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Biomedical subjects

J LeBlanc

Publications and source records attributed to J LeBlanc.

At least 19 recordsLinked to original sources
PubMed1992

Mechanisms of adaptation to cold.

The animal model used the most frequently for understanding the mechanisms of adaptation to cold in humans has been the rat. It has been established that rats kept in the cold for a few weeks stop shivering while preserving a normal internal temperature because of an enhanced thermogenic capacity of the brown adipose tissue (BAT) mediated by the sympathetic nervous system. Studies on groups of humans exposed to cold have shown that shivering is also attenuated but without compensatory increased in heat production possibly because of non-significant contribution of the BAT. However when humans and laboratory animals are exposed repeatedly to short severe cold evidence for adaptation has been described. This adaptation is not metabolic; instead it is related to the phenomenon of habituation. When exposed to a novel stress such as cold, the alarm reaction is initiated as evidenced by the activation of the sympathetic nervous system which opposes the stressing situation. However with time, when it is realized that the normal functioning of the body is not endangered the responses are attenuated and enhanced tolerance is observed. This type of adaptation was observed in Eskimos, fishermen, outdoor workers, etc.

Adaptation, Physiological↗
PubMed1992

Cold wind stimulation reflex.

The bradycardia induced by cold wind blown on the face and the early cephalic release of insulin induced by feeding have been shown to be caused by a vagal reflex stimulation. An experiment was designed to determine whether cold wind blown on the face would induce both pancreatic and cardiac stimulation. A 4 degrees C wind blown on the face for 4 min produced a rapid and persistent bradycardia, which interestingly persisted for up to 35 min after the test. The effect on respiration rate is more gradual and vanishes immediately after cold wind stimulation. Cold wind produced a slight reduction of insulin secretion, as evidenced by the fall of both plasma insulin and C-peptide, and caused a significant increase in plasma norepinephrine. These results suggest that the cold wind action of the vagus nerve is exerted on the heart and that of the sympathetic on the pancreas, whereas during the cephalic phase of feeding a vagal influence is observed on the pancreas and a sympathetic action on the heart. The mechanisms of the quantitative and qualitative control of these autonomic responses are not known and deserve further investigation.

Adult↗
PubMed1991

Thermogenic and hormonal responses to palatable protein and carbohydrate rich food.

Simultaneous variations of oxygen consumption, and plasma insulin and norepinephrine were measured during the postprandial cephalic and gastrointestinal phases of feeding in six human subjects following the ingestion of various nutrients. On alternative days the subjects were given foods (1280 kjoules) either rich in carbohydrates (sugar pie) or in proteins (fish). Both nutrients produced an initial (0-40 min) enhanced thermogenesis and an early (2 min) cephalic insulin release. During that period, elevations of plasma norepinephrine were also observed with pie feeding at 10 and 30 min and at 10 min with fish. Palatability ratings indicated that both food items were equally tasting. During the gastrointestinal phase (40 to 120 min) the variations of these same parameters including glucagon seem to be explained by the content in carbohydrates and proteins in the food rather than by its palatability. Indeed during that period the protein meal was more thermogenic and the carbohydrate meal induced the expected insulin secretion. These results suggest that the palatability of the food is responsible for the early cephalic increase in postprandial thermogenesis, and for the insulin and norepinephrine release. During the subsequent gastrointestinal phase the increased thermogenesis is related to the composition of the food which exerts its action by the biochemical processes involved in the disposal of the absorbed nutrients.

Adult↗
PubMed1991

Effect of patient positioning after needle aspiration lung biopsy.

Fifty-five patients who underwent fluoroscopically guided needle aspiration lung biopsy were randomly assigned to one of two postbiopsy treatment groups: Patients were placed recumbent with puncture site either down (n = 36) or up (n = 19) for at least 1 hour. No significant difference in pneumothorax rate was seen between the two groups. Chest tube placement, however, was required in 21% (four of 19) of the puncture-site-up group versus 3% (one of 36) of the puncture-site-down group, which was a significant difference (P = .04). Puncture-site-down postbiopsy positioning reduces the proportion of patients requiring chest tube placement after lung biopsy.

Biopsy, Needle↗
PubMed1989

Effects of aluminum and other cations on the structure of brain and liver chromatin.

The reactivity of aluminum and several other divalent and trivalent metallic cations toward chromatin from rat brain and liver has been investigated. Two criteria are used to determine the relative reactivity of these cations toward chromatin. The first involves the ability of the ions to compact the chromatin fibers to the point where chromatin precipitates. The second criterion measures the ability of cations to interfere with the accessibility of exogenous structural probes (nucleases) to chromatin. Of the divalent cations tested, nickel, cobalt, zinc, cadmium, and mercury were the most reactive toward chromatin, on the basis of their ability to induce precipitation of chromatin in the micromolar concentration range. The divalent cations magnesium, calcium, copper, strontium, and barium were much less effective, although all cations precipitate chromatin if their concentration is increased. Of the trivalent cations tested, aluminum, indium, and gallium were very effective precipitants, whereas iron and scandium were without effect at the concentrations tested. Of all the cations tested, aluminum was the most reactive. Aluminum's ability to alter the structure of chromatin was investigated further by testing its ability to interfere with nuclease accessibility. This test confirmed that aluminum does induce considerable changes in chromatin structure at micromolar concentrations. Furthermore, chromatin from cortical areas of the brain was much more sensitive to aluminum than chromatin from liver. These results are discussed in light of the known toxicity of these cations, with particular emphasis on the possible role of aluminum in Alzheimer's disease.

Aluminum↗
PubMed1989

Cephalic postprandial thermogenesis in human subjects.

To study the role of food palatability on postprandial thermogenesis, a study was designed in which human subjects ingested palatable food while O2 consumption was measured continuously during 30 minutes before and 60 minutes after the meal. In a first experiment (normal feeding), the subjects ate a portion of sugar pie containing 1672 kJ. A rapid increase in O2 consumption was noted which reached a peak value at about 15 minutes from the beginning of the meal. In a second experiment (sham feeding), the subjects were given the same food and they were asked to chew it and to spit it out. During the first 30 minutes following the meal, sham feeding produced a significantly larger increase in O2 consumption than meal feeding, whereas in the second postprandial period the thermogenic effect of food was larger with meal feeding. The integrated elevation of O2 during one hour was the same with meal feeding as with sham feeding. These results show that sensory stimulations without food being absorbed caused an important increase in O2, and confirms in humans the presence of a cephalic postprandial thermogenesis. In the third experiment (blank feeding), the subjects mimicked the muscular activities associated with feeding such as hands, arms, jaw and throat movements. Blank feeding produced a small and transient increase in O2 consumption. An elevation of plasma norepinephrine was observed during the cephalic phase and this effect was significantly larger with sham than with meal feeding. Subjective ratings for palatability, hunger reduction and degree of fullness were higher with meal than with sham feeding.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Influence of echocardiography in pre-operative cardiac catheterization in congenital heart disease.

The influence of echocardiography on pre-operative cardiac catheterization was assessed in a retrospective analysis comparing two 12-month periods. Of 245 operations in 1983, 200 (82%) had pre-operative cardiac catheterization when two-dimensional echocardiography only was used in the pre-operative assessment compared to 162 of 238 (68%) operations in July 1985-June 1986 when pulsed Doppler echocardiography also was used (P less than 0.001). Significant reductions in pre-operative cardiac catheterization were present in both open (87/87 vs 89/102, P less than 0.001) and closed (113/158 vs 73/136, P less than 0.005) heart procedures. The group with the most significant reduction in pre-operative cardiac catheterization before open heart surgery were children with atrial septal defects; of the closed heart surgical groups, the greatest reductions were in patent ductus arteriosus, coarctation of the aorta and tetralogy of Fallot. Echocardiogram diagnostic errors occurred in 22/245 (9%) in 1983 compared to 9/238 (4%) in 1985/86 (P less than 0.05). Echocardiography has resulted in a significant reduction in pre-operative cardiac catheterization and has become more accurate in diagnosis.

Cardiac Catheterization↗
PubMed1979

Effects of physical training and adiposity on glucose metabolism and 125I-insulin binding.

Eighteen young male subjects, aged 18-30 yr, with maximal oxygen intake (VO2max) varying between 36 and 80 ml.kg-1.min-1, were studied. Between 20 and 120 min after injection, tolerance to iv glucose (20 g/m2) was not affected by VO2max but the insulin response was very significantly reduced in the better trained subjects. 125I-insulin binding to monocytes was found to be greater in the best trained subjects. Simple correlation analysis indicates that both VO2max and adiposity are related to plasma glucose and plasma insulin levels as well as to 125I-insulin binding. Because VO2max is negatively correlated to percent of body fat, a partial correlation analysis was made. Results indicate that the differences observed in athletes with regard to glucose and insulin levels and 125I-insulin binding are related to reduced adiposity rather than to enhanced VO2max.

Adipose Tissue↗
PubMed1979

Plasma catecholamines and cardiovascular responses to cold and mental activity.

Plasma epinephrine (E) and norepinephrine (NE) as well as blood pressure and heart rate variations were measured in 12 male subjects before, during, and after a cold hand test (5 degrees C for 2 min), a mental arithmetic test, and a combination of both these tests. Although the cold and mental tests had comparable effects on blood pressure, the heart rate response was greater than the mental test. The mental test produced a greater increase of E than the cold test, but the effect of the cold test was greater on NE than on E. Changes in heart rate were significantly correlated with E variations but not with NE, whereas changes in blood pressure were correlated with NE. Resting NE was correlated with resting blood pressure and resting E with resting heart rate. Finally the levels of basal E were positively correlated with the increase in E during the test. Cardiovascular changes were shown to be differently modified by a mental and a cold test. Evidence was given indicating that these changes are related to differences in E and NE responses in the presence of these tests.

Adrenal Medulla↗
PubMed1979

An economic evaluation of present and proposed methods of compensating hearing loss.

The basis for compensation of industrial hearing loss in the Province of Ontario is described, and contrasted with schemes utilized in other parts of Canada, United Kingdom, Australia, and the United States. Changes are suggested for the method used to derive the percentage of permanent disability related to hearing loss. A randomly selected population of claimants for industrial hearing loss have been used to model the economic effect of such changes, which are discussed.

Audiometry↗
PubMed1978

Effects of age, sex, and physical fitness on responses to local cooling.

The response to local cooling was estimated by the cold hand test (5 degrees C for 2 min) and the cold face test (0 degrees C with 66 km.h-1 wind for 2 min). Heart rate, blood pressure, and skin temperature were measured before, during, and after the tests. The increase in blood pressure (cold hand test) and the fall in Tsk (cold face test) were reduced in trained subjects. Similarly older subjects (53-60 yr of age) responded less to a cold hand test than younger subjects aged 20-40. However, the bradycardia caused by the cold face test was more pronounced in the older subjects. The responses to the cold hand and cold face tests were the same for male and female subjects. During the 2 min after the test, blood pressure and heart rate fell below initial values in the female group but not in the male. It is concluded that, besides adaptation to cold, individual factors such as age, sex, and physical fitness also have a relative importance in the responses to local cooling.

Adult↗
PubMed1977

Metabolic and cardiovascular responses to norepinephrine in trained and nontrained human subjects.

Forty young male adults, aged 18-30 yr, with maximal oxygen intake (VO2 max) varying between 35 and 76 ml-kg-1-min-1 were studied. The fasting subjects were perfused for 15 min with saline and thereafter for 30 min with norepinephrine (0.1 mug/kg per min). Blood variables were determined at the end of slaine perfusion, at 15 and 30 min during norepinephrine perfusion and 15 min after the end of NE perfusion. Trained subjects are characterized by lower basal plasma glucose and insulin concentration. NE perfusion produced a larger increase in plasma glucose in the trained subjects. Levels of insulin in the postperfusion period were smaller in the trained group. Serum free fatty acids (FFA) and glycerol increased less in the trained subjects during NE perfusion and this difference persisted in the post-perfusion period. During NE perfusion, blood lactate increased only in the nontrained subjects. Initial heart rate and blood pressure were lower in trained subjects but, during NE perfusion, elevated levels of blood pressure and decreased levels of heart rate were comparable in both groups. Because of similarities in responses to exercise and to NE in trained subjects, the results of the present study suggest a possible role for NE in exercise training.

Adolescent↗
PubMed1976

Effect of adrenaline on insulin secretion in rats treated chronically with adrenaline.

To determine whether rats could adapt to a chronic exogenous supply of adrenaline by a decrease in the well-known inhibitory effect of adrenaline on insulin secretion, plasma glucose and insulin levels were measured in unanesthetized control and adrenaline-treated rats (300 mug/kg twice a day for 28 days) during an adrenaline infusion (0.75 mug kg-1 min-1), after an acute glucose load (0.5 g/kg), and during the simultaneous administration of both agents. Chronic treatment with adrenaline did not modify the initial glucose levels but it greatly diminished the basal insulin values (21.57+/-2.48 vs. 44.69+/-3.3muU/ml, p less than 0.01). In the control rats, despite the elevated glucose concentrations, a significant drop in plasma insulin levels was observed within the first 15 min of adrenaline infusion, followed by a period of recovery. In the adrenaline-treated group, in which plasma glucose levels were lower than in control animals, plasma insulin levels did not drop as in control rats, but a significant increase was found after 30 min of infusion. During the intravenous glucose tolerance test, the plasma glucose and insulin responses showed similar patterns; however, during the concomitant adrenaline infusion, the treated rats showed a better glucose tolerance than their controls. These results indicate that rats chronically treated with adrenaline adapt to the diabetogenic effect of an infusion of adrenaline by have a lower inhibition of insulin release, although the lower basal insulin levels may indicate a greater sensitivity to endogenous insulin.

Animals↗
PubMed1976

Effects of temperature and wind on facial temperature, heart rate, and sensation.

Skin temperature measurements of the face have shown that the cheek cools faster than the nose and the nose faster than the forehead. The cooling effect of wind is maximum at wind speeds between 4.5 and 6.7 m/s. Cold winds produce significant bradycardia, which is, however, much more pronounced during the expiratory phase of respiration. A significant correlation was noted between cooling of face and the reflex bradycardia observed. Similarly, a very significant correlation was noted between drop in skin temperature and subjective evaluation of cold discomfort. Consequently, the drop in skin temperature, reflex bradycardia, and subjective evaluation are parameters which are directly affected by cold wind and can be used as adequate indicators of the degree of discomfort. When comparing the present results with the windchill index, it was found that in the zone described as "dangerously cold" the index fits well with the physiological measurements. In the zone described as "bitterly cold," the index by comparison with actual skin temperature measurements and subjective evaluation underestimates the cooling effects of combined temperature and wind by approximately 10 degrees C.

Adult↗