Sex-related effects on venous compliance and capillary filtration in the lower limb

Abstract

Recent studies in humans have suggested sex differences in venous compliance of the lower limb, with lower compliance in women. Capillary fluid filtration could, however, be a confounder in the evaluation of venous compliance. The venous capacitance and capillary filtration response in the calves of 12 women (23.2 Ϯ 0.5 years) and 16 men (22.9 Ϯ 0.5 years) were studied during 8 min lower body negative pressure (LBNP) of 11, 22, and 44 mmHg. Calf venous compliance is dependent on pressure and was determined using the first derivative of a quadratic regression equation that described the capacitance-pressure relationship [compliance ϭ ␤ 1 ϩ (2 ⅐ ␤2 ⅐ transmural pressure)]. We found a lower venous compliance in women at low transmural pressures, and the venous capacitance in men was increased (P Ͻ 0.05). However, the difference in compliance between sexes was reduced and not seen at higher transmural pressures. Net capillary fluid filtration and capillary filtration coefficient (CFC) were greater in women than in men during LBNP (P Ͻ 0.05). Furthermore, calf volume increase (capacitance response ϩ total capillary filtration) during LBNP was equivalent in both sexes. When total capillary filtration was not subtracted from the calf capacitance response in the calculation of venous compliance, the sex differences disappeared, emphasizing that venous compliance measurement should be corrected for the contribution of CFC. lower body negative pressure; capillary filtration coefficient; venous capacitance THE VENOUS SECTION OF THE cardiovascular system can be looked upon as a voluminous blood reservoir (70% of total blood volume), designed to preserve a proper inflow of blood into the heart during various cardiovascular adjustments. Thus central venous pressure and filling of the heart may be maintained at a fairly stable level, despite variations in venous blood volume (49). During upright posture, however, the pooling of blood in the veins of the lower part of the body decreases central blood volume and venous return (4, 5, 16). The venous compartment in the legs, rather than the pelvic or abdominal region, seems to have a hemodynamic impact during lower body negative pressure (LBNP) (16), and in studies on men, a greater calf venous compliance has been linked to an increased venous capacitance response with a concomitant reduction in central blood volume (44,56). This, in turn, elicits an increased sympathetic response with higher peripheral resistance and increased heart rate (4, 5, 10, 16, 44, 58). Thus venous compliance of the lower limb may have an impact on cardiovascular responses to orthostatic stress and orthostatic tolerance, although there might be differences between sexes confounding such a link (4).Women are more susceptible to orthostatic stress than men (4,10,13,40,51,58), and in accordance with some findings in the arterial tree, it may be hypothesized that women have greater venous compliance in the lower limbs predisposing to orthostatic intolerance (52). This seems to be refuted however, by recent fi...

Decreased capillary filtration but maintained venous compliance in the lower limb of aging women

“…Venous compliance does not seem to change over the course of the menstrual cycle or by oral contraceptive use (30). Data from 12 of the young women have been previously published (26). Each subject gave informed consent to the experiments approved by the Ethics Committee of Linköping University, Sweden.…”

“…Subjects with increased limb venous compliance have been shown to have greater orthostatic intolerance, probably due to an increased venous capacitance (24,36,46), although this relationship has recently been challenged by Hernandez and Franke (18). Venous compliance in the lower limbs decreases with age in men (33,38,39,49), but there is no reason to believe that venous compliance and capacitance are similar in men and women, since a sex difference has been established in young adults (26,30,34). Furthermore, age-related changes might be sex specific, in accordance with age-related changes of arteries, with women having a slower decrease in arterial compliance with age compared with men, an effect probably attributed to estrogen (9, 48).…”

“…Furthermore, age-related changes might be sex specific, in accordance with age-related changes of arteries, with women having a slower decrease in arterial compliance with age compared with men, an effect probably attributed to estrogen (9, 48). Estrogen has been shown to affect cellular transcription of elastin and collagen, and estrogen-receptors are known to exist in vascular smooth muscle cells (21,22,32).There is a marked capillary fluid filtration in the lower limb during quiet standing or lower body negative pressure (LBNP), increasing the hypovolemic stimulus over time independently from venous compliance and capacitance, and its hypovolemic importance is indicated by the increased fluid filtration in lower limbs of subjects with postural tachycardia syndrome (25,26,46). We recently described an increased capillary fluid filtration and capillary filtration coefficient (CFC) in the calf of young women compared with men, possibly caused by higher levels of estrogen in women, since estrogen enhances capillary filtration (26,45,47).…”

“…We recently described an increased capillary fluid filtration and capillary filtration coefficient (CFC) in the calf of young women compared with men, possibly caused by higher levels of estrogen in women, since estrogen enhances capillary filtration (26,45,47). Despite the marked drop in estrogen levels during menopause, the effects of aging on capillary fluid filtration and CFC have not been examined in women.…”

“…There is a marked capillary fluid filtration in the lower limb during quiet standing or lower body negative pressure (LBNP), increasing the hypovolemic stimulus over time independently from venous compliance and capacitance, and its hypovolemic importance is indicated by the increased fluid filtration in lower limbs of subjects with postural tachycardia syndrome (25,26,46). We recently described an increased capillary fluid filtration and capillary filtration coefficient (CFC) in the calf of young women compared with men, possibly caused by higher levels of estrogen in women, since estrogen enhances capillary filtration (26,45,47).…”