Pitfalls in the assessment of vascular resistance.
Vascular resistance (R) to flow is calculated as the ratio of perfusion pressure between two points (P1-P2) to flow rate (Q). In high-pressure circuits (e.g., systemic), it is justifiable to use arterial pressure (P1) to represent perfusion pressure. It is not permissible to calculate resistance without measuring Q unless a comparison is being made in the resistance of different segments of a vascular bed; Q being constant, R: (P1-P2). In a low-pressure circuit (lower vertebrates, pulmonary) it is imperative to measure P2 to quantify the perfusion pressure. In closed circuits with a vertical orientation the effect of gravity on both the arterial and the venous pressures must be considered. In such circuits the perfusion pressure is due to viscous resistance only, excluding the gravitational pressure between the two points.
Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, NE 68178-0224.
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Badeer
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Hicks
D000818:Animals; D001783:Blood Flow Velocity; D001794:Blood Pressure; D006112:Gravitation; D006801:Humans; D008322:Mammals; D014655:Vascular Resistance