Single passive leg movement-induced hyperemia: a simple vascular function assessment without a chronotropic response

Abstract

Passive leg movement (PLM)-induced hyperemia is a novel approach to assess vascular function, with a potential clinical role. However, in some instances, the varying chronotropic response induced by PLM has been proposed to be a potentially confounding factor. Therefore, we simplified and modified the PLM model to require just a single PLM (sPLM), an approach that may evoke a peripheral hemodynamic response, allowing a vascular function assessment, but at the same time minimizing central responses. To both characterize and assess the utility of sPLM, in 12 healthy subjects, we measured heart rate (HR), stroke volume, cardiac output (CO), mean arterial pressure (MAP), leg blood flow (LBF), and calculated leg vascular conductance (LVC) during both standard PLM, consisting of passive knee flexion and extension performed at 1 Hz for 60 s, and sPLM, consisting of only a single passive knee flexion and extension over 1 s. During PLM, MAP transiently decreased (5 ± 1 mmHg), whereas both HR and CO increased from baseline (6.0 ± 1.1 beats/min, and 0.8 ± 0.01 l/min, respectively). Following sPLM, MAP fell similarly (5 ± 2 mmHg; P = 0.8), but neither HR nor CO responses were identifiable. The peak LBF and LVC response was similar for PLM (993 ± 189 ml/min; 11.9 ± 1.5 ml·min-1·mmHg-1, respectively) and sPLM (878 ± 119 ml/min; 10.9 ± 1.6 ml·min-1·mmHg-1, respectively). Thus sPLM represents a variant of the PLM approach to assess vascular function that is more easily performed and evokes a peripheral stimulus that induces a significant hyperemia, but does not generate a potentially confounding, chronotropic response, which may make sPLM more useful clinically.

New & noteworthy: Using the single passive leg movement (PLM) technique, a variant of the vascular function assessment PLM, we have identified a novel peripheral vascular assessment method that is more easily performed than PLM, which, by not evoking potentially confounding central hemodynamic responses, may be more useful clinically.

Keywords: cardiovascular disease assessment; endothelial function; flow-mediated dilation.

Figures

Fig. 1.

Between-day (3 days) reproducibility of the blood flow response to continuous passive leg movement (PLM; A) and single PLM (sPLM; B) in a representative subject. Horizontal dashed lines represent mean baseline values.

Fig. 2.

Central hemodynamic responses to continuous passive leg movement (PLM) and single PLM (sPLM) over time: mean arterial pressure (MAP; A), cardiac output (CO; B), stroke volume (SV; C), and heart rate (HR; D). Values are means ± SE. Horizontal dashed lines represent mean baseline values. *Significantly different from PLM baseline. §Significantly different from sPLM baseline. Shaded area indicates a significant difference between PLM and sPLM.

Fig. 3.

The leg blood flow (A) and leg vascular conductance (B) response to continuous passive leg movement (PLM) and single PLM (sPLM). Values are means ± SE. Horizontal dashed lines represent mean baseline values. *Significantly different from PLM baseline. §Significantly different from sPLM baseline. Shaded area indicates a significant difference between PLM and sPLM.

Fig. 4.

The correlations and agreement between peak leg blood flow (A and B), the change in peak leg blood flow (Δpeak; C and D), and blood flow (E and F) evoked by continuous passive limb movement (PLM) and single PLM (sPLM). The relationships and agreement (Bland-Altman plots) between PLM and sPLM achieved statistical significance for peak and Δpeak leg blood flow, while leg blood flow, area under the curve, did not.

Fig. 5.

Exemplar Doppler blood velocity spectra collected in the passively moved leg during continuous passive leg movement (PLM; A) and single PLM (sPLM; B). Anterograde (C) and retrograde (D) blood flow in the passively moved leg during PLM and sPLM are shown. Values are means ± SE. Horizontal dashed lines represent mean baseline values. *Significantly different from PLM baseline. §Significantly different from sPLM baseline. Shaded area indicates a significant difference between PLM and sPLM.