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.     

Ventilatory pattern following diazepam and lorazepam

The effect of intravenous diazepam (10 mg) or lorazepam (2 mg) on the ventilatory pattern has been studied in two groups of ten patients prior to elective surgery. Injection of lorazepam was followed by a periodic pattern of ventilation in nine patients.     

PHYSICAL CHARACTERISTICS OF AN ENCLOSED AFFERENT RESERVOIR BREATHING SYSTEM

We have assessed the characteristics of the Ohmeda EnclosedAfferent Reservoir Breathing System (EAR) using simulated spontaneousventilation and controlled ventilation. The additional workof breathing through the system was measured and shown to becomparable to that of a modified Mapleson D breathing system(Bain) for fresh gas flows producing similar end-tidal carbondioxide concentrations. It was shown under conditions of simulatedcontrolled ventilation that end-tidal gas concentration wasrelatively insensitive to variations in inspired to expiredratio (I:E), tidal volume (VT) and deadspace (VD). Measurementof the volume of carbon dioxide rebreathed using simulated spontaneousventilation led to the prediction that rebreathing of carbondioxide would begin to occur in the EAR when fresh gas flowto total ventilation ratio (VF: VE) was approximately 0.87.However, comparison of the results of model lung tests and clinicaldata suggests that great caution should be taken in extrapolatingsuch results into clinical advice.     

Bilateral endometriosis of the vulva

We have added the fifteenth case of endometriosis of the vulva to the medical record. Our case was unique, however, in that it was bilateral.