Augmentation of ventilatory response to asphyxia by prochlorperazine in humans

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Abstract
The effect of the dopamine-receptor blocking agent prochlorperazine on the ventilatory response to hypercapnic hypoxia was studied in six healthy adults. Repeated episodes of transient hypoxia were induced at the mixed venous PCO2 level by a nonrebreathing technique in five males and one female before and after an intravenous bolus injection of prochlorperazine mesylate (12.5 mg = 10 mg base). The ventilatory response to CO2 was also studied before and after drug administration. Prochlorperazine produced a modest (15%) increase in resting ventilation (P less than 0.05) but a marked increase in the ventilatory response to asphyxia such that the group mean response was double the control value [2.0 +/- 0.7 vs. 4.2 +/- 1.5 l . min-1 . % arterial O2 saturation (%SaO2); P less than 0.001]. Two-thirds of this change in ventilatory response was due to an increase in frequency response to hypoxia (0.34 +/- 0.20 vs. 0.81 +/- 0.52 breaths . min-1 . %SaO2; P less than 0.001). The position of the ventilatory response line, as judged by the computed ventilation at 95% SaO2, was increased by prochlorperazine (22.2 +/- 9.6 vs. 35.9 +/- 10.9 l . min-1; P less than 0.01) due to an increase in both tidal volume (P less than 0.05) and frequency of breathing (P less than 0.0125). The ventilatory response to CO2 was unchanged by drug injection. In separate experiments prochlorperazine was shown to 1) increase the ventilatory response to steady-state eucapnic hypoxia (P less than 0.01) demonstrating that the drug effect was not dependent on either the presence of hypercapnia or rapidly changing states of arterial oxygenation; and 2) reverse the depressant effect of intravenously infused dopamine hydrochloride (5 micrograms . kg-1 . min-1) on the ventilatory response to transient asphyxia (P less than 0.01). We conclude that prochlorperazine augments hypoxic responsiveness in humans. The mechanism may be blockade of dopaminergic receptors that modulate carotid body discharge.