Development and Evaluation of a Flow‐Dividing Unit for Differential Ventilation and Selective PEEP

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Abstract
Differential ventilation with selective positive end-expiratory pressure (PeEP) was studied in a 2-compartment lung model, using 1 ventilator and a flow-dividng unit consisting of inspiratory flow resistors and an inspiratory threshold valve. The compliance of each lung compartment was varied between 0.15 and 0.23 l .times. kPa-1 and the resistance was varied from 0-3.5 kPa .times. l-1 .times. s. The minute volume was 12 l and the respiratory frequency 12/min, with an inspiratory:expiratory ratio of 1:2. An even distribution of ventilation to the 2 lung comparments was obtained with the inspiratory flow resistors or the threshold valve under all conditions studied. A stepwise increase in the inspiratory resistance of 1 lung comparment from 1.0-2.5 or from 2.5-3.5 kPa .times. l-1 .times. s required readjustment of the inspiratory flow resistor to achieve an even distribution of ventilation, whereas the inspiratory threshold valve needed no readjustment. Large differences in the inspiratory impedance of the 2 lung compartments caused asynchronous gas delivery when the ventilation distribution was adjusted by means of the flow resistors. Use of the threshold value resulted in synchronous gas delivery. The flow-dividing unit consists of non-active elements and can thus be connected to any ventilator.