EFFECTS OF AEROBIC EXERCISE ON THE CIRCADIAN RHYTHM OF HEART RATE AND BLOOD PRESSURE

Although the effects of aerobic exercise on resting heart rate, heart rate variability, and blood pressure have been investigated, there are scant data on the effects of aerobic exercise on the circadian rhythm of such cardiovascular parameters. In this study, we investigated the effects of aerobic exercise on the 24?h rhythm of heart rate and ambulatory blood pressure in the morning, when cardiovascular events are more common. Thirty-five healthy young subjects were randomized to control and aerobic exercise groups. Subjects in the latter group participated in their respective exercise program for two months, while those in the former group did not exercise. Twenty-four-hour electrocardiogram and ambulatory blood pressure monitoring data were obtained at baseline and at the end of the exercise intervention. The control group showed no changes, while the aerobic exercise group showed a significant decrease in heart rate (73.7?±?6.6?bpm to 69.5?±?5.1?bpm, p?<?0.005) and sympathetic activity such as LF/HF ratio (2.0?±?0.7 to 1.8?±?0.6, p?<?0.05) throughout the 24?h period, particularly in the daytime. The decrease in the heart rate was most prominent in the morning. However, heart rate and LF/HF ratio showed no statistical changes during the night. No significant changes were observed in blood pressure. These findings suggest aerobic exercise exerts beneficial effects on the circadian rhythm of heart rate, especially in the morning. (Author correspondence: hshio@kobe-u.ac.jp)     

THE ROLE OF GRAVITY IN THE EVOLUTION OF MAMMALIAN BLOOD PRESSURE

Understanding of the factors involved in determining the level of central arterial blood pressure in mammals has been clouded by inappropriate allometric analyses that fail to account for phylogenetic relationships among species, and require pressure to approach 0 as body size decreases. The present study analyses systolic, mean arterial, and diastolic blood pressure in 47 species of mammal with phylogenetically informed techniques applied to two‐parameter equations. It also sets nonlinear, three‐parameter equations to the data to remove the assumption of the two‐parameter power equation that the smallest animals must have negligible blood pressure. These analyses show that blood pressure increases with body size. Nonlinear analyses show that mean blood pressure increases from 93 mmHg in a 10 g mouse to 156 mmHg in a 4 tonne elephant. The scaling exponent of blood pressure is generally lower than, though not significantly different from, the exponent predicted on the basis of the expected scaling of the vertical distance between the head and the heart. This indicates that compensation for the vertical distance above the heart is not perfect and suggests that the pressure required to perfuse the capillaries at the top of the body may decrease in larger species.     

心肺功能运动试验用于急性高山病的评价

为了进一步探讨急性高山病(AMS)的生理学评价指标,先对15名男性健康青年在海拔2261及3417m处进行心肺功能运动试验.结果观察到低氧通气及心搏反应以及动脉血氧饱和度(Sao_2)变化出现较早且敏感。随后对90名男性进入海拔4520m及攀登5620m过程中发生AMS时进行症状学调查,并证实静息动脉血氧分压(Pao_2)和肺泡一动脉氧阶差(AaDO_2)大小与AMS严重程度关系密切。在运动负荷(Vo_(2submax))时,测定静息及运动时最大心率差值(HRD)、动脉二氧化碳分压差值(Paco_2D)及动脉血氧饱和度差值(Sao_2D),由此求得HRD/Sao_2D及Paco_2D/Sao_2D两项指标,分别反映低氧心搏及通气反应能力。对AMS的判别具有敏感性,与以症状学判别相比,总吻合率达92.2％。     

THE VAPOR PRESSURE OF DOG'S BLOOD AT BODY TEMPERATURE

The vapor pressures of dog''s blood and blood plasma were determined at 37.5° by the dynamic method and the osmotic pressures calculated from the experimental data. The vapor pressures calculated from experimentally determined freezing point data agreed, within the experimental error, with the values obtained from direct measurement. The vapor pressure lowering produced by the colloid constituents of the blood was also determined and found to be minimal compared to that of the other constituents.     

HOMEOSTATIC ADJUSTMENTS AFTER EXERCISE : I. ACID-BASE EQUILIBRIUM OF THE BLOOD

The rate at which displacement and recovery of the acid-base equilibrium of the blood occur in young adult males subjected to short periods of maximal exertion has been determined. Displacement of acid-base equilibrium produced by severe exercise is along the fixed acid path, similar to the path of displacement produced by ingestion of acidifying agents such as ammonium chloride. Maximum displacement of the acid-base equilibrium is not reached until 7 to 10 minutes after the cessation of exercise. By this time over 50 per cent of the displacement in oxygen consumption, respiratory volume, and blood pressure have disappeared. A much greater metabolic acidosis was produced by exercise than could be induced by the oral administration of ammonium chloride. Recovery from the metabolic acidosis produced by exercise was much more rapid (10 times) than was recovery from the acidosis produced by ammonium chloride. After exercise the pH, returned to normal values more rapidly than did the bicarbonate content of the serum.