EFFECT OF SODIUM-NITROPRUSSIDE AND DIETHYLCARBAMAZINE ON HYPOXIC PULMONARY VASOCONSTRICTION AND REGIONAL DISTRIBUTION OF PULMONARY BLOOD-FLOW IN EXPERIMENTAL PNEUMONIA

The interaction between the effects of indomethacin and sodium nitropr usside or diethylcarbamazine infusion on the efficacy of hypoxic pulmo nary vasoconstriction (HPV) and regional distribution of lung blood fl ow was studied in 15 pentobarbital-anesthetized dogs with acute pneumo nia caused by Pseudomonas aeruginosa. After induction of pneumonia cen tral hemodynamics, gas exchange, and regional distribution of lung blo od flow (radionuclide-labeled microsphere method) were measured during ventilation of both lungs with oxygen and again with one lung ventila ted with nitrogen. The dogs were then randomly assigned to one of thre e treatment groups: Group I (n = 5) received indomethacin alone (2 mg/ kg); Group I-D received indomethacin and diethylcarbamazine (50 mg/kg over 20 min followed by 1 mg/kg/min for the rest of the experiment); G roup I-N (n = 5) received indomethacin with sodium nitroprusside to ac hieve a 20- to 30-mm Hg reduction in mean blood pressure. All measurem ents were then repeated during both oxygen ventilation and one-lung ni trogen ventilation. In all three groups there was no effect of nitroge n inhalation on distribution of lung blood flow prior to drug treatmen t, indicating absence of HPV. After treatment, in Group I, perfusion o f the pneumonic lung fell from 0.27 +/- 0.08 to 0.10 +/- 0.03 (p < 0.0 5) of total lung blood flow, and nitrogen ventilation of the left lung reduced perfusion to that region from 0.23 +/- 0.02 to 0.13 +/- 0.02 (p < 0.05), indicating restoration of HPV. In Groups I-D and I-N, HPV was persistently absent or markedly attenuated after treatment, but th e percentage of the cardiac output perfusing the pneumonia region fell by an amount similar to that in Group I (0.26 +/- 0.07 to 0.11 +/- 0. 04 in Group I-D and 0.35 +/- 0.03 to 0.21 +/- 0.06 in Group I-N, both p < 0.05). Because these two chemically unrelated pulmonary vasodilato rs effectively blocked HPV restoration but had no effect on vasoconstr iction in the pneumonia region after indomethacin, it is concluded tha t regional lung blood flow redistribution in pneumonia is mediated by a mechanism other than HIV.