P53: Zero Flow Pressure (Pinfinity) is Larger than Mean Circulatory Filling Pressure. A Systematic Review and Meta-Analysis

Background Zero flow pressure (P∞), the steady-state pressure following cardiac arrest or cessation of flow is often assumed to equal mean circulatory filling pressure (MCFP). [1] However, this assumes complete equilibration of circulatory pressures, which may not occur if there is a ‘critical closing pressure’ or ‘Waterfall’ in the circulation. We undertook a systematic review and meta-analysis to obtain robust estimates of P∞ and compared this with MCFP measured in the same studies. Methods A literature search was performed using PubMed and was limited to full articles in English using the search terms “mean circulatory filling pressure” OR “critical closing” OR “zero-flow”. Only data relating to measurements of pressure following cardiac arrest or cessation of blood flow were included. Other exclusions were: individual case-reports, pregnancy, non-adult animals, not mammalian, or any non-human models of disease. Meta-analysis was performed using a random effects model in Stata 15.1. Data are mean (95% confidence intervals). Results A total of 1082 unique publications were identified; 1062 were excluded during screening. The remaining 20 studies with P∞ data were used to perform a meta-analysis. These included data from dog, rat, pig and human; 8 of these articles also provided data on MCFP. From this analysis P∞ = 26.5(23.4, 29.5) mmHg (n = 20) and the difference between P∞ and MCFP was 15.1(12.0, 18.3) mmHg (n = 8). Conclusions P∞ and MCFP differ substantially, indicating non-equilibration of pressures in the circulation following cessation of flow at least in the short-term (seconds to minutes).