co the ly luan 1 cach gian di la boi vi su sut giam ve do cao cua nhung dia dem ben trong cot song. Cac dia vung dem goi tat dia dem nay chiu 1 luc de nen lon boi can nang cua khung nguoi khi ban di chuyen hoac ngoi tai cho. Trong nhung khi ngu vao dem toi, ap luc nay giam bot tao thoi co cho cac dia vung dem goi tat dia dem tro lai trang thai buoc dau. Tuy vay do qua trinhthoat vi dia dem ma do cao dia vung dem bi giam, du rang cac doi thay chinh la khong dang ke.