CHANGE IN THE WORK OF BREATHING IMPOSED BY FIVE ANAESTHETIC BREATHING SYSTEMS

Measurements of pressure and flow in five anaesthetic breathingsystems were studied with various fresh gas flows (FGF) usingvolunteers, and mechanically simulated breathing. Pressure measurementswere made at the patient connection and in the neck of the reservoirbag. A pneumotachograph was used to measure flow in the patientconnection. The change in the work of breathing imposed by thecircuit was derived from the pressure-volume graph and apportionedto stages of the breathing cycle. All the systems studied increasedthe work of breathing. Expiratory work was always increasedmore than inspiratory work. The additional work imposed on expirationand the total extra work imposed on breathing were further increasedat FGF greater than the minimum clinical requirement.