Chapter 3
Pressure measurement
Viet Dung Nguyen
Department of Electronic Technology and Biomedical Engineering, Hanoi University of Science and Tech
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3.1. OBJECT QUANTITIES
3.1.1. Unit of Pressure
- Force exerted per unit area (Pa, N/m2)
- Physiological pressures: millimeters of mercury (mmHg) or
centimeters of water (cmH2O)
1 cmH2O = 98,0665 Pa = 0,098066 kPa
1 mmHg = 133,322 Pa = 0,133322 kPa
Normally measured and expressed relative to the atmospheric pressure
(differential or direct measurement)
Direct measurement: need proper correction by means of the actual
atmospheric pressure
- Atmospheric pressure: atm, bar, kgf/cm2, Torr
1 atm = 101.325 kPa
1 bar = 105 Pa
1 kgf/cm2=98.0665 kPa
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3.1.2. Requirements for Pressure Measurement
- Pressures in the human body are measured as a part of clinical
examinations and for physiological studies
- Be measured in fluid-fill places like cavities, conduits or spaces…
Ranges of pressures in the body cavities in physiological
(thick lines) and unphysiological conditions (thin lines)
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- Arterial blood pressure is routinely measured and accepted as an
index of circulatory condition.
+ Systolic pressure (SP): reflects mechanical activity of the heart
ventricle
+ Diastolic pressure (DP) reflects movement of blood from the aorta
to the peripheral vascular system
+ Arterial pulse pressure, or the difference between SP and DP:
relaté to the characteristics of the heart and the arterial system
+ Mean arterial pressure: average arterial pressure during the cardiac
cycle. Usually used when considering characteristics of the
cardiovascular system as a whole
Ex: MAP/(Cardiac Output): approximation of peripheral of blood
flow resistance
Estimation: MAP= (2*DP + SP)/3
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-Left ventricular pressure: reflects pumping action of the ventricle
+ in normal heart, is below 1 kPa (8 mmHg)
+ dp/dt at ascending part: indicates force developed at the initiation
of a contraction and has been used for assessing the cardiovascular
function
- Right ventricular and pulmonary arterial pressures: generated by the
contraction of the right ventricle.
+ Lower than systemic arterial pressure since the resistance of the
pulmonary circulation is about 1/4 that of the systemic circulation
+ Exceptionally high pulmonary arterial pressure in patients with
severe pulmonary disease due to pulmonary arterial stenosis or a
ventricular septal defect →need cardiac catheterization pressure
measurements