Effect of Co2 Inhalation on Ventilation and Mechanics of Breathing in Mitral Disease.

Administration of different concentrations of CO2 is known to cause an increase in respiratory minute volume. This increase of ventilation in healthy subjects is directly related to the height of the inspired alveolar carbon dioxide tension. It has been shown, however, that in patients with emphysema and in those with mitral valvular disease the increment of minute volume is smaller than in the healthy subjects (Donald and Christie, 1949; Prime and Westlake, 1954; Cherniack and Snidal, 1956; Pauli, Noe, and Coates, 1960). Various explanations have been proposed for this diminished response to CO2 stimulation. Reduced responsiveness of the respiratory centre was assumed to be the cause by some authors (Donald and Christie, 1949; Prime and Westlake, 1954; Pauli et al., 1960), while the importance of increased resistance to airflow as a causative factor was stressed by others (Cherniack and Snidal, 1956; Brodovsky, Macdonell, and Cherniack, 1960). Most reports dealing with the effect of CO2 inhalation are based on the measurement of minute ventilation and CO2 in alveolar air or arterial blood; actual measurements of compliance and total lung resistance during carbon dioxide stimulation were obtained only in normal subjects but not in patients with mitral valvular disease (Butler et al., 1960). This paper deals with observations on these latter parameters in healthy subjects and in patients with mitral valvular disease.