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Biomedical subjects

T G Pickering

Publications and source records attributed to T G Pickering.

At least 253 records · Page 14Linked to original sources
PubMed1979

Arterial distensibility in normal and hypertensive man.

1. The pulse-wave velocity along the brachial radial artery was measured in 38 subjects and volume distensibility values were calculated. 2. Measurements made at each subject's resting blood pressure showed that those with high blood pressure had higher pulse-wave velocity values and hence less distensible arteries. 3. An acute rise in arterial distending pressure was accompanied by a rise in pulse-wave velocity. 4. When pulse-wave velocity was remeasured in all subjects at identical arterial distengin pressures, no difference was found between hypertensive and normal subjects. 5. It appears that poor distensibility of large arteries in hypertensive subjects is a consequence of the elevated distending pressures and not due to irreversible structural changes in the arterial wall.

Adult↗
PubMed1978

Beta-blockade and blood-levels after low-dose oral propranolol: The hepatic "first-pass" threshold revisited.

Heart-rate, arterial pressure, and plasmarenin activity were determined in six normal subjects at rest and after an injection of 8 microgram isoprenaline with and without prior propranolol administered orally in a dose of 5 mg 8-hourly for a total of five doses. After propranolol, resting heart-rate, systolic pressure, and plasma-renin activity all fell significantly (P less than 0.05 to less than 0.001). When the isoprenaline-induced changes of heart-rate, diastolic pressure, and plasma renin activity without propranolol were compared to those with propranolol, these responses were greatly diminished (P less than 0.01 to less than 0.001). The percent blockade by propranolol of the isoprenaline-induced changes ranged from 65% for diastolic pressure to 77% for heart rate and 78% for plasma-renin activity. Propranolol levels determined by conventional fluorometry were below accurate detection limits, whereas those determined by gas-liquid chromatography ranged from 2.3 to 8.5 ng/ml. These findings, which demonstrate beta-blockade with low-dose propranolol, are not consistent with the existence of a postulated threshold for the hepatic "first-pass effect" in man, which is said to require saturation by single doses of 30 mg or more before propranolol enters the systemic circulation.

Administration, Oral↗
PubMed1978

Comparison of the effects of sleep, exercise and autonomic drugs on ventricular extrasystoles, using ambulatory monitoring of electrocardiogram and electroencephalogram.

Ambulatory monitoring of the electrocardiogram (ECG) and the electroencephalogram (EEG) in 12 untreated patients with frequent ventricular extrasystoles showed a significant decrease in both ventricular extrasystoles and heart rate during sleep. The decrease in ventricular extrasystoles correlated more closely with the change in heart rate than with the level of arousal. During wakefulness, similar changes in ventricular extrasystoles and heart rate could be produced by the intravenous administration of propranolol and, to a lesser extent, by phenylephrine. Exercise produced an initial increase in ventricular extrasystoles, with suppression at higher levels in most patients. Thus, the frequency of ventricular extrasystoles is usually reduced at both extremes of heart rate, and the changes that occur during sleep can be explained by autonomic mediation, with the sympathetic limb of the autonomic nervous system having a greater effect than the vagus.

Adult↗
PubMed1978

Supression of ventricular extrasystoles by perhexiline.

The antiarrhythmic effects of perhexiline were investigated in 13 of 20 patients with frequent and long standing ventricular extrasystoles in a double blind crossover trial using 24-hour electrocardiograph tape recordings, routine electrocardiograms, and treadmill exercise testing. With a dose of 300 to 400 mg per day, there was a significant decrease (mean 41%) in the number of ventricular extrasystoles per 24 hours. There were large differences in the individual responses to perhexiline, which were significantly related to the diurnal variations of ventricular extrasystoles: those patients whose ventricular extrasystoles disappeared spontaneously during sleep were less likely to respond to perhexiline than those whose ventricular extrasystoles persisted throughout the night. Suppression of ventricular extrasystoles was also apparent from the routine electrocardiogram and the exercise tests. Side effects (dizziness and unsteadiness) were troublesome in 5 of 20 patients. It is concluded that in selected patients perhexiline is an effective antiarrhythmic drug, and is likely to be most useful in patients with coexisting angina and ventricular extrasystoles. Because of its potential toxicity, it should not be used as a drug of first choice.

Cardiac Complexes, Premature↗
PubMed1977

Cardiovascular and sympathetic response to exercise after long-term beta-adrenergic blockade.

The response to dynamic exercise was investigated in 21 patients receiving long-term treatment with beta-adrenoceptor antagonists and 22 controls. An electrocardiogram (ECG) and blood pressure were recorded before and after treadmill exercise, and plasma dopamine-beta-hydroxylase (DBH) activity was measured as an index of changes in sympathetic activity. Heart rate and blood pressure were lower at rest and throughout exercise in treated patients, although the pressor effect of exercise was not reduced. The ECG P-R interval was lengthened, and in addition the Q-T interval was prolonged. After exercise, plasma DBH activity was significantly increased in controls but not in treated patients. We conclude that long-term administration of beta-adrenergic blockers increases myocardial repolarisation time and reduces sympathetic nervous activity. These actions may contribute to the antiarrhythmic and hypotensive effects of long-term beta-blockade.

Adrenergic beta-Antagonists↗
PubMed1977

Learned voluntary control of heart rate and rhythm in two subjects with premature ventricular contractions.

Two people with frequent premature ventricular contractions and bigeminal rhythm not associated with other signs of heart disease, learned to suppress the arrhythmia using a biofeedback technique. In both cases, physical exercise and atropine suppressed the arrhythmia, and in both the learned control was related to the development of tachycardia. In Case 1, it appeared to depend on something more than speeding alone, for sinus rhythm could be maintained during voluntary control at a lower heart rate than during physical manoeuvres such as exercise. In Case 2, the premature ventricular contractions could be induced by a sudden fall of heart rate, e.g. after a Valsalva manoeuvre, and could be suppressed by voluntary increase of heart rate by up to 40 beats/minute produced with little change in breathing or muscle activity.

Adolescent↗