Venous capacity and compliance in hypertensive adults: influence of hypoxia and hyperoxia

In hypertension, the cardiorespiratory responses to peripheral chemoreflex activation (hypoxia) and inactivation (hyperoxia) are reportedly augmented, but the impact on peripheral venous function is unknown. We tested the hypothesis that in hyperten-sives, both hypoxia and hyperoxia evoke more pronounced changes in lower limb venous capacity and compliance, than in age -matched normotensives. In 10 hypertensive [HTN: 7 women; age: 71.7 +/- 3.7 yr, mean blood pressure (BP): 101 +/- 10 mmHg, mean +/- SD] and 11 normotensive (NT: 6 women; age: 67.7 +/- 8.0 yr, mean BP 89 +/- 11 mmHg) participants, great saphenous vein cross-sec-tional area (GSV CSA; Doppler ultrasound) was measured during a standard 60 mmHg thigh cuff inflation-deflation protocol. Separate conditions of room air, hypoxia [fraction of inspired oxygen (FIO2): 0.10] and hyperoxia (FIO2: 0.50) were tested. In HTN, GSV CSA was decreased in hypoxia (5.6 +/- 3.7 mm2, P = 0.041) compared with room air (7.3 +/- 6.9 mm2), whereas no change was observed with hyperoxia (8.0 +/- 9.1 mm2, P = 0.988). In NT, no differences in GSV CSA were observed between any condition (P = 0.299). Hypoxia enhanced GSV compliance in HTN (-0.0125 +/- 0.0129 vs. -0.0288 +/- 0.0090 mm2 center dot 100 mm2 center dot mmHg-1, room air vs. hypoxia, respectively; P = 0.004), but it was unchanged in NT (-0.0139 +/- 0.0121 vs. -0.0093 +/- 0.0066 mm2 center dot 100 mm2 center dot mmHg-1, room air vs. hypoxia, respectively; P < 0.541). Venous compliance was unaltered with hyperoxia in both groups (P < 0.05). In sum-mary, compared with NT, hypoxia elicits a decrease in GSV CSA and enhanced GSV compliance in HTN, indicating enhanced venom-otor responsiveness to hypoxia.NEW & NOTEWORTHY Hypertension remains a significant global health problem. Although hypertension research and therapies are keenly focused on the heart and arterial circulation, the venous circulation has been neglected comparatively. We deter-mined whether hypoxia, known to cause peripheral chemoreflex activation, evoked more pronounced changes in lower limb ve-nous capacity and compliance in hypertensives (HTN) than in age-matched normotensives (NT). We found that hypoxia reduced venous capacity in the great saphenous vein in HTN and increased its compliance twofold. However, hypoxia did not affect ve-nous function in NT. Our data indicate the venomotor response to hypoxia is enhanced in hypertension, and this may contribute to the hypertensive state.

Automated summary

This study investigates the changes in lower limb venous capacity and compliance in hypertensive and normotensive individuals in response to hypoxia and hyperoxia. The results indicate that in hypertensives, hypoxia leads to a decrease in venous capacity and an increase in compliance, while no changes are observed in normotensives.