Power spectral density of breathing pattern in patients with pulmonary, heart and liver diseases.

Pulmonary functions, breathing pattern and rhythmic oscillations of inspiratory time, expiratory time and tidal volume were studied by calculating autocorrelation functions and power spectral densities in patients with chronic obstructive pulmonary disease and respiratory insufficiency, in patients with cardiac valvular disease and in patients with liver disease at rest. Despite of the pathological results of pulmonary function tests the rhythmic oscillations of inspiratory time, expiratory time and tidal volume were present in all patients and they were intraindividually and interindividually different in the same way as in healthy man.