Reproducibility and Effect of Sampling Depth on Laser Doppler Flowmetry Measures During the Reflex Cutaneous Vasoconstriction Response

Abstract

During cold exposure, reflex cutaneous vasoconstriction is an important thermoregulatory mechanism that minimizes heat loss. Laser Doppler flowmetry (LDF) is a widely used, non-invasive method of assessing cutaneous microvascular blood flow. However, data on the reproducibility of LDF during a cooling stimulus is limited. Furthermore, various sampling depths of skin measurement are available depending on the type of LDF probe used; however, a comparison of different depths to the same cooling stimulus has not been determined. We hypothesized that LDF probes, particularly those sampling at deeper skin depths, would provide a reproducible measurement of cutaneous microvascular blood flow during whole-body cooling. Fourteen healthy, young adults completed two whole-body cooling bouts, each bout separated by 3-7 days. Participants wore a water-perfused whole-body suit to reduce skin temperature (Tsk) from 34°C to 30.5°C over 30 minutes, and held at 30.5°C for an additional 10 minutes. LDF flux was measured continuously at five forearm sites using 1 VP1-HP Doppler probe, 2 VP7b integrated probes, and 2 VP12 single point Dopplers (Moor Instruments, Axminster, UK) measuring at depths of 4.0 mm, 0.66 mm, and 0.33 mm, respectively. Cutaneous vascular conductance (CVC) was calculated as flux/mean arterial pressure at each 0.5°C reduction in Tsk and at plateau. CVC values were expressed as percent changes from baseline (%ᐃCVCBASELINE). A greater vasoconstriction response was recorded using the VP1-HP Doppler at plateau (34.7 ± 0.6%) compared to the VP7b (31.9 ± 0.5%, p < 0.001) and VP12 (30.3 ± 0.6%, p < 0.001) LDF probes. Additionally, test-retest reproducibility between visits displayed good reproducibility (coefficient of variation <9%) among all three Doppler probes. These data indicate that LDF provides reproducible measurements during reflex cutaneous vasoconstriction at different depths. However, deeper Dopplers, which analyze a greater area of skin, are more likely to discriminate differences in cutaneous microvascular blood flow than those at shallower depths.