Blood Pressure - Interlake School Division血压茵特拉根学校分部.pptVIP

Blood Pressure If blood is to reach the hands and feet, the brain, and every other part of the body, it must be pumped out of the heart under considerable pressure. Blood pressure – the force of blood against the walls of arteries. To reach all parts of the body, the heart pumps blood at high pressure. The highest pressure occurs in the aorta. As blood passes into smaller vessels and the distance from the heart increases, the pressure reduces. The pressure in any artery varies as a result of five major factors: The volume (amount) of blood. If an injured person has lost a lot of blood, the pressure drops because of the decrease in volume of blood. The heart rate. More pressure builds up as the heart pumps more blood out. Pressure falls as heart rate decreases (especially during rest/sleep). The size of the arteries. When arteries dilate, the volume of the vessels increases and the pressure falls. If the arteries constrict, pressure is built up because of the extra resistance to blood flow. The elasticity. Flexible and elastic arteries expand as a surge of blood is forced from the heart (and relax after surge passes). If they cannot stretch this way, they are hardened. The viscosity of the blood. Thickness of blood. Thick, sticky fluids flow less readily than thin, watery fluids. Measuring Blood Pressure Two different pressures are measured in a blood pressure reading: Systolic pressure – amount of pressure that the blood exerts on the walls of the arteries when the ventricles contract. Diastolic pressure is the amount of pressure that the blood exerts on the artery walls when the ventricles are relaxed. Blood pressure can be measured using a sphygmomanometer. An inflatable rubber cuff is wrapped around the upper arm. Air is pumped into the cuff. Cuff presses on arteries in the arm, until the blood flow through the arteries stops. A stethoscope is placed over one of the arteries in the elbow: Air is gradually released. At first no sound, but then a sharp