Time delay effects in the estimation of pulmonary diffusing capacity.

Steady state estimates of the pulmonary diffusing capacity for carbon monoxide require measurement of the uptake and the average partial pressure of CO in the lung. The expired alveolar sample obtained by different experimental methods and/or breathing patterns rarely represents the actural average alveolar partial pressure. This error in choosing the correct alveolar sample arises in the sampling time chosen by the experimental method. The time (TAV) at which the correct alveolar sample (FAV) is obtained occurs one-half of a breathing period after the effective inspiration time. If TAV and the sample time chosen by the experimental method are known then the measured diffusing capacity can be corrected to the actual diffusing capacity.