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Biomedical subjects

R M Robertson

Publications and source records attributed to R M Robertson.

126 records · Page 7Linked to original sources
PubMed1981

A corollary discharge of total foregut motor activity is monitored by a single interneurone in the lobster Homarus gammarus.

1. In Homarus, an identified interneurone (the L cell), which possesses the largest cell body in the commissural ganglion and projects to the brain, exhibits a complex firing pattern (Fig. 2 a). 2. It is shown that the L cell discharges with each of the 4 pattern generators of the stomatogastric nervous system which organize the rhythmic motor activity of the foregut (Fig. 2 b-e). 3. Manipulation of the membrane potential of the L cell does not induce any change in the 4 rhythms (Fig. 3), and it is concluded that the L cell is driven by the 4 pattern generators. 4. The functional meaning of this complex corollary discharge of the total foregut motor activity is discussed.

Animals↗
PubMed1980

Platelet aggregates in peripheral and coronary-sinus blood in patients with spontaneous coronary-artery spasm.

Five out of twenty patients with vasotonic angina had frequent spontaneous attacks with dramatic ST-segment alterations. These attacks were consistently associated with an increase in platelet aggregates in coronary-sinus blood but not arterial blood. This increase in platelet aggregates during coronary-artery spasm suggests a potential causal role for the platelet in this subset of patients with ischaemic heart-disease. However, the increase in platelet aggregates could be secondary to reduced coronary blood-flow.

Adult↗
PubMed1980

Elevated plasma free drug concentrations of propranolol and diazepam during cardiac catheterization.

Patients who undergo cardiac catheterization are frequently taking propranolol and are often premedicated with diazepam. Because the intensity of a drug's action is determined by free, or non-protein-bound, levels in plasma, changes in the degree of protein binding may profoundly alter the pharmacologic effect. We examined the effects of heparin on the free levels of propranolol and diazepam in six patients who underwent cardiac catheterization. After heparinization, the free fraction of diazepam increased more than fourfold, from 1.8 +/- 0.1% to 7.9 +/- 1.2% (p < 0.002) and the free levels increased from 2.0 +/- 0.5 to 8.4 +/- 2.2 ng/ml (p < 0.025); the free fraction of propranolol increased from 7.4 +/- 0.9% to 12.5 +/- 1.4% (p < 0.001). The increase in free drug concentration was associated with elevated free fatty acid levels, which rose from 181 +/- 7 micrograms/ml to 596 +/- 119 micrograms/ml (p < 0.02). Increases in the free levels of propranolol and diazepam produced by heparinization during cardiac catheterization may result in increased pharmacolaogic effect, such as excessive sedation or respiratory depression.

Adult↗
PubMed1979

The structure and function of the labrum in the lobster Homarus gammarus (L.).

The labrum of decapod crustaceans is a soft lobe overhanging the mouth. The labral skeleton, musculature and innervation of Homarus gammarus are described. There are three bilateral groups of sensory neurons innervating the floor, lobe and lateral walls of the labrum. These are probably responsible for the phasic afferent activity that can be recorded from the inner labral nerve on mechanical deformation of the labrum. The labrum undergoes rhythmical retraction-protraction movements during ingestion and is shown to be active during both mandibular activity and oesophageal peristalsis. Studies were made on the duration and frequency of labral "swallowing" activity. The role of the labrum in feeding is discussed.

Animals↗
PubMed1979

Oesophageal sensors and their modulatory influence on oesophageal peristalsis in the lobster, Homarus gammarus.

The musculature and innervation of the oesophagus of Homarus gammarus are described as a prerequisite to studies on the mechanisms and control of food ingestion. Of particular interest are two paired sensors (the anterior and posterior oesophageal sensors) which are bilaterally situated at the oesophageal-cardiac sac valve. These are similar to contact chemoreceptors previously described in insects and are classified as such on morphological grounds and with indirect electrophysiological evidence. Oesophageal peristalsis is effected by the coordinated contraction of the Oesophageal musculature. This is controlled by rhythmical bursting neuronal activity, which can be recorded from the nerve trunks in the area. A characteristic burst recorded from the superior oesophageal nerve is used as an indication of oesophageal dilatation during peristalsis for studies on the feedback effects of the oesophageal sensors. Electrical and chemical stimulation of the posterior oesophageal sensors can initiate and increase the frequency of oesophageal peristalsis, while stimulation of the anterior oesophageal sensors can slow and terminate oesophageal peristalsis. The results are discussed and a model presented of the role of the oesophageal sensors in feeding.

Animals↗
PubMed1979

Variant angina pectoris: investigation of indexes of sympathetic nervous system function.

One thousand forty-five spontaneous episodes of S-T segment elevation were observed in three patients over a total of 72 days of continuous electrocardiographic monitoring. Eighty-nine percent of episodes were asymptomatic; chest pain tended to occur with episodes longer than 3 minutes, and ventricular ectopy occurred almost exclusively with symptomatic episodes. Nitroglycerin regularly relieved angina or S-T elevation, or both. Plasma and urinary catecholamines and their metabolites were normal. Episodes of variant angina were not associated with a generalized increase in sympathetic outflow because serum catecholamine levels at the onset and termination of the S-T abnormalities were not elevated. Controlled trials of propranolol showed no significant beneficial effect. Propranolol significantly increased the length of episodes of S-T elevation in one patient, increasing ventricular irritability. The overall course of variant angina was quite variable, with spontaneous and long-lasting remissions, necessitating cautions interpretation of clinical trials.

Angina Pectoris↗
PubMed1979

Chronic recurrent angina.

The natural history of variant angina is described in a patient with multiple exacerbations and remissions over a period of several years. Constant in-hospital electrocardiographic monitoring for 26 days documented 569 episodes of ST elevation, 89% of which were asymptomatic. Episodes ranged in duration from 15 seconds to 11 1/2 minutes, with 4% of episodes associated with premature ventricular contractions. Over the course of hospitalization, the episodes of ST elevation decreased in frequency and length, as did episodes of pain. During this period, a number of therapeutic agents, including propranolol, indomethacin, and chlorpheniramine were evaluated using double-blind crossover trials. No agent had a significant beneficial effect on the course of the disease, and there was an increase in the length of episodes with high doses of propranolol. Because of the great variability in the course of this disease, only double-blind crossover trials should be allowed to dictate the efficacy of therapeutic agents.

Angina Pectoris↗
PubMed1979

Comparative assessment of stimuli that release neuronal and adrenomedullary catecholamines in man.

We assessed the release of neuronal and adrenomedullary catecholamines in response to various stimuli of the sympathetic nervous system in normal subjects. Plasma catecholamines and their urinary metabolites, normetanephrine and metanephrine, were measured. Sodium restriction increased supine plasma norepinephrine by 37% and ambulatory plasma norepinephrine by 22%, with urinary normetanephrine excretion increased 29%. The sodium restriction did not elevate plasma epinephrine or urinary metanephrine. The most potent stimuli of norepinephrine were treadmill exercise, orthostasis, caffeine, the cold pressor test, sodium restriction and handgrip exercise, in descending order. Plasma epinephrine was increased by caffeine, treadmill exercise, the cold pressor test, handgrip exercise and the Valsalva maneuver, in that order. Syncope resulted in profound changes in plasma epinephrine but only modest changes in plasma norepinephrine. We conclude that in man, there is frequent dissociation between the effects of different stimuli on neuronal and adrenomedullary catecholamine release.

Adolescent↗
PubMed1979

Measurement of aortic and mitral regurgitation by gated cardiac blood pool scans.

A simple, noninvasive radionuclide technique which measures the severity of valvular regurgitation has been developed. The technique compares right and left ventricular stroke volume indices (change in counts between diastole and systole over the left and right ventricles) from 45 degrees LAO gated cardiac blood pool scans. In 14 control subjects, the left-to-right ventricular stroke index ratio was near unity (1.15 +/- 0.15 [SD]). In 26 patients with mitral and/or aortic regurgitation it was larger (range 1.36--5.30, mean 2.44). Comparison between the stroke index ratio and qualitative angiographic estimates of regurgitation revealed good agreement (F = 45.5, p less than 0.001). Gated cardiac blood pool scans permit noninvasive assessment of the severity of valvular regurgitation.

Adult↗
PubMed1978

Echocardiographic evaluation of porcine heterograft valves in the mitral and aortic positions.

We evaluated 15 porcine heterograft valves in the mitral position and seven in the aortic position by echocardiography. Combining our quantitative description of valve stent and leaflet motion with 31 previously reported cases, we suggest echocardiographic criteria for the range of normal porcine heterograft valve motion in the mitral position. Quantitative evaluation of valve leaflet and stent motion for valves in the aortic position is described for the first time. Correlative hemodynamic and echocardiographic data is provided for three patients who underwent postoperative catheterization. The use of echocardiography in following the function of porcine heterograft valves is discussed.

Adult↗
PubMed1978

Acute right ventricular overload: an echocardiographic clue to pulmonary thromboembolism.

Serial echocardiographic changes and angiographic correlation are presented in a patient with multiple pulmonary emboli. Interval development of right ventricular dilatation and paradoxical septal motion coincided with a clinical event which was proven angiographically to represent pulmonary thromboembolism. Echocardiographic findings suggested right ventricular pressure and/or volume overload. The differential diagnosis of this finding when acute is limited; pulmonary embolism is a prominent consideration. Echocardiography performed after the patient received anticoagulant therapy showed a complete return to normal. Echocardiographic evidence of right ventricular overload, particularly when acute, may indicate the presence of a pulmonary embolism, and may be clinically useful in selected cases.

Angiography↗
PubMed1976

The structure and function of thoracic exopodites in the larvae of the lobster Homarus gammarus (L.).

The first three larval stages of the lobster Homarus gammarus are pelagic swimming animals. A description is given of the exopodite apparatus of the thoracic appendages that provide lift and propulsive power in these stages. Setal arrangement and display provides greater surface area during power strokes. Musculature is peculiar to the exopodites and concerned with rotational movements of the appendage. Metachronal beating takes place with the segmental appendages moving in a variable sequence.

Animals↗
PubMed1975

Effect of noise exposure during primary flight training on the conventional and high-frequency hearing of student pilots.

This investigation was part of a larger study conducted by Memphis State University. This laboratory's portion of the study focused on administering conventional audiometry (manual and self-recording), high-frequency audiometry (4 kHz-18 kHz), and a speech intelligibility test in noise to 108 Naval Aviation Officer Candidates prior to and following primary flight training in T-34 aircraft. Hearing protection consisted of either the APH-6C or APH-6D flight helmet. Cockpit noise levels in the T-34 range from 96-115 dBA; during cruise the noise level is approximately 100 dBA. Results indicate no significant change in hearing sensitivity or speech discrimination that could be attributed to noise exposure during primary flight training. Pre- and postprimary hearing levels obtained for the high frequencies compare favorably with high-frequency hearing levels obtained by Northern et al. (1968) for males in the age range 20-29 years. Questionnaire data indicated that a considerable number of the subjects had been exposed to potentially harzardous noise before entry into military service.

Adult↗