Venous pressure in the saphenous vein near the ankle during changes in posture and exercise at different ambient temperatures

Summary

The venous pressure in the saphenous vein at the ankle was measured in ten healthy subjects (5 men, 5 women) aged 19–33 years during supine posture, orthostasis and cycle ergometer exercise (50 W, 50 rpm). Measurements were made at 20, 28 and 36°C at 50% relative humidity. A custom-built setup consisting of two pressure transducers and a differential amplifier was used to compensate for the hydrostatic effects, temperature influences and movement artefacts that disturbed the pressure measurements. Pressure was lowest in the supine position and varied only slightly with the ambient temperature. The mean pressures were 7 (SEM 1) mmHg [0.9 (SEM 0.13) kPa], 7 (SEM 1) mmHg [0.9 (SEM 0.13) kPa], 4 (SEM 1) mmHg [0.5 (SEM 0.13) kPa] at 20, 28 and 36° C. The venous pressure increased when the subjects were passively tilted from a supine to an upright posture. The rate of the increase was smaller at 20°C than at 28° and 36° C. The final level the pressure reached during motionless standing differed slightly. The mean pressures were 76 (SEM 2) mmHg [10.1 (SEM 0.27) kPa], 79 (SEM 7) mmHg [10.5 (SEM 0.93) kPa] and 75 (SEM 3) mmHg [10.0 (SEM 0.40)] at the three temperatures. When starting exercising, venous pressure decreased within the 1st min to a level which remained virtually constant until the end of exercise. However, this level was found to be temperature dependent. It was lowest at 20° C 26 (SEM 3) mmHg [3.5 (SEM 0.40) kPa] and increased with temperature. The mean values were 30 (SEM 3) mmHg [4.0 (SEM 0.40) kPal at 28° C and 35 (SEM 3) mmHg [4.7 (SEM 0.40) kPa] at 36° C. The difference between the venous pressures at 20° and 36° C was statistically significant. Overall, posture and exercise influenced the venous pressure at the ankle more intensely than did ambient temperature. Muscle exercise reduced the venous pressure considerably, even in the warm environment.