Carbon monoxide uptake and excretion: Testing assumptions made in deriving the Coburn–Forster–Kane equation

• The Haldane assumption made in deriving the CFK equation is supported.
• The assumption made in deriving the CFK equation that DLCO-Out is equal to DLCO-In is supported.
• The CFK equation accurately describes the physiology of pulmonary CO excretion in resting male humans with normal lungs.

The Coburn–Forster–Kane equation (CFKE) describes physiological variables that define pulmonary carbon monoxide (CO) uptake and excretion, and carboxyhemoglobin (COHb) levels. This equation is useful in predicting CO uptakes and COHb values in normal humans. However, some assumptions made in its derivation have never been proven and whether or not it accurately describes the physiology of CO excretion is not known. Two assumptions specifically addressed are: that the mean capillary PCO can be computed using the Haldane equation; and that the diffusing capacity relevant to CO uptake is equal to the diffusing capacity relevant to CO excretion. Both assumptions were supported by results obtained in this study. These findings plus results of experiments that compared measured and CFKE-calculated changes in the body CO stores suggest that the CFKE accurately describes the physiology of both pulmonary CO excretion and uptake.