Body height and arterial pressure in seated and supine young males during+2 G centrifugation

It is known that arterial pressure correlates positively with body height in males, and it has been suggested that this is due to the increasing vertical hydrostatic gradient from the heart to the carotid baroreceptors. Therefore, we tested the hypothesis that a higher gravito-inertial stress induced by the use of a human centrifuge would increase mean arterial pressure (MAP) more in tall than in short males in the seated position. In short (162-171 cm; n = 8) and tall (194-203 cm; n = 10) healthy males (18-41 yr), brachial arterial pressure, heart rate (HR), and cardiac output were measured during +2G centrifugation, while they were seated upright with the legs kept horizontal (+2G(z)). In a separate experiment, the same measurements were done with the subjects supine (+2G(x)). During +2G(z) MAP increased in the short (22 +/- 2 mmHg, P < 0.0001) and tall (23 +/- 2 mmHg, P < 0.0001) males, with no significant difference between the groups. HR increased more (P < 0.05) in the tall than in the short group (14 +/- 2 vs. 7 +/- 2 bpm). Stroke volume (SV) decreased in the short group (26 +/- 4 ml, P = 0.001) and more so in the tall group (39 +/- 5 ml, P < 0.0001; short vs. tall, P = 0.047). During +2G(x), systolic arterial pressure increased (P < 0.001) and SV (P = 0.012) decreased in the tall group only. In conclusion, during +2G(z), MAP increased in both short and tall males, with no difference between the groups. However, in the tall group, HR increased more during +2G(z), which could be caused by a larger hydrostatic pressure gradient from heart to head, leading to greater inhibition of the carotid baroreceptors.