Respiratory-induced vasoconstriction measured by light transmission and by laser Doppler signal.

Changes in finger tissue blood volume (TBV) measured by light transmission and in laser Doppler flow (LDF) were obtained during long breathing (of 12 s period) and associated with the respiratory phases, inspiration and expiration. For fifteen out of sixteen subjects TBV and LDF started to decrease 0-2 s after the start of expiration and increased during inspiration but the start of increase occurred before the start of inspiration, showing that the respiratory-induced changes in TBV and LDF are mainly associated with the expiration. Decrease of TBV and LDF after expiration was also found during the inspiratory gasps