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何双基老人: 您好!您来信询问为何蹲下后突然站起会头晕。在地球上,物体被地心引力不断地向地球中心吸引,就会产生重量,若是乘宇宙飞船,用火箭将您以8千米每秒的速度射入太空,地心引力则等于零,您就失去重量,飘浮在飞船内,血液也悬在血管中。失去了重量,头足的血压相等,不管是人体倒立或直立,不会发生头晕,因为没有血压差。 人在地球上,从心脏泵出的血流撞击动脉血管壁所产生的压力称为血压。头部的血压比标准血压低100毫米汞柱(1毫米汞柱=0.1333千帕),足部血压比标准压高100毫米汞柱,这样的压差人已完全适应。若是下蹲过久,下蹲时的血液集中在下身,突然站立起来,血液在血管中会产生离心力,头部的血压更低,血液达不到脑部,或只有很少的血液达到大脑,产生低血压(大脑重量仅占体重的2％,而大脑血液占全身供血量的20％),尤其大脑皮层在人类发展史上是最新发育的,非常娇嫩,对氧的需要量最大,对缺氧耐受力最小,一两秒钟缺氧,就
He Shuangji elderly: Hello! You asked for a letter after asking why suddenly standing up after squatting will be dizzy. On Earth, objects are gravitationally attracted to the center of the Earth, will have a weight, if by spacecraft, with a rocket you will be at a speed of 8 km per second into the space, gravity is equal to zero, you Lost weight, floating in the spacecraft, blood is also suspended in the blood vessels. Lost weight, head and shoulders blood pressure is equal, whether the body upside down or upright, will not happen dizzy, because there is no blood pressure difference. People on Earth, the blood flow from the heart impacted the wall of the artery pressure is called blood pressure. The head pressure is 100 mmHg lower than the standard blood pressure (1 mmHg = 0.1333 kPa) and the blood pressure in the head is 100 mmHg higher than the standard pressure. If the squat too long, squat blood concentrated in the lower body, suddenly stood up, the blood in the blood vessels will have centrifugal force, the lower the blood pressure of the head, the blood reaches the brain, or only a small amount of blood to reach the brain, Produce low blood pressure (the brain weighs only 2% of body weight, while the blood of the brain accounts for 20% of the body’s blood supply), especially in the history of human development of the cerebral cortex is the latest development, very delicate, oxygen demand is greatest, Oxygen tolerance of the smallest, one or two seconds of hypoxia, on