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Biomedical subjects

B J Martin

Publications and source records attributed to B J Martin.

At least 91 records · Page 5Linked to original sources
PubMed1992

Isocapnia blocks exercise-induced reductions in ocular tension.

Previous reports suggest that isometric exercise (2-min handgrip at 50% maximal voluntary contraction [MVC]) substantially lowers intraocular pressure (IOP). The authors questioned whether the mechanism for lowered IOP in exercise is secondary to hyperventilation. Accordingly, in this study 11 subjects, with elevated IOP (greater than or equal to 18 mm Hg) and otherwise healthy, did 2 min of handgrip exercise at 50% MVC with and without carbon dioxide supplementation to maintain isocapnic conditions. Compared with a control experiment that involved neither exercise nor CO2 addition, exercise induced a fall in IOP from 18.3 to 15.6 mm Hg (P less than 0.001). This statistically significant decline in IOP persisted for 15 min after the exercise session. At the point of minimum IOP (1 min after the end of exercise), the minute ventilation was elevated from 6.5-8.1 l/min (P less than 0.05), and the end-tidal partial pressure of CO2 (PCO2) was reduced from 37.0 to 33.7 mm Hg (P less than 0.05) with respect to control values. By contrast, adding CO2 sufficient to maintain isocapnic conditions (experimental end-tidal PCO2 = 38.9 versus 38.5 mm Hg in the control study; P = not significant) abolished the exercise-induced ocular hypotension (experimental IOP = 17.8 versus 18.1 mm Hg in the control study; P = not significant). It was concluded that prevention of hypocapnia during isometric handgrip exercise blocks the subsequent fall in IOP, suggesting both that isometric exercise per se has no direct influence on IOP and that therapy for ocular hypertension could involve manipulation of blood gases.

Adult↗
PubMed1991

Analysis of eye tracking movements using innovations generated by a Kalman filter.

A simple but efficient algorithm has been developed for computer analysis of eye tracking movements. The program separates smooth pursuit and saccadic eye movements. Separation of the two components is achieved using a two-step process of saccade detection. First, an AR model of the velocity of the smooth component is identified and used to determine a Kalman filter. Secondly the innovation sequence generated by this filter allows saccade detection. The precise beginning and end of each saccade are found using a Hinkley algorithm. Examples are given of analysis procedure for eye tracking of a random moving target. The method proved to be highly reliable and could be easily extended to other eye movements such as nystagmus.

Algorithms↗
PubMed1991

Rapid orocecal transit in chronically active persons with high energy intake.

Although chronic physical activity by humans can raise energy requirements and energy intake severalfold above sedentary levels, whether these increases alter digestive strategy remains unknown. To investigate this possibility, food passage rate (mouth-to-large intestinal lactulose transit) and absorption (xylose) were compared in a cross section of young men chosen to represent a wide range of daily physical activity and food intake. In 20 men (energy intake 1,272-5,342 kcal/day), resting mouth-to-cecum transit was faster in high caloric consumers (r = -0.69, P less than 0.01). In contrast, xylose absorption (n = 26; measured either as urinary xylose excretion or integrated breath H2 production from the sugar) was unrelated to food intake. Dietary fiber intake was uncorrelated with energy intake. This apparent human digestive strategy of rapid transit across the gut absorptive surface, without a sacrifice in absorption, parallels the adaptations made by several animal species similarly faced with increased energy demand at constant fiber intake. We therefore conclude that the hyperphagia of chronic exercise in humans may be linked with significant gastrointestinal adaptations.

Adaptation, Physiological↗
PubMed1991

Comparison of inorganic elements from autopsy tissue of young and elderly subjects.

Concentrations of nine inorganic elements in autopsy samples of kidney, liver, heart and skeletal muscle from 33 aged subjects, mean age 80 years, were compared with concentrations in similar samples from 12 young healthy accident victims, mean age 29 years. Tissue samples were removed within 48 hours of death and dry weight was used as a frame of reference. Potassium and magnesium were significantly lower in muscle (P less than 0.001) and heart tissue (P less than 0.001) of elderly subjects. There was evidence of accumulation of zinc in liver tissue of the elderly (P less than 0.01). Copper was significantly lower in the heart tissue of elderly subjects (P less than 0.001) whereas manganese was lower in both the heart (P less than 0.01) and the kidney tissue (P less than 0.001) of the elderly. Selenium concentrations were lower in the kidney (P less than 0.001) of the elderly. Elderly heart tissue appeared to accumulate chromium (P = 0.007) and aluminium (P less than 0.001). No significant differences were found for iron concentrations between these two populations. These major differences in tissue element concentrations between young and aged subjects merit further attention.

Age Factors↗
PubMed1991

The interaction of hand vibration with oculomanual coordination in pursuit tracking.

The effects of high frequency hand vibration (150 Hz) on simultaneous ocular and manual tracking performances were investigated in trained human subjects. First, a zero-order pursuit tracking task was performed with and without direct visual control of the hand. Second, eye tracking of an imaginary target linked to the hand was also performed. The results show that hand vibration significantly alters eye and hand tracking performances when the hand is out of sight. However, when the hand is placed in the visual field, tracking performances are less affected by vibration. Visual cues on limb segments may compensate to some extent for the vibration-induced alteration of proprioceptive information otherwise used to control movements. Eye movements are altered during vibration while the subject is tracking or fixating an imaginary target attached to the hand. These findings explicitly show that hand vibration can perturb oculo-manual coordination control. The present results imply that vibration-induced activity of somesthetic mechanoreceptors is likely to contribute to oculomanual coordination alteration and tracking decrement in vibratory environments. Furthermore, direct visual control of the hand and/or arm may be of particular interest in manipulation tasks executed under vibration.

Adult↗
PubMed1991

Light and scanning electron microscopic changes observed in experimental arterial forks of rabbits.

Experimental arterial forks were fashioned by anastomosing one common carotid artery to the contralateral vessel by microvascular surgery in rabbits. In one rabbit group the forks were examined histologically by the serial section technique from 5.5 to 25 months postoperatively. The second group was used for scanning electron microscopy of the arterial endothelial surface from 1 to 257 days post-operatively. Intimal proliferation was observed at the lateral angles histologically at sites comparable to those where intimal proliferation occurs spontaneously in human infants. In addition, disruption of the internal elastic lamina with minimal intimal proliferation occurred at the sides of the neo-apex, mostly in the transposed artery. These disruptions corresponded to predominantly transversely orientated tears of the internal elastic lamina from 8 days post-operatively in the scanning electron microscopic study. They were similar to the early atrophic changes preceding berry aneurysm formation in human cerebral arterial forks. The results indicate that both intimal pads (cushions) and elastic tears can be haemodynamically induced.

Anastomosis, Surgical↗
PubMed1991

Hypomagnesaemia in elderly hospital admissions: a study of clinical significance.

Serum magnesium estimations carried out on 1576 consecutive elderly patients at the time of hospital admission revealed that 10.7 per cent had a serum magnesium level below 0.7 mmol/l, with 4.4 per cent of the total having a serum level less than 0.65 mmol/l. Hypokalaemia was frequently associated with hypomagnesaemia, for which diuretic therapy was the most commonly found predisposing factor. Outcome of illness, measured at six months in terms of mortality, duration of hospital stay and percentage of patients discharged from hospital, was no worse in patients admitted with hypomagnesaemia than in normomagnesaemic controls.

Aged↗
PubMed1990

Identical orocecal transit time and serum motilin in hyperthermia and normothermia.

Fever, exercise, and exposure to a hot environment can all cause symptoms of gastrointestinal dysfunction as they elevate body temperature. Nonetheless, the link between hyperthermia per se and these symptoms is unknown. To test the functional significance of increased body temperature, we investigated the influence of substantial passive hyperthermia on orocecal transit in 12 young, healthy men. Transit time was determined by a consistent rise in H2 concentration in a rebreathing apparatus after oral ingestion of 0.7 g lactulose/kg body weight. Lactulose was given in combination with a 350-ml liquid meal (360 kcal). After raising core temperature in warm water to 38.3 degrees C, orocecal transit time was identical to control (90 +/- 13 min at 38.3 degrees C, 92 +/- 13 min at 37.1 degrees C). While hyperthermia did elevate heart rate and minute ventilation, serum motilin, gastrin, and cortisol were similar in the two conditions. The failure of a passive core temperature rise to alter mouth-to-cecum transit suggests that this aspect of alimentary function is independent of body temperature.

Adult↗
PubMed1990

The magnesium load test: experience in elderly subjects.

While serum magnesium is the simplest and most widely used approach to the evaluation of magnesium status, it is recognized that a normal serum level can occur in the presence of tissue depletion. The magnesium load test is a reliable indirect method of assessing whole body magnesium status, but experience with its use in older subjects is limited. The initial aim was to establish a range of results for the magnesium load test in older subjects who were likely to be tissue depleted. Such data would enable more accurate interpretation of the test in older subjects with normal serum levels who might be tissue-magnesium depleted. Magnesium loading was performed in 43 female subjects, average age 83 years, with serum magnesium levels not exceeding 0.75 mmol/l (mean 0.63 +/- 0.09 mmol/l) and lower than recommended dietary magnesium intakes. Magnesium sulphate was given intravenously, 0.25 mmol magnesium/kg body weight at a rate of 2.5 mmol/hour. Twenty-four-hour urine magnesium was determined for two days before the test and on the day of test from the start of the infusion. The test was abandoned in 13 other subjects because it was not possible to obtain three consecutive accurate urine collections despite careful selection. In the remaining 30 subjects, average magnesium retention was 62% (range 15-98%). Serum magnesium appeared a better guide to tissue status than urine magnesium, but creatinine clearance correlated better with the degree of magnesium retention than either serum or urine magnesium levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1990

The incidence of communication disorders in dysphagic patients.

A retrospective study investigated the incidence and types of communication problems in 115 patients referred for swallowing difficulties. Each patient had a bedside swallowing evaluation completed as well as a screening of communication abilities. A formal speech-language evaluation was done when warranted and possible. Of the 115 patients, 93 had suspected swallowing problems based on the bedside evaluation done by the speech-language pathologist. Videofluoroscopy was performed on 85 of these patients. A significant positive correlation was found between communication impairments and both suspected and videofluoroscopically confirmed dysphagia. Cognitive problems were the most frequent communication impairment with dysarthria being second. Neurological diseases were the most common medical diagnoses in patients with swallowing difficulties. The case is presented for the speech-language pathologist to be the primary diagnostician and manager of both communication and oral-pharyngeal swallowing disorders whether they co-occur or not.

Adult↗
PubMed1990

Orocecal transit during mild exercise in women.

Little is known of the influence of exercise on movement of ingested food through the alimentary tract or of the association of several gastrointestinal hormones with transit rate in exercise. In this study, orocecal transit during mild exercise was measured in 21 women by detecting a rise in expired H2 after ingestion of 20 g lactulose in a 350-ml (360 kcal) liquid meal. Motilin, gastrin, and cortisol were measured in peripheral venous blood when, as evidenced by a breath H2 rise, the first portion of the meal arrived at the cecum. Comparison was made between seated rest and a treadmill walk at 5.6 km/h up a 2% grade. The walk predictably elevated heart rate, O2 uptake, and rectal temperature and also reduced transit time from 98 min at rest to 75 min during exercise (P less than 0.001). Faster transit in exercise was associated with a significant rise in cortisol, while gastrin and motilin levels were both unchanged. In conclusion, in women mild concurrent exercise accelerates orocecal transit rate of at least the first portion of nonabsorbable carbohydrate in a liquid meal. Although the mechanism for the effect remains unknown, it may be secondary to some aspect of the stress response to physical activity.

Adult↗
PubMed1990

Cardiac arrhythmias associated with upper gastrointestinal endoscopy in elderly subjects.

Continuous Holter monitoring was performed before, during and after upper gastrointestinal endoscopy in 50 unselected, consecutive elderly patients (median age 80 years: range 68-89). In contrast to other studies the patients received no atropine or opiate premedication and were monitored for a prolonged period usually 24 hours after endoscopy. Comparison of a control period when the patient was lying at rest before endoscopy with the period of endoscopy itself revealed an increased frequency of arrhythmias during endoscopy. Forty-eight per cent of patients developed a new arrhythmia or an increased frequency of existing arrhythmia during endoscopy. All arrhythmias were short and self-terminating. Evidence of cardiac disease conferred a significantly increased risk of developing an arrhythmia during endoscopy.

Aged↗
PubMed1990

Modulation of cutaneous flexor responses induced in man by vibration-elicited proprioceptive or exteroceptive inputs.

The effects of muscle tendon or skin vibration on the early and late components of polyphasic cutaneous responses elicited in the flexor carpi radialis by electrical stimulation of the radial nerve at the wrist were studied in the human, with all muscles at rest. Both early and late flexor responses were enhanced by flexor vibration and depressed by extensor vibration; facilitation was accompanied by a reduction of latency. Furthermore, when an "antagonist vibration response" was present, inhibition of the flexor reflexes was replaced by a facilitation. Palm skin vibration depressed both components of the flexor reflex, while dorsal or "back-hand" skin vibration induced either a facilitation or an inhibition. In addition, back-hand vibration modified the location of the sensations evoked by electrical stimulation of the nerve. In all cases, vibratory stimulus attenuated the perceived intensity of the electrical stimulus. These observations indicate that proprioceptive or exteroceptive information can modulate the gain of the cutaneous reflex loops in a flexible way, under supraspinal control. These data also suggest a possible impairment of the protective withdrawal reflex under vibratory environmental conditions at rest and eventually in active muscles.

Adaptation, Physiological↗
PubMed1989

Characterization of a rat myosin alkali light chain gene expressed in ventricular and slow twitch skeletal muscles.

Mammalian cardiac muscle contains two myosin alkali light chains: 1) the atrial light chain (MLC1A), and 2) the ventricular light chain (MLC1V) predominantly expressed either in the atrium or in the ventricle. In this report we describe the isolation and characterization of the complete gene for rat MLC1V. The rat MLC1V gene is approximately 6.5 kb long and the mRNA coding sequences are organized in 7 different exons. Comparison of this gene sequence with other known MLC1 gene sequences revealed that the exon-intron organization is highly conserved within the MLC1 gene family. The derived protein sequence of rat MLC1V showed a higher sequence homology with human ventricular (96%) MLC1V than with rat fast skeletal MLC1f (74%), suggesting functional similarities between different MLC1V proteins. S1 nuclease mapping and primer extension analysis demonstrated that this gene is expressed only in ventricular and slow twitch skeletal muscle tissues and is transcribed from the same promoter and transcription initiation site.

Amino Acid Sequence↗