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The aims of this study were to quantify the changes in finger pulp skin temperature, laser Doppler flow (LDF, microvascular flux) and photoplethysmogram (PPG, microvascular blood volume pulsatility), induced by a deep inspiration in healthy subjects, and to investigate the repeatability of these responses within a measurement session and between measurement sessions on separate days. A system comprising an electronic thermometer, a laser Doppler flowmeter and a PPG amplifier measured simultaneous vasoconstrictor responses to a deep inspiratory gasp from three adjacent fingers of one hand. Clearly defined responses were obtained in 15 of the 17 subjects studied. Skin temperature fell in all of these subjects after each gasp, with a median fall of 0.089 degrees C (P < 0.001). The median value of LDF flux reduction was 93% (P < 0.001) indicating a momentary almost complete shut-down of microvascular blood flow; and PPG also showed a large response relative to pulse amplitude of 2.6 (P < 0.001). The median times for waveforms to reach their minimum were 4.6 s (PPG), 6.3 s (LDF) and 29.1 s (skin pulp temperature), with median delays between minima of LDF and PPG of 1.6 s (P < 0.001) and skin temperature and PPG of 23.5 s (P < 0.001). The vascular responses of skin temperature, LDF and PPG to an inspiratory gasp were repeatable, with temperature change repeatable to within 10% of the median subject change.
Allen et al. (Thu,) studied this question.