Mechanisms of Central Hemodynamic Changes Due to Limb Tourniquets and Cuffs: Mathematical Modeling Studies with Implications for Cardiopulmonary Resuscitation

Limb compression is proposed as a supplement to cardiopulmonary resuscitation (CPR) because it has the potential to increase central organ blood flow rates. This is significant because CPR only has a survival rate of 10-15%, and survival depends on the amount of blood flow generated during CPR. However, the underlying physiological mechanisms are not understood, thereby limiting optimal application of limb compression during CPR. Therefore, this study addressed the hypothesis that circuit pathway reduction, volume displacement, and wave reflection mechanisms contribute to higher central organ blood flow rates. Mathematical models were utilized because modeling is the only way to isolate physiological mechanisms.

This study utilized two validated mathematical models that were minimally altered to investigate limb compression during CPR. A lumped-parameter model addressed circuit pathway reduction and volume displacement while the other model isolated wave reflections.

Relative to standard CPR, the model simulating circuit pathway reduction via CPR with tourniquets predicted increases of cerebral and coronary flow rates by 3% each while the model simulating volume displacement via CPR with constant pressure cuffs predicted increased cerebral and coronary flow rates by up to 74% and 109%, respectively. Furthermore, the wave reflection model predicted increases in blood flow rates of major cerebral arteries up to 11% and across all major abdominal arteries up to 27%.

All limb compression configurations and modalities resulted in increased predicted central organ blood flow rates with volume displacement, wave reflection, and circuit pathway reduction mechanisms, in that order, being most influential.