Intermittent negative pressure influences popliteal artery shear rate during supine and sitting postures.

Abstract

Background: Intermittent negative pressure is an emerging treatment for lower limb vascular disease but the specific physiological effects, particularly upon large artery haemodynamics are unclear. This study examined the influence of intermittent negative pressure upon popliteal artery shear rate during both supine and sitting postures. Participants and methods: Eleven healthy participants (5 female; age: 28.3 ± 5.8 y; weight: 69.6 ± 9.8 kg, height: 1.75 ± 0.07 m) received intermittent negative pressure (-37 mmHg; 9.5-sec on, 7.5-sec off), upon the lower leg during both supine and sitting postures. Popliteal artery blood flow and shear rate were recorded (duplex ultrasound), accompanied by heart rate (3-lead ECG) and blood pressure (volume clamp method). Results: Compared to sitting, a supine posture led to greater mean shear rate during baseline (supine: 21[9]; sitting: 17[13] sec^-1; all median [IQR]) and negative pressure phases (supine: 24[15]; sitting: 17[14] sec^-1; both p<0.05). While supine, negative pressure raised mean shear rate above baseline levels (p<0.05) and reduced it upon return to atmospheric pressure (p < 0.05). In sitting, mean shear rate only differed from baseline at the points of peak and minimum shear (peak:18[17]; minimum: 10[9] sec^-1; both p<0.05). Shear pattern (oscillatory shear index) showed changes from baseline during both postures (p<0.05), but was not different between postures. Conclusions: Intermittent negative pressure influenced lower limb popliteal artery shear rate during both the supine and sitting postures, the effect was greater while supine. Fluctuation in shear pattern seen during both positions may account for positive clinical effects observed following intermittent negative pressure treatment. These findings are framed against previous work investigating clinical populations. Future work should investigate any differences in lower limb haemodynamics and markers of endothelial function among patients with vascular disease.