PubMed Health⌕ Search

Biomedical subjects

P M Szeto

Publications and source records attributed to P M Szeto.

5 recordsLinked to original sources
PubMed1983

Limitation of the atrial extrastimulus technique for assessment of the His-Purkinje system in patients with right bundle branch block.

A prospective study of the usefulness of the atrial extrastimulus technique for assessment of the His-Purkinje system was undertaken in 19 consecutive patients with complete RBBB and an abnormal or indeterminate frontal QRS axis. A total of 59 basic cycle lengths (BCLs) could be analyzed in detail. The most common patterns of His-Purkinje conduction seen were simple linear (V1V2 vs H1H2, N = 49) or flat (H2V2 vs H1H2, N = 44) curves. This finding is related to the limitation imposed by interposition of the slowly conducting AV node between the site of the extrastimulus and the His-Purkinje system. One or more refractory periods could be measured in only 27% of BCLs (10 Effective Refractory Periods of the remaining intact His-Purkinje system plus 16 Functional Refractory Periods and 19 Relative Refractory Periods). No refractory periods of the His-Purkinje system could be determined in 8 of 19 patients (42%), the major limitation being slowed AV node conduction. The results suggest limited likelihood that additional clinically useful information about His-Purkinje system conduction can be obtained by the atrial extrastimulus technique, as used in this study, although it may be helpful in assessing other parts of the conduction system.

Adult↗
PubMed1979

Baroreceptor influence on a spinal cardiovascular reflex.

A stretch of the walls of the thoracic aorta, performed in vagotomized cats without obstructing aortic flow, induces increases in heart rate, myocardial contractility, and arterial pressure. These reflex responses are still present after high spinal section. Cats under chloralose-urethane anesthesia were vagotomized and one carotid sinus was isolated and perfused with arterial blood at constant flow. The contralateral carotid sinus nerve and both aortic nerves were sectioned. A stretch of the walls of the thoracic aorta between the 7th and 10th intercostal arteries induced a reflex increase in mean arterial pressure 29 +/- 2 mmHg (mean +/- SE). Stepwise increases of carotid sinus pressure (CSP) or electrical stimulation of the carotid sinus nerve induced stepwise decreases of this reflex response. At maximal baroreceptor stimulation (CSP 212 +/- 9 mmHg) the reflex response to aortic stretch was reduced by 42%. These experiments show that this spinal cardiovascular reflex is at least partially under the inhibitory control of the baroreceptor input.

Animals↗
PubMed1978

Reflex effects of thoracic aorta wall stretch on regional vascular resistance.

In anesthetized, vagotomized cats with both carotid arteries occluded, a stretch of the walls of the thoracic aorta, performed without obstructing aortic flow, induced a significant reflex increase in arterial pressure (35 +/- 2-26 +/- 1 mmHg; systolic-diastolic). This pressure increase was accompanied by significant increases in peripheral resistance in the superior mesenteric (+30%), renal (+23%), and external iliac (+23%) vascular beds. The increase in iliac resistance observed in the skinned leg was comparable with that observed in the contralateral intact limb. All these vascular responses were drastically reduced by the administration of phenoxybenzamine. After alpha-adrenergic blockade no signs of reflex vasodilatation could be detected during aortic stretch in any of the vascular beds examined.

Animals↗
PubMed1977

Inhibition by atropine, phenoxybenzamine and propranolol of the autonomic nervous system of the domestic fowl.

Because of the paucity and inconsistency of information on blockage of the chicken autonomic nervous system for extended periods, the effects of atropine, phenoxybenzamine and propranolol in the anesthetized hen were examined. It was found that cholinergic blockade by atropine was very short lived. For effective (80%) parasympathetic blockage a priming dose of 0.25 mg./kg;, followed by an infusion at the rate of 17.5 microgram/kg./min., was required. Similarly, inhibition of the beta-sympathetic system required propranolol in a priming dose of 0.25 mg./kg. and an infusion of 5 microgram/kg./min. The alpha-sympathetic inhibitor, phenoxybenzamine, was effective when given as a single dose of 5 mg./kg. Using these levels of inhibitor it was possible to ensure blockade in all cases for periods of two hours or more.

Acetylcholine↗