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Biomedical subjects

P K Wraith

Publications and source records attributed to P K Wraith.

31 records · Page 2Linked to original sources
PubMed1991

Predictors of survival in patients with chronic obstructive pulmonary disease treated with long-term oxygen therapy.

Long-term oxygen is the only therapy that has been shown to improve survival in patients with chronic obstructive pulmonary disease. The aim of this study was to assess the predictors of survival in such patients treated with long-term oxygen therapy. We studied 179 patients who were assessed for long-term oxygen therapy in two Departments of Respiratory Medicine: in Warsaw and in Edinburgh. Those who died following the prescription of long-term oxygen therapy had a similar forced expiratory volume in the first second (FEV1) and arterial carbon dioxide tension, but a slightly lower arterial oxygen tensions (p less than 0.05) than those who survived (p less than 0.05). A small but significant fall in FEV1 and a rise in arterial carbon dioxide tension (p less than 0.05) occurred in both survivors and nonsurvivors after treatment with oxygen, but arterial oxygen tension breathing air continued to fall only in those who died (p less than 0.005). Only two variables were independent predictors of survival in patients with chronic obstructive pulmonary disease treated with long-term oxygen therapy. These were the arterial oxygen tension and the mean pulmonary arterial pressure (Ppa). However, when the calculation was made on patients with PaO2 less than or equal to 60 mm Hg (n = 154), then FEV1 and PaO2 but not Ppa were found to predict survival.

Aged↗
PubMed1990

A new method of analysing pulmonary quasi-static pressure-volume curves in normal subjects and in patients with chronic airflow obstruction.

1. Exponential analysis of lung pressure-volume curves is used to deal with the non-linearity of the pressure-volume relationship. A major problem of this procedure is to define the lower volume limit for exponential curve fitting. 2. In 12 healthy subjects and 24 patients with chronic airflow obstruction, a cubic function was fitted to the quasi-static pressure-volume curves to define an inflection point. 3. The exponential function of Colebatch et al. (Colebatch, H.J.H., Ng, C.K.Y. & Nikov, N.J. Applied Physiol. 1979; 46, 387-93) was then fitted to the data for volumes above the inflection point. 4. Exponential analysis with a cubic determination of an inflection point provides an objective way to describe the elastic properties of the human lungs in vivo.

Adult↗
PubMed1983

The ventilatory effects of doxapram in normal man.

1. To determine the mode of action of doxapram in man we have measured ventilation, oxygen uptake, CO2 production, hypoxic and hypercapnic ventilatory responses in six healthy men before and during intravenous infusion to maintain a constant plasma level. 2. Doxapram changed neither resting oxygen uptake nor CO2 production but produced a substantial increase in resting ventilation at both levels of end-tidal CO2 studied. 3. Doxapram increased the ventilatory response to isocapnic hypoxia from -0.8 +/- 0.4 litre min-1 (%SaO2)-1 to -1.63 +/- 0.9 litres min-1 (%SaO2)-1. This was similar to the increase in hypoxic sensitivity which resulted from raising the end-tidal CO2 by 0.5 kPa without adding doxapram. 4. The slope of the ventilatory response to rebreathing CO2 rose from 11.6 +/- 5.3 litres min-1 kPa-1 to 20.4 +/- 9.8 litres min-1 kPa-1 during doxapram infusion. 5. The marked increase in the ventilatory response to CO2 implies that doxapram has a central action, but the potentiation of the hypoxic drive also suggests that the drug acts on peripheral chemoreceptors, or upon their central connections, at therapeutic concentrations in normal unanaesthetized subjects.

Adult↗
PubMed1982

Preservation of the hypoxic drive to breathing in diabetic autonomic neuropathy.

1. Unexplained cardiorespiratory arrests have been reported in patients with diabetic autonomic neuropathy and these could be due to denervation of the carotid chemoreceptors. 2. We have studied the ventilatory response to transient hypoxia (Ve/Peto2) during exercise in 22 male diabetic patients, six with symptomatic and cardiovascular evidence to suggest diabetic autonomic neuropathy (DAN+) and 12 without these features (DAN-). 3. There was no difference in the ventilatory response to transient hypoxia between the different groups of diabetic patients (Ve/Peto2 in DAN+ patients = -0.9 +/- 0.2 litre min-1 kPa-1; Ve/Peto2 in DAN- patients = -1.2 +/- 0.6 litres min-1 kPa-1) even allowing for differences in the level of exercise achieved (CO2 production in DAN+ patients = 743 +/- 103 ml/min; CO2 production in DAN- patients = 800 +/- 144 ml/min). These results fell within our normal range for ventilatory response to transient hypoxia at this level of exercise. 4. The heart rate response to transient hypoxia varied within the groups but was significantly (P less than 0.05) less in the patients with established diabetic autonomic neuropathy. 5. We conclude that the peripheral chemoreceptors are intact in diabetic autonomic neuropathy and that other mechanisms must be implicated in the unexpected cardiorespiratory arrests seen in these patients.

Adult↗
PubMed1982

Effect of exercise and isoprenaline on left ventricular ejection fraction in patients with angina pectoris as assessed by radionuclide angiography.

The effect of supine leg exercise and an infusion of isoprenaline (2 micrograms/min) have been compared in 9 patients with angina pectoris and 8 normal control subjects. Left ventricular ejection fraction was measured by radionuclide angiography using the gated blood pool technique. The normal subjects increased their ejection fraction from 0.57 +/- 0.02 at rest to 0.71 +/- 0.02 during exercise, and 0.76 +/- 0.03 during isoprenaline infusion. In patients with angina pectoris, the resting ejection fraction of 0.47 +/- 0.04 decreased to 0.35 +/- 0.04 during exercise but increased to 0.63 +/- 0.06 during isoprenaline infusion. Our results suggest that the changes in ejection fraction probably depend on the changes in left ventricular segmental wall motion. When dyskinesia is increased, as with exercise, the ejection fraction declines, but when dyskinesia is unaffected or improved, as with isoprenaline, the ejection fraction increases.

Adult↗
PubMed1980

Computer measurement of dynamic compliance: technique and reproducibility in man.

A computer program was developed to calculate the frequency dependence of dynamic compliance (Cdyn) using continuous data analysis. Cdyn was measured repeatedly in eight normal human subjects over a 2-yr period. Comparison with Cdyn results measured manually showed that the computer program improved 10-fold the ratio of variance within subjects to between subjects of the compliance at specific frequencies, but there was only slight improvement in indices of the slope of the frequency dependence of compliance. We suggest that the absolute compliance at specific frequencies merits further consideration as a pathophysiological measurement and that, if the frequency dependence of compliance continues to be used, standardization of its calculation should be applied and the wide normal range should be more widely appreciated. Measurements of Cdyn in subjects breathing 80% helium-20% oxygen confirm that inertia is insignificant when breathing with tidal volumes of less than 500 ml and frequency of less than 1.5 Hz.

Diagnosis, Computer-Assisted↗
PubMed1980

The influence of ectopic heart beats in gated ventricular blood-pool studies.

Direct data collection from ventricular blood-pool studies were stored in frame mode in a computer and by means of a modified tape recorder, the blood-pool image and ECG were recorded on tape. At the end of the study the tape data were replayed into the computer. The ECG signal was passed through a trigger circuit that detected the R wave which was sampled by the computer once every msec. Contractions outside of the desired range could be rejected along with the subsequent contraction. Of seven patients whose calculated ejection fractions were changed by more than 0.03, all had frequent (one in 20) ectopic contractions. The distorted ventricular volume curves were effectively restructured by the constraining procedure, changing the end-systolic volume and EF. Computer modeling showed a linear relationship between the percent of ectopic contractions and the underestimate of ejection fraction. One ectopic beat in ten led to a 5% underestimate of EF.

Cardiac Complexes, Premature↗
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↗