Éva Zöllei

Human autonomic responses to blood donation

In order to characterize autonomic responses to acute volume loss, supine ECG, blood pressure (BP) and uncalibrated breathing signal (UBS) recordings were taken before and after blood donation in 48 healthy volunteers. Time and frequency domain parameters of RR interval (RRI), BP and UBS variability were determined. Baroreflex gain was calculated by the technique of the spontaneous sequences and cross-spectral analysis. The systolic (SAP), diastolic (DAP) and mean BP (MAP) increased after the blood withdrawal. The central frequency of breathing and mean heart rate did not change. RRI variability increased in low frequency band (LF), tended to decrease in high frequency band (HF). Systolic BP variability increased in both frequency bands, but was statistically significant only in the high frequency band. Diastolic BP power increased in both frequencies. From the different baroreflex gain estimates, up sequence BRS and HF alpha index decreased significantly. The phase angle between RRI and systolic blood pressure powers in LF band did not change (-58 +/- 24 degrees and -54 +/- 26 degrees ). In the high frequency range, the phase became more negative (-1 +/- 29 degrees and -17 +/- 32 degrees, p = 0.001). The withdrawal of 350-400 ml blood in 5 min resulted in sympathetic activation, which was reflected in increased systolic, diastolic and mean BP. The increased BP oscillation was a sensitive marker of the minor volume depletion. This was coupled by increased RRI oscillation via baroreflex mechanisms in the LF band. Changes in the RRI and BP oscillations in the HF band showed no similar coupling. That points to the fact that RRI oscillations in this band should not be explained entirely by baroreflex mechanisms. Vagal withdrawal was reflected in decreased root mean square of successive differences (RMSSD), decreased HF RRI power and decreased up sequence BRS.

Measures of cardiovascular autonomic regulation derived from spontaneous methods and the Valsalva maneuver.

The response of heart rate to a given change of systolic blood pressure is a fundamental characteristic of the cardiovascular system. The assessment of baroreflex gain (BRS) as an index of baroreflex function is based on the quantification of RR interval changes related to blood pressure changes. The spontaneous sequence and cross spectral methods describe baroreflex gain derived from spontaneous fluctuations of these parameters, yielding the up sequence and down sequence BRS and the alfa index. Phase IV of the Valsalva maneuver is also used to calculate cardiac vagal baroreflex gain. In this study, we compared the two spontaneous methods and the Valsalva maneuver in assessing baroreflex gain in 56 healthy volunteers. The BRS values calculated from different methods were as follows: up sequence BRS 12 +/- 8.6 ms/mm Hg, down sequence BRS 10 +/- 6.1 ms/mm Hg, low frequency alfa index 12.1 +/- 8.2 ms/mm Hg, Valsalva BRS 9.7 +/- 7.2 ms/mm Hg. We found close relationship between baroreflex gain derived from up and down sequences (R = 0.91, p < 0.001), down sequence BRS and low frequency alfa index (R = 0.81, p < 0.001); significant correlation between up sequence BRS and low frequency alfa index (R = 0.65, p < 0.001), the Valsalva-derived BRS and down sequence BRS (R = 0.37, p = 0.043), but no correlation between the Valsalva BRS and up sequence BRS, the Valsalva BRS and low frequency alfa index. BRS values calculated by different methods decreased with increasing age. There was no influence of age on mean arterial blood pressure elevation in late phase II of the Valsalva maneuver, nor any indication that the Valsalva BRS was related to the MAP changes. We concluded that all of these methods are useful in calculating baroreflex gain, but owing to the differences in underlying physiological mechanisms, they are not necessarily in correlation with each other.

Respiratory effects on the reproducibility of cardiovascular autonomic parameters

The aim of this study was to assess the influence of breathing pattern on the reproducibility of the most commonly used heart rate and blood pressure variability parameters and baroreflex indices. 5–5 min ECG and blood pressure recordings were made and repeated for 10 healthy volunteers in supine rest on 10 consecutive days during spontaneous and 6 min−1 patterned breathing. We investigated the following parameters: mean RR interval (RRI); the standard deviation of RR intervals (SDRR); the root mean square of successive differences in RRI (RMSSD); the percentage of RRIs which differed by 50% from the proceeding RRI (PNN50); mean systolic arterial pressure (SAP); the standard deviation of SAP (SAP SD); mean mean arterial pressure (MAP); mean diastolic blood pressure (DAP) and baroreflex indices from spontaneous sequence method (upBRS and downBRS) and from cross spectral analysis (LF alpha, HF alpha). To assess reproducibility for each parameter within‐ and between‐subject variability values were calculated and the ratio of within‐ and between‐subject variability was assessed. In addition, we calculated intraclass correlation coefficient (ICC). Compared to spontaneous respiration during 6 min−1 patterned breathing the heart rate and blood pressure variability increased; upBRS, LF alpha and HF alpha increased, downBRS did not change. However, ICC showed good reproducibility for most parameters, which did not improve further with controlled breathing. In conclusion, respiration had a strong influence on the most widely used cardiovascular autonomic parameters. The controlling of breathing did not result in consistent improvement in their reproducibility.

Hemodynamic effects of slow breathing: Does the pattern matter beyond the rate?

PURPOSE Patterned breathing allows standardized serial measurements of heart rate variability and baroreflex indices. The slow breathing augments these parameters, and regular exercises, including yoga breathing practices with even respiratory rates have long-term beneficial effects in cardiovascular diseases. The role of temporization of breathing phases, i.e. the ratio of expiration to inspiration, is not known. In order to characterize the hemodynamic and autonomic responses during varying breathing phases 27 volunteers performed three short breathing sessions at 6/minutes frequency with 5:5, 3:7 and 7:3 inspiration expiration ratios. RESULTS The immediate responses in arterial pressure and heart rate were negligible. The time domain parameters of heart rate variability (SDRR, PNN50,RMSSD) increased significantly with patterned breathing. So did the spontaneous baroreflex gain of increasing sequences (up-BRS, from 12 ± 7 to 17 ± 10 ms/mmHg, p < 0.05), and the cross-spectral low frequency gain, the LFalpha (from 11 ± 7 to 15 ± 7 ms/mmHg, p < 0.05). None of these parameters differed significantly from each other while using any of tested inspiratory-expiratory patterns. CONCLUSION The major determinant of autonomic responses induced by slow patterned breathing is the breathing rate itself. From our observations, it follows that slow breathing exercises performed either with diagnostic or therapeutic purpose could be simplified, allowing more extensive investigations.

Severe cardiovascular autonomic dysfunction in a patient with Guillain-Barre syndrome: a case report

Autonomic dysfunction is a frequent and severe complication of Guillain-Barre syndrome. It is often responsible for cardiovascular abnormalities, even cardiac arrest. We report a 49-year-old patient, who suffered from Guillain-Barre syndrome necessitating mechanical ventilation. He showed wide fluctuations of blood pressure and heart rate spontaneously or in relation with medical procedures. Though heart rate variability (HRV) and baroreflex sensitivity (BRS) values derived from different methods were extremely low, vigorous stimuli, like eyeball pressure test and carotid sinus massage, produced exaggerated responses, like severe bradycardias, hypotension and cardiac arrest. Despite the plasma exchange and supportive therapies, the patient finally developed adult respiratory distress syndrome (ARDS), sepsis and died due to septic shock.

Spectral analysis problems of heart rate and blood pressure fluctuations

The spectral analysis of electrocardiogram (ECG) and blood pressure fluctuations is an important tool both in medical diagnostics and in theories that endeavour to account for the complex, feedbacked patterns of control mechanisms that regulate human circulation. In the case of ECG signals, the researcher is often interested not in the morphology but in the rate of heartbeats, which means that it is not the whole signal but only a so-called RR signal, containing the distances of beats, that serves as the basis of spectral processing. This RR signal is inherently discrete and unevenly sampled, which introduces a number of methodological problems: fast Fourier transformation assumes even sampling, and this means that an artificial re-sampling (inserting new samples at equal distances) is necessary. In the case of blood pressure signals, the information is both in the amplitude itself and in the rate, consequently both an RR-like and a full recording-based treatment are usable here. In the present paper we review the different approaches to dealing with unevenly sampled ECG and blood pressure signals, including the Lomb periodogram that does not require re-sampling at all, and argue for a full recording-based treatment of blood pressure fluctuations, as it requires no peak detection and thus avoids all the artefacts that peak detection may cause.

Noninvasive continuous arterial pressure measurements in the assessment of acute, severe central hypovolemia

UNLABELLED Acute, severe hypovolemia is a medical emergency. Traditional vital sign parameters allow no optimal triage. High predictive power of finger plethysmography-based stroke volume (SV) and pulse pressure (PP) was recently suggested. To assess the performance of the PP and SV parameters, lower body negative pressure of -40 mmHg, than -60 mmHg - corresponding to moderate and severe central hypovolemia - was applied in 22 healthy males (age 35 ± 7 years). Slow breathing induced fluctuations in the above indices, characterized by stroke volume variability (SVV), and pulse pressure variability (PPV), were assessed. Responses in heart rate (HR) and shock index (SI) were also studied. Discriminative capacity of these parameters was characterized by the area under the ROC (receiver operating characteristic) curves (AUC). RESULTS In comparison of baseline to severe central hypovolemia SV, PP, HR, and SI showed good discriminating capacity (AUC 99%, 88%, 87%, and 93%, respectively). The discriminating capacity of SVV and PPV was poor (77% and 70%, respectively). In comparison of moderate and severe hypovolemia, the discriminating capacity of the studied parameters was uniformly limited. CONCLUSIONS Plethysmography-based SV and PP parameters can be used to detect acute severe volume loss. Sensitive parameters discriminating moderate and severe central hypovolemia are still lacking.

Valsalva maneuver, Müller maneuver: hemodynamic and reflex mechanisms, relevances

The time honored ancient reflex tests, the Valsalva and Müller maneuvers are still popular in the everyday clinical practice. These maneuvers are capable of imitating both trivial situations and significant pathological conditions. The Valsalva maneuver is still frequently used for the assessment of autonomic neuropathy. Addition of continuous noninvasive blood pressure monitoring allows assessment of both cardiac vagal and sympathetic driven peripheral vasomotor responses. The Müller maneuver has recently gained renewed popularity in simulating episodes of obstructive sleep apnea (OSA). Continuous monitoring of arterial pressure and muscle sympathetic nerve activity (MSNA) casts light on the close relationship between OSA and circulatory abnormalities.

Cyclic Nonrespiratory Pulse Pressure Oscillations Caused by Atrioventricular Dissociation

Dynamic preload assessment tests, especially pulse pressure variation (PPV) and stroke volume variation (SVV), are increasingly acknowledged in mechanically ventilated patients as being predictors of fluid responsiveness. However, the limitations of this method are often neglected or overlooked. One of the prerequisites for PPV and SVV evaluation, in addition to intermittent positive pressure ventilation, is a “regular heart rhythm,” which may be an ambiguous term. We present a case where, despite a regular (paced) rhythm, atrioventricular dissociation was present and resulted in marked PPV elevation, which subsequently disappeared once sinus rhythm returned. Our case indicates that PPV and SVV should be interpreted with caution when atrioventricular dissociation is present.

Comment on arterial flow waveforms, vascular tone, and chronic fatigue by Zundel et al.

We read with interest the article by Zundel et al. on a unique plethysmographic waveform recorded in a patient with chronic fatigue (Zundel et al., 2015).We have seen similar cases during our hemodynamic studies on healthy volunteers, who had no history of orthostatic intolerance or chronic fatigue. Similar to Zundels patient, our subjects exhibited the peculiar biphasic plethysmographic waveform only at times of central hypovolemia, induced by upright tilt, or lower body negative pressure. Occasionally, the appearance of the biphasic waveform was also related to the breathing phase. Fig. 1 illustrates such situation. This chance observation allows further speculation regarding the mechanism of the biphasic waveform pattern. The biphasic morphology coincides with deep inspiration. Inspiration