A combined oxygen concentrator and compressed air unit. Assessment of a prototype and discussion of its potential applications.

A prototype combined oxygen concentrator and air compressor is described. Laboratory assessment demonstrated satisfactory oxygen concentrations, flows, pressures and reliability. Its various modes of use in clinical practice are described. It is likely to be a valuable method to provide oxygen for anaesthesia both in remote areas and where nitrous oxide-free anaesthesia is required, as well as a reliable alternative to commercially produced oxygen for therapeutic purposes.

The oesophageal obturator airway: A study of cadaver lund ventilation through obturator airways and tracheal tubes.

Ventilation of cadaver lungs using a Pneupac ventilator through oesophageal obturator airways (EOA), oesophageal gastric tube airways (EGTA), and tracheal tubes was studied in 23 subjects. The mean tidal volume obtained through tracheal tubes was 381 ml compared with a mean tidal volume of 156 ml obtained through the EOA and a mean tidal volume of 237 ml through the EGTA. Considerable leakage occurred at the pressure relief valve of the ventilator and at the face mask. With the pressure relief valve occluded and better mask fit achieved by observation of maximum possible tidal volume, the mean tidal volume obtained through obturator gastric airways was 606 ml compared with 906 ml obtained through tracheal tubes. This represents adequate ventilation in these very stiff lungs. Subject to modification of the device and prevention of leakage the oesophageal gastric tube airway is a useful alternative to tracheal intubation in certain adverse conditions.

Left ventricular ejection and the Heather Index measured by non-invasive methods during postural changes in man.

Differences have been found, which are usually 1% or less, between the left ventricular ejection time measured from the external carotid pulse tracing, and from the rate of change of thoracic impedance (dZ/dt) waveform, using either the second heart sound or the X-point of the dZ/dt tracing as the end-point. The Heather Index obtained from the ECG and dZ/dt tracings has been correlated with other indices of cardiac performance. The changes observed in the physiological variables during head-up and head-down tilting were in the expected directions.