RESPIRATORY MODULATION OF BLOOD-FLOW IN NORMAL AND SYMPATHECTOMIZED SKIN IN HUMANS

Sympathetic vasoconstrictor neurons innervating hairless skin of the c at show a respiratory rhythm of activity discharging in inspiration. T he following questions arise: (1) Is it possible to detect respiratory variations in cutaneous blood flow in humans? (2) Are these variation s actively mediated by rhythmic activity in vasoconstrictor neurons (a ctive rhythms), or do they depend on blood flow changes induced passiv ely due to respiratory blood pressure waves (passive rhythms)? Three p atients who had been sympathectomized unilaterally and four healthy co ntrols were studied. Cutaneous blood flow was measured bilaterally usi ng a laser-Doppler flowmeter during physiological breathing (14/min, t idal volume 500-600 ml, minute volume 8 1/min) and during slower respi ratory rate with a higher tidal and smaller minute volume (5/min, 1 1, 5 1/min). The temporal pattern of skin blood flow was analyzed with r espect to respiration by constructing peri-event-time histograms after summation and averaging of 10-15 respiratory cycles. During physiolog ical breathing no or minimal variation of cutaneous blood flow could b e detected. During slower respiratory rate with higher tidal and small er minute volume a potentiation of variations appeared. Tn controls th e inspiratory phase was followed by a considerable decrease in cutaneo us blood flow with a latency of 4.6 s. Identical rhythms were also pre sent on the unoperated side of the patients. In contrast, on the sympa thectomized side a respiratory rhythm appeared that was lower in ampli tude and phase shifted by about half a cycle. We conclude: (1) Respira tion-related cutaneous blood flow variations can be detected, in parti cular if slower respiratory rates, higher tidal and smaller minute vol umes are present. (2) Passive oscillations can be differentiated from active rhythms due to sympathetic vasoconstrictor activity by their te mporal pattern. (3) The observations suggest that the neurons responsi ble for the active rhythm discharge during inspiration.