RESPIRATION AND THE AIRWAY Effects of alveolar dead - space , shunt and _ V = _ Q distribution on respiratory dead - space measurements

Background. Respiratory dead-space is often increased in lung disease. This study evaluates the effects of increased alveolar dead-space (VDalv), pulmonary shunt, and abnormal ventilation perfusion ratio ( _ V= _ Q) distributions on dead-space and alveolar partial pressure of carbon dioxide (PACO2) calculated by various methods, assesses a recently published non-invasive method (Koulouris method) for the measurement of Bohr dead-space, and evaluates an equation for calculating physiological dead-space (VDphys) in the presence of pulmonary shunt. Methods. Pulmonary shunt, _ V= _ Q distribution and VDalv were varied in a tidally breathing cardiorespiratory model. Respiratory data generated by the model were analysed to calculate dead-spaces by the Fowler, Bohr, Bohr–Enghoff and Koulouris methods. PACO2 was calculated by the method of Koulouris.