Ultrasound Doppler estimates of femoral artery blood flow during dynamic knee extensor exercise in humans

Ultrasound Doppler has been used to measure arterial inflow to a human limb during intermittent static contractions. The technique, however, has neither been thoroughly validated nor used during dynamic exercise. In this study, the inherent problems of the technique have been addressed, and the accuracy was improved by storing the velocity tracings continuously and calculating the flow in relation to the muscle contraction-relaxation phases. The femoral arterial diameter measurements were reproducible with a mean coefficient of variation within the subjects of 1.2 +/- 0.2%. The diameter was the same whether the probe was fixed or repositioned at rest (10.8 +/- 0.2 mm) or measured during dynamic exercise. The blood velocity was sampled over the width of the diameter and the parabolic velocity profile, since sampling in the center resulted in an overestimation by 22.6 +/- 9.1% (P < 0.02). The femoral arterial Doppler blood flow increased linearly (r = 0.997, P < 0.001) with increasing load Doppler blood flow = 0.080 . load (W) + 1.446 l/min and was correlated positively with simultaneous thermodilution venous outflow measurements (r = 0.996, P < 0.001). The two techniques were linearly related (Doppler = thermodilution . 0.985 + 0.071 l/min; r = 0.996, P < 0.001), with a coefficient of variation of approximately 6% for both methods.