The effect of grunting respiration before and after induction of pneumonia was studied in 14 experiments on five dogs artificially ventilated with a modified piston respirator. An end-inspiratory pause was produced which was exactly the same duration as the pause that usually occurs after normal expiration. Only the respiratory pattern was changed; frequency, tidal volume, and flow rates remained constant. Before pneumonia, grunting produced a mean increase in PaO2 of 10.5% (± 7.0%), a mean decrease in PaCO2 of 11.0% (± 5.1%), and a mean increase in VA of 21.8% (± 9.5%). The results after pneumonia were not significantly different. Intrapulmonary gas distribution was somewhat improved by grunting in normal lungs, but the ellect was not as pronounced after pneumonia.

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