Quantitative studies of ventilation during inhalation of carbon dioxide in normal and emphysematous patients

Abstract

Quantitative studies on the response of the ventilation to carbon dioxide inhalation were carried out on twelve normal subjects, twelve patients with emphysema, and one patient with fibrosis of the lung (Boeck's sarcoid). Tidal air, respiratory rate, minute ventilation, arterial serum carbon dioxide, and pH determinations were made before and during hyperpnea produced by addition of carbon dioxide to the spirometer. Minute liter ventilation increase, divided by the millimeter increase in tension of carbon dioxide of the normal group, showed an average increase of 2.71 liters per minute for each millimeter of mercury in crease of carbon dioxide, or a median value of 1.6 liters. In terms of pH this was shown to be an increase of 3.16 liters per minute for each 0.01 decrease in pH, or a median value of 2.5 liters. The patients with emphysema were shown to have an average of 3.0 volumes per cent (7.0 per cent) more total carbon dioxide content than did the normal subjects. The average response was 1.85 liters per minute increase in ventilation for each millimeter increase in carbon dioxide tension (66 per cent that of the normal group) when both groups are considered as a whole. There was a wide variation in the response within each group and considerable overlapping between the response of the two groups existed. A statistical analysis would seem to indicate that the difference was not significant. However, the patients with emphysema did not get as much tidal exchange for a given amount of respiratory effort as did the normal subjects, and were shown by the relationship ventilation (in liters per minute) vital capacity (in liters) to have an increased resting respiratory effort as well as a greater increment of respiratory effort for a given change in pH consequent to carbon dioxide inhalation. From the evidence presented, it seems apparent that in terms of respiratory effort, the emphysematous patient is actually more sensitive to carbon dioxide inhalation than the normal individual. The explanation for this phenomenon is unknown at the present time.