New Assessment of Respiratory Muscle Oxygen Consumption

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Failure of respiratory muscles leads to alveolar hypoventilation and hypercapnic respiratory failure. This state may be caused by an imbalance between oxygen demand and oxygen delivery to the respiratory muscles. Therefore, oxygen consumption of the respiratory muscles (VO_2resp) may be an important index in assessing not only the normal physiological state but also pulmonary disease.The first purpose of the present study was to develop a new method to examine VO_2resp in human subjects. We modified Cherniack's method using a continuously increasing dead space volume consisting of a low-resistance plastic tube that was extended at at constant rate. The movable end of this expanding dead space was connected to the oxygen consumption-measuring system. Oxygen consumption (VO_2) was measured by the decrease in volume of a 9-liter Collins spirometer filled with 100% oxygen and connected to the movable end of the expanding dead space by pair of flexible tubes. Circulating airflow from the sp … More irometer to the termination of the dead space through the pair of tubes was provided by a 40-1/min fan in one arm. A soda lime box was placed in the other arm to absorb carbon dioxide. VO_2 in the continuous method was calculated as the 1-min increase in end-expiratory volume recorded spirometrically minus the increase in dead space. When the dead space was increased at a constant rate (-100ml/min), minute ventilation (V_E) and VO_2resp increased gradually. Because the logarithm of VO_2 was found to be approximately linearly related to V we characterized this relationship by the slope (logVO_2/V_E) and the intercept at V_E=0 of the semilog regression line.The second purpose of this study was to examine the relationship between logVO_2/V_E and aging and to compare logVO_2/V_E of patients with chronic obstructive pulmonary disease with that of age-matched normal group using this devise. We found a significant increase in logVO_2/V_E with age and greater logVO_2/V_E than that of normal group.These findings suggest that age is one of the factors accounting for the increase in VO_2 resp with age, and that ventilatory efficiency in COPD patients is lower than normal group.In this projects, we could not yet developed a device of an ambulant type for measuring respiratory oxygen consumption using a microcomputer system. Further studies are needed. Less