Resistance of humidifiers, and inspiratory work imposed by a ventilator-humidifier circuit.
The pressures and resistances of a bubble humidifier (Bennett Cascade) and a blow-by humidifier (Fisher and Paykel) were measured and computed at gas flow rates from 4.5 to 100 litre min-1. Pressures increased with flows, with the Bennett pressures being greater at all flows. The resistance of the Fisher-Paykel increased with flows, but remained less than that of the Bennett. An inverse resistance-flow relationship was seen with the Bennett up to a flow of 35 litre min-1. The work of breathing through a Servo 900C ventilator-humidifier circuit was computed, using a lung model. Work was performed by the Servo 900C on the lung, especially with the Fisher-Paykel circuit. The Bennett circuit required considerably greater (3.7 times more) inspiratory work. Thus the Bennett Cascade humidifier may present an unacceptable inspiratory load during spontaneous breathing.
Oh
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Department of Anaesthesia and Intensive Care, Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, N.T.
Lin
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Bhatt
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D000776:Anesthesiology / Q000295:instrumentation*; D006801:Humans; D006813:Humidity; D012121:Respiration, Artificial / Q000295:instrumentation*; D014939:Work of Breathing / Q000502:physiology*