Non-invasive beat-to-beat cardiac output monitoring by an improved method of transthoracic bioimpedance measurement

Endothelin system polymorphisms in tilt test-induced vasovagal syncope

OBJECTIVES

As the endothelin system participates in the regulation of cardiovascular homeostasis, the aim of this study was to analyse the role of endothelin system polymorphisms in influencing tilt-induced vasovagal syncope.

METHODS

We evaluated 107 otherwise healthy subjects with recurrent unexplained syncope who underwent a head-up tilt test. All subjects were genotyped for the 3A/4A polymorphism of the EDN1 gene and the H323H T/C polymorphism of the EDNRA gene.

RESULTS

Fifty-eight patients (54%) fainted. In terms of the EDNRA polymorphism, eight subjects (8%) had the T/T genotype, 41 were heterozygous (38%) and 58 homozygous (54%) for the C allele. Sixty subjects (56%) carried homozygosis for the 3A allele of the EDN1 polymorphism and 47 were heterozygous (44%). The 4A allele was significantly more frequent in the patients who responded positively to the tilt test than in those who did not: the relative odds ratios and confidence intervals at univariate and multivariate analyses were respectively 2.37 (1.07-5.26) and 2.41 (1.05-5.49). Comparisons with a control group further supported these data. Among the tilt-positive patients, the carriers of the 4A allele were more likely to have a vasodepressive pattern than those who were homozygous for the 3A variant.

INTERPRETATION

The 3A/4A polymorphism of the EDN1 gene affects susceptibility to syncope, and the 4A variant associated with increased endothelin-1 expression may promote vasodepressive hemodynamic responses during tilt testing.

Heart rate and stroke volume response patterns to augmented orthostatic stress

AIMS

Combined head up tilt (HUT) and lower body negative pressure (LBNP) can be used to exploit the full spectrum of cardiovascular control mechanisms and to reveal characteristics of individual blood pressure control. We studied whether the response to combined HUT and LBNP was reproducible within subjects and whether characteristic response patterns could be distinguished between different subjects.

MATERIALS AND METHODS

Ten healthy young males were subjected to combined HUT and graded LBNP to achieve a presyncopal end point in four tests, each separated by more than 2 weeks. Heart rate, blood pressure and thoracic impedance were monitored, cardiac output and peripheral vascular resistance were computed.

RESULTS

From supine control to presyncope, heart rate, mean arterial blood pressure, pulse pressure and stroke index changed as expected. The time courses of heart rate and stroke volume as well as orthostatic tolerance times (15 +/- 6 to 18 +/- 7 minutes, n.s) appeared reproducible between trials within subjects but different between different subjects.

CONCLUSION

LBNP-tilt approach was repeatable in time and pattern. Furthermore, differences observed between subjects indicated preferred activation of selected pathways of blood pressure control in different individuals while at the same time, reproducibility measured within the same subject showed that preferential mechanisms were highly conserved within the same individual. These characteristics are a prerequisite to use the combined graded orthostatic paradigm for hemodynamic testing and identification.

Continuous non-invasive arterial pressure technique improves patient monitoring during interventional endoscopy

INTRODUCTION

Close monitoring of arterial blood pressure (BP) is a central part of cardiovascular surveillance of patients at risk for hypotension. Therefore, patients undergoing diagnostic and therapeutic procedures with the use of sedating agents are monitored by discontinuous non-invasive BP measurement (NIBP). Continuous non-invasive BP monitoring based on vascular unloading technique (CNAP, CN Systems, Graz) may improve patient safety in those settings. We investigated if this new technique improved monitoring of patients undergoing interventional endoscopy.

METHODS

40 patients undergoing interventional endoscopy between April and December 2007 were prospectively studied with CNAP(R) in addition to standard monitoring (NIBP, ECG and oxygen saturation). All monitoring values were extracted from the surveillance network at one-second intervals, and clinical parameters were documented. The variance of CNAP values were calculated for every interval between two NIBP measurements.

RESULTS

2660 minutes of monitoring were recorded (mean 60.1+/-34.4 min/patient). All patients were analgosedated with midazolam and pethidine, and 24/40 had propofol infusion (mean 90.9+/-70.3 mg). The mean arterial pressure for CNAP was 102.4+/-21.2 mmHg and 106.8+/-24.8 mmHg for NIBP. Based on the first NIBP value in an interval between two NIBP measurements, BP values determined by CNAP showed a maximum increase of 30.8+/-21.7% and a maximum decrease of 22.4+/-28.3% (mean of all intervals).

DISCUSSION

Conventional intermittent blood pressure monitoring of patients receiving sedating agents failed to detect fast changes in BP. The new technique CNAP improved the detection of rapid BP changes, and may contribute to a better patient safety for those undergoing interventional procedures.

Impaired arterial baroreflex function before nitrate-induced vasovagal syncope during head-up tilt test

AIMS

The aim of this study was to evaluate arterial baroreflex control of heart rate immediately before head-up tilt test (HUT)-induced vasovagal syncope (VVS).

METHODS AND RESULTS

We enrolled 97 otherwise healthy subjects with recurrent unexplained syncope. After 10 min of rest in supine position, they underwent a passive HUT potentiated with nitroglycerin administration after 20 min. Beat-to-beat heart rate and systolic blood pressure were continuously recorded. Sequence method was used to measure two complementary parameters reflecting arterial baroreflex control of heart rate: the baroreflex sensitivity (BRS) and the baroreflex effectiveness index (BEI). Twenty-one patients fainted before nitrate administration (HUT+) and 37 after nitrate administration (NTG+). Immediately before syncope, the NTG+ patients showed significantly lower BRS values than those observed at the end of the test in the patients without syncope (5.5 +/- 2.8 vs. 7.7 +/- 3.4 ms/mmHg; P = 0.004) and a significantly lower BEI (30 +/- 20% vs. 53 +/- 24%; P < 0.001). The HUT+ patients did not show any significant differences in BRS and BEI before syncope from the values observed during the corresponding tilt period in the other groups.

CONCLUSION

A significant depression in BRS and BEI occurs immediately before syncope in patients who faint after nitrate administration, thus suggesting that arterial baroreflex dysfunction plays a role in mediating nitrate-induced VVS.

Social support predicts hemodynamic recovery from mental stress in patients with implanted defibrillators

OBJECTIVE

Emotionally stressful events appear to trigger malignant ventricular arrhythmias and myocardial infarction in cardiac patients. However, the physiological pathways linking psychological stress to arrhythmias and adverse disease outcomes remain incompletely understood. In patients with implanted cardioverter-defibrillators (ICD) we investigated the impact of emotions and social support on cardiovascular recovery from mental stress. The hypothesis tested was that psychosocial resources help to maintain adaptive hemodynamic responses to mental stress.

METHODS

In 55 ICD patients we noninvasively measured hemodynamic and autonomic parameters during two sequentially performed mental stress tests (arithmetic and anger recall tests). The cardiovascular data obtained were associated with results from well-validated psychometric self-rating tests for anxiety and depression (HADS), anger (STAXI), and perceived social support (FSozU).

RESULTS

In the rest period after mental stress application the majority of the study participants (82%) showed a rapid fall in cardiac index, arterial blood pressure, and heart rate, as well as an increase in high-frequency heart rate variability, while the remainder had no or unexpected changes in the hemodynamic parameters examined. Patients missing hemodynamic recovery in the post-stress phase reported significantly less social support than normally reacting patients (P<.05). Multivariate logistic regression models confirm that social support is an independent and significant predictor of preserved hemodynamic recovery from mental stress, even after controlling for somatic confounders (multivariate odds ratio 4.1; 95% confidence interval 1.3-12.7; P=.015).

CONCLUSIONS

Our data indicate that in ICD patients better perceived social support is associated with a more pronounced hemodynamic recovery after mental stress.

Autonomic function testing in children and adolescents with diabetes mellitus

Cardiac autonomic neuropathy (CAN) is a common complication in type 1 diabetes mellitus (T1DM) and associated with an increased mortality. Early detection of CAN would be desirable for a better individual risk stratification. The aim of this study was to determine whether autonomic dysfunction can be diagnosed in young patients with a recent history of T1DM. Autonomic function was assessed in 20 pediatric patients with T1DM, aged 10-19 yr, and a control group of 136 non-diabetic patients using four cardiorespiratory reflexes: heart rate and blood pressure response in standing position, deep breathing, and Valsalva maneuver. Furthermore, power spectral analyses of the low- and high-frequency band of heart rate variability (HRV) and baroreflex sensitivity (BRS) were tested with the non-invasive Task force monitor (CNSystems, Graz, Austria). Cardiorespiratory reflexes were pathologic for at least one item in 75% of the diabetic and 60% in the healthy control group. A reduced BRS was always combined with abnormal HRV. We found this pattern in 30% of diabetic patients and never in the control group. In patients with impaired BRS, mean hemoglobin A1c (HbA1c) was 7.7% and duration of diabetes 6.5 yr. This did not differ from the overall value of the diabetic group: HbA1c level 8.4% and diabetes duration 7.3 yr. In conclusion, signs of autonomic dysfunction are not uncommon in an early stage of diabetes in young patients. Classical cardiorespiratory reflexes seem to be less specific than HRV and BRS as testing methods.

Sympathetic predominance of cardiovascular regulation during mild orthostatic stress in adolescents with chronic fatigue

Haemodynamic abnormalities have been documented in the chronic fatigue syndrome (CFS), indicating functional disturbances of the autonomic nervous system responsible for cardiovascular control. This study was designed to explore the pathophysiology in adolescent CFS-patients by analysing RR-interval (RRI) variability and diastolic blood pressure (DBP) variability during mild orthostatic stress, using an algorithm which accounts for non-stationary biosignals. A total of 27 adolescents with CFS and 33 healthy control subjects having equal age- and sex distribution underwent 15 min of 20 degrees head-up tilt (HUT). The spectral power densities of RRI and DBP were computed in the low-frequency (LF) band (0.04-0.15 Hz) and the high-frequency (HF) band (0.15-0.4 Hz) using an adaptive autoregressive algorithm to obtain a time-varying spectrum. RMSSD, a time domain index of RRI variability, was also computed. At rest, all indices of variability were similar in the two groups. During tilt, CFS patients had a larger increase in the LF/HF ratio (P<or=0.001) and normalized LF power of RRI (P<or=0.01), and a larger decrease in normalized HF power (P<or=0.01) of RRI than controls. CFS patients also had trends towards a larger decrease in absolute HF power of RRI and a larger increase in normalized LF power of DBP. These findings suggest that adolescents with CFS have sympathetic predominance of cardiovascular regulation during very mild orthostatic stress. Possible underlying mechanisms are moderate hypovolemia, abnormalities of reflex control or physical de-conditioning.

Noninvasive Measurement of Cardiac Output in Hemodialysis Patients by Task Force Monitor: A Comparison with the Transonic System

Cardiovascular disease is the leading cause of morbidity and mortality in maintenance hemodialysis (MHD) patients. The Transonic (TRS; Transonic Systems, Ithaca, NY) device is frequently used for determination of cardiac output (CO) by an indicator dilution technique. The Task Force Monitor (TFM; CN Systems, Graz, Austria) has gained attention as noninvasive tool for continuous beat-to-beat assessment of cardiovascular variables, including CO by impedance cardiography. Despite its use in cardiology and intensive care settings, the TFM has yet not been validated in dialysis patients. This study compares CO measurements in 12 MHD patients by TFM and TRS. Bland-Altman and regression analysis were used. CO was measured simultaneously by TRS and TFM. Average CO was 5.4 L/min by TRS and 5.0 L/min by TFM, respectively. Bland-Altman analysis revealed no significant systematic differences between the two methods (mean difference: 0.4 L/min; SD: 0.6; p > 0.05). Linear regression analysis showed significant correlation between both techniques (r = 0.802, p = 0.002). The SD of mean individual CO values was 1.1 L/min with TRS and 0.8 L/min with TFM, respectively.CO measured by TFM and TRS does not differ significantly, thus making the TFM an attractive noninvasive tool for the continuous beat-to-beat assessment of CO in MHD patients.

Arterial stiffness, central blood pressures, and wave reflections in cardiomyopathy-implications for risk stratification

BACKGROUND

In general, pulse pressure (PP), augmentation index (AIx), and pulse wave velocity (PWV) are directly and positively associated with cardiovascular risk. However, in patients with systolic heart failure, the opposite (ie, an association between a lower PP and a worse outcome) has been reported as well.

METHODS AND RESULTS

We assessed central PP and AIx, using applanation tonometry (SphygmoCor, AtCor Medical) in 63 patients with cardiomyopathy (CMP) and 126 controls, matched for age, gender, and brachial blood pressure (BP). All patients underwent coronary angiography for suspected coronary artery disease. In a subgroup (21 patients, 42 controls), we additionally measured aortic PWV invasively during catheter pullback. Mean age was 63.9 versus 64.1 years and ejection fraction (EF) was 29.9 versus 72.2% in patients versus controls, respectively. Calculated aortic systolic BP as well as invasively measured systolic BP was lower in patients versus controls. Central (but not peripheral) PP (33.8 versus 37.8 mm Hg, P = .01) and AIx (17.5 versus 23.3, P = .002) were lower and ejection duration was shorter (265 versus 314 ms, P < .00001) in patients as compared with controls. When we subdivided the CMP patients with respect to AIx, those with values below and equal to the median (median AIx = 17) had more advanced systolic dysfunction. In multiple regression analysis, EF was an independent predictor of AIx. PVW did not differ between CMP patients and controls (8.6 versus 8.2 m/s in patients versus controls, P = .43). Within the group of CMP patients, however, we observed a strong, positive correlation (r = 0.62, P = .003) between PWV and EF.

CONCLUSIONS

Central PP, AIx, but also aortic PWV, key measures of arterial function, are susceptible to left ventricular performance.

Influence of comorbidities and medication use on tilt table test outcome in elderly patients

BACKGROUND

The tilt table test (TTT) is a useful diagnostic tool in people with unexplained syncope, dizziness, and falls. However, preexisting comorbidities and medications affecting hemodynamic response might affect TTT outcome (i.e. presence or absence of vasomotor syncope). We studied the influence of these compounding factors on TTT outcome.

METHODS

One hundred and sixty-four elderly patients with a mean (+/-SD) age of 80.0 +/- 6.1 years (M:F 104:60) underwent TTT. Heart rate and blood pressure were recorded continuously using a noninvasive device (Task Force Monito, CNS systems, Graz, Austria). Predictors of TTT outcome in a backward regression analysis included age, gender, comorbidities (chronic heart failure, hypertension, diabetes, and cerebrovascular disease), and drugs (beta-blockers, angiotensin-converting enzyme inhibitors, calcium channel blockers, diuretics, digoxin, opioids, antidepressants, and nonsteroidal antiinflammatory agents).

RESULTS

TTT was positive in 30 patients (18.3%). None of the above factors were a significant predictor of TTT outcome. The use of calcium channel blockers predicted a drop in systolic blood pressure after 2 minutes of TTT (P = 0.048, R(2)= 0.018). However, this was not associated with significant changes in heart rate and did not influence TTT outcome.

CONCLUSION

The TTT outcome was not influenced by comorbidities or medications. TTT is a reliable diagnostic tool in a population characterized by significant comorbidities and polypharmacy.

Usefulness of an abnormal cardiovascular response during low-grade head-up tilt-test for discriminating adolescents with chronic fatigue from healthy controls

Hemodynamic dysfunction is documented in chronic fatigue syndrome (CFS). This study was conducted to investigate cardiovascular responses to orthostatic stress in adolescents with CFS, using a novel procedure for tilt-table testing. A total of 27 adolescents with CFS and 33 healthy control subjects with equal age and gender distribution underwent 15 minutes of 20 degrees head-up tilt testing. Heart rate, systolic blood pressure (BP), mean BP, diastolic BP, stroke index, total peripheral resistance index, end-diastolic volume index, and acceleration index were continuously and noninvasively recorded. At rest, patients with CFS had higher total peripheral resistance index values (p<0.01) and lower stroke index and end-diastolic volume index values (p<0.05) than controls. During 20 degrees head-up tilt testing, patients with CFS had greater increases in heart rate, diastolic BP (p<0.001), mean BP (p<0.01), and total peripheral resistance index (p<0.05) than controls and greater decreases in stroke index (p<0.05). Syncope or near syncope was not observed. In conclusion, this study found that adolescents with CFS have significant abnormalities of cardiovascular regulation in response to mild orthostatic stress, differentiating them from healthy controls.

The effects of the extent of spinal block on the BIS score and regional cerebral oxygen saturation in elderly patients: A prospective, randomized, and double-blinded study

BACKGROUND

Patients may become sedated with spinal anesthesia; however, the effect of the extent of spinal block on the Bispectral index (BIS), a processed electroencephalographic variable, has not been fully investigated. We evaluated the influence of the extent of spinal block on BIS values and on regional cerebral oxygen saturation (rSO(2)) in elderly patients.

METHODS

A prospective, randomized, double-blinded study was performed in 55 ASA II patients undergoing urological surgery. The patients were randomly allocated into one of two groups to receive 2.7 ml of 0.5% hyperbaric bupivacaine or 1.5 ml, and then divided into two groups according to level of spinal blockade: high spinal group (Th6 and above) or low spinal group (Th12 and below). Systolic blood pressure (SBP), heart rate (HR), cardiac output (CO), stroke volume (SV), BIS values, and rSO(2) were measured for 30 min. CO and SV were evaluated using impedance cardiograph methods.

RESULTS

The level of spinal blockade was Th4.7 +/- 1.0 in high spinal group (n = 20) and L2.5 +/- 2.2 in low spinal group (n = 20). High spinal anesthesia produced a significant decrease in SBP (p < 0.01) and SV (p < 0.01), but had no effect on CO. High spinal anesthesia significantly decreased BIS values (p < 0.01) without affecting rSO(2). There was relationship between level of spinal blockade and BIS values (r = 0.566). In contrast, no changes in above parameters were found in low spinal group.

CONCLUSIONS

This study provides evidence that the extent of spinal block may have significant influence on BIS values without affecting rSO(2) in elderly patients.

Heart rate variability and spontaneous baroreflex sequences in supine healthy volunteers subjected to nasal positive airway pressure

To determine the dynamic effects of short-term nasal positive airway pressure (nPAP) on cardiovascular autonomic control, continuous recordings of noninvasively obtained hemodynamic measurements and heart rate variability (HRV) were obtained in 10 healthy subjects during frequency-controlled breathing (between 0.20 and 0.24 Hz) in supine posture under different pressures of nPAP ranging from 3 to 20 cmH(2)O. HRV was assessed using spectral analysis of the R-R interval. The slope of the regression line between spontaneous systolic blood pressure and pulse interval changes was taken as an index of the sensitivity of arterial baroreflex modulation of heart rate (sequence method). Application of nPAP resulted in a pressure-dependent decrease of cardiac output and stroke volume (P < 0.05, ANOVA) and in an increase in total peripheral resistance (P < 0.03, ANOVA). Hemodynamic changes under increasing nPAP were accompanied by a decrease in total power of HRV despite mean R-R interval remaining unchanged. The overall decrease in HRV was accompanied by a reduction across all frequency bands when absolute units were used (P < 0.01). When the power of low frequency and high frequency was calculated in normalized units, a diminished high frequency and an increased low-to-high frequency ratio were observed (P < 0.05). Compared with low levels of nPAP, pressure levels of >10 cmH(2)O were associated with a significant decline in the mean slope of spontaneous baroreceptor sequences (P < 0.04). These findings indicate that short-term administration of nPAP in normal subjects exerts significant alterations in R-R interval variability and spontaneous baroreflex modulation of heart rate.