Effect of sleep restriction on orthostatic cardiovascular control in humans.

We hypothesized that sleep restriction (4 consecutive nights, 4 h sleep/night) attenuates orthostatic tolerance. The effect of sleep restriction on cardiovascular responses to simulated orthostasis, arterial baroreflex gain, and heart rate variability was evaluated in 10 healthy volunteers. Arterial baroreflex gain was determined from heart rate responses to nitroprusside-phenylephrine injections, and orthostatic tolerance was tested via lower body negative pressure (LBNP). A Finapres device measured finger arterial pressure. No difference in baroreflex function, heart rate variability, or LBNP tolerance was observed with sleep restriction (P > 0.3). Systolic pressure was greater at -60 mmHg LBNP after sleep restriction than before sleep restriction (110 +/- 6 and 124 +/- 3 mmHg before and after sleep restriction, respectively, P = 0.038), whereas heart rate decreased (108 +/- 8 and 99 +/- 8 beats/min before and after sleep restriction, respectively, P = 0.028). These data demonstrate that sleep restriction produces subtle changes in cardiovascular responses to simulated orthostasis, but these changes do not compromise orthostatic tolerance.