Water immersion resulted in a lower causal relationship from R-R intervals to respiration compared with 6-degree head-down tilt.
Does Granger causality analysis reveal differences in autonomic regulation between water immersion, head-down tilt, and supine position in healthy subjects?
Granger causality analysis reveals differences in cardiovascular regulation (specifically the causal link from R-R intervals to respiration) between water immersion and head-down tilt that are not accessible with standard methods.
NEW FINDINGS: What is the central question of this study? Can Granger causality analysis of R-R intervals, systolic blood pressure and respiration provide evidence for the different physiological mechanisms induced during thermoneutral water immersion, 6 deg head-down tilt and supine position tests that are not accessible using traditional heart rate variability and baroreflex methods? What is the main finding and its importance? The Granger analysis demonstrated a significant difference in the causal link from R-R intervals to respiration between water immersion and head-down tilt. The underlying physiological mechanism explaining this difference could be the variation in peripheral resistances. ABSTRACT: Thermoneutral head-out water immersion (WI) and 6 deg head-down tilt (HDT) are used to simulate SCUBA diving, swimming and microgravity, because these models induce an increase in central blood volume. Standard methods to analyse autonomic regulation have demonstrated an increase in parasympathetic activity and baroreflex sensitivity during these experimental conditions. However, such methods are not adapted to quantify all closed-loop interactions involved in respiratory and cardiovascular regulation. To overcome this limitation, we used Granger causality analysis between R-R intervals (RR), systolic blood pressure (SBP) and respiration (RE) in eight young, healthy subjects, recorded during 30 min periods in the supine position, WI and HDT. For all experimental conditions, we found a bidirectional causal relationship between RE and RR and between RR and SBP, with a dominant direction from RR to SBP, and a unidirectional causality from RE to SBP. These causal relationships remained unchanged for the three experimental tests. Interestingly, there was a lower causal relationship from RR to RE during WI compared with HDT. This causal link from RR to RE could be modulated by peripheral resistances. These results highlight differences in cardiovascular regulation during WI and HDT and confirm that Granger causality might reveal physiological mechanisms not accessible with standard methods.
Corbier et al. (Thu,) conducted a other in Healthy (n=8). Thermoneutral head-out water immersion and 6-degree head-down tilt vs. Supine position was evaluated on Granger causality between R-R intervals, systolic blood pressure, and respiration. Water immersion resulted in a lower causal relationship from R-R intervals to respiration compared with 6-degree head-down tilt.
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