The role of sensory components in reactions of the human respiratory system to increasing loads

: In 13 healthy male subjects performing an increasing work on veloergometer in conditions of resistive respiratory loads, the moments of sensation of respiratory difficulties and refusal from the work, were recorded. The analysis of the respiratory system functions revealed that the respiratory discomfort occurred with increasing of the alveolar PCO2 up to a certain value and that the refusal occurred on a certain level of inspiratory activity. The subjects believed that the moment of refusal coincided with the complete exhaustion of the respiratory system reserves. Their lung ventilation, however, as well as inspiratory effort were far from reaching the maximal values obtained in special tests. Apparently, the sensory components of responses to the combination of muscular work with an increased resistance against breathing are of a defensive character and directed to the prevention of the exhaustion of the respiratory system functional reserves.