Bed rest affects ventricular and arterial elastances in monkeys: implications for humans.
METHODS
Experimental data were obtained from five chronically instrumented rhesus monkeys exposed to 96 h of 10 degrees head-down bed rest (HDBR) and another 96 h of 80 degrees upright control separated by 9 d of ambulatory recovery in a counter-balanced, crossover experiment design to test the hypotheses that: 1) headward and footward fluid shifts would increase systemic arterial (Eart) and left ventricular end-systolic (Ees) elastances; and 2) changes in Eart and Ees would be related in magnitude and direction. Ees and Eart were calculated from measurements taken during five observation periods for initial 2-h and 4-d exposures to HDBR that produced headward volume shifts, and acute exposure to graded levels of lower body negative pressure (LBNP) designed to produce orthostatic volume shifts.


RESULTS
There was no effect of HDBR on Ees and Eart for any observation period (initial 2-h, 4-d, or LBNP). Eart increased in a similar pattern during the 4-d exposure to both control and HDBR. Ees increased with increasing LBNP levels for both control and HDBR while Eart remained unchanged.


CONCLUSIONS
Our data are consistent with the notion that elevated Eart may represent an adaptation to physical inactivity that is associated with cardiovascular deconditioning.
Koenig
Steven C
SC
Jewish Hospital Heart and Lung Institute, Department of Surgery, University of Louisville, Louisville, KY 40202, USA. sckoen01@athena.louisville.edu
Ewert
Dan L
DL
Ludwig
David A
DA
Fanton
John F
JF
Convertino
Victor A
VA
D000222:Adaptation, Physiological; D000818:Animals; D001158:Arteries / Q000502:physiology*; D001510:Bed Rest; D006339:Heart Rate / Q000502:physiology; D006439:Hemodynamics; D006801:Humans; D008253:Macaca mulatta; D008297:Male; D008991:Monitoring, Physiologic; D014655:Vascular Resistance / Q000502:physiology*; D016276:Ventricular Function