Effects Of Compression Timing On Femoral Blood Flow During Rhythmical Calf Compression Synchronized To HR

Abstract

Arterial blood flow is not a steady stream; it is pulsatile, which means that during the cardiac cycle the blood flow rate in the arteries varies depending on the timing of the flow wave. Given that rhythmical muscle contraction can temporarily obstruct blood flow by externally compressing the veins and arteries, we hypothesized that with rhythmical muscle contraction, the timing of the vessel compressions during the cardiac cycle will affect the muscle blood flow response. Furthermore, the blood flow response can depend on the level of the pressure and the body posture. PURPOSE: To investigate the effects of timing, the level of the pressure and posture on femoral arterial blood flow (FBF) during rhythmical external calf compressions synchronized to the heartbeat. METHODS: In 10 male subjects, a calf cuff was rhythmically inflated for 250 ms. In experiment 1 (EX1), the inflation was triggered 140-ms after the ECG-R wave (systolic timing: ST), 40 ms after the R wave (diastolic timing: DT), or at a constant rate irrespective of the resting HR (Random timing: RT). In experiment 2 (EX2), external compressions at three pressures (70, 130, 190 mmHg) were applied with DT. Each compression was applied for 3 min while the subject was in a supine position (SUP) or a 60° head-up tilt (HUT). FBF determined using the Doppler ultrasound method and cardiovascular responses were measured. RESULTS: In EX1, FBF was markedly increased after compression for 1 min, then gradually declined, but remained higher than resting level with all compressions. In a SUP, the increase in FBF with ST was smaller than with DT or RT. In a HUT, the increase in FBF was greater than in a SUP and differed among the three timing protocols. In EX2, in a SUP, the increase in FBF with 190 mmHg compressions was greater than with 70 or 130 mmHg compressions. With 130 or 190 mmHg compressions, the increase in FBF was smaller when the subject was in a HUT than when he was in a SUP. CONCLUSION: These results suggest that during rhythmical calf compression synchronized to the cardiac cycle, the contraction timing, the pressure level and posture all influence FBF. (1798/2000 characters). Supported by grants from COE projects, and from the Ministry of Education, Science, and Culture, Japan.