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 (+2Gz). In a separate experiment, the same measurements were done with the subjects supine (+2Gx). During +2Gz 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 +2Gx, systolic arterial pressure increased (P < 0.001) and SV (P = 0.012) decreased in the tall group only. In conclusion, during +2Gz, MAP increased in both short and tall males, with no difference between the groups. However, in the tall group, HR increased more during +2Gz, which could be caused by a larger hydrostatic pressure gradient from heart to head, leading to greater inhibition of the carotid baroreceptors.

[1]  F H Previc,et al.  Effects of vestibular and oculomotor stimulation on responsiveness of the carotid-cardiac baroreflex. , 1997, The American journal of physiology.

[2]  O Henriksen,et al.  Local reflex in microcirculation in human subcutaneous tissue. , 1976, Acta physiologica Scandinavica.

[3]  N. Secher,et al.  Jugular venous pooling during lowering of the head affects blood pressure of the anesthetized giraffe. , 2009, American journal of physiology. Regulatory, integrative and comparative physiology.

[4]  J. Patterson,et al.  CARDIORESPIRATORY DYNAMICS IN THE OX AND GIRAFFE, WITH COMPARATIVE OBSERVATIONS ON MAN AND OTHER MAMMALS * , 1965, Annals of the New York Academy of Sciences.

[5]  Chikara Abe,et al.  Vestibular system plays a significant role in arterial pressure control during head-up tilt in young subjects , 2009, Autonomic Neuroscience.

[6]  T Kamo,et al.  Central volume expansion is pivotal for sustained decrease in heart rate during seated to supine posture change. , 2001, American journal of physiology. Heart and circulatory physiology.

[7]  P. Sejrsen,et al.  Effect of orthostatic blood pressure changes upon capillary filtration-absorption rate in the human calf. , 1981, Acta physiologica Scandinavica.

[8]  K. E. Klein,et al.  Influence of stature and physical fitness on tilt-table and acceleration tolerance. , 1969, Aerospace medicine.

[9]  P. Norsk,et al.  Atrial distension in humans during microgravity induced by parabolic flights. , 1997, Journal of applied physiology.

[10]  A. Gabrielsen,et al.  Arterial pressure in humans during weightlessness induced by parabolic flights. , 1999, Journal of applied physiology.

[11]  Chikara Abe,et al.  Role of the vestibular system in the arterial pressure response to parabolic-flight-induced gravitational changes in human subjects , 2011, Neuroscience Letters.

[12]  A. Gabrielsen,et al.  Non-invasive measurement of cardiac output in heart failure patients using a new foreign gas rebreathing technique. , 2002, Clinical science.

[13]  R. Millard,et al.  Gravitational haemodynamics and oedema prevention in the giraffe , 1987, Nature.

[14]  P. Norsk,et al.  Effects of ventilation on cardiac output determined by inert gas rebreathing , 2005, Clinical physiology and functional imaging.

[15]  L. Rowell.  Human Cardiovascular Control , 1993 .

[16]  P. Norsk,et al.  Left atrial distension and antiorthostatic decrease in arterial pressure and heart rate in humans. , 1997, American journal of physiology. Heart and circulatory physiology.

[17]  D. Eckberg.  Adaptation of the human carotid baroreceptor‐cardiac reflex. , 1977, The Journal of physiology.

[18]  J. Patterson,et al.  Circulation of the Giraffe , 1960, Circulation research.

[19]  D L Eckberg,et al.  Baroreflex inhibition of the human sinus node: importance of stimulus intensity, duration, and rate of pressure change. , 1977, The Journal of physiology.

[20]  A. Gabrielsen,et al.  Contribution of the leg vasculature to hypotensive effects of an antiorthostatic posture change in humans , 1999, The Journal of physiology.

[21]  C. Ray,et al.  Neck afferents and muscle sympathetic activity in humans: implications for the vestibulosympathetic reflex. , 1998, Journal of applied physiology.

[22]  A. Gabrielsen,et al.  Mechanisms of inhibition of vasopressin release during moderate antiorthostatic posture change in humans. , 1999, The American journal of physiology.

[23]  R. Glenny,et al.  Effects of gravity on lung diffusing capacity and cardiac output in prone and supine humans. , 2003, Journal of applied physiology.

[24]  G. Grimby,et al.  Spirometric Studies in Normal Subjects , 2009 .

[25]  P. Sejrsen,et al.  Local reflex in microcirculation in human cutaneous tissue. , 1976, Acta physiologica Scandinavica.

[26]  P. Norsk,et al.  Body height and blood pressure regulation in humans during anti-orthostatic tilting. , 2012, American journal of physiology. Regulatory, integrative and comparative physiology.

[27]  C. G. Blomqvist,et al.  Cardiovascular Adjustments to Gravitational Stress , 2011 .

[28]  R. Glenny,et al.  Protective effect of prone posture against hypergravity-induced arterial hypoxaemia in humans. , 2003 .

[29]  D L Eckberg,et al.  Temporal response patterns of the human sinus node to brief carotid baroreceptor stimuli. , 1976, The Journal of physiology.