Cournand lecture. Expiratory partial pressure curves in the diagnosis of emphysema

The deformation of expiratory partial pressure curves of respiratory and inert gases (O2, CO2, He, Ar, SF6), as measured by means of mass spectrometry, was analysed in healthy subjects and in patients with asthma, chronic bronchitis and/or pulmonary emphysema. Patients with emphysema could best be distinguished from the other groups when the comparison was based on the shape of expirogram phase II. Phase II was characterized by the volume V25-50 which was expired between 25% and 50% of the inspiratory/end-tidal partial pressure difference. Comparative measurements of V25-50 of O2, CO2, He and SF6 in 10 healthy subjects (mean age: 30.8 yr) and in 10 patients with advanced emphysema (mean age: 60.8 yr) showed a linear increase of V25-50 with increasing inspired volume (VI) being 3-5 times higher in the patients than in normals. V25-50 increased with the sequence He less than SF6 approximately equal to CO2 less than O2 in both groups. The separation between phase II volumes of He and SF6 was more pronounced in the patients with emphysema than in the healthy subjects. Variations of the breathing pattern in eight healthy subjects revealed a linear increase of V25-50 with increasing VI and, to a lower extent, with increasing respiratory frequency, while a decrease of V25-50 with increasing breath-holding time and only very small changes with variations of inspiratory as well as expiratory duration were observed.(ABSTRACT TRUNCATED AT 250 WORDS)