effect of a-blocker [Phentolamine] on patients with bronchial asthma

This work was performed on 12 asthmatic patients who showed a 15% improvement or more in the forced expiratory flow [FEF] between 25-75% of the forced vital capacity [FVC] following 2.5 mg isoproterenol inhalation. An alpha-blocker phentolamine [regitine] was administered in ascending [1, 2.5, 5, 7.5 and 10 mg] doses by inhalation on separate days after performing a baseline spirometric study. A placebo dose was administered randomly between the phentolamine doses. Spirometric recordings were performed at 1, 5, 30, 60, 90 and 120 minutes. Pulse rate and blood pressure recordings were obtained for each trial. Arterial blood samples were obtained as a baseline and at 10 and 60 minutes of the optimum 10 mg phentolamine dose for arterial pH, oxygen tension [PaO2] and carbon dioxide tension [PaCO2]. The results generally indicated a failure of the alpha-blocker phentolamine in reproducing bronchodilatation. It had a significant effect on PaCO2 levels. The response of pulse rate and blood pressure was variable