Cardiovascular and respiratory responses to pychophysiological tasks : methodological issues for assessing autonomic regulation

The current work studies the correlation between birth-weight and autonomic cardiovascular modulation in adult life, in order to investigate the physiological mechanisms underlying the fetal origins of cardiovascular disease. However, factors other than autonomic modulation may strongly influence the estimation of cardiovascular indexes. In this thesis, two such confounding factors were investigated in detail. Firstly, the between-task and inter-individual differences in respiratory patterns, especially in tasks involving speech were found to be strongly reflected in cardiovascular indexes. Clear evidence was found that a very significant part of changes in indexes during the psychophysiological experimental protocol considered can be explained by modifications in respiration, without assuming between-tasks or inter-individual differences in autonomic activation elicited by psychological/cognitive processes. The second factor is the presence of within-task dynamics in the cardiovascular reaction to psychophysiological tasks. The common approach in psychophysiological investigations is to estimate cardiovascular indexes as average values over the whole length of the task. However, the results found show that such an approach may obscure significant within-task changes in the indexes that might carry useful psychophysiological information. Choosing shorter epochs within the tasks for estimating the indexes has also a notable impact in terms of assessing changes elicited by the tasks. Since these two factors are intrinsic in the reaction to psychophysiological tasks, they can have a profound impact on the indirect estimates of autonomic reaction through cardiovascular indexes. Controlling them during psychophysiological experiments may be difficult (if not impossible). However, their effects should be minimized, for example by avoiding tasks involving speech and choosing appropriate data epochs for the analysis.