Systemic blood pressure is expressed as the ratio of the systolic pressure (when
ID: 1977269 • Letter: S
Question
Systemic blood pressure is expressed as the ratio of the systolic pressure (when the heart first ejects blood into the arteries) to the diastolic pressure (when the heart is relaxed): systemic blood pressure = systolic pressure/diastolic pressure. Both pressures are measured at the level of the heart and are expressed in millimeters of mercury (or torr), although the units are not written. Normal systemic blood pressure is 120/80.Blood pressure is normally measured on the upper arm at the same height as the heart. Due to therapy for an injury, a patient's upper arm is extended 30.0 cm above his heart. In that position, what should be his systemic blood pressure reading, if he has normal blood pressure? The density of blood is 1060 kg/m^3.
Give your answer as a pair of values for systolic and diastolic pressure, separated with a comma.
Explanation / Answer
1) According to the reference: 1 torr = 133.322 Pa ; Pa = N/m^2 The minimum pressure is 80 torr = 80*133.322 = 1.067e4 Pa Since a cm^2 = 1e-4 m^2, the minimum force / cm^2: Fmin = 1.067e4 * 1e-4 = 1.067 (N) 2) Taking the ratio, the maximum force is: Fmax = (120/80)*Fmin = (3/2)*1.067 = 1.6 (N) 3) If the point of pressure measurement is raised by 30 cm above the normal point, each pressure measurement will be have a value of pressure reduced by: ?P = - g*density*height = 9.8 * 1060 * (30/100) = 9.8*106*3 = 3116 (Pa) = 3116/133.322 = 23.4 torr (This is deduced from the equation for hydrostatic equilibrium.) Ps' = 120 - 23 = 97 Pd' = 80 - 23 = 57 So the answer is: 97, 57
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