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Biomedical subjects

H M Brash

Publications and source records attributed to H M Brash.

30 records · Page 2Linked to original sources
PubMed1979

Accuracy sensitivity to carboxyhemoglobin, and speed of response of the Hewlett-Packard 47201A ear oximeter.

We have shown that the Hewlett-Packard 47201A ear oximeter measures arterial O2 saturation within 95 per cent confidence limits of +/- 4 per cent when arterial blood saturation is more than 65 per cent, but at lower saturations the oximeter consistently provides a reading that is too low. The oximeter is sensitive to carboxyhemoglobin, progressively overestimating arterial saturation as carboxyhemoglobin concentration increases from 0 to 18 per cent. The time response is exponential, with a normal time constant of 3 sec, but this is halved in the fast mode or operation.

Carboxyhemoglobin↗
PubMed1977

The assessment of left ventricular ejection fraction in patients with ischaemic heart disease by contrast ventriculography and nuclear angiography.

1. In 18 patients with ischaemic heart disease left ventricular ejection fraction, measured by two different nuclear angiographic methods, has been compared with ejection fraction measured by single-plane contrast angiography. 2. The first nuclear angiographic technique involves detection of variation in the radio-activity from the left ventricle during the initial passage of a bolus of 99Tcm-labelled human serum albumin injected intravenously; the second is our own modification of a "gated" method, which accumulates the radioactivity detected during the continuing recirculation of the plasma bound radioisotope, so presenting an "averaged" ventricular volume curve. 3. Ejection fraction, measured by the "bolus" method, is lower than that measured either by contrast ventriculography or by the "gated" method. This may be due to a damping effect. 4. Ejection fraction measured by the "gated" method is well correlated with that measured by contrast ventriculography (r = 0-89). 5. Our modification of the "gated" method, which presents the changes in ventricular volume throughout the cardiac cycle, without needing computer facilities, is a useful non-invasive means for assessment of left ventricular function.

Angiography↗
PubMed1975

Cardiorespiratory effects of rapid saline infusion in normal man.

We have studied the cardiorespiratory effects of the rapid infusion (100 ml/min) of 2 liters of saline in four normal seated subjects. Cardiac output and pulmonary arterial pressure increased, while vital capacity (VC) and total lung capacity (TLC) decreased. There was an increase in closing volume (CV) without any detectable change in lung compliance or flow-volume characteristics. There was an increase in Pao2 during infusion period which can be related to better matching of ventilation to perfusion and to improved hemoglobin transport. In the recovery stage as cardiac output, pulmonary arterial pressure, TLC, and VC all returned toward control values CV remained high. In two subjects CV occurred within the normal tidal range of ventilation and in these two subjects Pao2 fell significantly below values obtained in the control period. The results suggest that rapid saline infusion in man can cause interstitial edema and lead to premature airway closure and hypoxemia.

Airway Resistance↗
PubMed1975

Reproducibility of dynamic compliance and flow-volume curves in normal man.

To evaluate methods proposed for the early detection of small airways obstruction. we have compared the precision of the forced expiratory flow-volume curve and of measurements of the frequency dependence of lung compliance in normal subjects, in 10 of whom these measurements were made on four occasions, and in 5 on two occasions. The maximal expiratory flow rate was highly reproducible, revealing consistent differences between these normal subjects, particularly when measured at 60% of TLC and corrected for differences in body size. The frequency-dependence measurements, expressed as the slope of the regression line relating dynamic compliance to frequency, showed much greater variation between repeated measurements in the same subject. Comparison with earlier published accounts is difficult in view of lack of quantitative data, but the variability between single measurements on different normal subjects appears to be similar to that which we have found when the results are expressed in a comparable manner. Dynamic compliance at a frequency of 1 Hz lay between 48% and 141% of the value obtained by extrapolation to zero frequency.

Adult↗