Reduced venous compliance in lower limbs of aging humans and its importance for capacitance function

Age-related changes in vasomotor reflex control of calf venous capacitance response to lower body negative pressure in humans

The present study was performed to test the hypothesis that calf venous capacitance would be reduced by mild gravitational stress through a vasomotor reflex in humans, and this response could be diminished with advancing age. Nine young (31 +/- 1 years, mean +/- SE) and 9 elderly (69 +/- 1 years) healthy males were exposed to a lower body negative pressure (LBNP) of 15 mmHg. Venous occlusion plethysmography was used to measure calf venous capacitance and calf blood flow. Muscle sympathetic nerve activity (MSNA) was recorded microneurographically from the tibial nerve along with cardiovascular variables. It was found that baseline MSNA was higher [21 +/- 4 (mean +/- SE) vs. 37 +/- 5 bursts x min(-1), young vs. elderly; p < 0.05] and calf venous capacitance was lower (1.71 +/- 0.12 vs. 1.44 +/- 0.10, ml x 100 ml(-1), young vs. elderly; p < 0.05) in the elderly group. At 15 mmHg-LBNP, heart rate and mean arterial pressure both remained unchanged, MSNA was enhanced, and calf blood flow was reduced in all subjects. Calf venous capacitance during LBNP decreased in the young, but did not change in the elderly. A significant negative correlation between percent changes in MSNA and percent changes in calf venous capacitance existed in the young group (y = 20.171x-11.863, r = 20.682; p = 0.0432), but disappeared in the elderly group. The ratio of percent changes in calf venous capacitance to percent changes in MSNA was markedly lower in the elderly (p < 0.01). In conclusion, these results substantiate our hypothesis that calf venous capacitance is reduced by mild LBNP through the vasomotor reflex, and this response is diminished in the elderly.

Smaller age-associated reductions in leg venous compliance in endurance exercise-trained men

We determined the independent and interactive influences of aging and habitual endurance exercise on calf venous compliance in humans. We tested the hypotheses that calf venous compliance is 1) reduced with age in sedentary and endurance-trained men, and 2) elevated in young and older endurance-trained compared with age-matched sedentary men. We studied 8 young (28 +/- 1 yr) and 8 older (65 +/- 1) sedentary, and 8 young (27 +/- 1) and 8 older (63 +/- 2) endurance-trained men. Calf venous compliance was measured in supine subjects by inflating a venous collecting cuff, placed above the knee, to 60 mmHg for 8 min and then decreasing cuff pressure at 1 mmHg/s to 0 mmHg. Calf venous compliance was determined using the first derivative of the pressure-volume relation during cuff pressure reduction (compliance = beta(1) + 2. beta(2). cuff pressure). Calf venous compliance was reduced with age in sedentary (approximately 40%) and endurance-trained men (approximately 20%) (both P < 0.01). Furthermore, calf venous compliance was approximately 70-120% greater in endurance-trained compared with age-matched sedentary men and approximately 30% greater in older endurance-trained compared with young sedentary men (both P < 0.01). These data indicate that calf venous compliance is reduced with age in sedentary and endurance-trained men, but compliance is better preserved in endurance-trained men.

Human calf microvascular compliance measured by near-infrared spectroscopy

The purpose of this study is to develop a new method for the measurement in humans of the compliance of the microvascular superficial venous system of the lower limb by near-infrared spectroscopy (NIRS). This method is complementary to strain-gauge plethysmography, which does not allow compliance between deep and superficial venous or between venous and arterial compartments to be distinguished. In practice, hydrostatic pressure (P) changes were induced in a calf region of interest by head-up tilt of the subject from alpha = -10 to 75 degrees. For P < or = 24 mmHg, the measured compliance [0.086 +/- 0.005 (SD) ml. l(-1). mmHg(-1)] based on NIRS data of total, deoxygenated, and oxygenated hemoglobin, reflects essentially that of the superficial venous system. For P > or = 24 mmHg, no distinction can be made between arterial and venous volumes changes. However, by following the changes in oxy- and deoxyhemoglobin in the P range -16 to 100 mmHg, it appears to be possible to assess the characteristics of the vasomotor response of the arteriolar system.

Cardiovascular response to acute hypovolemia in relation to age. Implications for orthostasis and hemorrhage

Venous compliance in the legs of aging man has been found to be reduced with decreased blood pooling (capacitance response) in dependent regions, and this might lead to misinterpretations of age-related changes in baroreceptor function during orthostasis. The hemodynamic response to hypovolemic circulatory stress was studied with the aid of lower-body negative pressure (LBNP) of 60 cmH(2)O in 33 healthy men [18 young (mean age 22 yr) and 15 old (mean age 65 yr)]. Volumetric technique was used in the study of capacitance responses in the calf and arm as well as transcapillary fluid absorption in the arm. LBNP led to smaller increase in heart rate (P < 0.001) and peripheral resistance (P < 0.01) and reduced transcapillary fluid absorption in the arm (P < 0.05) in old subjects. However, blood pooling in the calf was reduced in old subjects (1.66 +/- 0.10 vs. 2.17 +/- 0.13 ml/100 ml tissue; P < 0. 01). Accordingly, during similar blood pooling in the calf (LBNP 80 cmH(2)O in old subjects), no changes in cardiovascular reflex responses with age were found. The capacitance response in the arm (mobilization of peripheral blood to the central circulation) was still reduced, however (0.67 +/- 0.10 vs. 1.37 +/- 0.11 ml/100 ml tissue; P < 0.01). Thus the reduced cardiovascular reflex response found in the elderly during orthostatic stress seems to be caused by a reduced capacitance response in the legs with age and a concomitant smaller central hypovolemic stimulus rather than a reduced efficiency of the reflex response. With similar hypovolemic circulatory stress, no changes in cardiovascular reflex responses are seen with age. The capacitance response in the arm (mobilization of peripheral blood toward the central circulation) is reduced, however, by approximately 50% in the elderly. This might seriously impede the possibility of survival of an acute blood loss.