A simple low-resistance flap valve for pulmonary ventilation studies

Details of a simple low-resistance flap valve for pulmonary ventilation studies are presented. It has a space of 11 ml, weighs 28 g and is constructed from 3 mm thick perspex sheet. The opening pressure for both the inlet and the outlet is zero as its flaps normally remain open. The resistance of the valve to a flow of air at a rate of 20 l min-1 is 2.2 mm of water at the inlet and 4.2 mm of water at the outlet. At a rate of flow of 100 l min-1 the corresponding figures are 8.9 and 24.6 mm of water. All these values compare favourably with those obtained from three commercially available units. The valve has been in use over the past four years and the patient compliance has been found to be excellent.