Effect of thyrotoxicosis on the reflex hypoxic respiratory drive.

1. Oxygen breath tests were performed in seven patients with thyrotoxicosis. The inspired air was replaced by oxygen without their knowledge for 20 s and the fall in ventilation was recorded. 2. Ventilation fell significantly in all the patients within 40 s. The mean fall was 21-1% (se +/-1-7) below the control value. 3. beta-Adrenoreceptor blockade with propranolol had little effect on this reduction in ventilation. The fall observed in five patients receiving propranol was 19-6% (se +/-1-0). 4. After definitive treatment, which rendered the patients euthyroid, the observed reduction in ventilation after breathing oxygen was significantly less at 11-7% (se +/-1-2). 5. It is concluded that patients with thyrotoxicosis have an increased resting reflex hypoxic drive to respiration, when compared with the euthyroid state, and this is unaffected by beta-adrenoreceptor blockade.