Abstract
Respiratory activity introduces oscillations both in arterial pressure and heart period, through mechanical and autonomic mechanisms. Respiration, arterial pressure, and heart period are, generally, non-stationary processes and the interactions between them are dynamic. In this study we present a methodology to robustly estimate the time course of cross spectral indices to characterize dynamic interactions between respiratory oscillations of heart period and blood pressure, as well as their interactions with respiratory activity. Time-frequency distributions belonging to Cohen’s class are used to estimate time-frequency (TF) representations of coherence, partial coherence and phase difference. The characterization is based on the estimation of the time course of cross spectral indices estimated in specific TF regions around the respiratory frequency. We used this methodology to describe the interactions between respiration, heart period variability (HPV) and systolic arterial pressure variability (SAPV) during tilt table test with both spontaneous and controlled respiratory patterns. The effect of selective autonomic blockade was also studied. Results suggest the presence of common underling mechanisms of regulation between cardiovascular signals, whose interactions are time-varying. SAPV changes followed respiratory flow both in supine and standing positions and even after selective autonomic blockade. During head-up tilt, phase differences between respiration and SAPV increased. Phase differences between respiration and HPV were comparable to those between respiration and SAPV during supine position, and significantly increased during standing. As a result, respiratory oscillations in SAPV preceded respiratory oscillations in HPV during standing. Partial coherence was the most sensitive index to orthostatic stress. Phase difference estimates were consistent among spontaneous and controlled breathing patterns, whereas coherence was higher in spontaneous breathing. Parasympathetic blockade did not affect interactions between respiration and SAPV, reduced the coherence between SAPV and HPV and between respiration and HPV. Our results support the hypothesis that non-autonomic, possibly mechanically mediated, mechanisms also contributes to the respiratory oscillations in HPV. A small contribution of sympathetic activity on HPV-SAPV interactions around the respiratory frequency was also observed.
Highlights
IntroductionIt is well known that respiratory activity affects cardiovascular regulation [1,2,3,4], the mechanisms responsible for the coordination between the autonomic control of circulation and respiration are still unclear and currently matter of debate [5,6,7]
Non-stationary signal processing techniques applied to electrophysiological signals have been successful in the assessment of important features of cardiovascular control physiology. it is well known that respiratory activity affects cardiovascular regulation [1,2,3,4], the mechanisms responsible for the coordination between the autonomic control of circulation and respiration are still unclear and currently matter of debate [5,6,7]
Respiration affects both heart period length and arterial pressure, which in turn are mutually related. Interconnections between these three physiological parameters can be broadly reduced to four interactions: (i) Blood pressure decreases during inspiration and increases during expiration, following the changes in intrathoracic pressure. (ii) Heart period decreases during inspiration and increased during expiration, a phenomenon called respiratory sinus arrhythmia (RSA) [1,2], that may be due to direct central nervous modulation, reflex phenomena and mechanical influence of respiration [5,6,7]. (iii) A decrease in blood pressure provokes a decrease in heart period, via the baroreflex, a negative feedback mechanism that buffers short-term fluctuations in arterial pressure. (iv) A change in heart period causes a change in blood pressure through direct mechanical effects
Summary
It is well known that respiratory activity affects cardiovascular regulation [1,2,3,4], the mechanisms responsible for the coordination between the autonomic control of circulation and respiration are still unclear and currently matter of debate [5,6,7] Respiration affects both heart period length and arterial pressure, which in turn are mutually related. The purpose of this study is to present a methodology to robustly estimate the time course of cross spectral indices to characterize dynamic interactions between cardiovascular signals in non-stationary conditions. The purpose of this study is to present a methodology to robustly estimate the time course of cross spectral indices to characterize dynamic interactions between respiration, heart period and arterial pressure, simultaneously. We present a comprehensive framework which includes TF phase difference and TF partial coherence to simultaneously characterize the dynamic interactions between these signals during tilt table test in spontaneous and controlled breathing, and after autonomic blockade
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