CENTRAL RESPIRATORY DRIVE IN ACUTE RESPIRATORY-FAILURE OF PATIENTS WITH CHRONIC OBSTRUCTIVE PULMONARY-DISEASE

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Abstract
Control of breathing was studied in patients with chronic obstructive pulmonary disease, in the chronic state and during acute respiratory failure. Results were compared to those in age-matched normal subjects. In patients breathing air, minute ventilation was not different during acute and chronic states, and was similar to that in normal subjects. Breathing pattern was different: acutely ill patients took shorter and smaller breaths, with a breathing frequency higher than that of normal subjects. The pattern of the chronic group was intermediate between that of acutely ill patients and that of normal subjects. Mouth occlusion pressure, an index of neuromuscular respiratory drive, was 5 times greater in acutely ill patients than in normal subjects. Administration of O2 at a flow of 5 l/min caused a small (14%), but significant, decrease in minute ventilation due to decreased respiratory frequency. Tidal volume did not change, so the decrease in minute ventilation was the result of decreased inspiratory flow. This was associated with a decreased mouth occlusion pressure that was 3 times greater than that of normal subjects. Increase in arterial PCO2 [CO2 partial pressure] after administration of O2 was not correlated with the decrease in ventilation, indicating that other factors must be responsible for the increase in arterial PCO2. Despite the poor mechanical advantage of the respiratory muscles in acute respiratory failure, the increased drive to breathe results in high mouth occlusion pressure and inspiratory flow. Increase in arterial PCO2 during administration of O2 is not related solely to changes in respiratory drive.