Toshiaki Miyagawa

The Medial Canthal Tendon Is Composed of Anterior and Posterior Lobes in Japanese Eyes and Fixes the Eyelid Complementarily with Horner’s Muscle

PurposeTo report that the medial canthal tendon (MCT) is not simply the aggregate of the orbicularis oculi muscle (OOM) and its tendon.MethodsTwenty eyelids of 10 cadavers were used. The cadavers, seven male and three female, were all Japanese, with an average age of death of 76.2 years. The relationship between the MCT and the OOM, and between the tarsus and Horner’s muscle were investigated. Histological findings were obtained with hematoxylin and eosin staining.ResultsThe MCT was structured with an anterior lobe, the tendon from the tarsal area of the OOM, and a posterior lobe, the muscle–tendon transition area in the orbital area of the OOM. The nasal aspect of the tarsus was fixed by Horner’s muscle.ConclusionsThe MCT and Horner’s muscle are located in an important area of the eyelid; therefore, it is essential to understand their precise anatomy.

Myoneural Junctions of Extraocular Muscles: Distances from the Orbital Rim and Widths

PURPOSE To examine both the distances from the orbital rim to the myoneural junctions (MNJs) and the widths of the MNJs of all extraocular muscles. METHODS Six orbits of 3 post-mortem cadavers were used. The cadavers (1 female and 2 males) were all Japanese with an average age of 76.3 years. The MNJs of the extraocular muscles and their motor nerves were exposed, and then the distance from the orbital rim to each MNJ and the width of each MNJ were examined. RESULTS The distance from the orbital rim to each MNJ in the 6 extraocular muscles ranged from 24.4 to 33.6 mm and the width of each MNJ ranged from 5.0 to 8.5 mm. CONCLUSIONS It is essential for orbital surgeons to understand both the distance from the orbital rim to MNJs and the widths of MNJs. This information not only aids the understanding of MNJ damage, but also prevents iatrogenic nerve impairment during orbital surgery.

Oral administration of γ-aminobutyric acid affects heat production in a hot environment in resting humans

BackgroundCentral administration of γ-amino butyric acid (GABA) induces lower body temperature in animals in hot ambient air. However, it is still unknown whether oral GABA administration affects temperature regulation at rest in a hot environment in humans. Therefore, in the present study, we specifically hypothesized that systemic administration of GABA in humans would induce hypothermia in a hot environment and that this response would be observed in association with decreased heat production.MethodsEight male participants drank a 200-ml sports drink with 1 g of GABA (trial G) or without GABA (trial C), then rested for 30 minutes in a sitting position in a hot environment (ambient air temperature 33°C, relative humidity 50%).ResultsWe found that changes in esophageal temperature from before drinking the sports drink were lower in trial G than in trial C (-0.046 ± 0.079°C vs 0.001 ± 0.063°C; P < 0.05), with lower heat production calculated by oxygen consumption (41 ± 5 W/m2 vs 47 ± 8 W/m2; P < 0.05).ConclusionsIn this study, we have demonstrated that a single oral administration of GABA induced a larger decrease in body core temperature compared to a control condition during rest in a hot environment and that this response was concomitant with a decrease in total heat production.

Thermoregulatory responses are attenuated after fructose but not glucose intake.

PURPOSE We examined whether plasma hyperosmolality induced by oral monosaccharide intake attenuated thermoregulatory responses and whether the responses were different between fructose and glucose. METHODS Ten healthy young subjects performed three trials in a sitting position in an artificial climate chamber (ambient temperature, 28°C; relative humidity, 40%). After resting for 10 min, the subjects drank 300 mL of water alone (control), or 300 mL of water supplemented with 75 g fructose or 75 g glucose. Twenty minutes later, they were heated passively by immersing the lower legs in water at 42°C for 60 min. Plasma osmolality (Posm), sodium ([Na+]p) and insulin concentrations ([Ins]p), and percent change in plasma volume (%ΔPV) were measured, and esophageal temperature (Tes) thresholds for cutaneous vasodilation (THCVC) and sweating (THSR) at the forearm were determined. RESULTS Posm was significantly increased by fructose and glucose intake compared with water alone, although %ΔPV and [Na+]p were not significantly different among the three trials. [Ins]p was significantly higher after glucose intake than after fructose or water alone. THCVC and THSR were significantly higher after fructose intake than after glucose intake, which showed similar values to water intake. CONCLUSIONS These results suggest that the Tes threshold for thermoregulation is elevated after fructose intake, indicating the attenuation of thermoregulatory responses, whereas it is not attenuated after glucose intake. These results provide a novel insight to better determine the carbohydrate component of oral rehydration fluids for preventing dehydration and/or heat disorders.

Forced respiration during the deeper water immersion causes the greater inspiratory muscle fatigue in healthy young men.

[Purpose] The purpose of the present study was to evaluate the effect of water immersion at different water depths on respiratory function and the effect of inspiratory load breathing (ILB) during water immersion at different water depths on respiratory muscle strength evaluated by maximum inspiratory and expiratory pressures (PImax and PEmax, respectively). [Subjects] Eight healthy men participated randomly in three trials. [Methods] All sessions were conducted with the participants in a sitting position immersed in a water bath. We evaluated respiratory function, PImax and PEmax during submersion at three different levels of water depth (umbilicus; 4th-rib; or clavicle, CL) and after subsequent 15-min ILB. [Results] Decreases in vital capacity and expiratory reserve volume from baseline by water immersion were significantly greater in the CL trial than those in the other trials. In the CL trial, PImax was immediately reduced after ILB compared to that at baseline, and the reduction was significantly greater than those in the other trials. PEmax was not affected by ILB in any of the trials. [Conclusion] Forced respiration during deeper water immersion caused greater inspiratory muscle fatigue in healthy young men.