The physiology of recovery in experimental pneumococcal pneumonia

Lobar distribution of pulmonary perfusion, arterial PO2 (PaO2), intrapulmonary shunt (Qs/Qt) and post mortem lobe wts were measured in 12 dogs with experimental lobar pneumococcal pneumonia. Six dogs (group I) had both perfusion and gas exchange measurements performed 48 h after an inoculum of Streptococcus pneumoniae was placed in a left lower lobe bronchus. Six other dogs (group II) had perfusion determinations before the induction of pneumonia and again 96 h after inoculation, at which time gas exchange measurements were performed. To ensure that group II dogs were recovering from the acute pneumonia, penicillin treatment was instituted at 48 h and continued until the time of study at 96 h. An improvement in gas exchange between the acute and convalescent states was demonstrated and was associated with a 50% reduction in excess wet wt and a 25% reduction in perfusion of the infected lower lobe. We conclude that improvement in gas exchange during recovery from acute lobar pneumonia is due, in part, to air space clearing with improved ventilation and, in part, to reduced perfusion of poorly ventilated lung. The results suggest that arterial hypoxemia in acute pneumonia is aggravated by vasodilatation or blockade of local hypoxic vasoconstriction by some aspect of the acute inflammatory response, and that the hypoxic vasoconstrictor response is restored during convalescence.