Respiratory centre sensitivity and exercise tolerance in healthy Thais

To determine the range of normal values of respiratory centre sensitivity and exercise tolerance in Thais, 69 healthy subjects, 18 to 72 years of age, participated in a series of tests, i.e. ventilatory drive, ventilatory response, musculo-ventilation transfer and the two-minute walking test with rating of the breathing sensation on a visual analogue scale. Our results showed higher end-tidal Pco2 and tidal volume response to CO2 and less exercise tolerance in the elderly than in the young. Only in young males was the ventilatory response to CO2 higher than in females. No attempt has yet been made to explain the lower ventilatory response in Thais as compared with Americans. Apparently, the defective respiratory apparatus, viz. increased airways resistance and not the blunting of respiratory centre sensitivity, contributes principally to relative hypoventilation and exercise limitation in the elderly. The compensation, with high tidal volume response to CO2, seems ineffective in maintaining normo-ventilation.