Intermittent negative pressure applied to the lower limb increases foot macrocirculatory and microcirculatory blood flow pulsatility in people with spinal cord injury

Abstract

Study Design: Experimental prestudy and poststudy. Objectives: Examine the acute effects of intermittent negative pressure (INP) applied to the lower limb on foot circulation in people with spinal cord injuries (SCIs). Setting: Vascular laboratory, Oslo University Hospital. Methods: Twenty-four people with SCI (median age 59 years, range 29-74) were exposed to lower leg INP (-40 mm Hg) using an air-tight pressure chamber connected to an INP generator. The contralateral leg was placed outside the pressure chamber. We continuously measured arterial blood flow velocity (ultrasound Doppler), skin blood flow (laser Doppler), skin temperature of the dorsum of the foot, heart rate (ECG) and systemic blood pressure (Finometer) during 5-min baseline (atmospheric pressure), followed by 10-min INP (alternating 10 s-40 mm Hg and 7 s atmospheric pressure), and 5-min post-INP (atmospheric pressure). Skin blood flow was measured on the foot placed outside the pressure chamber. A mixed effects regression model was applied to estimate the effect of INP on blood flow. To quantify flow fluctuations, we calculated cumulative up-and-down changes in arterial blood flow velocity per minute. Results: Flow fluctuations increased during INP compared to baseline [32.3 cm/s/min (95% CI 26.9 to 37.7) vs. 15.2 cm/s/min (95% CI 9.8 to 20.6), P < 0.001]. Peak blood flow velocity and skin blood flow was reached 2-3 s after the onset of negative pressure and increased 33% (95% CI 16 to 46, P < 0.001) and 11% (95% CI-4.1 to 60, P = 0.14) above baseline, respectively. Conclusions: INP induced increased foot arterial blood flow fluctuations compared to baseline. Sponsorships: The Norwegian Research Council provided funding to Otivio (grant: 241589).