The Helium-mixing Curve Low Point as an Index of Pulmonary Disability: A Study of 496 Patients

¹ Clinical Assistant Professor of Medicine, Seton Hall College of Medicine, and Associate Director, Thomas J. White Cardiopulmonary Institute
² Chief Respiratory Physiology Technician

1. A modification of the closed circuit helium technique was used to measure the functional residual volume of the lungs, and catharometer readings were recorded during the rebreathing periods of 496 patients. The helium-mixing curve low point was determined, and the patients classified on the basis of this equilibration time.

2. The low point time for 400 patients was three minutes or less, and for 96 patients was more than three minutes. The latter category included a higher percentage of men and an older age group. There was progressive deterioration of vital capacity, 1.0 second timed vital capacity, maximum minute ventilation, air velocity index, breathing reserve ratio and a rise in residual volume/total lung capacity ratio with mixing delay. A residual volume/total lung capacity ratio above 50 per cent was four times as common in patients reaching equilibrium after three minutes as in those mixing more rapidly.

3. Distributive delay occurred in patients with emphysema, emphysema and fibrosis, bronchial asthma, chronic bronchitis, bronchogenic carcinoma and pulmonary tuberculosis, in descending order of frequency. Five of 43 patients with portal cirrhosis exhibited retarded mixing.

4. A progressive fall in pulmonary function values and a rise in residual volume/total lung capacity ratio with increasing mixing difficulty in 93 patients with diffuse obstructive pulmonary emphysema did not appear to be a consequence of aging.

5. The convenience and modest cost of this method are appropriate for routine clinical appraisal of intrapulmonary air distribution and estimation of pulmonary disability in the physician's office or clinic lung laboratory.