Previous studies have shown that some patients with
chronic obstructive lung disease and
hypercapnia will respond to
medroxyprogesterone with improvement in arterial blood
gases. The exact mechanism of this effect is unclear but it is presumed to be a result of ventilatory stimulation. To determine whether the ability to correct arterial blood gas abnormalities by voluntary
hyperventilation would predict a subsequent favourable response to
progesterone, we studied 11 subjects with
chronic obstructive lung disease and chronic
hypercapnia. Five subjects had
chronic obstructive lung disease of moderate severity with mean (SE) FEV1 1.8 (0.34) 1 maximum voluntary ventilation (MVV) 40.4 (7.16) 1/min-1, arterial
oxygen tension (Pao2) 53.8 (2.40 mm Hg, and arterial
carbon dioxide tension Paco2) 49.6 (3.91) mm Hg, and were able to normalise their blood gas tensions during voluntary
hyperventilation (Pao2 85.4 (8.01) mm Hg; Paco2 32.8 (3.43) mm Hg). Six subjects had severe
chronic obstructive lung disease with FEV1 0.77 (0.12) 1, MVV 19 (3.09) 1/min-1, Pao2 60.0 (2.89) mm Hg and Paco2 50.5 (1.38) mm Hg, and they could not significantly alter their blood
gases with voluntary
hyperventilation (Pao2 62.5 (3.19) mm Hg, Paco2 49.7 (1.84) mm Hg). The groups were similar in age, height, weight, and resting Pao2 and Paco2. Each subject received one month of oral placebo and one month of
medroxyprogesterone acetate (
Provera). 20 mg orally thrice daily, given in a randomised, double blind fashion. The groups responded similarly with a significantly higher Pao2 and lower Paco2 while having
medroxyprogesterone acetate than while having placebo. Two patients with polycythaemia showed a reduction in haemoglobin concentration while taking
progesterone. It is concluded that the response to
medroxyprogesterone is not predictable from spirometric or blood gas changes after voluntary
hyperventilation.