1. The ventilatory response to maximal incremental exercise and the accompanying sensation of breathlessness were studied after the inhalation of 0.9% sodium chloride (saline) and 5% bupivacaine aerosols in six patients with interstitial lung disease.

2. The adequacy of airway anaesthesia induced by bupivacaine aerosol was confirmed by the absence of the cough reflex to 5% citric acid aerosol on completion of exercise.

3. All subjects first performed a trial exercise test to familiarize them with the procedure and to assess the degree of arterial oxygen desaturation on exercise. In subsequent tests, supplementary oxygen was given to maintain the saturation at 95% or above.

4. Airway anaesthesia had no effect on the ability to perform exercise as assessed by maximum workload, CO2 production or heart rate. No significant changes were seen on the pattern of breathing, minute ventilation or endtidal Pco2 on exercise. There was, however, a small but statistically significant increase in ventilation related to CO2 production (VE/Vco2) at the end of exercise.

5. There was a tendency for breathlessness to be increased by airway anaesthesia but this did not reach statistical significance.

6. These results provide no evidence that vagal afferent activity is responsible for the abnormal ventilatory response to exercise in patients with interstitial lung disease. The perception of breathlessness in these patients was not diminished by anaesthesia of the airway.

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