Pulse transit time (PTT) is the time it takes for pressure waves to propagate through the arterial system. Arterial stiffness assessed via PTT has been extensively examined in the conduit arteries; however, limited information is available about PTT to the skeletal muscle microcirculation. Therefore, the purpose of this study was to assess PTT to the skeletal muscle microcirculation (PTTm) with near-infrared spectroscopy (NIRS) and to determine whether PTTm provides unique information about vascular function that PTT assessed in the conduit arteries (PTTc) cannot provide. This pilot study was conducted with 10 (male = 5; female = 5) individuals of similar age (21.5 ± 1.2 yr). The feasibility of using the intersecting tangents method to derive PTTm with NIRS was assessed during reactive hyperemia with the cross-correlation of PTTm produced by the intersecting tangents method and a different algorithm that used signal spectral properties. To determine whether PTTm was distinct from PTTc, the cross-correlation of PTTm and PTTc during reactive hyperemia was assessed. Cross-correlation indicated agreement between PTTm derived from both algorithms (r2 = 0.77, P < 0.01) and a lack of agreement between PTTm and PTTc during reactive hyperemia (r2 = 0.07, P < 0.01). Therefore, we conclude that it is feasible to assess PTTm using NIRS, and PTTm provides unique information about vascular function, including skeletal muscle microvascular elasticity, which cannot be achieved with traditional PTTc. PTTm with NIRS may provide a comprehensive and noninvasive assessment of vascular function and health.NEW & NOTEWORTHY Pulse transit time to the skeletal muscle microcirculation can be assessed using near-infrared spectroscopy and the intersecting tangents method. Pulse transit analysis to the microcirculation provides a comprehensive assessment of the vascular response to postocclusive reactive hyperemia that pulse transit analysis in the conduit arteries cannot provide. Pulse transit time to the skeletal muscle microcirculation using near-infrared spectroscopy provides unique information about microvascular elasticity in the skeletal muscle. These findings indicate that the combination of near-infrared spectroscopy and pulse transit analysis may be a useful method for assessing the skeletal muscle microcirculation.
Keywords: arterial stiffness; intersecting tangents method; near-infrared spectroscopy; reactive hyperemia; skeletal muscle microcirculation.