Abdominal counter pressure in CPR: What about the lungs? An in silico study

Mathematical model of modified hybrid pump mechanism for cardiopulmonary resuscitation

BACKGROUND AND OBJECTIVE

The "Cardiac pump theory" and "Thoracic pump theory" are representative theories of cardiopulmonary resuscitation (CPR) mechanisms. Based on these theories, many studies on mathematical modeling have been performed to help understand hemodynamics during CPR. However, there are parts that do not yet properly reflect the physiology of CPR. Therefore, this study aims to develop a lumped parameter model of CPR that can more accurately reflect the current CPR physiology.

METHODS

By adding compartments of the superior and inferior vena cava of the thoracic cavity to the existing CPR model, and the "Hybrid pump" mechanism was applied to simulate CPR. To compare the hemodynamics of the conventional CPR model and the developed CPR model, various conditions, such as active compression-decompression CPR with an impedance threshold valve device (ACD-CPR+ITV), head-up-tilt (HUT), and head-down-tilt (HDT), were simulated. The coronary perfusion pressure (CPP) was compared by modulating the compression ratio of the atrium and ventricle with the thoracic pump factor.

RESULTS

The result for the comparison of coronary blood flow showed that the existing model is predominant in the compression phase, whereas the developed model is dominant in the relaxation phase. ACD-CPR + ITV results showed that the CPP decreased by 5 % in the existing model, and increased by about 46 % in the developed model, revealing a distinct hemodynamic difference between the two models. Likewise, as a result of comparing the hemodynamic differences of the two models according to the changes in tilt angle, the HUT showed similar trends, while the HDT showed slightly different results. The CPP varied accordingly with the ratio of the ventricular and atrial thoracic pump factor.

CONCLUSION

Comparison of the hemodynamics with the existing model by simulating various conditions showed that the developed CPR model reflects the CPR physiology better. The model suggests that the hemodynamics may vary depending on the ventricle and atrium compression ratio. This study may provide an important basis for helping understand various situations and patient-specific hemodynamic characteristics during CPR through in-depth research, such as patient-specific model and parameter optimization.

Computer-Based CPR Simulation Towards Validation of AHA/ERC Guidelines

As per the AHA 2015 and ERC 2015 guidelines for resuscitation, chest compression depth should be between 5 and 6 cm with a rate of 100-120 compressions per minute. Theoretical validation of these guidelines is still elusive. We developed a computer model of the cardiopulmonary resuscitation (CPR) system to validate these guidelines. A lumped element computer model of the cardiovascular system was developed to simulate cardiac arrest and CPR. Cardiac output was compared for a range of compression pressures and frequencies. It was observed from our investigation that there is an optimum compression pressure and rate. The maximum cardiac output occurred at 100 mmHg, which is approximately 5.7 cm, and in the range of 100 to 120 compressions per minute with an optimum value at 110 compressions per minute, validating the guidelines. Increasing the pressure or the depth of compression beyond the optimum, limits the blood flow by depleting the volume in the cardiac chambers and not allowing for an effective stroke volume. Similarly increasing the compression rate beyond the optimum degrades the ability of the chambers to pump blood. The results also bring out the importance of complete recoil of the chest after each compression with more than 400% increase in cardiac output from 90% recoil to 100% recoil. Our simulation predicts that the recommendation to compress harder and faster is not the best counsel as there is an optimum compression pressure and rate for high-quality CPR.

Development and validation of an improved mechanical thorax for simulating cardiopulmonary resuscitation with adjustable chest stiffness and simulated blood flow

Investigations of compressive frequency, duty cycle, or waveform during CPR are typically rooted in animal research or computer simulations. Our goal was to generate a mechanical model incorporating alternate stiffness settings and an integrated blood flow system, enabling defined, reproducible comparisons of CPR efficacy. Based on thoracic stiffness data measured in human cadavers, such a model was constructed using valve-controlled pneumatic pistons and an artificial heart. This model offers two realistic levels of chest elasticity, with a blood flow apparatus that reflects compressive depth and waveform changes. We conducted CPR at opposing levels of physiologic stiffness, using a LUCAS device, a motor-driven plunger, and a group of volunteers. In high-stiffness mode, blood flow generated by volunteers was significantly less after just 2min of CPR, whereas flow generated by LUCAS device was superior by comparison. Optimal blood flow was obtained via motor-driven plunger, with trapezoidal waveform.

Not Bad: Passive Leg Raising in Cardiopulmonary Resuscitation-A New Modeling Study

Aim: To evaluate, using a simulated haemodynamic circulation model, whether passive leg raising (PLR) is able to improve the effect during cardiopulmonary resuscitation (CPR); to expose the possible reasons why PLR works or not. Materials and Methods: We adapted a circulatory model for CPR with PLR. First we compared cardiac output (CO), coronary perfusion pressure (CPP), blood flow to heart (Q_heart), and blood flow to neck and brain (Q_head) of standard chest compression-only CPR with and without PLR; second we simulated the effects of PLR in different situations, by varying the thoracic pump factor (TPF) from 0 to 1; third we simulated the effects when the legs are lifted to the different heights. Finally, we compared our results with those obtained from a published clinical study. Results: According to the simulation model, (1) When TPF is in the interval (0,1), CPP, CO, Q_heart, and Q_head are improved with PLR, among them with half-thoracic/half-cardiac pump effect (TPF is 0.5), CPP, CO, Q_head, and Q_heart increase the most (by 14, 14, 15, and 17%). (2) When TPF is 1 (pure thoracic pump, with an emphysema or extremely thick thorax), PLR has almost no effect on CPP, CO, and Q_heart (-1, 2, and 0%), whereas Q_head is increased by 9%; (3) Regardless of whether there is a cardiac or thoracic pump effect, PLR is able to increase Q_head by 9-15%. (4) When the legs are lifted to 30° to the ground, the volume transferred from legs to upper body is 36% of the initial volume in legs; when the legs are lifted to 45°, the volume transferred is 43%; when the legs are lifted to 60°, the volume transferred is 47%; when the legs are lifted to 90°, the volume transferred is 50%. Conclusion: Generally PLR is able to achieve improved cerebral perfusion and coronary perfusion. In some extreme situations, it has no effect on cardiac output and coronary perfusion, but still improves cerebral perfusion. PLR could be a beneficial supplement to CPR, and it is not necessary to lift the legs too high above the ground.

Combination of chest compressions and interposed abdominal compressions in a swine model of ventricular fibrillation

PURPOSE

The aim of this study was to investigate the effects of the combination of chest compressions and interposed abdominal compressions (IAC-CPR) in a swine model of ventricular fibrillation (VF).

METHODS

Twenty healthy female Landrace-Large White pigs were the study subjects. At the end of the eighth minute of VF, animals in the control group (Group A) received chest compressions at a rate of 100/min, while animals in the experimental group received chest compressions and simultaneous interposed abdominal compressions (CC-IAC - Group B), both at a rate of 100/min. The primary end point of the experiment was return of spontaneous circulation (ROSC). Secondary outcomes were 48-h survival rate and 48-h neurologic outcome.

RESULTS

Six animals (60%) from Group A and 9 animals (90%) from Group B achieved ROSC (P=.121). There was a statistically significant difference in systolic aortic pressure, mean aortic pressure, right atrial pressures, and end-tidal carbon dioxide (ETCO2) between the two groups during the first cycle of CPR, while during the second cycle, diastolic aortic pressure was significantly higher in Group B. Coronary perfusion pressure (CPP) values in group B were significantly higher compared with those in Group A during the first and second cycle of CPR. Neurologic examination was statistically significantly better in Group B (75.00±10.00 vs. 90.00±10.00, P=.037).

CONCLUSION

ROSC did not differ statistically significant in the IAC-CPR compared to the CPR group only, while CPP was significantly higher in IAC-CPR-treated animals.

Interposed abdominal compression-cardiopulmonary resuscitation after cardiac surgery

OBJECTIVES

The management of cardiac arrest after cardiac surgery differs from the management of cardiac arrest under other circumstances. In other studies, interposed abdominal compression-cardiopulmonary resuscitation (IAC-CPR) resulted in a better outcome compared with conventional CPR. The aim of the present study was to determine the feasibility, safety and efficacy of IAC-CPR compared with conventional CPR in patients with cardiac arrest after cardiac surgery.

METHODS

Data on all cardiac surgical patients who suffered a sudden cardiac arrest during the first 24 h after surgery were collected prospectively. Cardiac arrest was defined as the cessation of cardiac mechanical activity with the absence of a palpable central pulse, apnoea and unresponsiveness, including ventricular fibrillation, asystole and pulseless electrical activity. Forty patients were randomized to either conventional CPR (n = 21) or IAC-CPR (n = 19). IAC-CPR was initially performed by compressing the abdomen midway between the xiphoid and the umbilicus during the relaxation phase of chest compression. If spontaneous circulation was not restored after 10-15 min, the surgical team would immediately proceed to resternotomy. The endpoints of the study were safety, return of spontaneous circulation (ROSC) >5 min, survival to hospital discharge and survival for 6 months.

RESULTS

With IAC-CPR, there were more patients in terms of ROSC, survival to hospital discharge, survival for 6 months and fewer CPR-related injuries compared with patients who underwent conventional CPR.

CONCLUSIONS

IAC-CPR is feasible and safe and may be advantageous in cases of cardiac arrest after cardiac surgery.

Is a palpable pulse always restored during cardiopulmonary resuscitation in a patient with a left ventricular assist device?

End-stage heart failure patients are being supported with continuous flow left ventricular assist devices (CF-LVAD) in increasing numbers. The severe physiologic and pharmacologic derangements associated with end-stage heart failure therapies predispose these patients to delirium. During a delirious episode, a patient may inadvertently disconnect CF-LVAD equipment, which may have dangerous consequences. Unfortunately, it is not yet routine to use readily available clinical monitoring tools to allow early detection of delirium in this high-risk population. The authors present a case of acute hyperactive delirium leading to pump power disconnection and cardiopulmonary arrest occurring 7 days after CF-LVAD implantation. The case highlights the need for delirium awareness in the cardiovascular intensive care unit and the unique challenges associated with resuscitation of CF-LVAD patients. The authors propose that cardiovascular intensive care unit patients undergo at least twice daily delirium monitoring and provide a novel resuscitation algorithm for patients who have CF-LVADs.

Mechano-regulation of the beating heart at the cellular level--mechanosensitive channels in normal and diseased heart

The heart as a contractile hollow organ finely tunes mechanical parameters such as stroke volume, stroke pressure and cardiac output according to filling volumes, filling pressures via intrinsic and neuronal routes. At the cellular level, cardiomyocytes in beating hearts are exposed to large mechanical stress during successive heart beats. Although the mechanisms of excitation-contraction coupling are well established in mammalian heart cells, the putative contribution of mechanosensitive channels to Ca²⁺ homeostasis, Ca²⁺ signaling and force generation has been primarily investigated in relation to heart disease states. For instance, transient receptor potential channels (TRPs) are up-regulated in animal models of congestive heart failure or hypertension models and seem to play a vital role in pathological Ca²⁺ overload to cardiomyocytes, thus aggravating the pathology of disease at the cellular level. Apart from that, the contribution of mechanosensitive channels (MsC) in the normal beating heart to the downstream force activation cascade has not been addressed. We present an overview of the current literature and concepts of mechanosensitive channel involvement in failing hearts and cardiomyopathies and novel data showing a likely contribution of Ca²⁺ influx via mechanosensitive channels in beating normal cardiomyocytes during systolic shortening.