Abstract Body: Background: Limb compression is commonly used in medicine to address many physiological and pathological conditions. Limb compression is also proposed as a supplement to cardiopulmonary resuscitation (CPR) because it has the potential to increase central organ blood flows. This is significant since 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 application of limb compression during CPR.
Hypothesis: Circuit pathway reduction and volume displacement are limb compression mechanisms that contribute to higher central organ blood flows during CPR.
Methods: This study utilized a modified but previously validated lumped-parameter mathematical model (Figure 1, Halperin et al., Annals of Biomedical Engineering 1987) that isolated the effects of circuit pathway reduction and volume displacement. Briefly, CPR was simulated by applying extramural pressure to the compartments of the thorax via a sine wave at 60 Hz with a duty cycle of 0.40 and a maximum of 100 mmHg. Circuit pathway reduction via tourniquets was simulated by increasing arterial and venous resistances (R17 and R19, respectively) of the limbs. Volume displacement via cuffs was modeled by applying constant (100 mmHg) or cyclic extramural pressure to the arterial and venous compartments (C17 and C18) of the limbs. Limb and chest compression waveforms were the same but 180° out-of-phase from one another. All models simulated 90 seconds of CPR, and flows were taken as the time-averaged flow throughout the last three cycles.
Results: Relative to standard CPR (Figure 2, orange), tourniquets (Figure 2, red) were predicted to increase cerebral and coronary flows by 3%. Simulations involving constantly inflated cuffs (Figure 2, blue) forecasted cerebral and coronary blood flow increases of 74 and 109%, respectively, as compared to standard CPR. Cyclic counterpulsation cuffs (Figure 2, black) were predicted to increase cerebral and coronary blood flows by 40 and 67%, respectively, relative to standard CPR. All limb compression modalities resulted in increased predicted abdominal blood flows and decreased cardiac outputs and venous returns, compared to standard CPR.
Conclusion: Limb compression during CPR, via circuit pathway reduction and volume displacement mechanisms, is predicted to contribute to higher central organ blood flows, which could increase survival.