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Biomedical subjects

S M Johnson

Publications and source records attributed to S M Johnson.

At least 163 records · Page 9Linked to original sources
PubMed1982

Continuous electrocardiographic monitoring in patients with unstable angina pectoris: Identification of high-risk subgroup with severe coronary disease, variant angina, and/or impaired early prognosis.

We assessed the value of two-channel Holter monitoring during the initial hours of hospitalization in patients with unstable angina pectoris (UAP) to identify those with severe coronary artery disease (CAD), variant angina, and/or poor prognosis over the next 3 months. Accordingly, 116 UAP patients had Holter monitoring for 27 +/- 7 (mean +/- SD) (range 12 to 50) hours following hospitalization. Of these, 24 evolved myocardial infarction (MI) during monitoring and 92 did not. Transient ST segment alterations occurred in 21 of the 92. Of these 21, 4 had variant angina, were treated with calcium antagonists, and did well. Each of the remaining 17 had severe fixed CAD (left main or three-vessel) (n = 12) and/or poor prognosis over the 3 months after discharge as manifested by death (n = 1), MI (n = 3), and/or severe angina (n = 3). In contrast, 71 patients did not demonstrate transient ST segment alterations: none had variant angina (p less than 0.001), nine had left main or three-vessel CAD (p less than 0.001), and 50 were alive and well 3 months after discharge (p less than 0.001). Ventricular tachycardia (VT) was demonstrated by Holter monitor in 5 of the 92 patients: four had three-vessel CAD and the other had severe persistent angina. Thus in patients hospitalized with unstable angina, transient ST segment alterations and/or VT on Holter monitor are specific predictors of "high-risk" subgroup UAP patients with left main or three-vessel CAD, variant angina, and/or impaired 3-month prognosis.

Aged↗
PubMed1982

Clinical relevance of verapamil plasma levels in stable angina pectoris.

Plasma levels of verapamil and norverapamil were evaluated in 77 patients who received oral verapamiL for treatment of angina pectoris. There was a sixfold interpatient variation in verapamil plasma concentrations, but plasma concentrations were linearly related to doses of the drug (240 to 480 mg/day) in the same patient (r = 0.81). Plasma concentrations of norverapamil, the major active metabolite of verapamil, were similar to those of verapamil. Although verapamil produced a significant improvement in exercise tolerance in most patients, the increase in exercise time was not related to plasma levels of the drug; however, most patients with improvement had plasma levels exceeding 100 ng/ml. An increase in the dose of verapamil from 320 to 480 mg daily produced a substantial (71%) increase in plasma levels of the drug but no significant increase in exercise tolerance (4%). The average increase in the P-R interval with 480 mg of verapamil in these 77 patients was small (8%) (161 +/- 18 to 174 +/- 22 ms); on.y six patients had first-degree heart block. These minor effects on atrioventricular conduction were noted despite plasma verapamil concentrations in 76 patients that exceeded 100 ng/ml, a level that successfully converts supraventricular tachycardias after intravenous drug administration. We differences between the effects of oral and intravenous verapamil on atrioventricular conduction may be the result of stereoselective hepatic inactivation of verapamil's I-isomer. Determination of plasma levels of verapamil is of limited value in the management of patients with angina pectoris, but may be useful in the identification of nonresponders with plasma levels less than 100 ng/ml who may benefit from a further increment in drug dose.

Administration, Oral↗
PubMed1982

Verapamil therapy for Prinzmetal's variant angina: comparison with placebo and nifedipine.

This study was performed (1) to assess the efficacy and safety of verapamil in patients with variant angina, and (2) to compare verapamil and nifedipine in patients with this clinical syndrome. In 27 patients, placebo and verapamil were administered in a long-term randomized, and double-blind study of 9 months' duration. In comparison to placebo, verapamil reduced the frequency of angina, nitroglycerin usage, transient episodes of electrocardiographic S-T segment deviation (as assessed by 2-channel Holter monitoring), and hospitalizations required for clinical instability. Subsequently, 23 patients were treated with nifedipine in a nonblind fashion for 2 months, and this agent exerted a beneficial effect similar to that of verapamil. Finally, gated equilibrium blood pool scintigraphy, performed in 10 patients at rest and during exercise during treatment with placebo, verapamil, and nifedipine, demonstrated that neither calcium antagonist caused a deterioration of left ventricular performance. Thus, (1) long-term oral verapamil and nifedipine are each superior to placebo and are of similar efficacy in patients with variant angina, and (2) neither agent adversely influences left ventricular performance in patients with relatively normal left ventricular function.

Angina Pectoris, Variant↗
PubMed1982

Assessment of reproductive knowledge in an inner-city clinic.

A number of studies have shown that misinformation and lack of information about the menstrual cycle contributes to unwanted fertility, particularly among black women. A short, self-administered questionnaire was developed and tested in an inner-city, prenatal clinic serving a primarily low-income undereducated, black clientele. Data were gathered concerning numbers of pregnancies and abortions, knowledge of the menstrual cycle, past contraceptive use, including dissatisfaction and discontinuance, and planned future use of contraception. Results showed that the majority of women had had at least one unwanted pregnancy. Their knowledge base about female reproductive function and their poor use of contraception contributed to these unwanted pregnancies. It is concluded that a few key questions can help identify the woman with special informational needs, enabling the health professional to gear educational efforts to the individual patient.

Adolescent↗
PubMed1981

Differing distributions of receptors for morphine and Met5-enkephalinamide in the dorsal horn of the cat.

In the dorsal horn of barbiturate-anaesthetized cats evidence was obtained for a different distribution of enkephalin-preferring and morphine-preferring receptors. When ejected electrophoretically from micropipettes, morphine reduced the nociceptive responses of neurones of laminae IV and V when administered in the substantia gelatinosa but not at more ventral sites including sites near cell bodies. By contrast, Met5-enkephalinamide reduced nociceptive responses at all of these sites of administration often with increased potency near cell bodies. It is proposed that morphine-preferring receptors are located mainly near the terminals of primary afferent fibres whereas those for enkephalin are present on these fibres and also on the dendrites and somata of dorsal horn neurones. These dendritic receptors may be located adjacent to sites of termination of nociceptive afferents, a mechanism which would inhibit nociceptive but not other inputs to these neurones.

Animals↗
PubMed1981

Medullary raphé lesions do not reduce descending inhibition of dorsal horn neurones of the cat.

In anaesthetized cats spinal cold block was used to examine the effects of medullary raphé lesions on the responses of dorsal horn neurones to impulses in unmyelinated primary afferents. Lesions failed to affect these responses, casting doubt on the importance of this region and its serotonergic spinal projections to the control of nociceptive transmission at the spinal level.

Afferent Pathways↗
PubMed1981

Verapamil administration in variant angina pectoris. Efficacy shown by ecg monitoring.

Six patients with Prinzmetal's variant angina were treated with oral verapamil administration. Before and after the initiation of therapy, ambulatory ECG monitoring was performed to assess objectively the response to therapy. With verapamil administration, the frequency of both chest pain and transient ST-segment deviations was sharply diminished.

Administration, Oral↗
PubMed1981

A controlled trial of verapamil for Prinzmetal's variant angina.

To assess the efficacy and safety of verapamil in variant angina pectoris, we entered 16 patients in a double-blind, randomized trial of nine months, duration. During treatment with verapamil, the frequency of angina fell substantially (12.6 +/- 25.9 chest pains per week with placebo, 1.7 +/- 2.8 pains per week with verapamil, mean +/- S.D.; P less than 0.01), as did the use of nitroglycerin tablets (14.4 +/- 34.4 tablets per week with placebo, 2.1 +/- 3.3 tablets per week with verapamil; P less than 0.05). The number of hospitalizations for clinical instability was significantly lower with verapamil (P less than 0.01). The number of episodes of transient ST-segment deviation during treatment with verapamil was reduced (33.1 +/- 39.3 ST-segment deviations per week with placebo, 7.7 +/- 11.7 deviations per week with verapamil; P less than 0.01). Verapamil caused no side effects forcing a reduction in dosage or a discontinuation. We conclude that verapamil is safe and effective in the therapy of variant angina pectoris.

Adult↗
PubMed1981

Supraspinal inhibition of the excitation of dorsal horn neurones by impulses in unmyelinated primary afferents: lack of effect by strychnine and bicuculline.

In barbiturate anaesthetized cats, tonic descending inhibition of the excitation of lumbar dorsal horn neurones by impulses in unmyelinated primary afferents was measured by reversibly cooling a more cephalic segment. Administered electrophoretically in the substantia gelatinosa and at sites progressively closer to cell bodies, amounts of bicuculline and strychnine adequate to reduce segmental inhibition failed to reduce supraspinal inhibition. Intravenous bicuculline and strychnine also failed to reduce supraspinal inhibition.

Afferent Pathways↗
PubMed1981

Evidence that the opiate receptors of the substantia gelatinosa contribute to the depression, by intravenous morphine, of the spinal transmission of impulses in unmyelinated primary afferents.

In barbiturate anaesthetized cats, dorsal horn neurones were excited by electrical stimulation of the common tibial nerve. The numbers of action potentials evoked by excitation of C fibres were depressed by analgesic doses of morphine (1-4 mg/kg i.v.). Naloxone, administered electrophoretically in the substantia gelatinosa, fully reversed the inhibitory action of morphine. The results suggest that opiate receptors in the substantia gelatinosa play a role in morphine analgesia.

Afferent Pathways↗
PubMed1981

Effect of verapamil and nifedipine on left ventricular function at rest and during exercise in patients with Prinzmetal's variant angina pectoris.

To assess the effects of verapamil and nifedipine on left ventricular function at rest and during exercise in patients with Prinzmetal's variant angina pectoris, 10 patients (6 men and 4 women with a mean age of 52 years) with variant angina were each treated for 2 months periods with placebo, verapamil (400 +/- 80 mg/day, mean +/- standard deviation [SD]) and nifedipine (82 +/- 31 mg/day). During the final week of each 2 month treatment period equilibrium gated blood pool scintigraphy was performed at rest and during exercise. At rest, heart rate during verapamil therapy was lower than during treatment with nifedipine; systolic blood pressure and left ventricular volumes and ejection fraction were similar for the three interventions. The maximal work load achieved was similar during placebo, verapamil and nifedipine therapy. At the maximal work load common to all three exercise studies, heart rate and systolic blood pressure were lower with verapamil than with placebo and nifedipine; ventricular volumes and ejection fraction were similar with the three agents. Thus, in patients with variant angina and a wide range of left ventricular function at rest, neither verapamil nor nifedipine significantly alters left ventricular volumes or ejection fraction at rest or during exercise.

Angina Pectoris↗
PubMed1981

Double-blind, randomized, placebo-controlled comparison of propranolol and verapamil in the treatment of patients with stable angina pectoris.

This study was performed to compare the relative efficacies of propranolol and verapamil in patients with stable angina pectoris. In 18 patients (16 men, two women, mean age 58 years) with coronary artery disease and angina of effort, the results of low (40 mg every 6 hours) and high-dose (80 mg every 6 hours) propranolol therapy were compared to those of low (80 mg every 6 hours) and high-dose (120 mg every 6 hours) verapamil therapy in a double-blind, randomized, placebo-controlled evaluation which lasted eight weeks: two weeks of placebo therapy, two weeks of propranolol or verapamil (one week low-dose, one week high-dose) therapy, three days of down-titration followed by one week of placebo therapy, two weeks of propranolol or verapamil therapy (whichever was not given earlier in the trial) (one week low-dose, one week hgh-dose) and three days of down-titration. During each period the following were quantitated: (1) chest pains/week; (2) nitroglycerin used/week; (3) transient ischemic S-T segment deviations and highest grade of ventricular ectopic activity on two-channel Holter monitor; (4) S-T segment deviations during supine bicycle exercise; (5) left ventricular volumes and ejection fraction at rest and during exercise (assessed by equilibrium gated blood pool scintigraphy); and (6) pulmonary function studies. Propranolol and high-dose verapamil therapy significantly reduced the frequency of angina, and high-dose verapamil therapy diminished both the need for nitroglycerin and the frequency of transient ischemic S-T segment deviations on Holter monitor. Neither agent exerted a clinically-important deleterious influence on left ventricular volumes or the ejection fraction. Forced vital capacity and forced expiratory volume were worsened by propranolol but not by verapamil. Thus, in the patient with angina of effort, verapamil is a satisfactory therapeutic alternative to propranolol.

Adult↗
PubMed1981

Mediators of slow synaptic potentials in the myenteric plexus of the guinea-pig ileum.

1. Intracellular recordings were made from neurones in the myenteric plexus of the ileum isolated from adult guinea-pigs.2. Three synaptic potentials were evoked in different myenteric neurones by focal stimulation of the ganglion surface at a distance of up to 100 mum from the cell body from which the recording was made. These were the fast cholinergic excitatory post-synaptic potential (e.p.s.p.), the slow e.p.s.p. and the slow inhibitory post-synaptic potential (i.p.s.p.).3. 5-hydroxytryptamine and substance P were applied to the neurones by superfusion (10 nm-1 mum) or by electrophoresis within 5 mum of the neurone cell body. 5-HT depolarized, hyperpolarized or had no effect on approximately equal numbers of neurones, whereas substance P depolarized 90% of neurones.4. Many neurones with a depolarizing slow e.p.s.p. were hyperpolarized by superfusion or electrophoretic application of 5-HT.5. Superfusion with 5-HT reversibly depressed the fast e.p.s.p., slow e.p.s.p. and slow i.p.s.p. Superfusion with substance P depressed the slow e.p.s.p.6. Methysergide (10-30 mum) reduced the amplitude of the fast e.p.s.p., the slow e.p.s.p. and the slow i.p.s.p.7. Chymotrypsin (200 mug/ml.) reversibly reduced the amplitude of the slow e.p.s.p., but had no effect on membrane potential, the action potential or the fast e.p.s.p. Chymotrypsin reduced or abolished the depolarization caused by electrophoretic application of substance P, but had no effect on the depolarization or hyperpolarization caused by 5HT.8. The results provide evidence that 5-HT is not the transmitter which mediates the slow e.p.s.p. in myenteric neurones. The slow e.p.s.p. may be caused by substance P or another similar peptide.

Animals↗
PubMed1980

Incubation of exogenous fatty acids with lymphocytes. Changes in fatty acid composition and effects on the rotational relaxation time of 1,6-diphenyl-1,3,5-hexatriene.

Lymphocytes were incubated with various long chain fatty acids bound to albumin. Incubation for 20 h with unsaturated fatty acids resulted in uptake into the neutral lipids and phospholipids. The addition of concanavalin A enhanced the uptake. With the unsaturated fatty acids the rotational relaxation time of 1,6-diphenyl-1,3,5-hexatriene (DPH) was decreased, while with saturated fatty acids there was only a very small effect. The effect on the rotational relaxation times with unsaturated fatty acids was found to be due to the formation of lipid droplets in the cytoplasm. When plasma membrane free of lipid droplets was prepared, there was no effect on the rotational relaxation time despite incorporation of either linoleate or palmitate into the membrane phospholipids. Phospholipid liposomes prepared from plasma membranes obtained from cells which had been cultured with and without exogenous linoleate gave identical rotational relaxation times regardless of the history of the cells from which they were obtained. It is concluded that although the fatty acid composition of lymphocyte plasma membrane can be modified by exogenous fatty acids, there is little effect on the degree of order of the membrane phospholipid fatty acyl chains as monitored by the effects on the rotational relaxation time of DPH.

Animals↗
PubMed1980

Effect of selective coronary arteriography on left ventricular volumes and ejection fraction in man.

This study was performed to assess the influence of selective coronary arteriography on left ventricular volumes and ejection fraction in man. In 30 patients with assorted cardiac diseases, left ventricular end-diastolic and end-systolic volumes and ejection fraction were quantitated immediately before and after selective coronary arteriography. In 19 patients (Group A), contrast left ventriculography was performed immediately before and after selective coronary arteriography. In the remaining 11 patients (Group B), multigated equilibrium blood pool imaging was performed just before and after coronary arteriography. In both groups, mean systemic arterial pressure and heart rate did not change from just before the first to immediately before the second assessment of left ventricular volumes and ejection fraction, but left ventricular end-diastolic pressure increased. End-diastolic and end-systolic volume indexes, and ejection fraction did not change from just before to immediately after selective coronary arteriography. Therefore, selective coronary arteriography (1) consistently causes an increase in left ventricular end-diastolic pressure but (2) exerts no effect on left ventricular volumes and ejection fraction, even in patients with severely compromised left ventricular function.

Adult↗