Systolic time intervals in passive head down position (-85 degrees) and exercise

Variations of cardiac time intervals (CTI) in head-down (HD) condition and during an 120 watts bicycle exercise were investigated by the method of ear densitogram associated with an automatic system of evaluation of systolic time intervals (STI), in young subjects, aged 25-30 years. In the HD experiment unchanged heart rate (HR) and left ventricular ejection time (LVET) values were increased, whereas pre-ejection time (PEP) values decreased. Exercise increased HR and decreased PEP and LVET values. Two different mechanisms are involved in the decrease of PEP in the two circumstances, by increasing the end diastolic volume and, respectively, by a sympatho-adrenergic reaction.