The passive leg movement technique for assessing vascular function: defining the distribution of blood flow and the impact of occluding the lower leg

Abstract

New Findings What is the central question of this study?What is the distribution of the hyperaemic response to passive leg movement (PLM) in the common (CFA), deep (DFA) and superficial (SFA) femoral arteries? What is the impact of lower leg cuff‐induced blood flow occlusion on this response? What is the main finding and its importance?Of the total blood that passed through the CFA, the majority was directed to the DFA and this was unaffected by cuffing. As a small fraction does pass through the SFA to the lower leg, cuffing during PLM should be considered to emphasize the thigh‐specific hyperaemia. Abstract It has yet to be quantified how passive leg movement (PLM)‐induced hyperaemia, an index of vascular function, is distributed beyond the common femoral artery (CFA), into the deep femoral (DFA) and the superficial femoral (SFA) arteries, which supply blood to the thigh and lower leg, respectively. Furthermore, the impact of cuffing the lower leg, a common practice, especially with drug infusions during PLM, on the hyperaemic response is, also, unknown. Therefore, PLM was performed with and without cuff‐induced blood flow (BF) occlusion to the lower leg in 10 healthy subjects, with BF assessed by Doppler ultrasound. In terms of BF distribution during PLM, of the 380 ± 191 ml of blood that passed through the CFA, 69 ± 8% was directed to the DFA, while only 31 ± 8% passed through the SFA. Cuff occlusion of the lower leg significantly attenuated the PLM‐induced hyperaemia through the SFA (∼30%), which was reflected by a fall in BF through the CFA (∼20%), but not through the DFA. Additionally, cuff occlusion significantly attenuated the PLM‐induced peak change in BF (BFΔpeak) in the SFA (324 ± 159 to 214 ± 114 ml min−1), which was, again, reflected in the CFA (1019 ± 438 to 833 ± 476 ml min−1), but not in the DFA. Thus, the PLM‐induced hyperaemia predominantly passes through the DFA and this was unaltered by cuffing. However, as a small fraction of the PLM‐induced hyperaemia does pass through the SFA to the lower leg, cuffing the lower leg during PLM should be considered to emphasize thigh‐specific hyperaemia in the PLM assessment of vascular function.

The passive leg movement technique for assessing vascular function: the impact of baseline blood flow

“…The purpose of this study was to evaluate the impact of increased baseline CFA blood flow on PLM‐induced vasodilation and subsequent hyperaemia. As ∼70% of the PLM response measured in the CFA is primarily driven by vasodilation of the thigh microvasculature, downstream from the DFA, upper leg cutaneous heating was employed to increase blood flow through the DFA (Shields et al., 2019). Upper leg heating significantly increased baseline blood flow in the CFA, DFA and SFA.…”

“…All data collection took place at the Utah Vascular Research Laboratory located in the Salt Lake City VAMC Geriatric Research, Education, and Clinical Center. These subjects also participated in another study focused upon defining the distribution of blood flow and the impact of occluding the lower leg during PLM (Shields et al., 2019). Of note, the occlusion assessments were performed on a separate visit from the visits described in this study.…”

“…Utilizing real‐time Duplex visualization of the ultrasound image and the pulse wave spectra, a sustained insonation angle of 60 degrees was ensured, and the sample volume was centred within the vessel and maximized according to vessel size. As in previous studies, based upon the conservation of mass, DFA blood flow was calculated as CFA blood flow minus SFA blood flow (Shields et al., 2019; Wray et al., 2005).…”

“…The ensuing initial hyperaemia stimulates additional, shear stress‐mediated vasodilation. The vasodilation‐induced hyperaemia is evident in the conduit arteries supplying blood to the thigh (Broxterman et al., 2017), both the common femoral artery (CFA) and the DFA, and to some extent, the superficial femoral artery (SFA) (Shields et al., 2019). The PLM technique measures the blood flow response in the CFA, a relatively simple place to scan with Doppler ultrasound, which does not vasodilate during this assessment (Gifford & Richardson, 2017).…”

“…Therefore, this study aimed to assess the impact of increased baseline CFA blood flow, achieved by cutaneous heating, on the PLM‐induced hyperaemic response. As the PLM technique induces predominantly thigh‐specific hyperaemia, upper leg cutaneous heating was employed to increase blood flow to the vessels which experience mechanical deformation as a consequence of PLM, the thigh muscle microvasculature downstream of the DFA (Shields et al., 2019). We hypothesized that increasing baseline blood flow assessed in the CFA, through an increase in DFA blood flow, will result in an attenuated PLM response.…”