PULMONARY VENOUS CONGESTION AUGMENTS RESPIRATORY MOTONEURONAL RESPONSES TO CIGARETTE-SMOKE IN RABBIT

We examined the effects of cigarette smoke inhaled during subthreshold pulmonary venous congestion (sPVC) on phrenic nerve (PN) and unit act ivity in the ventral respiratory group in rabbits. sPVC was achieved b y in-dating a balloon in the left atrium. Inhalation of low-nicotine c igarette smoke produced initial prolonged bursts in 34 (19 bulbospinal ) out of 43 inspiratory (I) cells and in PN. Smoke decreased the activ ity of 29 out of 36 expiratory (E) cells (27 of 32 early E and 2 of 4 late E). The prolonged PN bursts occasionally progressed to doublets s uperimposed over regularly occurring PN bursts. sPVC augmented the smo ke effects: I cells displayed greater increases in spikes/burst (27 vs . 12%; P = 0.02) and burst duration (42 vs. 20%; P = 0.02) and greater decreases in interburst interval (34 vs. 10%; P < 0.02); PN displayed greater increases in I time (40 vs. 27%; P < 0.05), greater decreases in E time (18 vs. 26%; P < 0.05), and a greater incidence and duratio n of time of PN doublets (29 +/- 9 vs. 9 +/- 4 s; P < 0.03); E cells d isplayed greater decreases in spikes/burst (43 vs. 29%; P = 0.01) and burst durations (35 vs. 18%; P < 0.01). Smoke-induced respiratory chan ges may be exaggerated during sPVC.