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

New Findings: What is the central question of this study? The passive leg movement (PLM) assessment of vascular function utilizes the blood flow response in the common femoral artery (CFA): what is the impact of baseline CFA blood flow on the PLM response? What is the main finding and its importance? Although an attenuated PLM response is not an obligatory consequence of increased baseline CFA blood flow, increased blood flow through the deep femoral artery will diminish the response. Care should be taken to ensure that a genuine baseline leg blood flow is obtained prior to performing a PLM vascular function assessment.

Abstract: The passive leg movement (PLM) assessment of vascular function utilizes the blood flow response in the common femoral artery (CFA). This response is primarily driven by vasodilation of the microvasculature downstream from the deep (DFA) and, to a lesser extent, the superficial (SFA) femoral artery, which facilitate blood flow to the upper and lower leg, respectively. However, the impact of baseline CFA blood flow on the PLM response is unknown. Therefore, to manipulate baseline CFA blood flow, PLM was performed with and without upper and lower leg cutaneous heating in 10 healthy subjects, with blood flow (ultrasound Doppler) and blood pressure (finometer) assessed. Baseline blood flow was significantly increased in the CFA (∼97%), DFA (∼109%) and SFA (∼78%) by upper leg heating. This increase in baseline CFA blood flow significantly attenuated the PLM-induced total blood flow in the DFA (∼62%), which was reflected by a significant fall in blood flow in the CFA (∼49%), but not in the SFA. Conversely, lower leg heating increased blood flow in the CFA (∼68%) and SFA (∼160%), but not in the DFA. Interestingly, this increase in baseline CFA blood flow only significantly attenuated the PLM-induced total blood flow in the SFA (∼60%), and not in the CFA or DFA. Thus, although an attenuated PLM response is not an obligatory consequence of an increase in baseline CFA blood flow, an increase in baseline blood flow through the DFA will diminish the PLM response. Therefore, care should be taken to ensure that a genuine baseline leg blood flow is obtained prior to performance of a PLM vascular function assessment.