The Respiratory Response to Carbon Dioxide in Health and in Emphysema

The tension of carbon dioxide in the cells of the medullary respiratory center stimulates it to transmit efferent nervous impulses to the muscles of respiration. These, in turn, perform mechanical work upon the lung and thorax, and result in the complex movement of air known as ventilation. Ideally, therefore, the stimulus (tissue carbon dioxide tension) and the response (efferent impulses) should be measured in order to assess the response of the respiratory center to carbon dioxide. Arterial carbon dioxide tension is generally considered to be a satisfactory approximation of the stimulus delivered to the respiratory center, but the response is far more difficult to measure. While most investigations have reported the response in terms of ventilation (1-3), this may be modified by the ventilatory capacity and the degree of airway obstruction (4). The response of the respiratory muscles, therefore, should be a more accurate measure of respiratory center activity. This can be assessed by measuring the total amount of mechanical work done by these muscles.