Measurement
TPR is represented mathematically by the formula R = ΔP/Q.
- R is TPR.
- ΔP is the change in pressure across the systemic circulation from its beginning to its end.
- Q is the flow through the vasculature (equal to cardiac output)
In other words:
- Total Peripheral Resistance = (Mean Arterial Pressure - Mean Venous Pressure) / Cardiac Output
The numerator can be seen as representing the change in pressure that occurred immediately after having left the heart (i.e., mean arterial pressure) to when it finally returned to the heart via the IVC to the right atrium (i.e., mean venous pressure).
Mean Arterial Pressure (MAP) is calculated from the values of systolic and diastolic pressure, but it is not an average of the two. Diastole lasts almost twice as long as systole does therefore MAP is closer to the diastolic blood pressure value. MAP is calculated from the following formula: MAP = diastolic + (systolic - diastolic) / 3. Another way, and perhaps easier way, to write this is MAP = diastolic + systolic.
Mean Venous Pressure is measured at the right atrium and is usually very low (normally around 4mm Hg). As a result, it is sometimes disregarded. A synonymous term is central venous pressure.
Read more about this topic: Total Peripheral Resistance
Famous quotes containing the word measurement:
“That’s the great danger of sectarian opinions, they always accept the formulas of past events as useful for the measurement of future events and they never are, if you have high standards of accuracy.”
—John Dos Passos (1896–1970)