Design of near-optimal waveforms for chest and abdominal compression and decompression in CPR using computer-simulated evolution

Active decompression during automated head-up cardiopulmonary resuscitation

BACKGROUND

The combination of active compression-decompression cardiopulmonary resuscitation (ACD-CPR) with an impedance threshold device (ITD) and controlled head-up positioning (AHUP-CPR) is associated with improved outcomes compared with conventional CPR (C-CPR). This study focused on the role of active decompression (AD) during AHUP-CPR.

METHODS

Farm pigs (n = 10, ∼40 kg) were anesthetized, intubated and ventilated. Physiological parameters and right ventricular pressure-volume loops were recorded continuously. Ventricular fibrillation was induced and left untreated for 10 mins, followed by automated C-CPR (2 min), ACD + ITD CPR in the flat position (2 min), and then AHUP-CPR with 3 cm of lift above the neutral chest position. After 15 min of CPR, AD was discontinued and then restarted incrementally to 4 cm. Data were analyzed with a linear mixed-effects model, using random intercepts for individual pigs.

RESULTS

Upon cessation of AD during AHUP-CPR, decompression right atrial pressure (+59%) increased (p < 0.01), whereas multiple hemodynamic parameters positively associated with perfusion, including coronary (-25%) and cerebral perfusion pressures (-11%), end-tidal CO2 (-13%), stroke volume and cardiac output (-26%), decreased immediately and significantly with p < 0.05. Restoration of AD reduced right atrial pressure and increased positive perfusion parameters in an incremental manner. Only with ≥ 3 cm of AD were all hemodynamic parameters restored to ≥ 90% of pre-AD discontinuation levels.

CONCLUSION

Full chest wall lift, achieved with ≥ 3 cm of AD, was needed to maintain and optimize hemodynamics during AHUP-CPR in pigs. These findings should be considered when optimizing care with this new approach.

Metrics of impulsiveness of manual chest compressions for out-of-hospital cardiopulmonary resuscitation

Aim

Propose new metrics of impulsiveness of manual chest compressions (CCs) that account for shape and duration, separate the characteristics of the compressive part of the CC cycle from those of the recoil part, and are uncorrelated to CC depth and rate.

Methods

We conducted a retrospective analysis of adult out-of-hospital cardiac arrest monitor-defibrillator recordings having CPR data. Specifically, episodes of adult patients with ≥ 1000 compressions free of leaning were examined. CCs were obtained from the depth signal of the valid episodes, and we calculated the novel metrics: compression area index (CAI), recoil area index (RAI), compression impulsiveness index (CII) and recoil impulsiveness index (RII). Generalized linear mixed-effects models and Jonckheere-Terpstra trend analyses were employed to measure differences between populations and trends, and the absolute value of Pearson's correlation coefficient | r | was used to report dependence between variables. Statistics are reported as median and interquartile range.

Results

We analyzed 982,340 CCs corresponding to 453 episodes, for which we calculated their CAI, RAI and duty cycle (DC). We analyzed the metrics for various populations: age, sex, any ROSC achieved and disposition, and found that CAI was significantly different according to patient disposition and RAI relative to age and sex (p < 0.05 ). None of the metrics was correlated strongly to depth or rate (| r | values of 0.22 or smaller), and all of them varied for CC series corresponding to the same rescuer over the course of resuscitation (p trend < 0.05 ). However, we observed that the metrics are not balanced, in that for any value of DC, CAI and RAI span almost their entire ranges.

Conclusion

The proposed metrics correctly and completely describe manual CC waveforms, improve upon the DC, since they depend on the signal waveform, and provide additional information to current indicators of quality CPR, depth and rate. Furthermore, they allow to differentiate the compressive and recoil parts of the CC cycle, reflecting influence of the rescuer (via CAI or CII) and of the biomechanics of the patient's chest (via RAI or RII). Thus, they have the potential to contribute to better understanding CPR dynamics and, eventually, to enhanced quality of CPR practice as additional indicators of proper manual CC technique.

Hemodynamics, survival and neurological function with early versus delayed automated head-up CPR in a porcine model of prolonged cardiac arrest

AIM

To determine if controlled head and thorax elevation, active compression-decompression cardiopulmonary resuscitation (CPR), and an impedance threshold device combined, termed automated head-up positioning CPR (AHUP-CPR), should be initiated early, as a basic (BLS) intervention, or later, as an advanced (ALS) intervention, in a severe porcine model of cardiac arrest.

METHODS

Yorkshire pigs (n = 22) weighing ∼40 kg were anesthetized and ventilated. After 15 minutes of untreated ventricular fibrillation, pigs were randomized to AHUP-CPR for 25 minutes (BLS group) or conventional CPR for 10 minutes, followed by 15 minutes of AHUP-CPR (ALS group). Thereafter, epinephrine, amiodarone, and defibrillation were administered. Neurologic function, the primary endpoint, was assessed 24-hours later with a Neurological Deficit Score (NDS, 0 = normal and 260 = worst deficit score or death). Secondary outcomes included return of spontaneous circulation (ROSC), cumulative survival, hemodynamics and epinephrine responsivity. Data, expressed as mean ± standard deviation, were compared using Fisher's Exact, log-rank, Mann-Whitney U and unpaired t-tests.

RESULTS

ROSC was achieved in 10/11 pigs with early AHUP-CPR versus 6/11 with delayed AHUP-CPR (p = 0.14), and cumulative 24-hour survival was 45.5% versus 9.1%, respectively (p < 0.02). The NDS was 203 ± 80 with early AHUP-CPR versus 259 ± 3 with delayed AHUP-CPR (p = 0.035). ETCO2, rSO2, and responsiveness to epinephrine were significantly higher in the early versus delayed AHUP-CPR.

CONCLUSION

When delivered early rather than late, AHUP-CPR resulted in significantly increased hemodynamics, 24-hour survival, and improved neurological function in pigs after prolonged cardiac arrest. Based on these findings, AHUP-CPR should be considered a BLS intervention.

Evaluating current guidelines for cardiopulmonary resuscitation using an integrated computational model of the cardiopulmonary system

OBJECTIVE

We aimed to use a high-fidelity computational model that captures key interactions between the cardiovascular and pulmonary systems to investigate whether current CPR protocols could potentially be improved.

METHODS

We developed and validated the computational model against available human data. We used a global optimisation algorithm to find CPR protocol parameters that optimise the outputs associated with return of spontaneous circulation in a cohort of 10 virtual subjects.

RESULTS

Compared with current protocols, myocardial tissue oxygen volume was more than 5 times higher, and cerebral tissue oxygen volume was nearly doubled, during optimised CPR. While the optimal maximal sternal displacement (5.5 cm) and compression ratio (51%) found using our model agreed with the current American Heart Association guidelines, the optimal chest compression rate was lower (67 compressions min^-1). Similarly, the optimal ventilation strategy was more conservative than current guidelines, with an optimal minute ventilation of 1500 ml min^-1 and inspired fraction of oxygen of 80%. The end compression force was the parameter with the largest impact on CO, followed by PEEP, the compression ratio and the CC rate.

CONCLUSIONS

Our results indicate that current CPR protocols could potentially be improved. Excessive ventilation could be detrimental to organ oxygenation during CPR, due to the negative haemodynamic effect of increased pulmonary vascular resistance. Particular attention should be given to the chest compression force to achieve satisfactory CO. Future clinical trials aimed at developing improved CPR protocols should explicitly consider interactions between chest compression and ventilation parameters.

Identification of an optimal CPR chest compression protocol

In this study, we used a high-fidelity integrated computational model of the respiratory and cardiovascular systems to investigate cardiopulmonary resuscitation (CPR) after cardiac arrest in a virtual healthy subject. For the purpose of this work, a newly developed thoracic model has been integrated to the current model, to study the influence of external chest compressions upon the arrested circulation during CPR. We evaluated the chest compression (CC) parameters, namely, end compression force, compression rate, and duty cycle to optimize the coronary perfusion pressure and the systolic blood pressure, using a genetic algorithm. While the sternal displacement associated with the CC force agreed with the ERC guidelines, the CC rate and duty cycle were respectively higher and lower than the ones recommended by the ERC guidelines. The effect of these CC parameters on cardiac output (CO) were also assessed. The end compression force was the parameter with the largest impact on CO, while the compression rate and duty cycle scarcely influence it.Relevance- Our results may aid in understanding the underlying pathophysiology of cardiac arrest and help guide research into the refinement of CPR strategies, without sacrificing animals or conducting clinical trials, which are difficult to undertake in crisis scenarios.

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.

Alternating fast and slow chest compression rates during CPR improved hemodynamics

INTRODUCTION

Mechanical chest compression devices allow for variation in chest compression (CCs) characteristics from moment to moment, enabling therapy that is not feasible for manual CCs. Effects of varying compressions over time have not been studied. In a randomized trial in an experimental model of prolonged cardiac arrest, we compared time-varying CPR (TVCPR), alternating between 100 and 200 compressions per minute (cpm) every 6 s, to guidelines CPR (Control).

METHODS

Ventricular fibrillation (VF) was electrically induced in 20 anesthetized pigs (28.4-45.8 kg). Following 10 min of untreated VF, cardiopulmonary resuscitation (CPR) began, randomized to TVCPR or Control. Rate of return of spontaneous circulation (ROSC), 4-h survival, and hemodynamics during the first 5 min of CPR were compared between groups. Moment-to-moment hemodynamic effects of changing the CC rate were analyzed.

RESULTS

TVCPR improved the proportion of ROSC over time compared to Control (p < 0.05) but ROSC (9/10 vs. 5/10) and 4-h survival (8/10 vs 5/10) did not differ significantly between groups. During CPR, coronary and cerebral perfusion pressures and femoral artery pressure did not differ between groups; however, end-tidal CO2 and mixed venous O2 saturation were higher, and pulmonary artery pressure was lower (p < 0.05) for TVCPR than Control. During TVCPR, switching to 100 cpm increased coronary perfusion pressure (p < 0.05), and switching to 200 cpm increased cerebral perfusion pressure (p < 0.05).

CONCLUSIONS

Time-varying CPR significantly improved indicators of net forward blood flow and proportion of ROSC over time without negatively impacting perfusion pressures. Alternating CC rate alternates between perfusion pressures favoring the brain and those favoring the heart. Time-varying CPR represents a new avenue of research for optimizing CPR.

INSTITUTIONAL PROTOCOL NUMBER

University of Alabama at Birmingham Institutional Animal Care and Use Committee (IACUC) Protocol Number 140406860.

Effect of compression waveform and resuscitation duration on blood flow and pressure in swine: One waveform does not optimally serve

BACKGROUND

Chest compression (CC) research primarily focuses on finding the 'optimum' compression waveform using a variety of compression efficacy metrics. Blood flow is rarely measured systematically with high fidelity. Using a programmable mechanical chest compression device, we studied the effect of inter-compression pauses in a swine model of cardiac arrest, testing the hypothesis that a single 'optimal' CC waveform exists based on measurements of resulting blood flow.

METHODS

Hemodynamics were studied in 9 domestic swine (∼30 kg) using multiple flow probes and standard physiological monitoring. After 10 min of ventricular fibrillation, five mechanical chest compression waveforms (5.1 cm, varying inter-compression pauses) were delivered for 2 min each in a semi-random pattern, totaling 50 compression minutes. Linear Mixed Models were used to estimate the effect of compression waveform on hemodynamics.

RESULTS

Blood flow and pressure decayed significantly with time in both arteries and veins. No waveform maximized blood flow in all vessels simultaneously and the waveform generating maximal blood flow in a specific vessel changed over time in all vessels. A flow mismatch between paired arteries and veins, e.g. abdominal aorta and inferior vena cava, also developed over time. The waveform with the slowest rate and shortest duty cycle had the smallest mismatch between flows after about 30 min of CPR.

CONCLUSIONS

This data challenges the concept of a single optimal CC waveform. Time dependent physiological response to compressions and no single compression waveform optimizing flow in all vessels indicate that current descriptions of CPR don't reflect patient physiology.

Corpuls cpr resuscitation device generates superior emulated flows and pressures than LUCAS II in a mechanical thorax model

The provision of sufficient chest compression is among the most important factors influencing patient survival during cardiopulmonary resuscitation (CPR). One approach to optimize the quality of chest compressions is to use mechanical-resuscitation devices. The aim of this study was to compare a new device for chest compression (corpuls cpr) with an established device (LUCAS II). We used a mechanical thorax model consisting of a chest with variable stiffness and an integrated heart chamber which generated blood flow dependent on the compression depth and waveform. The method of blood-flow generation could be changed between direct cardiac-compression mode and thoracic-pump mode. Different chest-stiffness settings and compression modes were tested to generate various blood-flow profiles. Additionally, an endurance test at high stiffness was performed to measure overall performance and compression consistency. Both resuscitation machines were able to compress the model thorax with a frequency of 100/min and a depth of 5 cm, independent of the chosen chest stiffness. Both devices passed the endurance test without difficulty. The corpuls cpr device was able to generate about 10-40% more blood flow than the LUCAS II device, depending on the model settings. In most scenarios, the corpuls cpr device also generated a higher blood pressure than the LUCAS II. The peak compression forces during CPR were about 30% higher using the corpuls cpr device than with the LUCAS II. In this study, the corpuls cpr device had improved blood flow and pressure outcomes than the LUCAS II device. Further examination in an animal model is required to prove the findings of this preliminary study.

Computational simulation of passive leg-raising effects on hemodynamics during cardiopulmonary resuscitation

BACKGROUND AND OBJECTIVE

The passive leg-raising (PLR) maneuver has been used for patients with circulatory failure to improve hemodynamic responsiveness by increasing cardiac output, which should also be beneficial and may exert synergetic effects during cardiopulmonary resuscitation (CPR). However, the impact of the PLR maneuver on CPR remains unclear due to difficulties in monitoring cardiac output in real-time during CPR and a lack of clinical evidence.

METHODS

We developed a computational model that couples hemodynamic behavior during standard CPR and the PLR maneuver, and simulated the model by applying different angles of leg raising from 0° to 90° and compression rates from 80/min to 160/min.

RESULTS

The simulation results showed that the PLR maneuver during CPR significantly improves cardiac output (CO), systemic perfusion pressure (SPP) and coronary perfusion pressure (CPP) by ∼40-65% particularly under the recommended range of compression rates between 100/min and 120/min with 45° of leg raise, compared to standard CPR. However, such effects start to wane with further leg lifts, indicating the existence of an optimal angle of leg raise for each person to achieve the best hemodynamic responses.

CONCLUSIONS

We developed a CPR-PLR model and demonstrated the effects of PLR on hemodynamics by investigating changes in CO, SPP, and CPP under different compression rates and angles of leg raising. Our computational model will facilitate study of PLR effects during CPR and the development of an advanced model combined with circulatory disorders, which will be a valuable asset for further studies.

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.

A mechanical chest compressor closed-loop controller with an effective trade-off between blood flow improvement and ribs fracture reduction

Chest compression (CC) is a significant emergency medical procedure for maintaining circulation during cardiac arrest. Although CC produces the necessary blood flow for patients with heart arrest, improperly deep CC will contribute significantly to the risk of chest injury. In this paper, an optimal CC closed-loop controller for a mechanical chest compressor (OCC-MCC) was developed to provide an effective trade-off between the benefit of improved blood perfusion and the risk of ribs fracture. The trade-off performance of the OCC-MCC during real automatic mechanical CCs was evaluated by comparing the OCC-MCC and the traditional mechanical CC method (TMCM) with a human circulation hardware model based on hardware simulations. A benefit factor (BF), risk factor (RF) and benefit versus risk index (BRI) were introduced in this paper for the comprehensive evaluation of risk and benefit. The OCC-MCC was developed using the LabVIEW control platform and the mechanical chest compressor (MCC) controller. PID control is also employed by MCC for effective compression depth regulation. In addition, the physiological parameters model for MCC was built based on a digital signal processor for hardware simulations. A comparison between the OCC-MCC and TMCM was then performed based on the simulation test platform which is composed of the MCC, LabVIEW control platform, physiological parameters model for MCC and the manikin. Compared with the TMCM, the OCC-MCC obtained a better trade-off and a higher BRI in seven out of a total of nine cases. With a higher mean value of cardiac output (1.35 L/min) and partial pressure of end-tidal CO2 (15.7 mmHg), the OCC-MCC obtained a larger blood flow and higher BF than TMCM (5.19 vs. 3.41) in six out of a total of nine cases. Although it is relatively difficult to maintain a stable CC depth when the chest is stiff, the OCC-MCC is still superior to the TMCM for performing safe and effective CC during CPR. The OCC-MCC is superior to the TMCM in performing safe and effective CC during CPR and can be incorporated into the current version of mechanical CC devices for high quality CPR, in both in-hospital and out-of-hospital CPR settings.

Virtual arterial blood pressure feedback improves chest compression quality during simulated resuscitation

INTRODUCTION

Quality chest compressions (CC) are the most important factor in successful cardiopulmonary resuscitation. Adjustment of CC based upon an invasive arterial blood pressure (ABP) display would be theoretically beneficial. Additionally, having one compressor present for longer than a 2-min cycle with an ABP display may allow for a learning process to further maximize CC. Accordingly, we tested the hypothesis that CC can be improved with a real-time display of invasively measured blood pressure and with an unchanged, physically fit compressor.

METHODS

A manikin was attached to an ABP display derived from a hemodynamic model responding to parameters of CC rate, depth, and compression-decompression ratio. The area under the blood pressure curve over time (AUC) was used for data analysis. Each participant (N=20) performed 4 CPR sessions: (1) No ABP display, exchange of compressor every 2 min; (2) ABP display, exchange of compressor every 2 min; (3) no ABP display, no exchange of the compressor; (4) ABP display, no exchange of the compressor. Data were analyzed by ANOVA. Significance was set at a p-value<0.05.

RESULTS

The average AUC for cycles without ABP display was 5201 mm Hgs (95% confidence interval (CI) of 4804-5597 mm Hgs), and for cycles with ABP display 6110 mm Hgs (95% CI of 5715-6507 mm Hgs) (p<0.0001). The average AUC increase with ABP display for each participant was 20.2±17.4% 95 CI (p<0.0001).

CONCLUSIONS

Our study confirms the hypothesis that a real-time display of simulated ABP during CPR that responds to participant performance improves achieved and sustained ABP. However, without any real-time visual feedback, even fit compressors demonstrated degradation of CC quality.

An optimal closed-loop control strategy for mechanical chest compression devices: a trade-off between the risk of chest injury and the benefit of enhanced blood flow

OBJECTIVES

The widespread application of chest compression (CC) as a first aid measure inevitably has the potential for both harm and benefit. The present study was therefore undertaken to design an optimal CC closed-loop control strategy (OCCCS) for mechanical CC devices that will present an effective trade-off between the risk of chest injury and the benefit of blood flow during CPR. Additionally, to evaluate the CC performance of the OCCCS, the differences between the OCCCS and the traditional mechanical CC method (TMCM) of performing standard CC were explored.

METHODS

Using the computer simulation technique, partial pressure of end-tidal CO₂ (PETCO2) and human chest stiffness are simulated based on the Babbs' model in present study. PETCO2 was regarded as a benefit factor (BF), which was divided into 3 levels, while chest stiffness was regarded as a risk factor (RF), which was divided into 4 levels. A benefit versus risk index (BRI) was also constructed for the comprehensive evaluation of risk and benefit. An OCCCS was developed with the combination of the BF, RF, BRI and fuzzy control strategy. A comparison between the OCCCS and TMCM was then performed based on computer simulations.

RESULTS

The OCCCS obtained a greater BRI and a better trade-off between risk and benefit than the TMCM in 6 out of a total 9 cases, and the OCCCS also resulted in a significantly improved cardiac output (CO) and PETCO2 in 6 of the 9 cases. The mean BRI, CO and PETCO2 resulting from the OCCCS were 5.69, 1.45 L/min and 15.51 mmHg, respectively, while the mean BRI, CO and PETCO2 resulting from TMCM were 4.76, 1.18 L/min and 13.26 mmHg, respectively.

CONCLUSIONS

The OCCCS can provide safer and more effective CC during cardiopulmonary resuscitation (CPR) compared to the TMCM, and has great potential in the future mechanical CC device development.

The impact of a step stool on cardiopulmonary resuscitation: a cross-over mannequin study

OBJECTIVE

Shallow chest compressions and incomplete recoil are common during cardiopulmonary resuscitation (CPR) and negatively affect outcomes. A step stool has the potential to alter these parameters when performing CPR in a bed but the impact has not been quantified.

METHODS

We conducted a cross-over design, simulated study of in-hospital cardiac arrest. Rescuers performed a total of four 2-min segments of uninterrupted chest compressions, half of which were on a step stool. Compression characteristics were measured using a CPR-sensing defibrillator and subjective impressions were obtained from rescuer surveys. Paired analyses were performed to measure the impact of the step stool, taking into account rescuer characteristics, including height.

RESULTS

Fifty subjects, of whom 36% were men, with a median height of 169.8 cm (range 148.6-190.5) volunteered to participate. Use of a step stool resulted in an average increase in compression depth of 4 mm (p<0.001) and 18% increase in incomplete recoil (p<0.001). However, unlike with incomplete recoil, the effect was more pronounced in rescuers in the lowest height tertile (9±9 mm vs 2±6 mm for those rescuers taller than 167 cm, p=0.006).

CONCLUSIONS

Using a step stool when performing CPR in a bed results in a trade-off between increased compression depth and increased incomplete recoil. Given the nonlinear relationship between the increase in compression depth and rescuer height, the benefit of a step stool may outweigh the risks of incomplete release for rescuers ≤167 cm in height. The benefit is less clear in taller rescuers.

Computational models for the study of heart-lung interactions in mammals

The operation and regulation of the lungs and the heart are closely related. This is evident when examining the anatomy within the thorax cavity, in the brainstem and in the aortic and carotid arteries where chemoreceptors and baroreceptors, which provide feedback affecting the regulation of both organs, are concentrated. This is also evident in phenomena such as respiratory sinus arrhythmia where the heart rate increases during inspiration and decreases during expiration, in other types of synchronization between the heart and the lungs known as cardioventilatory coupling and in the association between heart failure and sleep apnea where breathing is interrupted periodically by periods of no-breathing. The full implication and physiological significance of the cardiorespiratory coupling under normal, pathological, or extreme physiological conditions are still unknown and are subject to ongoing investigation both experimentally and theoretically using mathematical models. This article reviews mathematical models that take heart-lung interactions into account. The main ideas behind low dimensional, phenomenological models for the study of the heart-lung synchronization and sleep apnea are described first. Higher dimensions, physiology-based models are described next. These models can vary widely in detail and scope and are characterized by the way the heart-lung interaction is taken into account: via gas exchange, via the central nervous system, via the mechanical interactions, and via time delays. The article emphasizes the need for the integration of the different sources of heart-lung coupling as well as the different mathematical approaches.

Uniform reporting of measured quality of cardiopulmonary resuscitation (CPR)

BACKGROUND

CPR quality is an important determinant of cardiac arrest outcome. Recent investigations have demonstrated that quality of clinical CPR is variable and often not in compliance with international consensus guidelines. The 2005 update of these guidelines included new recommendations for the measurement of resuscitation and CPR performance and the institution of measures to improve resuscitation care. Common definitions and reporting templates need to be established for the variables of CPR quality. This will allow for meaningful comparisons between treatment groups in clinical trials as well as a common system for quality improvement and documentation of this improvement.

METHODS/RESULTS

In this report, we present the results from an international consensus working group to propose common definitions and criteria for reporting variables of CPR quality, based on the best available data for the importance of various CPR variables. The recommendations are discussed in light of the different purposes outlined above.