Session P32.2

Model Based Processing of CV Variability Applied to Bed-Rest Case Studies

F Vallais*, F Aletti, G Baselli, E Tam,
M Cautero, M Pagani, C Capelli

Politecnico di Milano
Milano, Italy

The cardiovascular adaptation to exercise is of particular importance during postural changes, exercise, or gravity. The role of many reflexes such as the baroreflex, cardio-pulmonary reflexes among others in the short-term control of the CVS was shown and described in numerous studies, employing various experimental manoeuvres. However, the causal effects of those reflexes and their exact role during CVS deconditioning induced by prolonged bed rest are not fully understood. Differentiation can occur inside those mechanisms leading to the prevalence or inhibition of some of them. Their interactions may also play a major role not only in the short-term scale but also in the long-term scale. Three healthy subjects were enrolled in the study, which intended to evaluate changes occurring in the cardiorespiratory response to exercise after a prolonged bed rest (BR) period. Each subject underwent an incremental workload bicycle-ergometer test before and after the BR period. The test included five epochs, including successively a period of rest (Rest), a period of exercise at 50W (Exe1), a period of recovery of about 5 min. (Rec1), a second epoch of exercise at 100 W (Exe2), and finally a period of recovery (Rec2). EKG, arterial blood pressure (AP), respiration were continuously recorded. Each signal was sampled at a frequency of 100 Hz. Parametric modelling was applied in the description of interaction between RR, diastolic AP (DAP), pulse pressure (PP), and systolic AP (SAP), obtaining indexes of baroreflex gain (BRG) and vascular response. Diastolic decay was also parameterized by means of a deconvolution procedure. All subjects displayed tachycardia and hypotension after BR. The baroreflex control of HR was altered after the prolonged BR as shown by the decrease of the BRG after BR among epochs. Significant changes were displayed in hemodynamic indexes, which were enhanced by exercise response, though superimposed to individual differences which may suggest different sensitivity and timing in the adaptation to simulated micro-gravity. Results may also suggest a differentiation of the cardiac and the vascular adaptation in response to exercise .

(Abstract Control Number: 202)