1. The respiratory and circulatory effects of bilateral block of the IXth and Xth cranial nerves (IX and X) with local anaesthetic were studied in two subjects with obstructive airways disease (asthma).
2. In one subject bilateral block of IX and X decreased alveolar ventilation as evidenced by a rise in Pa,co2 and a fall in Pa,o2. There was no apparent ventilatory change in the other subject. The lung volumes (ERV and FRC) were unaffected by the block; however, the forced vital capacity and 1 s forced expired volume were slightly improved in both subjects.
3. During bilateral IX and X block neither subject showed a ventilatory response after 3 min of breathing 8·7% O2 in 91·3% N2. In one subject during a left-sided IX and X block, there was a normal hypoxic-ventilatory increase, whereas during a right-sided IX and X block the hypoxic-ventilatory response was slightly less than normal.
4. Unilateral IX and X block in both subjects produced tachycardia and hypertension which was approximately one half the increased heart rate and blood pressure that followed bilateral IX and X blockade.
5. Unlike the control responses, breathing 8·7% O2 in 91·3% N2 during bilateral IX and X block produced no change in heart rate and there was a continuous fall in the systemic blood pressure. The pulmonary arterial pressure, however, increased in response to hypoxia in the same manner as before the block.