Effect of medroxyprogesterone on ventilatory control and pulmonary gas exchange in chronic obstructive patients

Chronic obstructive hypercapnic patients were monitored for blood gases and breathing pattern, before, during and after a 7-day treatment with 75 mg/day of medroxyprogesterone (MPA). In 9 out of the 15 patients the PaCO2 level decreased (+/- 8 mm Hg) significantly with return to nearly control values at stop. 4 subjects still continued to improve after cessation of therapy and were considered as not being stable. In 2 patients PaCO2 did not change. We were unable to find any significant difference between the control values of these three categories. The study of the breathing pattern in responsive subjects showed an increase in minute ventilation and tidal volume, with a small increase in mean inspiratory flow and no change in inspiratory time as a function of total respiratory cycle time. We conclude that MPA lowers the PaCO2 of hypercapnic chronic obstructive pulmonary disease patients through an increased tidal volume, which could result from an increased central nervous inspiratory output, or from better mechanical performance of the respiratory muscles due to the same central stimulation.