Cardiovascular effects of 20 days bed rest in healthy young subjects

To evaluate the effects of inactivity on the cardiovascular system in normal subjects, left ventricular echocardiography and vascular ultrasound of the common carotid artery, abdominal aorta and femoral artery, and lower body negative pressure tests were performed in 14 healthy volunteers (mean age: 22 years) before and after 20 days of strict bed rest. Cardiac output was calculated from echocardiographic measurements and peripheral arterial flows by multiplying cross-sectional area of an artery by heart rate and time-velocity integral measured by pulsed Doppler ultrasound with angle correction. Systemic vascular resistance, lower body vascular resistance, leg vascular resistance and head vascular resistance were also calculated. After bed rest, heart rate increased (69 +/- 2 to 79 +/- 3 bpm), while left ventricular diastolic dimension (49 +/- 1 to 45 +/- 1 mm), systolic blood pressure (137 +/- 5 to 116 +/- 4 mmHg), cardiac output (6.2 +/- 0.3 to 5.4 +/- 0.3 1.min-1), abdominal aortic flow (4.1 +/- 0.4 to 3.1 +/- 0.3 1.min-1), femoral artery flow (0.66 +/- 0.07 to 0.33 +/- 0.04 1-min-1), and lower body negative pressure test tolerance time (750 +/- 71 to 582 +/- 48 s) decreased significantly (p < 0.05). However, common carotid artery flow (0.97 +/- 0.09 to 1.03 +/- 0.08 1.min-1) did not change. Although no significant changes in systemic vascular resistance, lower body vascular resistance or head vascular resistance were observed, leg vascular resistance increased significantly after 20 days of bed rest (6933 +/- 2905 to 13221 +/- 2606 dyn.s.cm-1) (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)