Abstract:
Blood oxygen is an important modulator of arterial function, but its impact on peripheral venous function is incompletely understood. Herein, we sought to determine the effect of hypoxia and hyperoxia on venous capacity and compliance in the lower limb. In sixteen healthy individuals (7 women; age: 28.3±7.6 years, mean±SD), we assessed peripheral oxygen saturation (SpO<sub>2</sub>), the cross-sectional area (CSA) of the great saphenous vein (GSV; Doppler ultrasound) and calf volume (strain gauge plethysmography) during a standard 60 mmHg thigh cuff inflation-deflation protocol. Separate trials were undertaken during breathing of room air, hypoxia (fraction in inspired oxygen [FIO<sub>2</sub>]: 0.10) and hyperoxia (FIO<sub>2</sub>: 0.50), according to a single-blinded, randomized design. Lower limb pressure-CSA and pressure-volume relationships were modelled using a quadratic regression equation and compliance derived. SpO<sub>2</sub> was decreased by hypoxia (83.6±5.6%) and increased by hyperoxia (98.7±0.5%) compared to room air (96.4±1.0%, p<0.001). Compared to room air (17.0±7.9 mm<sup>2</sup>), hypoxia decreased GSV CSA (13.4±5.7 mm<sup>2</sup>, p<0.001), while no change was observed with hyperoxia (17.1±8.7 mm<sup>2</sup>, p=0.883). GSV compliance derived from the pressure-CSA relationships were elevated approximately two-fold with hyperoxia (-0.0061±0.0046 a.u.) when compared to room air (-0.0029±0.002 a.u., p=0.027) and hypoxia (-0.0030±0.0032 a.u., p=0.007). No differences were observed in calf pressure-volume parameters with either hypoxia or hyperoxia (p > 0.05). Our data indicate that GSV capacity is reduced by hypoxia, and that GSV compliance is increased by hyperoxia, thus highlighting the often overlooked role of oxygen in the regulation of venous circulation.
