Considerations of the physiological variables that determine the blood carboxyhemoglobin concentration in man.

Abstract

The relationships between the rate of endogenous CO production, blood carboxyhemoglobin % saturation and body CO stores and CO exchange via the lungs were analyzed. The body CO stores are influenced by the production and excretion of endogenous CO and the respiratory exchange of exogenous CO. The principal physiological parameters are: rate of CO production, alveolar ventilation, diffusing capacity of the lung, mean O tension in the pulmonary capillaries and concentration of CO in inspired air. Calculations demonstrate the relative influence of the determining parameters on the blood carboxyhemoglobin % saturation and body CO stores. The time constants of transient states are very long, and the blood carboxyhemoglobin is not markedly influenced by short duration cyclic variations of the determining variables. Measured values of blood carboxyhemoglobin compare closely with values for normal patients and normal volunteers who breathed 100% Qj for 5-7 hours and were probably in a steady state. The blood carboxyhemoglobin measurement is not a precise index of rate of endogenous CO production (Vco) since it is markedly influenced by other parameters. The rate of CO production could be calculated from blood carboxyhemoglobin % saturation measurement with a precision of only [plus or minus] 0.80 ml/hour SD.