[Pulmonary carbon monoxide exchange constants in the "stable state" at rest in healthy non-smokers]

During simultaneous evaluation of pulmonary O2, CO2, and CO in the stable state (ES) at rest, CO volume per minute (V'CO) standardized (V'COs) for FICO = 0.001 [2, 3] can be expressed relative to simultaneous flow of "respiratory" gases (V'O2 and V'CO2) by the quotient of the gas concentrations concerned, if its is admitted that V'I = V'E. Whether at the "expired"mean E or "alveolar" A levels, these concentrations have identical paired relationships. In the strict stable state, the proposed expressions of V'CO are constants independent of age, sex, stature, and ventilatory regimen in healthy non-smokers [6]; the result is that V'COs in relation to alveolar ventilation, V'COs/V'A, which is related to V'COs/V'CO2 by PaCO2, is also a constant. When the so-called "stable" state is not a strict one, experimental arguments suggest that V'COs/V'CO2 alone is not markedly influenced by ventilatory instability. Measurements conducted by means of different biological modalities and techniques in 3 groups of healthy women of homogeneous age breathing in a semi-open circuit: 1) established the value of the constants V'COs/V'CO2, V'COs/V'O2, V'COs/V'A in the true stable state (ESV) controlled by R and by gasometry on simultaneously collected blood samples; and 2) confirmed the constant character of V'COs/V'CO2 whatever the degree of respiratory stabilization, even when the ventilatory regimen was in reality not stabilised (ENS); V'COs/V'CO2 should therefore be the only value for defining a "specific capacity of pulmonary CO exchange". V'COs/V'A appears to be related to Q'/V'A. As DuCO/(DuCO2.1,21), which measures this ratio, it is independent of age and of ventilatory frequency. Several facts indicate that the "parallelism" of modifications affecting DuCO and DuCO2 [15] is not found in all physiological and pathological circumstances.