Blood Pressure Lab Write-up Part I:
Introduction
The ability to maintain normal blood pressure is crucial aspect of human life. Blood pressure refers to the pressure that blood puts on the arteries it flows through. This is dependent on many factors, including resistance to flow, cardiac output, and volume status of the individual. That flow is maintained ensures that the body receives blood that contains oxygen, nutrients, and many other important substances that are critical for survival. As resistance increases, the cardiac flow becomes more restricted. An example of this happening is when an individual has a plaque/cholesterol build-up in their arteries. To compensate for the decreased blood flow, there is an increased blood pressure. This is beneficial in acute settings, but longstanding high blood pressure can damage the arteries and heart muscle.
Blood flow does not only change in response to disease. Blood flow changes based on our body position as well. The blood is evenly distributed throughout our bodies because there is no gravitational forces acting on our vascular system. If someone is lying down and suddenly stands up, the venous blood quickly flows into our lower limbs due to gravity, causing a rapid decrease in blood flow to the heart. The normal body response to this is rapid activation of baroreceptors that increase the pressure to restore flow. Individuals with certain diseases may not have this response and may experience orthostatic hypotension – fainting with position change.
Due to its importance, blood pressure is routinely measured in the healthcare setting. It is measured using a sphygmomanometer and stethoscope. The sphygmomanometer device is wrapped around the patient’s upper arm and is inflated to put pressure on the brachial artery. The individual measuring the blood pressure places their stethoscope on the brachial artery and listens for Korotkoff sounds. These are sounds due to blood flowing through the brachial artery. The first, the systolic value, represents the pressure in the major arteries as blood is pumped out of the left ventricle. The diastolic pressure represents the pressure when the left ventricle is relaxed. Due to the importance of blood pressure, there are a range of normal values for individuals based on sex, age, and more.
Our experiment aims to assess how blood pressure changes in the sitting versus supine position. Based on the physiology explained above regarding blood flow and gravity, we hypothesize that blood pressure will be lower when the patient is supine versus sitting. This hypothesis will be tested using participants’ position as the independent variable, and the resultant blood pressure as the dependent variable.
Methods:
We will be conducting the experiment on our colleagues, the demographics for which can be found in the results. We will be using an automatic sphygmomanometer, a stethoscope, and mat or towel.
The participants will have the blood pressure cuff around their right arm in a seated position. The experimenter will press start and measure the blood pressure twice. The above sequence will be repeated on the same participant on the left arm. Following completion of both arms, the participant will lay down on the mat/towel for three minutes. The blood pressure cuff will then be attached to the right arm, and the machine will be started. The participant will get their left arm pressure read while supine following this.
The measurements will all be taken twice, and their values will be averaged. These averages will be used to calculate the mean arterial pressure (MAP).
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