Yasunori Yanagidaira

Effects of high altitudes on finger cooling test in Japanese and Tibetans at Qinghai Plateau

The influences of both hypobaric hypoxia and cold on peripheral circulation were studied using the finger cooling test (measurement of the decrease in finger temperature, measured at the dorsal surface of the finger, during immersion of the hand in 0° C water for 20 min) at Qinghai Plateau. The same test was carried out at simulated altitudes in a 25° C climatic chamber to separate the hypobaric hypoxia influence from that of cold. In Japanese subjects at Qinghai Plateau there was a significant difference between finger skin temperatures (FSTs) during 20 min of 0° C water immersion at altitudes of 2260 m and 4860 m by ANOVA. Mean finger skin temperature during the 20-min immersion (5–20 min, MST) measured at 4860 m was significantly lower than that at 2260 m. In Tibetan subjects, there was also a significant difference between FSTs at 2260 m and at 4860 m by ANOVA. MST at 4860 m tended to be lower than that at 2260 m. In the 25° C climatic chamber, there was a significant difference between FSTs of Japanese expedition members at 2000 m and at 4000 m by ANOVA. MST was higher at 4000 m than at 2000 m, contrary to the data obtained in Qinghai. In conclusion, the higher skin temperature in response to local cold immersion, which would have been caused by stronger hypobaric hypoxia, must have been masked by the lower ambient temperature.

Cardio-pulmonary function of cyclists competing on an ascending mountain course between altitudes of 1400 m and 2800 m

Physiological changes were investigated in the cardio-respiratory function of competitors in a bicycle race which involved not a flat course but ascending a mountain, from 1400m to 2800m. Heart rate throughout the race, arterial oxygen saturation and pulmonary function before and after the race of well trained competitors were measured. The individuals maximal heart rate during the race was designated as HRmax for the calculations. (1) There were significant correlations between the age and the mean %HRmax during the race, between mean %HRmax and time, and between age and time (n=15); the mean %HRmax had a 3.90 times greater effect on time than did age. (2) The individuals who performed best had lower values of oxygen saturation just after finishing the race (n=51). (3) At 1 min after reaching the finishing line, oxygen saturation levels had recovered to the value of 20 min after finishing the race, whereas the heart rate was still in the process of recovery (n=18). (4) Maximum expiratory flow at 50% vital capacity measured 30 min after reaching the finishing line was significantly higher than at the starting point. The intensity of the load on the cardiac system produced by completion of this course was estimated to be almost the same as that of a full marathon on a flat course. The time depended on both the youth of the cyclist and on his ability to maintain a high value of %HRmax during the race.

The effects of prolonged exposure to cold on hypoxic pulmonary hypertension in rats

Pulmonary artery hypertension is a common occurrence in mammals exposed to high altitude, yet little is known about the response of cold-acclimated animals. To study this problem pulmonary arterial pressure (Ppa), systemic blood pressure (Psa) and the ratio of Ppa/Psa in cold-acclimated rats (CA, 8 weeks, 6°C, n = 11) during exposure to low oxygen (10% O 2 ) were measured by direct catheter methods and compared with those of controls raised at 22°C (C, n = 10). There was no difference between CA and C in values of Ppa at a normal oxygen level (20.9% O 2 ). When rats were exposed to 10% O 2 Ppa increased significantly in C, while the increase in CA was not significant. The weights of the total ventricle (TV), right ventricle (RV) and left ventricle (LV) in the CA animals were increased significantly above the C values. The ratio of RV weight (RVW) to LV weight (LVW), however, was higher in C than in CA. During exposure to low oxygen, Psa did not change between the two groups. The ratio of Ppa/Psa was increased significantly in both groups when exposed to hypoxia. There were no significant differences in hematological measurements, including hematocrit (Ht), blood viscosity (CP) and red blood cells (RBC) between the CA and the C. It was concluded that the animals exposed to cold over a long period had no right ventricular hypertrophy (RVH) and the response to hypoxia in Ppa was lower in CA than that in C. The depression in hypoxic pulmonary vasoconstriction in CA may be caused by the decrease of RVW/LVW.

Abnormal Breathing Pattern and Oxygen Desaturation during Sleep at High Altitude

It is well known that healthy low-altitude residents often develop abnormal breathing pattern and oxygen desaturation during sleep at high altitude, although few studies of sleep during long-term sojourn at high altitude have been conducted. The purpose of this study was to investigate changes in breathing pattan and oxygen desaturation during sleep at high altitude, and their relation to pattern of ascent and descent, as well as to the acclimatization process in low-altitude residents.

Morphological differences in hearts of rats well adapted and poorly adapted to chronic hypoxia.

We carried out an experiment to analyze morphological differences in hearts of rats well adapted and poorly adapted to chronic hypoxia. Male and female Wistar rats, 1 week, 4 weeks and 9 weeks old, were employed on the assumption that adaptive ability was dependent on age and sex. These rats were raised at an altitude of 2,400 m and were kept for 7 to 9 weeks. Control groups were maintained at an altitude of 600 m during the same period of time. Each group consisted of 4 to 6 rats. At the end of the experiment, body weight, heart weight, ratio of heart weight to body weight and hematocrit were measured, and ventricular wall thickness, myocardial fiber diameter, capillary supply and mitochondria were morphometrically studied. Of the 6 experimental groups, the 4‐week‐old male rats (M2) had the highest body weight, as compared with the other experimental groups. In addition, relative to these other experimental groups, the following features were found for M2. Heart weight was intermediate, heart weight/body weight ratio was low and hematocrit was also low. Ventricular wall thickness was intermediate in the right ventricle (RV) and interventricular septum (IVS) but was thin in the left ventricle (LV). Myocardial fiber diameter was intermediate in the RV, large in the IVS and small in the LV. Capillary supply was intermediate in the RV and dense in the IVS and LV. Mitochondria were small but cristal density and percentage area, estimated from electron micrographs, were found to be high. These data showed that in well developed rats under chronic hypoxia, there is good development of capillary supply with corresponding restriction of cardiac hypertrophy, while hematocrit count and mitochondria are also affected.