Effects of prolonged bed rest on cardiovascular oxygen transport during submaximal exercise in humans.
The hypothesis was tested that prolonged bed rest impairs O2 transport during exercise, which implies a lowering of cardiac output Qc and O2 delivery (QaO2). The following parameters were determined in five males at rest and at the steady-state of the 100-W exercise before (B) and after (A) 42-day bed rest with head-down tilt at -6 degrees: O2 consumption (VO2), by a standard open-circuit method; Qc, by the pressure pulse contour method, heart rate (fc), stroke volume (Qh), arterial O2 saturation, blood haemoglobin concentration ([Hb]), arterial O2 concentration (CaO2), and QaO2. The VO2 was the same in A and in B, as was the resting fc. The fc at 100 W was higher in A than in B (+17.5%). The Qh was markedly reduced (-27.7% and -22.2% at rest and 100 W, respectively). The Qc was lower in A than in B [-27.6% and -7.8% (NS) at rest and 100 W, respectively]. The CaO2 was lower in A than in B because of the reduction in [Hb]. Thus also QaO2 was lower in A than in B (-32.0% and -11.9% at rest and at 100 W, respectively). The present results would suggest a down-regulation of the O2 transport system after bed rest.
Ferretti
G
G
Département de Physiologie, Centre Médical Universitaire, Geneva, Switzerland.
Girardis
M
M
Moia
C
C
Antonutto
G
G
D000328:Adult; D001510:Bed Rest; D001784:Blood Gas Analysis; D002302:Cardiac Output / Q000502:physiology*; D006801:Humans; D008297:Male; D010100:Oxygen / Q000097:blood*; D005082:Physical Exertion / Q000502:physiology*; D018667:Tilt-Table Test; D013997:Time Factors
D010100:Oxygen