宮本 忠吉

The purpose of this study was to examine the relation ships among muscle oxygenation level measured by a near-infrared spectroscopy (NIRS), blood lactate concentration (La) and substrate utilization during a prolonged 60-min steady-state exercise below the anaerobic threshold (AT). Ten healthy adult subjects (3 males and 7 females) completed an orientation trial, a maximal exercise test, and a submaximal exercise for 60 min. The oxygenated hemoglobin and myoglobin saturation (muscle oxygenation level) measured by NIRS was recorded continuously throughout the tests. The probe was located on the vastus lateralis muscle. At 30 mm after exercise, the calibration of NIRS was performed by the cuff occlusion at 260 mmHg for 10 min. The relative change in muscle oxygenation level was estimated by regarding muscle oxygenation level in the resting condition as 0% and that obtained during thigh occlusion as - 100%. Oxygen consumption (V^^・O_2), carbon dioxide production (V^^・CO_2), minute ventilation (V^^・E), respiratory exchange ratio (RER), heart rate (HR) and La were measured at rest and during exercise. Muscle oxygenation level decreased immediately after the onset of exercise and gradually increased from -24.2±10.8% at 5 min to -3.3± 11.8% at 60 min. From 10 to 60 min, muscle oxygenation level increased by 11.6±3.9% with a significant increase in total hemoglobin. Muscle oxygenation level indicated the balance between oxygen delivery and oxygen utilization. Therefore, the gradual increase in muscle oxygenation level during the prolonged cycle exercise may be affected by more increase in O_2 de livery to exercising muscles than O_2 utilization. From 10 to 60 min, La and RER significantly decreased while the muscle oxygenation level increased. Therefore, Change in muscle oxygenation level between 10 and 60 min was correlated with bothΔLa (r=-0.66, P<0.05) andΔRER (r=-0.71, P<0.05). These results indicated that increase in muscle oxygenation level might facilitate blood lactate disposal and fat oxidation during the prolonged exercise below AT.

<jats:p>We propose a current confinement structure which can be self-formed by thermal annealing of a electrode metal with a self-aligning process. The migrated metal selectively destroys an AlAs/InP tunnel junction to form a high resistance isolation layer. The hole current can be injected through a preserved tunnel junction window. We confirmed its lateral confinement effect from the near-field pattern of fabricated GaInAsP/InP stripe lasers. The proposed current confinement structure is very simple and useful for the lateral injection in semiconductor optical devices including long-wavelength vertical-cavity surface-emitting lasers.</jats:p>

We demonstrate InP-based long-wavelength lasers with an AlAs/InP tunnel junction prepared in the upper cladding of a standard laser structure to convert electron current supplied by the upper n-electrode to hole current. A carbon auto-doped AlAs layer was employed as a heavy p-type layer required for the tunnel junction. The tunnel junction diode showed a small electrical resistance under a reverse-biased condition. In addition, a negative differential resistance characteristic was clearly observed under a forward-biased condition. The introduction of such a tunnel junction can eliminate the p-electrode which normally exhibits a high resistivity in InP-based lasers. In the fabricated lasers with tunnel junctions, it was observed that the tunnel junction can enhance lateral current spreading due to low resistance in the n-layer. The proposed structure for hole sources may be useful for reducing the resistance and homogenizing the carriers in the active region of long-wavelength vertical-cavity surface-emitting lasers (VCSEL).