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Biomedical subjects

R M Whitlock

Publications and source records attributed to R M Whitlock.

At least 73 records · Page 4Linked to original sources
PubMed1978

The underfilled coronary artery: some pre- and post-operative observations on recipient arterial quality and left ventricular function after coronary artery surgery.

In a series of 141 saphenous vein aortocoronary bypass grafts in 59 patients undergoing routine restudy of the coronary arteries within four weeks of operation, an overall graft occlusion rate of 12% was found. A trend towards a higher occlusion rate was seen in arteries that were small (19%), that had a limited run-off (15%), significant distal disease (24%) or severe atheroma at the graft site (22%). Statistically, these occlusion rates are not significantly different from the overall failure rate and do not give absolute contra-indications to grafting. A particular group of arteries which seemed underfilled in the pre-operative angiogram (1.5 mm or less in diameter but apparently healthy with smooth walls and supplying a larger area of myocardium than would be expected from their apparent size) was identified. These arteries showed a significant increase in diameter in the post-operative angiograms and had a low occlusion rate (1 of 15 grafts; 7%). When all grafts were patent, the mean post-operative left ventricular ejection fraction showed a significant increase over the pre-operative valve, but when one or more grafts were occluded there was no significant change.

Arterial Occlusive Diseases↗
PubMed1978

Revised standards for normal resting dead-space volume and venous admixture in men and women.

1. Data have been combined from three previous series to provide revised standards for the prediction of physiological dead-space volume (VD), arterial oxygen tension (Pa,O2), alveolar-to-arterial oxygen-tension difference (PAO2--Pa,O2) and venous admixture fraction (QVa/Qt) in the sitting position. 2. These standards, based on measurements in 96 healthy men and women aged from 20 to 74 years, largely confirm conclusions drawn from the first series of 48 subjects. 3. VD is best predicted on age, height, tidal volume and the reciprocal of respiratory frequency. Pa,O2,(PA,O2--Pa,O2) and Qva/Qt are adequately predicted on age alone.

Adult↗
PubMed1978

The effects of cardiopulmonary bypass upon pulmonary gas exchange.

Cardiac output, venous admixture, physiological dead space, blood gas tensions, inspired gas distribution, and other respiratory variables were measured in 10 patients breathing both air and oxygen before and on five occasions up to 10 days after coronary artery vein-graft operations under cardiopulmonary bypass with moderate hypothermia. Cardiac output was unchanged at 8 hours but fell 8 percent by 22 hours. Thereafter it progressively increased and at 10 days was higher than before the operation. Venous admixture rose to a maximum at 28 to 48 hours, postoperatively, but the increase was inversely related to the magnitude of preoperative admixture. The part played by airway and alveolar closure in determining venous admixture is discussed. While admixture increased, the nitrogen-clearance curve improved, presumably due to progressive "dropout" of the worst-ventilated regions. Physiological dead space fell to a minimum at 28 hours after operation; this was attributed to a fall in the end-inspiratory position consequent upon a reduction in both functional residual capacity and tidal volume. There was an increase in ventilation after operation, and this persisted at 10 days; it appeared to be due to reflex stimulation from the lungs and chest wall.

Adolescent↗
PubMed1977

Six year review of the results of freehand aortic valve replacement using an antibiotic sterilized homograft valve.

The long-term behavior of an antibiotic-treated homograft aortic valve inserted in a freehand fashion was assessed in 121 patients operated upon for aortic valve disease and followed from four to six and one-half years. There were seven hospital deaths (5.7%) and 30 late deaths, only one of which was related to the homograft valve. The six year survival was 69% (77% for single valve and 52% for multiple valve surgery). At six years 9% had important homograft aortic valve incompetence (HAVI) and most of these required reoperation. Important HAVI occurred in only 5% of patients with an aortic root diameter less than 24 mm and in 38% of those with a markedly dilated or distorted proximal aorta (P less than 0.01). The freehand aortic homograft was considered superior to prosthetic devices because of the absence of chronic anticoagulation, thromboembolism, sudden death from valve failure and significant obstruction in a small aortic root. With slightly restricted patient selection the valve failure rate is expected to fall to less than 1% per year.

Adolescent↗
PubMed1976

Effects of cardioselective beta adrenoceptor blockade on specific airways resistance in normal subjects and in patients with bronchial asthma.

The effects of single oral doses of the cardioselective beta adrenoceptor blocking drugs, metoprolol and tolamolol, on specific airways resistance (SRaw) were compared with those of propranolol and practolol in 6 healthy volunteers and in 12 patients with bronchial asthma. Whole-body plethysmography was used to measure SRaw and the blocking potency of different antagonists assessed by the degree of inhibition of tachycardia due to exercise on a treadmill. The changes correlated with plasma drug levels. Propranolol and practolol were measured fluorometrically and metoprolol by electron-capture gas-liquid chromatography. In normal subjects, about 30% reduction in exercise-induced tachycardia resulted from single doses of 80 mg propranolol (plasma levels, 50.3, SD, 29.5 to 60.8, SD, 26 ng/ml), 250 mg practolol (plasma levels, 1.05, SD, 0.32 to 1.10, SD, 0.55 mug/ml), 100 mg metoprolol (plasma levels, 137, SD, 111 to 152, SD, 100 ng/ml), and 100 mg tolamolol. In patients, these doses of the drugs produced significant increases in SRaw. These increases were greater than those after placebo but significantly so only during the peak effect 1 hr after propranolol. Compared with changes after placebo, significant effects on SRaw were also found in 3 patients given 200 mg of tolamolol. None of the drugs had a significant effect on SRaw in normal subjects. It is concluded that metoprolol, practolol, and tolamolol may impair ventilatory function in asthmatics less than propranolol and that at high doses this difference may not be demonstrable.

Adrenergic beta-Antagonists↗
PubMed1976

Gas exchange during exercise in healthy people. I. The physiological dead-space volume.

1. Physiological dead-space volume (V D) was measured in twenty-four healthy men and women aged from 20 to 71 years, at rest and at two rates of work on a treadmill, whilst breathing air and breathing oxygen. 2. The effect of correction of arterial carbon dioxide tension (Pa,CO2) to pulmonary capillary temperature on the resulting value for V D was investigated. We find that the effect is substantial and that a correction should be made. 3. Equations have been derived for the prediction of normal V D during exercise. The best prediction was given by a regression on height, age, carbon dioxide output, ventilation and respiratory frequency, with an upper 95% confidence limit of +81 ml.

Adult↗
PubMed1976

Gas exchange during exercise in healthy people II. Venous admixture.

1. Venous admixture/cardiac output ratio (Qva/Qt) has been measured in twenty-four healthy volunteer subjects of both sexes aged 20-71 years, at rest and during the steady state of treadmill exercise at two rates of work, and breathing air and breathing oxygen. 2. With oxygen breathing, Qva/Qt was considerably less during exercise than during the time subjects were taking either normal or deep breaths of oxygen at rest, and did not significantly increase with the intensity of exercise. It is postulated that the increase in ventilation during exercise opens most or all of those alveoli which, during oxygen breathing at rest, close because of critically low ventilation/perfusion (V/Q) ratios. 3. With air breathing, Qva/Qt fell from rest to exercise (especially in older subjects), presumably due to improved ventilation of alveoli at the lung bases. With an increase in work rate Qva/Qt increased in all age groups. This increase was not due to increase in the shunt fraction (Qs/Qt), nor to limitation of diffusing capacity; it arose from an increase in V/Q variance. 4. Equations have been derived for the prediction of normal Qva/Qt during exercise, with or without correction for the effects of increasing pulmonary capillary temperature. These effects do not materially influence the accuracy of prediction, but may be relevant to some of the interpretations. In particular, they provide a further indication that Qs/Qt probably cannot be measured by breathing oxygen at rest, even in deep breathing.

Adult↗
PubMed1976

Enzyme release after myocardial infarction: comparison of serial serum alpha-hydroxybutyrate dehydrogenase with creatine phosphokinase levels.

Serial measurements on serum creatine phosphokinase (CPK) and alpha-hydroxybutyrate dehydrogenase (HBD) activity were made in 17 patients with acute myocardial infarction. Activities of both enzymes were measured 4-hourly from less than 12 h after the onset of chest pain until CPK activity had returned to near-normal levels. Blood was then sampled twice daily for a further 4--6 days in order to follow the decline in HBD activity. Degradation rates (KD) were calculated for both enzymes, and individual figures for KD were used in order to estimate the total cumulative release of each enzyme. We found a significant correlation between the duration (r = 0.66, P less than 0.01) and magnitude (r = 0.67, P less than 0.01) of release of the 2 enzymes, comparing different patients with one another. Duration od HBD release was 11 h greater than the duration of CPK release in 9 of the 17 patients who were suffering from cardiac failure (t = 0.01, P less than 0.02). Degradation rate (KD) for HBD was on average about one quarter of that for CPK, but there was no significant correlation between KD for the 2 enzymes. KD did not appear to be reduced in patients with cardiac failure. We conclude that the release patterns of CPK and HBD after myocardial infarction are similar, and this strengthens the case for acceptance of total enzyme release as a valid index of myocardial infarct size.

Adult↗
PubMed1975

A comparison of the actions of ICI66082 and propranolol on cardiac and peripheral beta-adrenoceptors.

The relative blocking potencies of ICI66082 and propranolol with respect to heart rate contractility, diastolic blood pressure and peripheral vascular conductance were compared in anaesthetized dogs. Peripheral blood flow was measured with an electromagnetic flow-probe around the descending aorta with retrograde cannulation of the inferior mesenteric artery for intra-arterial injections of isoprenaline. Cardiac and peripheral vascular effects of ICI66082 and propranolol were compared in terms of the shifts in the dose--response curves after i.v. and intra-arterial injections of isoprenaline. Propranolol was twice as potent as an equimolar dose of ICI66082 on cardiac beta-adrenoceptors. It was 70--130 times more potent in its action on the peripheral vascular receptors. Propranolol itself was 3 times more potent in blocking peripheral vascular receptors than cardiac beta-receptors. ICI66082 was 17--21 times more active in blocking the myocardial beta-adrenoceptors than those in the peripheral vessels. Electrophysiological studies showed that ICI66082 is devoid of membrane-depressant properties in concentrations up to 100 mg/l.

Action Potentials↗
PubMed1975

Clinical measurement of myocardial infarct size. Modification of a method for the estimation of total creatine phosphokinase release after myocardial infarction.

A modified method for the measurement of total creatine phosphokinase release from venous blood samples taken four-hourly after myocardial infarction has been used in 43 patients admitted to a Coronary Care Unit. The fractional decay rate (Kd) of enzyme activity has been measured by a standardized method in each patient, and accuracy of the calculation of total enzyme release has been improved by allowance for individual variations in decay rate, and discarding of data from which decay rates cannot be measured within confidence limits of less than plus or minus 15 per cent. Total enzyme release was greater in cases of transmural infarction than in patients with subendocardial infarction, and showed a good positive correlation with clinical indices of the extent of myocardial damage. As noted by previous workers, this method allows for the measurement of the rate as well as the extent of enzyme release, and so should prove useful in the clinical evaluation of therapeutic agents which might accelerate or retard the rate of myocardial necrosis in patients with acute myocardial infarction.

Blood Specimen Collection↗