Control of breathing in patients with chronic obstructive lung diseases and secondary polycythemia after venesection.

Using the mouth occlusion pressure technique, we have studied the control of breathing in 10 hypercapnic patients with chronic obstructive pulmonary diseases and polycythemia before and after venesection. The mean hematocrit value was 59.9 +/- 5.5% which, following venesection (approximately 1,200-1,600 cm3 of blood was removed from each patient over three consecutive days), fell to 44.4 +/- 2.2%. Respiratory drive, expressed as P0.1 (mouth occlusion pressure 0.1 s after the onset of occluded inspiration at functional residual capacity) and as mean inspired flow (VT/TI), was diminished after venesection (p less than 0.001 and p less than 0.05); in contrast to that, we found no changes in respiratory timing (TI and TI/Ttot). The arterial PCO2 was decreased (p less than 0.001) and arterial PO2 was increased after venesection, these improvements are mainly attributed to decreased dead space ventilation (p less than 0.05). It seems that the improvements of blood gases after venesection is probably responsible for the decrease in respiratory drive.