypotension. After review of microvascular decompression of the rostral ventrolateral medulla, stereotactic CT and MRI guided deep brain stimulation of the periaqueductal grey matter (PAG) is evaluated. Results are presented from patient studies showing reductions in blood pressure with ventral PAG stimulation and increases in blood pressure with dorsal PAG stimulation. A rationale for the treatment of autonomic disorders by neurosurgical intervention is discussed.

Controlling the Heart Via the Brain: A Potential New Therapy for Orthostatic Hypotension

OBJECTIVE:

Electrical stimulation of the midbrain is known to influence blood pressure in animals. In humans, it is used for the treatment of chronic neuropathic pain. Our aim was to assess whether orthostatic hypotension can be successfully treated with deep brain stimulation of the periventricular/periaqueductal gray areas in humans.

METHODS:

We recruited 11 patients who had chronic neuropathic pain and who had undergone implantation of a deep brain stimulator in the periventricular/periaqueductal gray areas. Patients were divided into three groups depending on whether they had orthostatic hypotension (one patient), mild orthostatic intolerance (five patients), or no orthostatic intolerance (five patients). Postoperatively, we continuously recorded blood pressure and heart rate with stimulation off and on and in both sitting and standing positions. From these values, we derived the blood pressure changing rate. Using autoregressive modeling techniques, we calculated changes in low- and high-frequency power spectra of heart rate and baroreflex sensitivity.

RESULTS:

Electrical stimulation reduced the decrease in systolic blood pressure on standing from 28.2 to 11.1% in one patient with orthostatic hypotension (P &lt; 0.001). In the mild orthostatic intolerance group, an initial drop in systolic blood pressure of 15.4% was completely reversed (P &lt; 0.001). There were no side effects in the remaining group. These changes were accompanied by increases in the blood pressure changing rate, the baroreflex sensitivity, and the baseline (sitting) low-frequency power of the RR interval, but not the high-frequency power.

CONCLUSION:

Electrical stimulation of the human periventricular/periaqueductal gray areas can reverse orthostatic hypotension. The cause seems to be an increase in sympathetic outflow and in baroreflex sensitivity. This has important implications for future therapies.

Effect of paced breathing on ventilatory and cardiovascular variability parameters during short-term investigations of autonomic function

Paced breathing (PB) around 0.25 Hz has been advocated as a means to avoid confounding and to standardize measurements in short-term investigations of autonomic cardiovascular regulation. Controversy remains, however, as to whether it causes any alteration in autonomic control. We addressed this issue in 40 supine, middle-aged, healthy volunteers by assessing the changes induced by PB (0.25 Hz for 8 min) on 1) ventilatory parameters, 2) the indexes of autonomic control of cardiovascular function, and 3) the spectral indexes of cardiovascular variability. Subjects were grouped into group 1 (n = 31), if spontaneous breathing was regular and within the high-frequency (HF) band (0.15-0.45 Hz), or group 2 (n = 9), if it was irregular or slow (< 0.15 Hz). In both groups, PB was accompanied by an increase in minute ventilation (both groups, P < 0.01), whereas tidal volume increased only in group 1 (P = 0.0003). End-tidal CO2 decreased by [median (lower quartile, upper quartile)] -0.2 (-0.5, -0.1)% (group 1, P < 0.0001) and -0.6 (-0.8, -0.5)% (group 2, P = 0.008). Mean R-R interval and systolic and diastolic pressure remained remarkably stable (all P > or = 0.13, both groups). No significant changes were observed in spectral indexes of R-R and pressure variability (all P > or = 0.12, measured only in group 1 to avoid confounding), except in the HF power of pressure signals, which significantly increased (all P < 0.05) in association with increased tidal volume. In conclusion, PB at 0.25 Hz causes a slight hyperventilation and does not affect traditional indexes of autonomic control or, in subjects with spontaneous breathing in the HF band, most relevant spectral indexes of cardiovascular variability. These findings support the notion that PB does not alter cardiovascular autonomic regulation compared with spontaneous breathing.

Serial assessment of cardiovascular control shows early signs of developing pre-eclampsia

PURPOSE

To evaluate whether differences in autonomic cardiovascular control between normal pregnant women and women who develop pre-eclampsia later in pregnancy can be detected even before or early in pregnancy.

DESIGN

We studied 42 women, 21 multigravid with a history of pre-eclampsia and 21 primigravid, before pregnancy, at 6, 8, 12, 16, 20 and 32 weeks gestation and 15 weeks after delivery.

METHODS

The outcome of pregnancy was classified after delivery as normal pregnancy (NP group) or pre-eclampsia (PE group). Continuous heart rate and blood pressure were recorded by Portapres (TNO, Amsterdam, The Netherlands) during orthostatic stress, during rest in a supine and sitting position, and during paced breathing for periods of 1 min at breathing frequencies of 6, 10 and 15 breaths/min. Baroreflex gain from heart rate and blood pressure variability and the phase angle between both signals at low (approximately 0.1 Hz) and high frequency (respiratory rate) were analyzed by spectral analysis.

RESULTS

Eight women were diagnosed with pre-eclampsia. Subgroups did not differ in age, weight or height. The PE group showed a significantly higher mean arterial pressure before and during pregnancy [analysis of variance (ANOVA), P = 0.001], a significantly larger initial blood pressure drop to orthostatic stress before and in the first half of pregnancy (ANOVA, P = 0.002) and a significantly larger negative phase difference during supine rest at low frequency from 8 weeks onward (ANOVA P = 0.003).

CONCLUSIONS

These findings are compatible with increased resting sympathetic activity and decreased circulating volume, already present before and early in pregnancy, in women who will later develop pre-eclampsia.

Role of mastication and swallowing in the control of autonomic nervous activity for heart rate in different postures

Mastication and swallowing increase the heart rate, and posture change and respiration also modulate the heart rate. To clarify the role of mastication and swallowing in the modulation of the autonomic nervous activity, we investigated how they interact with modulation of the heart rate by changing body positions and respiration in young healthy subjects. R-R intervals of electrocardiogram at rest were significantly changed with different body positions, compared with supine and standing. A net shortening by mastication of a chewing gum base was similar in various postures. Respiration induced a periodic change in the R-R intervals, depending on the body postures, but mastication did not markedly change them in each posture. Dry swallowing at rest and spontaneous swallowing during the mastication in the sitting position induced a similar transient shortening and suppressed the respiration-induced changes after the swallowing. The net transient shortening by dry swallowing at rest was similar in the different postures. These results suggest that signals from mastication and swallowing are summated with those from body positions and respiration for shortening the R-R intervals and that signals from swallowing suppress the respiration-induced periodic changes.

Age-related changes in cardiac autonomic control during sleep

Aging is commonly associated with decreased sleep quality and increased periodic breathing (PB) that can influence heart rate variability (HRV). Cardiac autonomic control, as inferred from HRV analysis, was determined, taking into account the sleep quality and breathing patterns. Two groups of 12 young (21.1 +/- 0.8 years) and 12 older (64.9 +/- 1.9 years) volunteers underwent electroencephalographic, cardiac, and respiratory recordings during one experimental night. Time and frequency domain indices of HRV were calculated in 5-min segments, together with electroencephalographic and respiratory power spectra. In the elderly, large R-R oscillations in the very-low frequency (VLF) range emerged, that reflected the frequency of PB observed in 18% of the sleep time. PB occurred more frequently during rapid eye movement sleep (REM) sleep and caused a significant (P < 0.02) increase in the standard deviation of normal R-R intervals (SDNN) and absolute low-frequency (LF) power. With normal respiratory patterns, SDNN, absolute VLF, LF, and high frequency (HF) power fell during each sleep stage (P < 0.01) compared with young subjects, with no significant sleep-stage dependent variations. An overall decrease (P < 0.01) in normalized HF/(LF + HF) was observed in the elderly, suggesting a predominant loss of parasympathetic activity which may be related to decreased slow-wave sleep duration. These results indicate that two distinct breathing features, implying different levels of autonomic drive to the heart, influence HRV in the elderly during sleep. The breathing pattern must be considered to correctly interpret HRV in the elderly.

Effects of external periodic perturbations on short-term heart rate variability in healthy subjects and ischemic heart disease patients

AIMS

To characterise the frequency response of short-term heart rate variability to external periodic perturbations in healthy and ischemic heart disease subjects.

METHODS

Eleven healthy men and 11 ischemic heart disease patients were enrolled in this study. The frequency response of heart rate variability was assessed during periodic eyes opening test and controlled breathing at frequencies ranging from 0.08 to 0.25 Hz using autoregressive spectral analysis.

RESULTS

In subjects of both groups the mean heart rate and blood pressure were unchanged across experimental sessions. In healthy subjects eyes opening at rate of 8 and 6 times/min (0.12 and 0.10 Hz) evoked high-power peaks (P<0.05) at the same frequencies in the R-R power spectrum. The largest frequency response of heart rate variability was seen during eyes opening at 0.1 Hz (P<0.05). Ischemic heart disease patients failed to respond to periodic eyes opening with any changes in heart rate variability. During controlled breathing healthy subjects showed the highest heart rate variability frequency responses when breath frequency was 0.1 Hz (P<0.05). Comparatively, patients with ischemic heart disease had reduced frequency responses of heart rate variability at all breath rates and its magnitude did not depend on the perturbation frequency.

CONCLUSIONS

Our results demonstrate that the frequency response of short-term heart rate variability to external periodic perturbations is dependent on the perturbation frequency and the presence disease processes in the cardiovascular system.

Non-invasive assessment of autonomic cardiovascular control in normal human pregnancy and pregnancy- associated hypertensive disorders: a review

PURPOSE

Pre-eclampsia is a major complication of pregnancy. Although the disorder usually becomes apparent only in the third trimester of pregnancy, evidence is available that underlying pathophysiological abnormalities are already present early in pregnancy. The association between alterations in autonomic cardiovascular control and the development of hypertension in pregnancy has been investigated for some time. Non-invasive methods are especially of interest, since they have the advantage of minimal risk for the mother and the conceptus and enable repeated measurements during pregnancy. If non-invasive tests for autonomic cardiovascular control could demonstrate the increased sympathetic activity, as observed by microneurography than this method is a candidate for early identification of pre-eclampsia. Therefore, the literature on non-invasive testing of autonomic cardiovascular control in normal pregnancies and pre-eclampsia was summarized.

DATA IDENTIFICATION AND SELECTION

Medline was searched and 36 articles on autonomic cardiovascular control in human pregnancy by non-invasive test methods were reviewed. For each test method, data of different studies were summarized to evaluate if the method could discriminate between healthy pregnancy and pre-eclampsia.

CONCLUSION

Although small differences have been observed between normal pregnancy and pre-eclampsia in individual studies using non-invasive methods, the consistency in the available data is insufficient to discriminate between normal pregnancy and pre-eclampsia. The failure to demonstrate the increased sympathetic activity, as observed by direct microneurography, might be due to methodological factors of the non-invasive studies. Alternatively, sympathetic activity to resistance vessels in skeletal muscle may not be a proper reflection of autonomic cardiovascular control in pregnancy. Well-designed longitudinal research could be useful to test these suppositions.

Autonomic function in elderly patients with chronic heart failure

AIMS

Autonomic function (AF) is attenuated by heart failure (HF). Reports have been based on studies of young patients with systolic heart failure (SHF). However, HF is a disease of older patients who are more likely to have diastolic heart failure (DHF). We investigated whether age alters AF in elderly HF patients and whether the haemodynamic type of HF influences AF.

METHOD AND RESULTS

Thirty-six elderly HF (Framingham criteria) patients (11 with SHF, 25 with DHF) and 21 matched healthy subjects underwent simple bedside AF tests. Compared with the reference values for healthy adults, the mean E:I ratios and the median 30:15 ratios standing were all essentially normal. The median 30:15 ratios tilt and the mean Valsalva ratios were all significantly below the reference value (P for all cases <<0.050). Comparing three groups, there were no significant differences for mean E:I ratio (P=0.111), 30:15 tilt (P=0.619) and 30:15 standing (P=0.167), whereas there were significant differences for the mean Valsalva ratios (P=0.001). The mean Valsalva ratio of the SHF patients was significantly lower than that for the DHF patients (P<0.001) which in turn was significantly lower than the result of the healthy subjects (P<0.001).

CONCLUSION

There is an age-related impairment in AF with further impairment occurring in patients with HF. However, the severity of autonomic dysfunction is less in patients with DHF compared with patients with SHF.

Modulatory effects of respiration

Respiration is a powerful modulator of heart rate variability, and of baro- and chemoreflex sensitivity. Abnormal respiratory modulation of heart rate is often an early sign of autonomic dysfunction in a number of diseases. In addition, increase in venous return due to respiration may help in maintaining blood pressure during standing in critical situations. This review examines the possibility that manipulation of breathing pattern may provide beneficial effects in terms not only of ventilatory efficiency, but also of cardiovascular and respiratory control in physiologic and pathologic conditions, such as chronic heart failure. This opens a new area of future research in the better management of patients with cardiovascular autonomic dysfunction.

Shift work modifies the circadian patterns of heart rate variability in nurses

OBJECTIVE

The influence of shifting the work-sleep cycle on the circadian rhythm of cardiac autonomic activity was investigated by the spectral analysis of heart rate variability (HRV).

METHODS

The subjects were 10 healthy Japanese female nurses aged 33+/-3 (S.D.) years. The subjects underwent ambulatory 24-h electrocardiogram (ECG) recordings on the days of day shift (working from 08:00 to 17:00 h) and night shift (working from 21:40 to 08:40 h). Variables of the frequency domain of HRV were calculated for three activity states (work, awake but not working, and sleep).

RESULTS

The mean values of HRV variables over 24 h were not different between day shift and night shift. For both shifts, variables related to the sympathetic control (low frequency component in normalized units and low/high frequency component ratio) were the largest during the work period and the smallest during the sleep period, while an opposite order was present for variables related to the vagal control (high frequency component in absolute value and normalized units). HRV variables in each activity state were not different between the two shifts.

CONCLUSIONS

The circadian rhythm of cardiac autonomic activity is largely modified by the level of physical activity regardless of the clock hour, which may have clinical implications when studying the circadian fluctuations of the onset of cardiovascular disease in shift workers.

Time domain, geometrical and frequency domain analysis of cardiac vagal outflow: effects of various respiratory patterns

The purpose of this study was to compare the applicability of four different measures of heart rate variability (HRV) in the assessment of cardiac vagal outflow, with special reference to the effect of breathing pattern. The anticholinergic effects of an intravenous glycopyrrolate infusion (5 microg x kg(-1) x h(-1) for 2 h) during spontaneous and controlled (15 min(-1)) breathing rate were investigated in eight volunteers, and the effects of different fixed breathing rates (6-15-24 min(-1)) and hyperventilation in 12 subjects. Cardiac vagal activity was assessed by ECG recordings in which the following measures of HRV were computed: the high-frequency (HF) spectral component, the instantaneous RR interval (RRI) variability (SD1) analysed from the Poincaré plots, the percentage of differences between successive RRIs greater than 50 ms (pNN50), and the square root of the mean squared differences of successive RRIs (RMSSD). On average, glycopyrrolate reduced the HF spectral component by 99.8%, SD1 by 91.3%, pNN50 by 100% and RMSSD by 97.0%. The change of breathing pattern from controlled to spontaneous decreased significantly the HF component and pNN50, but did not affect SD1 or RMSSD. Rapid breathing rate (24 min(-1)) decreased the HF component, but had no effects on the other measures. A controlled breathing rate is needed for a reliable assessment of cardiac vagal outflow by the spectral analysis technique. The quantitative geometrical analysis of short-term RRI variability from the Poincaré plots and the time domain measure RMSSD were not significantly affected by changes in the breathing rate, suggesting that these indices are more suitable for the measurement of cardiac vagal outflow during the 'free-running' ambulatory conditions.

Breathing patterns and cardiovascular autonomic modulation during hypoxia induced by simulated altitude

OBJECTIVE

To assess the influence of different breathing patterns on autonomic cardiovascular modulation during acute exposure to altitude-induced hypoxia.

DESIGN

We measured relative changes in minute ventilation (VE), oxygen saturation (%SaO2), spectral analysis of RR interval and blood pressure, and response to stimulation of carotid baroreceptors (neck suction) at baseline and after acute (1 h) hypobaric hypoxia (equivalent to 5,000 m, in a hypobaric chamber).

METHODS

We studied 19 human subjects: nine controls and 10 Western yoga trainees of similar age, while breathing spontaneously, at 15 breaths/min (controlled breathing) and during 'complete yogic breathing' (slow diaphragmatic + thoracic breathing, approximately 5 breaths/min) in yoga trainees, or simple slow breathing in controls.

RESULTS

At baseline %SaO2, VE and autonomic pattern were similar in both groups; simulated altitude increased VE in controls but not in yoga trainees; %SaO2 decreased in all subjects (P< 0.0001), but more in controls than in yoga trainees (17 versus 12%, 14 versus 9%, 14 versus 8%, all P< 0.05 or better, during spontaneous breathing, controlled breathing and yogic or slow breathing, respectively). Simulated altitude decreased RR interval (from 879 +/- 45 to 770 +/- 39, P < 0.01) and increased indices deducted from spectral analysis of heart rate variability (low frequency/high frequency (LF/HF) ratio from 1.6 +/- 0.5 to 3.2 +/- 1.1, P < 0.05) and systolic blood pressure (low-frequency fluctuations from 2.30 +/- 0.31 to 3.07 +/- 0.24 In-mmHg2, P< 0.05) in controls, indicating sympathetic activation; these changes were blunted in yoga trainees, and in both groups during slow or yogic breathing. No effect of altitude was seen on stimulation of carotid baroreceptors in both groups.

CONCLUSIONS

Well-performed slow yogic breathing maintains better blood oxygenation without increasing VE (i.e. seems to be a more efficient breathing) and reduces sympathetic activation during altitude-induced hypoxia.

Cardiovascular responses to anesthetic induction in patients chronically treated with angiotensin-converting enzyme inhibitors

PURPOSE

To investigate the effects of chronic ACE inhibition on cardiac neural function following induction of general anesthesia in patients with underlying coronary artery disease.

METHOD

In a prospective case-control study, heart rate variability (HRV) and baroreflex control were compared preoperatively and 30 min after anesthesia induction in patients receiving, or not, ACEI (n=16, control group and n=16, ACEI group). All patients had normal cardiac function and anesthesia consisted of a fixed dose regimen of fentanyl and midazolam. Anesthesia-related hypotension was defined by systolic blood pressure < 90 mmHg. Spectral density of HRV was calculated for low frequency and high frequency bands (LF, from 0.05 to 0.15 Hz and HF, from > 0.15 to 0.6 Hz). Baroreflex sensitivity was estimated after blood pressure changes induced by injections of phenylephrine (PHE) and nitroglycerin (NTG).

RESULTS

The HRV parameters and baroreflex sensitivity were not different between groups, during the awake and anesthesia periods. Anesthesia produced similar reduction in total HRV in the Control and ACEI groups (-93 +/- 28% vs -89 +/- 32%), and in baroreflex sensitivity during NTG (-64 +/- 21% vs -54 +/- 17%) or PHE tests (-74 +/- 25% vs -72 +/- 22%). Anesthesia-related hypotension occurred in nine patients in the ACEI group (vs two controls). Although the hypertensive response to phenylephrine was greater after anesthesia in both groups, the sensitivity to phenylephrine was attenuated in those patients experiencing hypotension in the ACEI group.

CONCLUSIONS

Chronic preoperative treatment with ACEIs does not influence cardiac autonomic regulation and anesthetic-induced hypotensive episodes are mainly attributed to decreased alpha-adrenergic vasoconstrictive response.

Effects of controlled breathing, mental activity and mental stress with or without verbalization on heart rate variability

OBJECTIVES

To assess whether talking or reading (silently or aloud) could affect heart rate variability (HRV) and to what extent these changes require a simultaneous recording of respiratory activity to be correctly interpreted.

BACKGROUND

Sympathetic predominance in the power spectrum obtained from short- and long-term HRV recordings predicts a poor prognosis in a number of cardiac diseases. Heart rate variability is often recorded without measuring respiration; slow breaths might artefactually increase low frequency power in RR interval (RR) and falsely mimic sympathetic activation.

METHODS

In 12 healthy volunteers we evaluated the effect of free talking and reading, silently and aloud, on respiration, RR and blood pressure (BP). We also compared spontaneous breathing to controlled breathing and mental arithmetic, silent or aloud. The power in the so called low- (LF) and high-frequency (HF) bands in RR and BP was obtained from autoregressive power spectrum analysis.

RESULTS

Compared with spontaneous breathing, reading silently increased the speed of breathing (p < 0.05), decreased mean RR and RR variability and increased BP. Reading aloud, free talking and mental arithmetic aloud shifted the respiratory frequency into the LF band, thus increasing LF% and decreasing HF% to a similar degree in both RR and respiration, with decrease in mean RR but with minor differences in crude RR variability.

CONCLUSIONS

Simple mental and verbal activities markedly affect HRV through changes in respiratory frequency. This possibility should be taken into account when analyzing HRV without simultaneous acquisition and analysis of respiration.

Frequency-domain heart rate variability in 24-hour Holter recordings: role of spectral method to assess circadian patterns and pharmacological autonomic modulation

Different spectral methodologies for heart rate variability were recently shown to provide the same qualitative results in the context of passive tilt test. However, the impact of the method and the use of normalized power units in long-term ECG monitoring is still debated. Autoregressive and Fast Fourier transform (FFT) spectral approaches were applied to assess circadian modulation and the effect of beta-blocker administration in mild hypertensive patients who underwent continuous ambulatory ECG recording (n = 44, 51 +/- 12 years, 30 men). Spectral analysis was applied to 5-minute sequences and spectral parameters representative of each circadian period (24 hour, day, night) were calculated. In baseline recordings, FFT spectral method provided a smaller estimate of total and very low frequency powers. On the contrary, low- and high-frequency components were systematically larger with FFT. Circadian variations were in favor of an increased overall nocturnal variability but of a reduced low frequency normalized power with both spectral methods. Chronic oral administration of beta-blocker induced an increase of all spectral components except for an unchanged low-frequency normalized power, independently from the spectral approach. In spite of quantitative differences, the qualitative assessment of circadian patterns and beta-blockade effect by autoregressive- and FFT-based spectral analyses is equivalent. The low-frequency component of heart rate variability cannot be considered a reliable direct marker of sympathetic activity in long-term ambulatory ECG recording.

Sympathovagal balance is major determinant of short-term blood pressure variability in healthy subjects

Short-term blood pressure variability (BPV) has been suggested to provide important information about cardiovascular regulation. However, the background of BPV, its determinants, and physiological correlates have remained obscure. The aim of this study was to characterize physiological correlates of BPV and to investigate associations between BPV and neural and hormonal regulatory systems at rest in healthy subjects. We studied 117 healthy, normal-weight, nonsmoking male and female subjects aged 23-77 yr. Spectral analysis of BPV and heart rate variability (HRV) was performed from 5-min blood pressure (Finapres) and electrocardiogram recordings during controlled breathing. Baroreflex sensitivity (BRS) was measured using the phenylephrine method. In addition, plasma concentrations of norepinephrine, epinephrine, and arginine vasopressin and plasma renin activity were measured. We found that the ratio between the low- and high-frequency components of HRV, an index of cardiac sympathovagal balance, correlated positively with total power and very low- and low-frequency components of systolic and diastolic BPV and inversely with high-frequency components of systolic and diastolic BPV. BRS, predominantly a measure of cardiac vagal regulation, correlated inversely with BPV. Furthermore, age, gender, body mass index, and systolic blood pressure contributed to BPV. Vasoactive hormones were not significant correlates of BPV. We conclude that sympathovagal balance of cardiovascular regulation is the major determinant of BPV. Other factors associated with BPV are age, gender, body mass index, blood pressure, and BRS.

Effect of breathing rate on oxygen saturation and exercise performance in chronic heart failure

BACKGROUND

In chronic heart failure (CHF), impaired pulmonary function can independently contribute to oxygen desaturation and reduced physical activity. We investigated the effect of breathing rate on oxygen saturation and other respiratory indices.

METHODS

Arterial oxygen saturation (SaO2) and respiratory indices were recorded during spontaneous breathing (baseline) and during controlled breathing at 15, six, and three breaths per min in 50 patients with CHF and in 11 healthy volunteers (controls). 15 patients with CHF were randomly allocated 1 month of respiratory training to decrease their respiratory rate to six breaths per min. Respiratory indices were recorded before training, at the end of training, and 1 month after training.

FINDINGS

During spontaneous breathing, mean SaO2 was lower in CHF patients than in controls (91-4% [SD 0.4] vs 95.4% [0.2], p<0.001). Controlled breathing increased SaO2 at all breathing rates in patients with CHF. Compared with baseline, minute ventilation increased at 15 breaths per min (+45.9% [9.8], p<0.01), did not change at six breaths per min, and decreased at three breaths per min (-40.3% [4.8], p<0.001). In the nine CHF patients who had 1 month of respiratory training, resting SaO2 increased from 92.5% (0.3) at baseline to 93.2% (0.4) (p<0.05), their breathing rate per min decreased from 13.4 (1.5) to 7.6 (1.9) (p<0.001), peak oxygen consumption increased from 1157 (83) to 1368 (110) L/min (p<0.05), exercise time increased from 583 (29) to 615 (23) min/s (p<0.05), and perception of dyspnoea reduced from a score of 19.0 (0.4) to 17.3 (0.9) on the Borg scale (p<0.05). There were no changes in the respiratory indices in the patients who did not have respiratory training.

INTERPRETATION

Slowing respiratory rate reduces dyspnoea and improves both resting pulmonary gas exchange and exercise performance in patients with CHF.

Assessment of cardiac vagal activity in patients with hyperthyroidism

Previous studies suggested that in patients with hyperthyroidism an autonomic imbalance and in particular a lower than normal vagal activity might be present. To verify this hypothesis we have evaluated the respiratory sinus arrhythmia (RSA, a measure of cardiac vagal activity) in ten hyperthyroid patients and in ten normal subjects. RSA was calculated from the power of the spectral component of the heart rate variability in high frequency band (HF-RR) during both spontaneous (supine and passive head-up tilt) and controlled breathing (supine). During controlled breathing the phase relation between heart rate and respiratory has been computed. The hyperthyroid patients showed a higher heart rate in all three conditions (P<0.001) and higher spontaneous respiratory rate in supine position (centered frequency of HF-RR: 0.342+/-0.015 vs 0.262+/-0.016 Hz; P<0.001). No difference was found in hyperthyroid patients compared to controls in terms of the HF-RR power in normalized units both during spontaneous breathing (supine, 43+/-8.3 vs 39.7+/-6.7%; tilt 18.8+/-5.9 vs 19.3 vs 4.1%; mean+/-SE) and controlled breathing (45.4+/-7.1 vs 48.9+/-6.9%). No difference was found also in terms of the phase relationship between the heart rate and the respiratory signals (77.5+/-32.3 vs 77.5+/-28.1, degrees). Hyperthyroid patients seem not to have an impaired cardiac vagal activity.