Simulations of Gravitational Stress on Normovolemic and Hypovolemic Men and Women

Abstract

Background Earth based simulations of physiologic responses to space mission activities are needed to develop prospective countermeasures. To determine whether upright lower body positive pressure (LBPP) provides a suitable space mission simulation, we investigated cardiovascular responses of normovolemic and hypovolemic, men and women, to supine and orthostatic stress, induced by head-up tilt (HUT) and upright LBPP, representing standing in lunar, Martian and Earth’s gravities. Methods Six men and six women were tested in normovolemic and hypovolemic (furosemide, intravenous, 0.5 mg/kg) conditions. Continuous electrocardiogram, blood pressure, segmental bioimpedance and stroke volume (echocardiography) were recorded supine and at lunar, Martian and Earth’s gravities (10°, 20°, 80° HUT vs. 20%, 40%, 100% body weight upright LBPP), respectively. Cardiovascular responses were assessed from mean values, spectral powers and spontaneous baroreflex parameters. Results Hypovolemia reduced plasma volume by ~10% and stroke volume by ~25% at supine and increasing orthostatic stress resulted in further reductions. Upright LBPP induced more plasma volume losses at simulated lunar and Martian gravities compared with HUT, while both techniques induced comparable central hypovolemia at each stress. Cardiovascular responses to orthostatic stress were comparable between HUT and upright LBPP in both normovolemic and hypovolemic conditions, however, hypovolemic blood pressure was greater during standing at 100% body weight compared to 80° HUT due to a greater increase of total peripheral resistance. Conclusions HUT and upright LBPP induced comparable cardiovascular responses, supporting the use of upright LBPP as a potential model to simulate activity in lunar and Martian gravities.

Body Size Predicts Cardiac and Vascular Resistance Effects on Men's and Women's Blood Pressure

“…Thirty-four young adults (19 men and 15 women, 8 Asian, 1 Hispanic, and 25 white) participated in 39 studies, conducted over three years. These original studies were designed to document cardiovascular effects of lower body positive pressure (LBPP) applied to subjects in a standing position (Evans et al, 2013 ; Kostas et al, 2014 ; Zhang et al, 2014 ). Postural controls for each of those studies consisted of data segments collected during the last 10 min of a 30-min supine control period and across 10 min of standing (without LBPP).…”

Association of gender with cardiovascular and autonomic responses to central hypovolemia

“…However, in some individuals, these compensatory responses are inadequate, and orthostatic intolerance develops ( 6 ). To assess a person's limit of cardiovascular stability during central hypovolemia, head up tilt and lower body negative pressure (LBNP) techniques are employed ( 7 , 8 ). Both are widely used techniques that have shown that there are inter-individual differences in hemodynamic and autonomic responses during central hypovolemia, and that intra-individual responses are highly reproducible ( 9 ).…”

Effects of menstrual cycle on hemodynamic and autonomic responses to central hypovolemia

“…Central hypovolemia, characterized by a reduction in blood volume within the central circulation ( 1 ), poses significant challenges to the cardiovascular system ( 2 ). The lower body negative pressure (LBNP) technique can be used to assess cardiovascular responses and stability during central hypovolemia ( 3 , 4 ). The application of LBNP shifts the blood from the upper body to the lower body and leads to a decrease in the amount of blood returning to the heart ( 5 , 6 ).…”