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Biomedical subjects

R H Johnson

Publications and source records attributed to R H Johnson.

At least 73 records · Page 4Linked to original sources
PubMed1987

Effects of ethanol ingestion on blood pressure reactivity.

We examined the acute effects of ethanol consumption on circulatory responses to the cold pressor test, to handgrip exercise and to intravenous infusion of methoxamine in eight normal male subjects. Ethanol consumption reduced systolic blood pressure responses to the cold pressor test and to handgrip exercise and depressed both systolic and diastolic blood pressure responses to infusion of methoxamine. The depressant effects of ethanol on blood pressure responses to methoxamine were considerably greater than the effects on the cold pressor test and handgrip exercise. Catecholamine concentrations during the cold pressor test and handgrip exercise were not significantly different with or without prior ethanol consumption. Alcohol has been shown to have an acute hypotensive action with all the stimuli.

Adult↗
PubMed1987

Respiratory responsiveness in male alcoholics after withdrawal.

Peripheral and central chemosensitivity were assessed in eight abstinent male alcoholic patients and in seven healthy normal male subjects. Hypoxic rebreathing (15% O2, 7% CO2) was used to stimulate the peripheral and central chemoreceptors together. Hyperoxic rebreathing (93% O2, 7% CO2) was used to examine the central chemoreceptor response independently of the peripheral chemoreceptors. Minute ventilation was examined in relation to end-tidal PACO2 under the two conditions. Neither peripheral nor central chemoreceptor responses were significantly altered in the alcoholic as compared to the control subjects. Abnormal chemoreceptor function is therefore unlikely to be an important factor in the development of abnormal respiratory events during sleep in abstinent alcoholic subjects.

Adult↗
PubMed1987

Local autonomic failure affecting a limb.

Three patients are described who presented with autonomic failure affecting predominantly one limb. Physiological studies revealed that there was sweating loss in the limb which appeared to be due to a preganglionic autonomic lesion and not to a sweat gland abnormality. In all three patients there was also evidence of failure of vasomotor control. There was no evidence of more generalised autonomic failure or neurological deficit. In two patients the condition appeared to be static and, according to the patients' accounts was life long. In the third the sweating loss was present for three years prior to pain loss becoming evident from C2/3 to T1 on the same side as the sweating loss. These patients, together with two recent case reports, indicate that isolated local autonomic failure, probably from a discrete cord lesion, can be a cause of presenting symptoms related to sweating loss or to change in temperature in a limb.

Adult↗
PubMed1986

Observations on the use of an inactivated canine parvovirus vaccine.

Data are presented on studies of field and experimental use of a formalin-inactivated canine parvovirus vaccine. There was an absolute correlation between a single successful vaccination and subsequent protection against clinical disease. Unsuccessful vaccinations were consistently associated with the presence of maternal antibody at the time of vaccination. The vaccine induced an antibody response within two days and anamnestic responses within 24 hours. It is suggested that a single successful vaccination probably protects against clinical parvovirus disease for life.

Animals↗
PubMed1986

Effects of ethanol on cardiovascular and catecholamine responses to mental stress.

The purpose of this study was to examine the effects of ethanol on heart rate, blood pressure and plasma noradrenaline and adrenaline responses to mental stress, involving reactions to anxiety and excitement produced using a cognitive task with electric shock and a competitive electronic game respectively. Twenty subjects were studied, each subject acting as his own control by participating twice, with and without prior ethanol consumption. Mental stress was associated with significant increases in all variables except plasma noradrenaline during the cognitive task. Ethanol raised baseline heart rate and plasma adrenaline, but significantly reduced the responses of these variables to the cognitive task but not to the electronic game. Systolic blood pressure responses to both experimental stressors and diastolic blood pressure responses to the electronic game were also significantly reduced after ethanol. These results may reflect a tension-reducing effect of ethanol in situations associated with anxiety, but suggest a more general effect of ethanol on blood pressure reactivity.

Adult↗
PubMed1986

The effects of acute and chronic ingestion of ethanol on the autonomic nervous system.

Evidence is reviewed linking clinical effects of ethanol with actions on the sympathetic and parasympathetic nervous systems. The studies reported include a series of investigations by the authors. Acutely, ethanol causes peripheral vasodilation and may also result in changes in heart rate and blood pressure. Ethanol may contribute to acute problems which may present clinically, including micturition syncope, accidental hypothermia and facial flushing. However, increased sympathetic nervous activity plays a role in causing hypertension and other symptoms during ethanol withdrawal in chronic alcoholics. Some chronic alcoholics may have neuropathy involving sympathetic nerves, and this can result in distal sweating loss and occasionally in orthostatic hypotension. Also, hypothalamic lesions associated with Wernicke's encephalopathy may result in hypothermia. Neuropathy involving parasympathetic nerves in not uncommon in alcoholics with other evidence of nervous system damage, but it is generally asymptomatic. Occasionally, vagal neuropathy may cause disorder of gastrointestinal motility, and neuropathy affecting the sacral innervation may be a factor in alcoholic impotence.

Alcoholic Intoxication↗
PubMed1986

Factors which influence the effectiveness of treatment of epilepsy.

Despite recent advances in the management of epilepsy, some patients continue to have seizures which defy therapeutic intervention. To examine factors which may influence the successful application of therapy a survey was carried out of 103 patients, with a previous diagnosis of epilepsy, who had a seizure for which an ambulance was called. It was evident that anticonvulsants are not always used to their maximum potential or under optimal conditions. Problems which were identified in treatment included the widespread use of polypharmacy. Patients contributed to failure of seizure control by lack of compliance with therapy (29 patients) and by excessive alcohol consumption (19 patients).

Alcohol Drinking↗
PubMed1986

Comparison of mefenamic acid and propranolol with placebo in migraine prophylaxis.

The prophylactic effects of the antiprostaglandin agent mefenamic acid on migraine attacks were compared with propranolol or placebo in a double-blind crossover study of 29 patients. In the 17 patients who completed the trial the frequency of attacks and their total duration were significantly reduced during mefenamic acid therapy or propranolol therapy as compared to placebo. There were no significant effects of mefenamic acid or propranolol on average duration or severity of migraine attacks. The study suggests that mefenamic acid and propranolol are equally effective for migraine prophylaxis.

Adult↗
PubMed1985

Non-compliance with anticonvulsant therapy as a cause of seizures.

Compliance with anticonvulsant therapy was assessed in 95 epileptic subjects with uncontrolled seizures. Following a seizure for which an ambulance was called, patients were interviewed and questioned on their medication taking. Compliance was also determined from measurement of anticonvulsant concentrations in saliva, and from intervals between collection of drugs from pharmacy. Compliance failure was found to be instrumental in precipitating 29 (31%) of seizures for which the ambulance was called. At the time of interview, 35 (37%) subjects were not taking their medication regularly in accordance with prescribing instructions. In addition to forgetting medication, many subjects deliberately stopped or changed doses of drugs. Other causes of non-compliance which were indentified included patient misunderstanding of prescribing instructions. Compliance with therapy was positively related to perceived benefit from anticonvulsant therapy.

Adolescent↗
PubMed1985

Properties of an Australian isolate of bovine parvovirus type 1.

An Australian bovine parvovirus isolate (BPV 267) was found to haemagglutinate human, guinea-pig, rat and dog erythrocytes, out of a range of 16 species of erythrocyte tested. The haemagglutinating activity was generally found to be both pH and temperature dependent. The virus was found to replicate best in intestinal epithelium, macrophage and lung cells, out of 9 bovine cell types tested. Highest yields of virus were obtained by the use of selected cell strains at low-passage levels which were maintained near neutral pH under conditions of high rates of cell growth. Studies of the rates of thermal inactivation with time showed the virus to be relatively stable at 37 degrees C, 56 degrees C and 70 degrees C, the incorporation of serum proteins, 1 M MgCl2 and 2 M NaCl in the medium having no influence on stability at 56 degrees C. The virus was resistant to the action of CHCl3, ether and 1% trypsin, and its replication was inhibited by BUDR, this effect being reversed by thymidine. Actinomycin D was found to inhibit virus replication, but only when applied during the first 8 h post-infection. Density gradient studies showed infective virus to have a density of 1.41 g cm-3; haemagglutinating non-infective virus with defective morphology having a density of 1.31 g cm-3. In addition, a proportion of morphologically-complete haemagglutinating, but non-infective virus particles was found at a density of 1.36 g cm-3. The virus proved to have a mean diameter of 22 nm.

Animals↗
PubMed1985

Studies on the replication of a bovine parvovirus.

Optimal replication of a bovine parvovirus type 1 was found to occur when parasynchronous bovine embryonic lung cells were infected during the S phase of the cell cycle, just prior to maximum DNA synthesis. Viral antigen was first detected in the cytoplasm by immunofluorescence at 8 h post-infection, reaching a maximum at this location by 16 h and then disappearing. In the nucleus, antigen was first detected at 12 h, concurrent with early inclusion body formation and first detection of intracellular virus production. Intranuclear antigen then increased rapidly to a maximum at 20 h, as the inclusions progressively matured, large amounts of virus were produced within the cell, with some release to the environment. From 24 h, the nuclear inclusions became increasingly shrunken and basophilic as virus migrated to the cytoplasm and was progressively released to the exterior concurrent with cell degeneration and fragmentation. The majority of virus remained cell associated, even at 28 h post-inoculation. Two morphological types of early and late stage intranuclear inclusions were produced by the virus, these appearing to be a distinct feature of bovine strains. In other aspects, the replication of bovine parvovirus appeared similar to that of other members of the genus.

Animals↗
PubMed1985

Plasma catecholamine responses to change of posture in alcoholics during withdrawal and after continued abstinence from alcohol.

Plasma catecholamine, blood pressure and heart rate responses to standing were measured in ten alcoholics during withdrawal, ten alcoholics after 2-7 weeks of abstinence from alcohol, six abstinent alcoholics with orthostatic hypotension and ten normal control subjects. Withdrawing alcoholics had supine and standing heart rates and plasma noradrenaline and adrenaline concentrations that were higher than in abstinent alcoholics or control subjects. Supine blood pressures were also higher in withdrawing alcoholics than in abstinent alcoholics or control subjects, but on standing blood pressures in withdrawing alcoholics fell, four patients having a fall of more than 30/5 mmHg. Abstinent alcoholics without orthostatic hypotension had higher basal and standing concentrations of noradrenaline than control subjects but normal heart rates and adrenaline concentrations. Abstinent alcoholics with orthostatic hypotension showed a wide range of basal plasma noradrenaline concentrations and were found to have variable plasma noradrenaline responses to standing, three subjects having normal responses and three subjects having no or little increase in plasma noradrenaline on standing. It is concluded that alcohol withdrawal is associated with increased sympathetic nervous activity, as reflected by raised supine and standing plasma concentrations of catecholamines, and that even after 2-7 weeks of abstinence from alcohol plasma noradrenaline concentrations may be higher than in control subjects. Despite increased sympathetic nervous responses to standing, alcoholics during withdrawal have impaired blood pressure control and some may exhibit orthostatic hypotension. Orthostatic hypotension may also be observed in alcoholics during continuing abstinence from alcohol; in some of these patients failure of reflex noradrenaline release in response to standing may contribute to orthostatic hypotension.

Adult↗
PubMed1985

Beta-adrenoceptor responsiveness and plasma catecholamines as determinants of cardiovascular reactivity to mental stress.

Twenty-five normotensive men were subjected to two periods of mental stress involving a cognitive task and a competitive electronic game. Plasma catecholamines, heart rate and blood pressure were measured before and during mental stress. Responsiveness to beta-adrenoceptor stimulation was also determined in each subject by measurement of heart rate responses to bolus injections of isoprenaline. Both periods of mental stress were associated with significant increases in systolic and diastolic blood pressures, heart rate and plasma adrenaline, but not plasma noradrenaline. Heart rate responses to mental stress varied widely, with increases ranging from 1 to 48 (mean +/- SD 13.5 +/- 10.6) beats/min for the cognitive task and from 2 to 49 (20.4 +/- 14.0) beats/min for the electronic game. Systolic blood pressure responses also varied widely and showed significant positive correlations with heart rate responses. Significant relationships were found between heart rate responses to both forms of mental stress and cardiac sensitivity to isoprenaline, subjects with low responsiveness to beta-adrenoceptor stimulation tending to have smaller heart rate responses to mental stress than subjects with high responsiveness to beta-adrenoceptor stimulation. Relationships were also found between plasma adrenaline responses and heart rate responses to mental stress, although these did not reach significance. Considerably improved relationships were found when heart rate responses were correlated with a single variable generated from the product of the adrenaline response and the inverse of the dose of isoprenaline required to raise heart rate by 25 beats/min. It is concluded that wide variation is shown between different individuals in responsiveness to beta-adrenoceptor stimulation and that this is an important factor in the variability between individuals in heart rate and systolic blood pressure responses to mental stress. Both catecholamines and adrenoceptor-mediated responses to catecholamines should be examined when determining the physiological basis for differences in cardiovascular reactivity to mental stress between individuals or groups.

Adult↗
PubMed1985

Sleep apnoea in alcoholic patients after withdrawal.

Respiration during sleep was studied in 16 withdrawn alcoholic patients and in 12 control subjects. The alcoholic patients had increased numbers of central (P less than 0.01) and of obstructive (P less than 0.05) apnoea and of hypopnoea episodes (P less than 0.01) as compared with controls. Significant positive associations were found between the frequencies of central apnoea (P less than 0.05) or hypopnoea (P less than 0.01) and clinical evidence of central nervous system damage in the alcoholic patients. Hypopnoea also showed a significant association with vagal neuropathy (P less than 0.05), assessed by tests of cardioreflexes. We conclude that abnormal respiratory events are common in abstinent alcoholic patients and that they are likely to be at least partly related to nervous damage.

Adult↗
PubMed1985

Autonomic responses to glucose ingestion in elderly subjects with orthostatic hypotension.

The cardiovascular and plasma catecholamine responses to oral glucose (50 g) ingestion were investigated in five elderly subjects with orthostatic hypotension and five elderly control subjects. All the orthostatic hypotension subjects showed blood pressure falls after glucose ingestion, as compared to only one of the control subjects. Significantly greater falls in the orthostatic hypotension as compared to control patients were observed for systolic blood pressure (P less than 0.01) at 60 and 90 min following glucose and mean blood pressure (P less than 0.05) at 60 min following glucose. The orthostatic hypotension subjects did not have evidence of reduced heart-rate or plasma catecholamine responses to the glucose ingestion. It is concluded that, in elderly patients with orthostatic hypotension, disorder of blood pressure control may also cause hypotension associated with eating.

Aged↗