Dco at various breath-holding times: comparison in patients with chronic bronchial asthma and emphysema

Measurement of Dco is known to be dependent upon functional inhomogeneities. Because different types of inhomogeneities are operative in patients with bronchial asthma and patients with emphysema, different changes of Dco with increasing breath-holding time, tA, are to be expected. We studied the change of Dco with increasing breath-holding time in healthy subjects, patients with asthma bronchiale and patients with emphysema. In the patients the severity of airway obstruction was about the same. The following results were obtained: (a) in healthy subjects and in the asthmatics Dco decreased with tA, in a similar manner, approaching a value (ml . min-1 . Terror-1) of 34.7 and 31.6 at 10 sec, respectively, and (b) in patients with emphysema Dco increased with tA, yielding negative values at small tA: 1.5 sec-23.4; 10 sec: 11.7. From these results we suggest that in healthy subjects and in patients with bronchial asthma parallel inhomogeneities influence the course of Dco. In emphysema the time couse of Dco is best explained with a faster intrapulmonary mixing of He compared to CO. This behavior indicates that in emphysema low Dco values can be mainly attributed to large diffusional resistances (stratification) within the lungs.