Ventilatory response to CO2. I. A psychobiologic marker of the respiratory system.

When a gas mixture containing CO2 is breathed by a healthy subject, alveolar ventilation is increased. The ratio delta ventilation/delta PCO2 has been termed the ventilatory response to CO2 (S). Since the development of a rebreathing method in 1967, it has proved easy to measure this index of the regulation of ventilation. This index, although showing considerable interindividual variation (range, 0.5-9 liters/min/mm PCO2), tends to be consistent over time for any given individual. Positive correlations between S and personality traits such as anxiety, extroversion, and aggression and negative correlations between S and certain scales of the Minnesota Multiphasic Personality Inventory (MMPI: depression, psychopathology, psychasthenia, and social introversion) have been found in previous studies. It was hypothesized that S may be a psychobiologic marker of the respiratory system. A project in which 82 normal subjects (50 male, 32 female) were studied with both psychologic (Eysenck Personality Inventory, Catell 16PF, and 168-item MMPI) and rebreathing tests was undertaken to investigate this possibility further. A strong correlation between S and neurotic personality traits was found, but this correlation appeared valid only in female subjects.