Ventilatory response to carbon dioxide inhalation in depression

The ventilatory response to carbon dioxide (CO2 response) was determined in 18 patients admitted to an inpatient service with endogenous depressive illness. Admission mean CO2 response value for the group was below the mean value for a control group. At the time of hospital discharge marked clinical improvement had occurred in depressive symptomatology; mean CO2 response had increased slightly and was no longer significantly below the control value. CO2 response deserves further investigation as a possible physiologic characteristic of certain depressed patients.