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Biomedical subjects

G E Johnson

Publications and source records attributed to G E Johnson.

At least 37 records · Page 2Linked to original sources
PubMed1984

Muscular synergism--I. On criteria for load sharing between synergistic muscles.

The use of optimization techniques to predict individual muscle forces in redundant biomechanical systems implies the formulation of a criterion for load sharing between the muscles. In part I of this paper, the characteristics and performance of several linear and non-linear criteria reported in the literature have been compared for static-isometric knee flexion. The results show that linear criteria inherently predict discrete muscle action (orderly recruitment of muscles) whereas non-linear criteria can predict synergistic action. All criteria predict that relatively more force is allocated to muscles with large moment arms. When muscle stresses (or ratios of muscle force to maximum muscle force) are used as the decision variables in the objective function, then relatively more force is allocated to muscles with large maximum possible force as well. Future formulations of the optimization should consider the differences in fiber type composition among the muscles. Such an approach is presented in part II of the paper.

Biomechanical Phenomena↗
PubMed1984

Muscular synergism--II. A minimum-fatigue criterion for load sharing between synergistic muscles.

P6new physiological criterion for muscular load sharing is developed. The criterion is based on the assumption that the endurance time of muscular contractions is maximized, hence muscular fatigue is minimized. The optimization problem is cast in the form of a linearly constrained, non-linear MINIMAX optimization. The new method predicts that: (1) there is synergistic muscle action, (2) muscle force increases non-linearly with external force (load), (3) relatively more force is allocated to muscles that have a large maximum force (large muscles), (4) relatively more force is allocated to muscles with a high percentage of slow-twitch fibers (muscles that are fatigue-resistant), (5) the load sharing does not depend on the moment arm of the muscles (although the absolute force levels do depend on this variable). The predicted load sharing between two cat muscles during standing and walking is in good agreement with direct force measurement data from the literature.

Animals↗
PubMed1983

A six-year follow-up study of 155 children with cleft lip and palate.

A total of 155 consecutive cases from three "Six-year-old follow-up clinics" have been reviewed to assess the speech results in boys and girls with cleft lip and palate belonging to Group II (complete labio-palatal clefts) and Group III (varying degrees of posterior median clefts of the palate). Clinical examination and assessment of speech was supplemented by X-ray-video assessment and the findings showed a good degree of correlation. The speech results between Group II and III and between the sexes are compared. Finally the extent of bone formation in the alveolar cleft was studied radiologically in 61 children with Group II clefts. Bone formation was present in 43 children, in 38 of whom a tooth had migrated into bone.

Child, Preschool↗
PubMed1982

Timolol and propranolol: bioavailability, plasma concentrations, and beta blockade.

Timolol, like propranolol, is a nonselective beta-adrenergic blocker, but it is much less lipid soluble and is formulated as a single enantiomer rather than a racemic mixture. We examined the effects of such differences on bioavailability, systemic clearance, and pharmacologic response. Ten healthy subjects received placebo, 0.2 mg/kg IV propranolol, 3.2 mg/kg oral propranolol, 0.025 mg/kg IV timolol, and 0.4 mg/kg oral timolol in double-blind, randomized crossover fashion. Plasma concentrations of total drug were monitored up to 8 hr, while responses to submaximal exercise were measured at 0, 2, and 6 hr. Timolol had greater bioavailability (F = 0.61 +/- 0.06(SEM) and 0.32 +/- 0.04) and lower systemic clearance (463 +/- 74 ml kg-1 hr-1 and 1040 +/- 120 ml kg-1 hr-1) than propranolol. Half-lifes were of the same order (2.7 and 2.9 hr). There was a marginal correlation between areas under the intravenous and oral plasma concentration-time curves for timolol (r = 0.66, P = 0.054), but none for propranolol (r = 0.48, P NS). There were also correlations of the response (percent reduction in heart rate) to oral and intravenous timolol at 2 hr (r = 0.72, P less than 0.05) and 6 hr (r = 0.84, P less than 0.01) hr, but none between responses to oral and intravenous propranolol. Finally, the response to oral timolol was related to the area under its plasma concentration-time curve, whereas that to propranolol was not. We conclude that the physicochemical properties of timolol lead to greater bioavailability. Pharmacologic response to an oral dose of timolol, unlike that to propranolol, can be predicted from the response to an intravenous dose and reflects its plasma concentration.

Administration, Oral↗
PubMed1981

Nonresponsiveness of serum high-density lipoprotein-cholesterol to high dose ascorbic acid administration in normal men.

In a prospective, single-blind, 12-wk study, serum lipids were measured serially in nine normal male volunteers before and during oral administration of megadose ascorbic acid (1 g vitamin C/day). Study results revealed no significant effect of vitamin therapy on serum cholesterol, high-density lipoprotein-cholesterol, triglycerides, or calculated low-density lipoprotein-cholesterol. Megadose ascorbic acid therapy is not effective in elevating serum high-density lipoprotein-cholesterol in normal adult men.

Adult↗
PubMed1981

Mechanical vibration in neonatal transport.

Mechanical vibration encountered in land transports was assessed objectively through measurement of vertical acceleration experienced by neonates in transit. Vibration was most predominant in the hazardous low frequency range of 3 to 18 Hz. The peak acceleration amplitudes (intermittent thrusts) ranged from 5 to 13 m/sq sec. The root mean square acceleration (averaged vibration) ranged from to 6 m/sq sec. These vibration levels are high when compared with adult vibration tolerance limits, and may jeopardize the safety of the transported infants, particularly in long-distance transports. Further research is needed to understand the possible effects of mechanical vibration in neonates and to define safe vibration thresholds in all modes of transport. Careful-evaluation of vibratory stress and its attenuation in newer designs of transport equipment may be desirable to enhance the safety of the transported infants.

Humans↗
PubMed1979

Drug prescribing for the elderly in Saskatchewan during 1976.

Over 11% of Saskatchewan's population is 65 years of age or older. To study patterns of prescribing for the elderly a computer file of more than 3.6 million prescriptions filled in Saskatchewan in 1976 was reviewed. The elderly population (aged 65 years or more) that year was 102 070, and 77.3% received at least one prescription drug listed in the Saskatchewan Formulary. In comparison with a "middle-aged" group (persons between the ages of 35 and 54 years) the elderly showed moderately higher average numbers of prescriptions filled and drugs used per person that year. However, the prescription of antihypertensive agents and diuretics increased dramatically with age, and barbiturates, in view of their potential toxicity, appeared to be overprescribed for the elderly.

Adult↗
PubMed1977

5,7-Dihydroxytryptamine lesions of the ascending 5-hydroxytryptamine pathways: habituation, motor activity and agonistic behavior.

Rats were injected stereotactically in mesencephalon with 5,7-dihydroxytryptamine (5,7-DHT) in the medial 5-hydroxytryptamine (5-HT) pathway (n = 8) and in the medial plus the lateral 5-HT pathways (n = 7) or injected with vehicle (n = 8), or sham-operated (n = 8). The 5,7-DHT lesions reduced the in vitro 3H-5-HT uptake in the hypothalamus and the cortex cerebri to 27-51% of control values, 3H-noradrenaline uptake was not significantly changed. 5,7-DHT lesions of the medial, and of the medial plus the lateral, 5-HT induced mouse killing behavior and increased number of boxing positions in the shock elicited fighting test. Both lesions also reduced the rate of habituation to touch, but only the lesion of the medial plus the lateral 5-HT pathway significantly reduced the rate of habituation to acoustic stimulation. Activity in the home cage was not significantly changed by the lesions. It was concluded that selective chemical lesions of the ascending 5-HT pathways result in prolonged habituation of the orienting response and increase in particular components of agonistic behavior. The increase in locomotor activity observed after electrolytic lesions of nucleus raphe medianus seems not to be due only to lesion of the 5-HT neurons ascending from this nucleus.

5,7-Dihydroxytryptamine↗
PubMed1977

Popliteal entrapment syndrome.

A probable cause of popliteal artery entrapment is proposed. The medial head of the gastrocnemius muscle during its embryological development crosses the popliteal fossa from lateral to medial. It is proposed that the migrating medial head carries the popliteal artery and vein across the fossa and entraps them against the medial condyle of the femur. Dissection of 86 anatomical specimens revealed two cases of unilateral and one case of bilateral entrapment of both popliteal vessels. Two surgical cases of popliteal entrapment are presented. This entrapment syndrome is a remedial cause of claudication and when considered, it is readily diagnosed and surgical correction is effective. Because of distal embolisation and occlusions, early recognition and treatment is desirable. Forty-seven cases from the literature are reviewed as to the entrapment type and the age and sex of the patients.

Adult↗
PubMed1976

Improved theophylline serum analysis by an appropriate internal standard for gas chromatography.

A gas chromatographic method is presented for the measurement of theophylline in serum. To serum samples containing the drug the internal standard, 3-isobutyl-l-methylxanthine, was added and the serum was saturated with ammonium carbonate. A mixture of isopropanol-chloroform (5:95) was used for extraction. The organic phase was filtered and evaporated. The residue, dissolved in chloroform, was extracted with sodium hydroxide. The basic solution was acidified, washed with hexane and reextracted with isopropanol-chloroform. The organic phase was dried with anhydrous sodium sulphate before evaporation. The sample was derivatized with n-Butyl-8 reagent. 85% of theophylline was recovered by extraction. 3-Isobutyl-l-methylxanthine was recovered with the same efficiency as theophylline and gas chromatographed well. The standard curve was linear between 1.0 and 50.0 mug/ml theophylline. No interference was encountered from normal serum constituents or methylxanthines such as caffeine, theobromine, or 3-methylxanthine. Serum samples were stared in the refrigerator for two weeks without significant loss of drug. The precision and accuracy of the method were good.

Chromatography, Gas↗
PubMed1976

Diagnosis and treatment of minimal brain dysfunction in adults: a preliminary report.

Minimal brain dysfunction (MBD) has long been considered a disorder limited to childhood. A number of longitudinal and adoption studies suggest that MBD may persist into adult life where its existence is concealed by the application of a variety of diagnostic labels. In order to test the hypothesis that MBD does persist into adulthood, 15 putative MBD adults were identified on the basis of current MBD-like complaints, self-description of MBD characteristics in childhood, and a parental rating (on a standardized form) of "hyperactivity" in childhood. Eleven of the 15 subjects were given a double-blind trial of methylphenidate hydrochloride, and all 15 were given an open trial of pemoline, imipramine hydrochloride, or amitryptiline hydrochloride. Eight of the 11 showed a significant response to the double-blind trial of methylphenidate. Of the 15, eight showed a good response to stimulants or tricyclic antidepressants, two showed a moderately favorable response, and five were unresponsive to drug therapy.

Adult↗
PubMed1976

The necessity of drug level monitoring in anticonvulsant drug therapy.

A survey of 'steady-state' serum levels of anticonvulsant drugs from 221 epileptic patients at a university hospital was conducted. Serum concentrations of phenobarbital, primidone, and diphenylhydantoin were determined by a gas chromatographic method. Sixty-five percent (130) of the patients receiving diphenylhydantoin had levels below the therapeutic range of 10-20mug/ml. Subtherapeutic levels appear to be due to inadequate dosage adjustment. Only 25% (33) of the patients receiving phenobarbital had levels below the therapeutic range. Serum levels of diphenylhydantoin or phenobarbital could not be predicted from dosage. Most patients received two or more drugs. Over 10% of the patients had potentially toxic levels of anticonvulsant drugs. High levels of diphenylhydantoin were easily recognized clinically but high levels of phenobarbital were not.

Body Weight↗
PubMed1976

The elimination of tritiated doxycycline in normal subjects and in patients with severely impaired renal function.

Tritiated doxycycline was administered to four normals, four patients with renal failure interdialysis, and three patients in renal failure who were not on dialysis. Elimination was followed by collection of urine and feces up to eight days. It was demonstrated that renal failure reduced the urinary excretion of doxycycline. In normal individuals the total of 86% of the radioactivity was eliminated in five days, half in the urine and half in the feces. In patients, with renal failure on dialysis, 32% of the radioactivity was eliminated in that time, 9.3% in the urine and 23% in the feces. In renal failure patients not on dialysis 49% was eliminated in that time, 4% in the urine and 45% in the feces; when followed up to eight days a total of almost 70% of the radioactivity was eliminated and the increase elimination was accounted for by fecal elimination such that 64% was eliminated in the feces and 5% in the urine. The disappearance from the plasma compartment in all three groups was similar. Thus, although the plasma half-life of doxycycline is not significantly prolonged in renal failure, it appears likely that the drug is taken up into a compartment from which it may slowly be eliminated and when followed for a continual period of time a significant percentage can be recovered from the feces. There remains however, up to 30% of the administered dose which was not recovered and it must be assumed that a significant per cent of doxycycline would accumulate in a compartment, as yet unidentified, in patients with renal failure.

Administration, Oral↗
PubMed1975

A gas chromatographic method for measuring 6-mercaptopurine in serum.

A method is presented for the measurement of 6-mercaptopurine (6-MP) in serum. Serum samples containing the drug were treated with dithioerythritol and saturated with ammonium carbonate. 6-MP was then extracted from the serum with a mixture of isopropanol-ethyl acetate (1:1, v/v) containing 0.01% ethanethiol. The solvent was evaporated, the residue dissolved in dilute hydrocholoric acid, washed with chloroform, and extracted with ethyl acetate. 6-MP was derivatized with trimethylanilinium hydroxide and measured gas chromatographically. The sulfhydryl-protecting reagents, dithioerythritol and ethanethiol, were added to prevent the decomposition of 6-MP. The extraction and clean-up method recovered 78 +/- 2% (S.E.) of the 6-MP present. Tracer amounts of [8-14C]6-MP served as the internal standard during the extraction part of the method. Theophyline was used as the internal standard during the gas chromatographic analysis. The standard curve obtained from the gas chromatograph was linear between 0.5 and 20 mug/ml of 6-MP. Serum samples were stored in the freezer for two weeks without significant loss of drug. No interference was encountered from normal serum constituents or xanthines, such as caffeine or theophylline added to serum.

Chromatography, Gas↗