Sex differences in vasoconstrictor reserve during 70 deg head-up tilt

• Published in: Experimental physiology Vol. 95; no. 1; pp. 184 - 193
• Main Authors: Jarvis, S. S., Florian, J. P., Curren, M. J., Pawelczyk, J. A.
• Format: Journal Article
• Language: English
• Published: Oxford, UK The Physiological Society 01.01.2010; Blackwell Publishing Ltd; John Wiley & Sons, Inc
• Subjects: Adolescent; Adult; Blood Pressure - physiology; Female; Heart Rate - physiology; Humans; Male; Sex Characteristics; Splanchnic Circulation - physiology; Tilt-Table Test - instrumentation; Tilt-Table Test - methods; Vasoconstriction - physiology; Young Adult
• ISSN: 0958-0670; 1469-445X
• DOI: 10.1113/expphysiol.2009.048819

Women are generally recognized to be less orthostatically tolerant than men. We hypothesized that during head-up tilt (HUT), women would demonstrate less splanchnic vasoconstriction, leading to splanchnic pooling, lower blood pressure and lower orthostatic tolerance. Mean arterial blood pressure (MAP), heart rate (HR), cardiac output ( , assessed by C 2 H 2 rebreathing), stroke volume, splanchnic blood flow (SpBF, assessed by Indocyanine Green clearance) and vascular conductance (systemic, ; splanchnic, SpVC = SpBF/MAP; non-splanchnic, non-SpVC = SVC – SpVC) were measured during supine baseline conditions, 70 deg HUT and recovery in 14 healthy women (23 ± 6 years old; mean ± s.d. ) and 16 men (23 ± 5 years old). The proportion of sexes surviving 45 min of HUT trended towards significance (χ 2 = 2.92, P = 0.09). The MAP was lower in women than in men (supine, 77 ± 5 versus 86 ± 9 mmHg, P < 0.01; tilt, 72 ± 8 versus 83 ± 10 mmHg, P < 0.01), while HR and cardiac index ( /body surface area) were not different between the sexes (heart rate supine, 66 ± 6 versus 64 ± 8 beats min −1 ; heart rate tilt, 96 ± 13 versus 94 ± 10 beats min −1 ; cardiac index supine, 3.8 ± 0.9 versus 3.7 ± 0.7 l min −1 m −2 ; cardiac index tilt, 2.7 ± 0.8 versus 2.3 ± 0.5 l min −1 m −2 ). The SpBF and SpVC were lower in women at rest but not during tilt (SpBF supine, 1174 ± 243 versus 1670 ± 391 ml min −1 , P < 0.01; SpVC supine, 14.83 ± 3.61 versus 19.59 ± 4.95 ml min −1 mmHg −1 , P < 0.01; SpBF tilt, 884 ± 300 versus 1094 ± 271 ml min −1 ; SpVC tilt, 13.14 ± 4.28 versus 14.82 ± 4.16 ml min −1 mmHg −1 ). However, in the women the SpVC did not decrease from baseline to tilt (ΔSpVC, in women, −1.70 ± 3.19 ml min −1 mmHg −1 , n.s.; in men, −4.81 ± 3.44 ml min −1 mmHg −1 , P < 0.01), suggesting a blunted vasoconstrictor response. In conclusion, women tended to have lower tilt-table tolerance associated with a smaller splanchnic vasoconstrictor reserve than men.