Pulmonary function results in healthy subjects breathing through external stenoses compared to patients with airway obstruction

We compared body plethysmographic data, flow-volume curves during spontaneous breathing, P0.1 and PETCO2 in healthy subjects breathing through external stenoses (ES) of varying magnitude to the results in patients suffering from chronic obstructive pulmonary disease (COPD). Inspiratory vital capacity (IVC) remained unchanged by experimental airway stenoses. IVC is mainly determined by the end-expiratory closure of the airways, which only weakly correlates with airway resistance in patients. External stenoses had no effect on the physiological end-expiratory closure of the airways. For the other spirometric parameters the available force of the respiratory muscles and the degree of the experimental stenosis played the major role. The mouth occlusion pressure (P0.1) showed considerably lower variation during ES as well as in COPD patients than total resistance (Rt). There was no increase in intrathoracic gas volume (IGV) causing increased tension of the lungs and the thorax during ES. The well-known correlation between Rt and IGV is attributed to the end-expiratory closure of the airways during increased flow resistance and to "trapped air". It remains open, if and how the expiratory muscles act to overcome the increased resistance. With consideration of the underlying factors of the different lung function measures, the combination and the analysis of the correlation between different values may lead to far-reaching results in lung function testing.