Perfusion

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In physiology, perfusion is the process of nutritive delivery of arterial blood to a capillary bed in the biological tissue.

Tests of adequate perfusion are a part of patient triage performed by medical or emergency personnel in a mass casualty incident.

Contents 1 Calculation 2 Overperfusion and underperfusion 3 Measurement using fMRI 4 See also 5 References 6 External links

[edit] Calculation

Perfusion ("F") can be measured with the following formula, where Pa is mean arterial pressure, Pv is mean venous pressure, and R is vascular resistance: ^[1]

The term "Pa - Pv" is sometimes presented as "ΔP", for the change in pressure.^[2]

The terms "perfusion" and "perfusion pressure" are sometimes used interchangably, but the equation should make clear that resistance can have an effect on the perfusion, but not on the perfusion pressure.

[edit] Overperfusion and underperfusion

The terms "overperfusion" and "underperfusion" are measured relative to the average level of perfusion across all tissues in an individual body, and the terms should not be confused with hypoperfusion and "hyperperfusion", which measure the perfusion level to the tissue's current need.

Tissues like the skin are considered overperfused, which means that they receive more blood than would be expected to meet the metabolic needs of the tissue. In the case of the skin, that is because the blood plays another important role apart from delivering oxygen - that of regulating temperature, or thermoregulation. When the body needs to reduce its temperature, it will deliver more blood to the skin, so that more of the heat carried by the blood dissipates into the surroundings.

[edit] Measurement using fMRI

Two main categories of functional magnetic resonance imaging (fMRI) techniques can be used to measure tissue perfusion in vivo.

• The first is based on the use of injected contrast agent that changes the magnetic susceptibility of blood and thereby the MR signal which is repeatedly measured during bolus passage.
• The other category is based on arterial spin labeling (ASL), where arterial blood is magnetically tagged before it enters into the tissue of interest and the amount of labeling is measured and compared to a control recording obtained without spin labeling.

[edit] See also

• Reperfusion injury

[edit] References

1. ^ Richard E. Klabunde. Cardiovascular Physiology Concepts. Retrieved on 9/12/06.
2. ^ Physiology at MCG 7/7ch04/7ch04p26 - "Renal Perfusion Pressure and Vascular Resistance"

[edit] External links

• Perfusion Protocol (requires Adobe Acrobat Reader)