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Biomedical subjects

R B Armstrong

Publications and source records attributed to R B Armstrong.

At least 127 records · Page 7Linked to original sources
PubMed1981

Photoallergic contact dermatitis to musk ambrette. Histopathologic features of photobiologic reactions observed in a persistent light reactor.

Studies concerning a patient with contact photosensitivity to musk ambrette, a commonly used fragrance, are reported. The patient had a persistent light reaction. The patient's history, clinical appearance, and phototest and photopatch test results are described. The observed patterns of these were identical to those previously noted in patients who had persistent light reactions after exposure to other photosensitizers such as the halogenated salicylanilides. The histopathologic findings in the phototest and photopatch test sites were those of an acute spongiotic dermatitis. No abnormal change was seen with ultraviolet A radiation exposure alone.

Aged↗
PubMed1981

Design of the mammalian respiratory system. II. Measuring maximum aerobic capacity.

We describe a simple and reproducible procedure for measuring maximal O2 consumption (Vo2max) that can be used for mammals spanning a wide range of body mass (Mb). Vo2 of trained animals was measured as a function of speed while they ran on a treadmill. Lactate concentration of the blood was determined at the beginning and end of the run. We considered that an animal had achieved Vo2max when Vo2 no longer increased with increasing tread-speed and the additional energy consumed by the muscles could be accounted for by anaerobic glycolysis. We found that Vo2 increased linearly with tread-speed up to a maximal rate and then remained unchanged with further increases in speed in nine species. When the animals ran at speeds faster than that where Vo2max was reached, they refused to continue when blood lactate concentrations reached 18-28 mmol . kg-1. Values for Vo2max obtained with this procedure were found to be about 20% greater than values obtained with the 'cold exposure' procedure for determining Vo2max. We conclude that our treadmill procedure is valid for determining the allometric relationship between Vo2max and Mb.

Aerobiosis↗
PubMed1981

Design of the mammalian respiratory system. VI Distribution of mitochondria and capillaries in various muscles.

The variability of structures supporting tissue oxygen transport (capillaries) and oxygen consumption (mitochondria) was analyzed in skeletal muscles of wildebeest and dik-dik. Regional differences in mitochondria and capillary densities within individual muscles were found for M. semitendinosus (twofold) but not for M. longissimus dorsi and diaphragm. Comparing 20 different muscles from both animals, the volume density of mitochondria in the muscle fibers [Vv(mt,f)] was significantly higher in diaphragm (10-12%) and varied considerably (1-6%) in the other muscles. The relation between Vv(mt,f) and the number of capillaries per cross-sectional fiber area NA(c,f) showed great variability. In glycolytic fibers Vv(mt,f) was typically low (1%) whereas in oxidative fibers it ranged from 5-15%. No systematic trend was found for the packing of cristae in subsarcolemmal and interfibrillar mitochondria from both types of fibers in large and small animals.

Animals↗
PubMed1981

Mitogenicity of influenza hemagglutinin glycoproteins and influenza viruses bearing H2-hemagglutinin.

The hemagglutinin glycoprotein is responsible for the mitogenic effect of influenza A viruses of the H2N2 subtype. This was indicated by the ability of viruses bearing the H2-hemagglutinin glycoprotein, regardless of its associated neuraminidase, to induce lymphocyte proliferation in normal spleen cell suspensions and by the ability of antisera with specificity for the H2-hemagglutinin to block this response. Moreover, purified hemagglutinin from representative viruses from the H0N1, H1N1, H2N2, H3N2, and influenza B subtypes were also shown to be mitogenic.

Glycoproteins↗
PubMed1981

Patterns of glycogen loss in muscle fibers: response to arterial occlusion during exercise.

This experiment was designed to determine if glycogen loss in active rat skeletal muscle fibers could be accentuated by periodic occlusion of blood to the muscles without significantly altering the numbers of types of fibers that lose glycogen. We attempted to augment glycogen loss by periodically occluding blood flow to the muscles while the animals ran on a treadmill. An occluder cuff was placed on the right common iliac artery of 10 rats. While the rats ran for 5 min at 26 m . min-1, blood flow to the right hindlimb was completely occluded for 16 +/- 5 (SD) s during every 30 s of the run. Glycogen loss in soleus (S), plantaris (P), and gastrocnemius (G) muscles was determined biochemically and histochemically. Muscles from both the occluded limb (S, P, and the deep red portion of G) and the nonoccluded limb (S and red G) of the runners showed significant glycogen loss compared with the controls. Furthermore, glycogen concentration was significantly lower in S, P, and red G of the occluded limb than in the same muscles of the nonoccluded limb. Significantly greater numbers of fibers within fiber type populations of P and G showed glycogen loss in the occluded limb, indicating that more motor units were recruited during the exercise bout in these muscles. The data suggest a sensitive link between motor unit recruitment and the metabolic condition of the contracting fibers, as the increased number of fibers showing glycogen loss presumably, resulted from fatigue of active units. We conclude that occlusion of blood flow to active muscles is not a feasible means of accentuating glycogen loss in active fibers while maintaining normal patterns of recruitment.

Animals↗
PubMed1980

Photoallergic contact dermatitis to musk ambrette. Clinical report of two patients with persistent light reactor patterns.

Two male patients with photoallergic contact dermatitis to musk ambrette, 2-methoxy-3,5-dinitro-4-methyl-t-butylbenzene, are reported. Musk ambrette is a synthetic fragrance material commonly used in foods and cosmetics. The clinical distribution of lesions presented by these patients strongly suggested an adverse reaction to light. Over a period of several years no etiology had been determined in these cases despite extensive testing and hospitalization. Photopatch tests to musk ambrette were positive. No other etiology for photosensitivity was found. This report emphasizes that exposure to household or cosmetic products represents a potential source of contact photosensitivity. Patients presenting with dermatoses of unknown origin confined to the light-exposed areas should have fragrances considered as possible etiologic agents.

Aged↗
PubMed1979

Acute hypertrophic response of skeletal muscle to removal of synergists.

The purpose of this project was to study the initial rapid enlargement phase of skeletal muscle in response to ablation of synergistic muscles. The first experiment tested the hypothesis that this initial phase is due to inflammation in the enlarging muscle. The wet weight of the plantaris muscle increased significantly (14%) within 1 h after removal of the ipsilateral gastrocnemius muscle. This increase was due to inflammation, as evidenced initially by edema, and within the next few hours, by leukocyte invasion of the interstitium and enhanced hexose monophosphate shunt-reducing capacity. In the second experiment we followed the time course of this inflammatory reaction. The response peaked at 1-5 days following surgery, after which it subsided to control levels by 16 days postsurgery. The final experiments were designed to uncover the factor(s) causing the inflammatory response. Two possible mechanisms were hypothesized: 1) trauma resulting from surgical manipulation of the tissue, and 2) trauma due to elevated stretch and/or tension on the muscle following removal of the synergists. The data indicate that surgical trauma is the causative factor of the inflammatory response in this hypertrophy model.

Animals↗
PubMed1979

Tympanostomy tubes, their use, abuse, and cost-benefit ratio.

Tympanostomy tubes are employed when middle ear ventilation is indicated, particularly when other forms of treatment have failed. Few other uses have broad acceptance. Any other insertion of a ventilating tube implies abuse, either through error in diagnosis or deliberate misapplication. Hard statistical data relating to abuse are impossible to obtain, but ample illustrations can be cited. The cost-benefit ratio is difficult to assess. Cost of a myringotomy and tube versus the cost of a tympanomastoidectomy was determined in four geographic areas. These figures, however, do not reveal how many ears were spared and how much hearing was conserved by tympanostomy tubes. Informed, diligently aggressive use of tympanostomy tubes offers greater potential to avoid serious middle ear disorders and complications than any other single modality.

Cost-Benefit Analysis↗
PubMed1978

Rat locomotory muscle fiber activity during trotting and galloping.

This study was designed to investigate the hypothesis that the trot-gallop transition in running guadrupeds occurs when active cross-sectional areas of muscles or fiber populations within muscles, reach some critical point as animals increase speed within trotting. Rats (Rattus norvegicus) were used as experimental animals, and glycogen depletion was used to estimate patterns or fiber activity. Our results indicate that 1) the contribution to power output by the front limb muscles was less than that of the hind limb muscles during trotting and galloping; 2) the active cross-sectional area of plantaris muscles peaked immediately prior to the transition in gait; 3) the ankle plantar flexor group of muscles as a whole did not attain a maximum active cross-sectional area during fast trotting; and 4) no major discontinuities in whole muscle or fiber type glycogen depletion rates occurred across the gait change. Although these findings do not prove the hypothesis, they support the concept that the trop-gallop transition follows the attainment of peak active muscle cross-sectional areas as animals increase trotting speed.

Adenosine Triphosphatases↗
PubMed1977

Compensatory hypertrophy of skeletal muscle fibers in streptozotocin-diabetic rats.

Previous studies have demonstrated an apparent differential response of the fiber types in mixed skeletal muscles of rats to streptozotocin diabetes. The purpose of the present study was to examine the ability of the different fiber types to hypertrophy in muscles from diabetic rats, which should further clarify the apparent differential trophic influence of insulin on the fibers. One group of rats was injected with streptozotocin to induce diabetes. The gastrocnemius muscle was then removed from one hindlimb of rats of both the diabetic and a second, normal group, resulting in compensatory growth of ipsilateral plantaris muscle. Rats were sacrificed 60 days following the surgery. Experimental muscles in normal and diabetic rats enlarged 79% and 61% over control muscles, respectively. In normal hypertrophied muscles there was an 8% increase in relative cross-sectional area composed of slow-twitch fibers, whereas in diabetic rats the slow-twitch component increased 17%. The results indicate that slow-twitch fibers in diabetic rats were capable of responding to the chronic power overloaded condition, but that the fast-twitch fibers had a reduced capacity to undergo compensatory growth. These findings support our previous observations suggesting that insulin may exert a differential trophic effect upon the muscle fiber types.

Animals↗
PubMed1977

Muscle fiber activity as a function of speed and gait.

These experiments were designed to test the hypothesis that locomotory gait transitions occur when some critical cross-sectional area of active muscle is reached as animals increase speed within a gait. We used glycogen depletion as evidence of muscle fiber activity and selected an experimental animal in which all muscle fibers in the locomotory muscles rely extensively on glycogen as a substrate--the lion. We found a high correlation between biochemically and histochemically determined rates of glycogen depletion (r = 0.906). Rates of glycogen depletion in the biceps femoris and triceps brachii muscles increased logarithmically with speed with no discontinuities at the gait transitions. However, we found large discontinuities both in the total cross-sectional area of muscle that showed depletion and in the rates at which the different types of fibers depleted glycogen at the trot-gallop transition. Our results indicate that 1) gait transition did not occur at a maximum tension level either for a particular type of fiber or the whole muscle, and 2) different configurations of motor units within an individual muscle may be recruited as an animal changes gait.

Animals↗