The Measurement of Arterial Blood Pressure

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23/09/13 Human Physiology prac questions.

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What is sphygmomanometry? The indirect measurement of blood pressure.
How would one measure blood pressure directly? By inserting a cannula attached to a diaphragm and transducer into the radial or dorsalis pedis arteries. The blood pulses against a column of fluid which in turn moves a diaphragm which signals a transducer.However, this is invasive.
Why does sphygmomanometry use the brachial artery? Sphygmomanometry uses the brachial artery because it branches directly off the aorta and can be measured at the level of the heart, so it is considered equal to aortic pressure.
What is the systolic pressure, and what does it sound like when measured using manual sphygmomanometry? The systolic pressure is the highest pressure produced when the ventricles contract. This is typically ~120 mmHg and heard as turbulent/noisy intermittent squirting of blood as the high pressure of the cuff is released. It reflects the amount of work the heart is being asked to perform with each beat to generate pressure.
What is the diastolic pressure and what does it sound like when measured using manual sphygmomanometry? The diastolic pressure is the lowest pressure produced when the ventricles fill. This is typically ~80 mmHg and it is a continuous, smooth (laminar) flow of blood only allowed when the cuff pressure is lower than diastolic pressure. It is heard as the pulse sounds disappearing – previously the cuff had been inflated above diastolic pressure and so the brachial artery was still closing and opening and creating pulse sounds as blood squirts through. This reflects the state of the blood vessels: both their stretchiness and how much resistance to blood flow there is (to maintain blood pressure).
What is auscultatory sphygmomanometry? It is a technique for measuring blood pressure which relies on the sounds emitted by the brachial artery when it is occluded between systolic pressure (the sounds will first appear at this pressure as the blood starts to be able to squirt through the occlusion) and when the occlusion is removed (the pulse sounds of the artery opening and closing with each ventricular systole will disappear as the cuff pressure is lower than the diastolic pressure so there will be no noise, just continuous blood flow). This can be done manually, with a stethoscope, or automatically with a device containing a microphone.
What is oscillometric sphygmomanometry? It is a technique for measuring blood pressure which relies on the vibrations emitted by the brachial artery as it opens and closes while occluded by the inflated cuff. The vibrations will start when cuff pressure is equal to systolic pressure, as blood begins to push through the occluded artery and force it open. It closes again during diastolic pressure as the cuff pressure is greater. The vibrations disappear when the cuff pressure is equal to the diastolic pressure, as the blood can flow continuously through the vessel, which is no longer occluded. This is the more common technique found in automatic blood pressure monitoring, in devices such as the Omron or Omega, which are used clinically.
What was the name of the manual cuff and stethoscope kit used to measure blood pressure? Aneroid.
In the class data, was there a difference between the manual and automated measurements of blood pressure? If so, offer an explanation. There was no difference between the manual and automated systolic measurements. However, there was a significant difference between the diastolic measurements in the manual and automated methods. This could have been as a result of hesitation in the manual method, if students were unsure whether the pulse sounds had stopped and waited for a further decrease in pressure.
According to the class data, was there a difference in male and female blood pressures? Using an unpaired T-test, it was established that there was a difference between male and female systolic and diastolic blood pressures. This physiological difference is likely a result of men generally being taller and composed of more muscle than women, and so requiring blood to be pumped further, and in larger volumes, in order to meet the oxygen demand of their tissues.
According to the class data there was no difference between male and female heart rates, when an unpaired T-test was performed. Why? Given that male blood pressure was found to be higher than female blood pressure, it is unlikely that a higher heart rate would be required to supply the greater amount of tissue, as the stroke volume appeared to be bigger according to the blood pressure. Further, the measurements were performed across a group of (mostly) age-matched, fit young people, so there was minimal variation in physiologies in either sex.
Roughly what pressure is venous pressure? ~0-6mmHg.
Why is venous blood pressure so much lower than arterial blood pressure? Because the pressure created in the ventricles is dissipated through the arterioles and venules (in the form of heat, caused by friction), and because the larger diameters of the veins offer little resistance to the blood flow.
How many times heavier is mercury than blood? 12.9x
How did you establish your venous pressure in this practical? We held our hands to our sides until the vessels on top of our hands bulged (venous blood had accumulated as a result of hydrostatic/gravitational forces being greater than the pressure returning blood to the heart). We then raised and lowered our arms slowly until we found the height at which our vessels became flat once more - the height which indicated venous pressure. It indicated venous pressure because, if we consider ourselves to be a column of blood, we just needed to convert the number of mm of blood to mmHg (multiply it by 12.9).
List some causes of high arterial and venous pressure. High intrathoracic pressure (for example as a result of a chest infection), arterial stenosis, hypervolaemia (either natural, as a result of high fluid consumption, or pathological, as a result of impaired kidney function), obstruction in the vessels, and heart failure.
Suggest some causes of low arterial/venous pressure. Hypovolaemia (as a result of dehydration, or impaired kidney function), or low intrathoracic pressure (perhaps as a result of acute airway obstruction).
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