QUANTITATIVE LEG BLOOD FLOW BY DOPPLER ULTRASOUND IN UPRIGHT AND SUPINE EXERCISE 818

Abstract

It has been suggested that a limitation to work performance in supine cycle ergometry is an impairment of peripheral circulation to the working muscles. We evaluated the effects of perfusion pressure on muscle blood flow using Doppler ultrasound to measure femoral artery mean blood velocity (MBV) and diameter (D). Nine healthy subjects were studied at rest and constant load knee extension (50W) while seated upright (UP) and supine (SU). Average resting MBV was 6.37±0.61 cm/sec (mean±SE) in UP and 8.28±0.96 cm/sec in SU. Average MBV at 50W was 36.6±3.58 cm/sec in UP and 44.2±5.69 cm/sec in SU. Average D was greater (P<0.05) in UP (10.1±0.32 mm) than in SU (9.06±0.31 mm) at rest. Average D was not different in UP (10.2±0.28 mm) vs SU (9.67±0.24 mm) during exercise. Leg blood flow was 0.31±0.04 l/min in UP rest and 0.32±0.04 l/min in SU rest and increased to 1.79±0.15 l/min in UP and 1.94±0.25 l/min in SU exercise. ˙VO2 was similar during rest (326±14 vs 341±24 ml/min) and exercise(902±36 vs 940±26) in UP and SU, respectively. Under the assumption the increase in ˙VO2 with exercise was in the legs only, we estimate an (a-v)O2 difference of 161 ml O2/l in UP and 154ml O2/l in SU exercise at 50W. These estimates of flow suggest that steady state blood flow to exercising muscle is not compromised in submaximal knee extension exercise in the supine position.