Oxyhaemoglobin equilibrium and chronic beta-adrenoceptor blockade in coronary heart disease.

In 20 patients with coronary heart disease the effect of long-term beta-adrenergic receptor blockade on the haemoglobin oxygen equilibrium was investigated. Study patients received alprenolol 200 mg twice daily for 12-41 months (mean: 24 months) as a secondary preventive measure following a myocardial infarction. While on and again following gradual withdrawal of alprenolol, the patients performed a maximum bicycle ergometer test. Haemoglobin oxygen affinity as expressed by the P50 value, 2,3-diphosphoglycerate (2,3-DPG) and carbon monoxide haemoglobin were measured before and following exercise. Pre-exercise P50 decreased from 25.2 +/- 0.3 mm Hg (mean +/- s.e. mean) while on beta-adrenoceptor blocker to 24.6 +/- 0.4 mm Hg in the off-treatment state (P less than 0.05). Five minutes after stopping exercise P50 was 25.1 +/- 0.3 in patients taking alprenolol as compared to 24.7 +/- 0.3 after withdrawal of the drug (P less than 0.01). It is concluded that the slight decrease in haemoglobin oxygen affinity in long-term treatment with alprenolol, which is observed in the present study probably is without clinical bearing. The question should be further elucidated by analysis of coronary sinus blood samples.