# Physiological and clinical significance of mean circulatory and mean systemic filling pressure

## TL;DR

This paper explains the physiological role of mean circulatory and systemic filling pressures in blood circulation and their clinical relevance.

## Contribution

The paper clarifies the clinical significance of mean systemic filling pressure in relation to capillary drainage and edema risk.

## Key findings

- Mean systemic filling pressure (MSFP) drives blood back to the right heart and acts as a downstream pressure for capillary drainage.
- A high MSFP increases the risk of tissue edema due to elevated capillary drainage pressure.
- MSFP can be approximated by adding 3 to 6 mmHg to the right atrial pressure under normal hemodynamic conditions.

## Abstract

A pressure distends blood vessels even when the heart is not beating and there is no blood flow. This is called mean circulatory filling pressure (MCFP). We will first discuss why it is physiologically necessary to have this base pressure. Although all pressures in the vasculature are the same when there is no flow, blood volume distributes based on the compliance of the walls in each compartment. The compliance of systemic venous compartment is by far the largest and contain most of the blood volume. When flow starts, volume redistributes among the vascular regions based on the compliance and resistance draining them. Because of it dominates the total compliance, pressure in the systemic venous compartment changes very little; it is called mean systemic filling pressure (MSFP). Under normal hemodynamic conditions, differences between MCFP and MSFP are trivial because venous compliance is so large compared to all other vascular regions. When cardiac function is maximal, MCFP determines the maximum possible cardiac output. MSFP is significant for two reasons. It is the upstream pressure driving blood back to the right heart. Importantly, it also is the downstream pressure for systemic capillary drainage. Thus, a high MSFP increases the risk of tissue edema. From our review of the studies, the pressure difference from MSFP to the right atrium (RAP) is generally in the 3 to 6 mmHg range so that MSFP can be approximated by adding values in this range to properly measured RAP. Ideally, MSFP should be less than 10 mmHg to limit capillary drainage.