Chest Stiffness Research Articles

Abstract 276: Characterization of Chest Dynamics During Out-of-Hospital Manual Cardiopulmonary Resuscitation

Introduction: Viscoelastic models are widely accepted in modern literature to explain the non-linear relationship between the force applied by the rescuer and the chest displacement that occurs during chest compressions (CCs). Various studies have shown that applying CCs for prolonged periods of time changes chest properties, but proposed models have mostly been tested under laboratory settings with few patients or during short CPR intervals. Aim: To retrospectively characterize the mechanical dynamics of the chest during manual CCs in pre-hospital cardiopulmonary resuscitation using a simple viscoelastic model. Methods: Force and acceleration signals were extracted from CPR monitors used during pre-hospital resuscitation efforts by TVF&R (OR, USA) on adult patients (≥ 18yo), from which individual CCs and series of CCs between pauses were identified. The model decomposes the measured force as the sum of an elastic term and a damped term, specifically F = k·x + d·v . We characterized each full cycle with a spring coefficient k (N/cm) to measure the stiffness of the chest; and with separated compression and recoil damping coefficients, d c and d r (N·s/cm), to measure its viscosity. Parameters were averaged for sets of 10 CCs. We characterized the variations of the model parameters within each series. We also assessed the chest recovery between consecutive series by comparing the values obtained at the end of each series with the beginning of the next series. Results: A total of 1,156,608 CCs from 615 patients were analysed. From these, 6,073 series of median (IQR) length 190 (119-222) CCs were selected. All parameters decreased within the series, with decreases of the median after 20 sets of 10 CCs of 9.8%, 7.1% and 11.1% for k , d c and d r , respectively (p trend < 0.05). When examining the first 5 series for all cases, k presented a mean recovery of 7%, d c of 5%, and d r of 5%. Conclusion: The proposed model allows the observation of a reduction in stiffness and viscosity of the chest within CC series. It further allows for evaluating the dynamics of the chest around pauses, showing recovery of its properties during the pause. Overall, the model reveals a gradual reduction in chest stiffness and viscosity during CPR.

Characterization of mechanical properties of adult chests during pre-hospital manual chest compressions through a simple viscoelastic model

AimThe purpose of this study was to develop a simple viscoelastic model to characterize the mechanical properties of chests during manual chest compressions in pre-hospital cardiopulmonary resuscitation (CPR). MethodsForce and acceleration signals were extracted from CPR monitors used during pre-hospital resuscitation attempts on adult patients. Individual chest compressions were identified and segmented from the chest displacement computed using the force and acceleration. Each compression-recoil cycle was characterized by its elastic coefficient k (a measure of stiffness) and its compression and recoil damping coefficients, dc and dr, respectively (measures of viscosity). We compared the estimated and the calculated chest displacement to assess the goodness of fit of the model. We characterized the chest of patients at the beginning of CPR in relation to sex and age, and their variation as CPR progressed. ResultsA total of 1,156,608 chest compressions from 615 patients were analysed. Mean (95% CI) coefficient of determination R2 for the viscoelastic model was 97.9% (97.8–98.1). At the beginning of CPR, k was 104.9 N⋅cm-1 (102.0–107.8), dc was 2.868 N⋅s⋅cm-1 (2.751–2.984) and dr was 4.889 N⋅s⋅cm-1 (4.648–5.129). Damping during recoil was significantly higher than during compression. Stiffness was lower in women than in men. There were no differences in damping coefficients with sex but a higher dr with increasing age. All model coefficients decreased with compression count, with an overall decrease after 3,000 chest compressions of 34.6%, 48.8% and 37.2%, respectively. ConclusionThe model accurately described adult chest mechanical properties during CPR, highlighting differences between compression and recoil, sex and age, and a progressive reduction in chest stiffness and viscosity along resuscitation. Our findings may merit further investigation into whether patient-tailored and time-sensitive chest compression technique may be appropriate.

AUTOMATIC BELT CARDIOPULMONARY RECISUTATION (CPR) DEVICE AND TEST SYSTEM DESIGN

The test system was created by adding flex and force sensors to this manikin to evaluate the results of heart massage applied on an artificial adult manikin, which has a spring that can give the chest stiffness of an adult human. This test system monitors and analyzes cardiopulmonary resuscitation (CPR) applications performed by the automated CPR device or manually by the person. The signals received from the sensor are transferred to the computer via the serial port with the Arduino Uno card and displayed in real-time in MATLAB graphical user interface (GUI). This GUI, designed with Matlab 2021a software, analyzes the sensor signals resulting from CPR. It gives a graph of the repeats of compression per minute, the depth of each compression, and the compressions rate variable performed by the user or the automatic CPR device during the CPR application. This created test system can evaluate the accuracy of both the automatic CPR device performed in this study and the manual CPR application. The test system designed in this respect can be used in the training and evaluation of cardiac massage applications, which is included in the first aid courses in secondary education, associate degree, undergraduate, and vocational education courses.

Chest compression release and recoil dynamics in prolonged manual cardiopulmonary resuscitation

Aim of the studyCharacterize release and recoil dynamics in chest compressions during prolonged cardiopulmonary resuscitation (CPR) efforts, which are increasingly prevalent. MethodsForce and depth of chest compressions, and their rates of change, were calculated from records extracted from CPR monitors used during prolonged resuscitation efforts for out-of-hospital cardiac arrest and tracked over time. Metrics were normalized to the median of the first 100 compressions.Kruskal-Wallis ANOVA and Jonckheere-Terpstra trend analyses were used for differences and trends. Averages are reported as median (interquartile range). Correlations among metrics are reported as coefficients of determination. ResultsIn 471 cases of adult subjects receiving at least 1000 compressions, peak depths varied modestly over the course of extended resuscitation efforts, staying within a narrow range without a trend over the course of resuscitation efforts. Increases in recoil velocity and decreases in recoil interval also remained within limited ranges (5%, 6% variation respectively). By contrast, force waveforms changed substantially. Peak force decreased monotonically reaching a 38% decrease for compression numbers > 3500, similar to a decrease in release rate (39%) and an increase in release interval (39%). ConclusionDepth waveforms change markedly less than do force waveforms over the course of prolonged CPR. With the benefit of feedback, CPR providers effectively adjust the application of force to compensate for changes in chest stiffness, documented previously. Despite slowing release and quickening recoil, interference between release of force and recoil of depth appears limited. Spontaneous chest recoil is well preserved in prolonged duration manual CPR.

Transcutaneous systemic photobiomodulation reduced lung inflammation in experimental model of asthma by altering the mast cell degranulation and interleukin 10 level.

Asthma is a chronic inflammatory disease characterized by recurrent and reversible episodes of wheezing, dyspnea, chest stiffness, and cough. Its treatment includes several drugs, high cost, and considerable side effects. Photobiomodulation (PBM) emerges as an alternative treatment, showing good results, and it can be applied locally or systemically. Here, we aim to evaluate the effect of transcutaneous systemic photobiomodulation (TSPBM) by red diode light. Therefore, adult rats were sensitized and challenged with ovalbumin (OVA) plus alum for induction of asthma and irradiated or not with TSPBM in the caudal vein (wavelength 660 ± 10nm; total radiant emission 15J; area 2.8 cm2; energy density 5.35J/cm2; irradiance 33.3 mW/cm2; exposure time 150s). Our investigations prioritized the cell migration into the alveolar space and lung, tracheal responsiveness, release and gene expression of cytokines, mast cell degranulation, and anaphylactic antibodies. Our results showed that TSPBM reduced the cell migration and mast cell degranulation without altering the tracheal responsiveness and ovalbumin antibody titers. Indeed, TSPBM increased the levels of interleukin 10 (IL-10) in the BAL fluid without altering the gene expression of cytokines in the lung tissue. Thus, this study showed that transcutaneous systemic irradiation reduced lung inflammation by altering mast cells degranulation and IL-10 level. Considering that this study is a pioneer in the used of light by the systemic route to treat asthma, the data are interesting and instigate future investigations, mainly in relation to the mechanisms involved and in dosimetry.

Chest stiffness dynamics in extended continuous compressions cardiopulmonary resuscitation

Aim of the studyTo characterize the effects of extended duration continuous compressions cardiopulmonary resuscitation (CPR) on chest stiffness, and its association with adherence to CPR guidelines. MethodsRecords of force and acceleration were extracted from CPR monitors used during attempts of resuscitation from out-of-hospital cardiac arrest. Cases of patients receiving at least 1000 compressions were selected for analysis to focus on extended CPR efforts. Stiffness was normalized per patient to their initial stiffness. Force remaining at the end of compression was used to identify complete release. Non-parametric statistical methods were used throughout as underlying distributions of all types of measurements were non-Gaussian. Averages are reported as median (interquartile range). ResultsMore than 1000 chest compressions were delivered in 471 of 703 cases. Rate of change in normalized stiffness (Sn) was unrelated to patient age, sex or initial ECG rhythm, and did not predict survival. Most (76%) chests became less stiff over the course of resuscitation efforts. While the remainder (24%) exhibited increased stiffness, overall Sn decreased monotonically, declining by 31% through 3500 compressions. Rate adherence did not show a consistent trend with Sn. Depth adherence and complete release improved modestly with decreasing Sn. ConclusionChest compressions during extended CPR reduced the stiffness of most patients’ chests, in the aggregate by 31% after 3500 compressions. This softening was associated with modestly improved adherence to depth and release guidelines, with inconsistent relation to rate adherence to guidelines.

Abstract 236: Complete Recoil Duration Declines Over the Course of Longer Resuscitations

Introduction: CPR guidelines call for chest compressions within rate and depth ranges and complete chest recoil. Guidelines development has relied on data from the first 10 minutes of resuscitations. We investigated the influence of rate, depth and chest stiffness on complete recoil duration in longer resuscitations. Hypothesis: Decreasing chest stiffness will contribute to reduced complete recoil duration over the course of long resuscitations. Methods: Acceleration and force signals were from monitors used in continuous compression CPR during out-of-hospital resuscitations of adults treated by Tualatin Valley Fire & Rescue (Tigard, OR) from 2013 through 2017. Complete recoil was defined as return to within 5 mm of baseline in the absence of leaning (release force > 2.5 kg-f), stiffness as peak force/peak depth. Influences of rate, depth and stiffness on complete recoil duration were modeled with linear mixed effects models with a random intercept and slope clustered by patient. Results: A total of 1,076,808 compressions without leaning (93% of compressions) were measured from 616 cases with 1888 ± 1118 compressions/case (mean ± std). Observed increases in rate (7%) and depth (2%) were modest, while stiffness declined markedly (-33%) (Fig 1a). All of these changes tend to reduce the duration of complete recoil (p < 0.001). Mean complete recoil duration decreased 21% (Fig 1a) from 160 ms to 126 ms (Fig 1b). Despite its large relative change, stiffness had little effect on complete recoil duration, as did depth. Increasing rate explained most of the decline in complete recoil duration (Fig 1b). Conclusions: Substantial decline in chest stiffness over the course of long resuscitations contributes to reduction of complete recoil duration but little compared to increasing rate. Careful compliance with rate guidelines is paramount in maintaining periods of complete recoil. Depth is relatively well-controlled. Chest molding (decreased stiffness) is of secondary importance.

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 5cm, 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.

Abstract 021: Most People Who Need to Perform CPR in Their Home Cannot

Objective: To determine by examining the physical characteristics of pairs of people who cohabitate whether each is physically capable of performing two-inch chest compression on the other. Methods: Name, gender, age, total body weight, and hands on scale weight (“HOSW”) data was collected from couples. HOSW is the reading on a scale when one is kneeling in front of the scale and pressing down with the hands as if performing CPR, until the knees barely leave the ground. One member of the cohort mechanically measured his chest stiffness. Chest stiffness for the cohort was calculated from a simplistic model where the measured subject’s relationship between chest stiffness and total body weight was assumed to prevail in all other test subjects. Doing so yielded an average chest stiffness of 128 pounds, as compared to the actual average adult chest stiffness of 130 pounds. A similar method was used with the heel of the foot. The result was FOSW, the force one could apply to a chest while performing Pedal Compression. A subject with an HOSW or FOSW equal to or greater than their partner’s chest stiffness was judged to be capable of performing guideline-compliant chest compression on the other using manual or pedal compression, respectively. The two outcome measures for each couple were: each’s physical ability to perform two-inch compression on the other, using manual and pedal compression. Results: At the time this abstract was submitted, data from twelve couples showed that slightly more than half the male subjects had sufficient HOSW to perform two-inch manual compression on their wife, and no wives had sufficient HOSW TO PERFORM a two-inch compression on their husband. In the 700 cardiac arrests in a private residence each day, two-thirds of the victims are male and will not receive two-inch compression. The results show the number of females and males that can apply enough force to their spouse’s chest to perform a two-inch compression with manual chest compression and pedal (heel) compression with FOSW at 95 and 90 percent of body weight. Zero of twelve females weighed enough to perform and seven of twelve males weighed enough to perform a two inch compression on their spouse using manual compression. One of twelve females and ten of twelve males weighed enough to perform a two inch compression on their spouse using pedal compression under the 95% of body weight equals FOSW model. Zero of twelve females and ten of twelve males weighed enough to perform a two inch compression on their spouse using pedal compression under the 90% of body weight equals FOSW model. Heel compression increases the likelihood of a male’s being able to perform a two inch compression significantly. Heel compression only improves a female’s likelihood of performing a two-inch compression using the 95% of body weight assumption.

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.

Application of an anatomically-detailed finite element thorax model to investigate pediatric cardiopulmonary resuscitation techniques on hard bed

ObjectivesImproved Cardiopulmonary Resuscitation (CPR) approaches will largely benefit the children in need. The constant peak displacement and constant peak force loading methods were analyzed on hard bed for pediatric CPR by an anatomically-detailed 10 year-old (YO) child thorax finite element (FE) model. The chest compression and rib injury risk were studied for children with various levels of thorax stiffness. MethodsWe created three thorax models with different chest stiffness. Simulated CPR׳s in the above two conditions were performed. Three different compression rates were considered under the constant peak displacement condition. The model-calculated deflections and forces were analyzed. The rib maximum principle strains (MPS׳s) were used to predict the potential risk of rib injury. ResultsUnder the constant peak force condition, the chest deflection ranged from 34.2 to 42.2mm. The highest rib MPS was 0.75%, predicted by the compliant thorax model. Under the normal constant peak displacement condition, the highest rib MPS was 0.52%, predicted by the compliant thorax model. The compression rate did not affect the highest rib MPS. ConclusionsResults revealed that the thoracic stiffness had great effects on the quality of CPR. To maintain CPR quality for various children, the constant peak displacement technique is recommended when the CPR is performed on the hard bed. Furthermore, the outcome of CPR in terms of rib strains and total work are not sensitive to the compression rate. The FE model-predicted high strains were in the ribs, which have been found to be vulnerable to CPR in the literature.

Abstract 82: Chest Stiffness and Force-Depth Relations Change Over Time During Prolonged CPR: An Animal Model

INTRODUCTION Chest deformation during CPR results in increased intrathoracic pressure and blood flow. A parameter linked to both deformation and internal pressures is reaction force. However, little is known about the time dependence of the force-depth relationship. In this study we assessed the hypothesis that chest stiffness and force-depth relations change during CPR in a pig model. MATERIAL AND METHODS Fourteen Yorkshire pigs with an average AP diameter of 20 cm were anesthetized after which ventricular fibrillation (VF) was induced. CPR was administered for 21 minutes at compression depths of 5 cm at frequencies of 80-120cpm during which absolute depth and force were measured continuously. The force-depth signal was divided into elastic and viscous components. Corrections were made for incomplete recoil. Chest stiffness was defined as the maximum force for each compression divided by its corresponding depth. Curvature and stiffness over time were studied. RESULTS The force versus depth relation shows that at the start of CPR the relationship is almost linear. As compressions continue, the curve becomes more curved. Chest stiffness starts at relatively high values of 118 +/- 28 N/cm which decreased to 96 +/- 19 N/cm of the original values after 250 compressions. After this point in time only minor changes in stiffness and nonlinearity were observed. CONCLUSION In conclusion, chest stiffness decreases and the force depth relation changes from linear to convex during CPR. Changes take mostly in the initial phase, where after they approach steady state. This is relevant for obtaining adequate blood flow during CPR.

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

ObjectivesThe 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. MethodsUsing 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. ResultsThe 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, 1.45L/min and 15.51mmHg, respectively, while the mean BRI, CO and PETCO2 resulting from TMCM were 4.76, 1.18L/min and 13.26mmHg, respectively. ConclusionsThe 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.

Expert clinical assessment of thorax stiffness of infants and children during chest compressions

Background High-fidelity manikins have been shown to be useful in teaching appropriate cardiopulmonary resuscitation (CPR) techniques. Similarity of manikin chest compression characteristics to real children is desirable. Little data exists on thorax stiffness in infants and children to guide manikin construction. Objective To determine a ‘consensus clinical-expert assessment’ of the pediatric chest stiffness for two specific age groups—infants and 5-year-olds. Methods Four manikins in each of two sizes (5-year child, 6-month infant) were identically constructed, except for thorax downstroke spring stiffness. Health care providers with pediatric CPR experience provided chest compressions to each manikin in random order, masked to thoracic stiffness. Each health care provider was instructed to identify the manikin with downstroke thoracic stiffness most similar to children on whom they have performed chest compressions. Duplicate assessment of a randomly selected, previously assessed manikin was performed to assess health care provider consistency using the kappa statistic. Subject inter-rater agreement on which manikin best approximated a child of that age was assessed by calculating the percentage of subjects who identified that manikin as the best approximation of an actual child. Results A convenience sample of 63 international experts was obtained: 52 from Critical Care, 3 from Emergency Medicine, 4 from Pediatrics, and 4 from other specialties. There were 6 and 8 experts whose assessments were inconsistent for the infant manikins and child manikins, respectively. Approximately half of the subjects agreed on a single manikin as the best approximation of the human for both the infant (46%) and child manikins (43%). Excluding assessments of stiffness “out of range”, the percentage of experts who agreed on a single manikin as the best approximation for the human increased to approximately 90% for each manikin size. Conclusion Experienced health care providers consistently identified and agreed on the manikin thorax stiffness which they felt best approximated downstroke chest compression stiffness of children and infants. Expert opinion can be used to create manikins with realistic spring stiffness for CPR training. Further study is needed to evaluate whether enhanced manikin biofidelity will improve CPR performance.

Comparison of mechanical characteristics of the human and porcine chest during cardiopulmonary resuscitation

Background Most studies investigating cardiopulmonary resuscitation (CPR) interventions or functionality of mechanical CPR devices have been performed using porcine models. The purpose of this study was to identify differences between mechanical characteristics of the human and porcine chest during CPR. Material and methods CPR data of 90 cardiac arrest patients was compared to data of 14 porcine from two animal studies. Chest stiffness k and viscosity μ were calculated from acceleration and pressure data recorded using a Laerdal Heartstart 4000SP defibrillator during CPR. K and μ were calculated at chest compression depths of 15, 30 and 50 mm for three different time periods. Results At a depth of 15 mm porcine chest stiffness was comparable to human chest stiffness at the beginning of resuscitation (4.8 vs. 4.5 N/mm) and clearly lower after 200 chest compressions (2.9 vs. 4.5 N/mm) ( p < 0.05). At 30 and 50 mm porcine chest stiffness was higher at the beginning and comparable to human chest stiffness after 200 chest compressions. After 200 chest compressions porcine chest viscosity was similar to human chest viscosity at 15 mm (108 vs. 110 Ns/m), higher for 30 mm (240 vs. 188 Ns/m) and clearly higher for 50 mm chest compression depth (672 vs. 339 Ns/m) ( p < 0.05). Conclusion In conclusion, human and porcine chest behave relatively similarly during CPR with respect to chest stiffness, but differences in chest viscosity at medium and deep chest compression depth should at least be kept in mind when extrapolating porcine results to humans.

Acute clinical benefits of chest wall-stretching exercise on expired tidal volume, dyspnea and chest expansion in a patient with chronic obstructive pulmonary disease: A single case study

Chest physical therapy (CPT) has an important role in a medical team to assist in resolving the critical problems deriving from chronic lung disease. These critical problems include increased secretion volume, difficult breathing or dyspnea, ineffective coughing, inability to be weaned off a ventilator, and physical deterioration resulting from low aerobic capacity and endurance after prolonged bed rest. The inability to be weaned off a ventilator does not only result from secretion production or muscle weakness, but other conditions including chest stiffness or immobility. The procedure to increase chest mobility includes specific chest stretching and mobilization. Chest wall-stretching exercises were composed of thoracic rotation and anterior compression with stretching in sitting position, trunk extension and rib torsion in supine lying, and lateral stretching in side lying. These exercises were given to the patient as a regular daily program along with postural drainage, percussion, breathing exercise and limb exercises. The expired tidal volume, dyspnea level, and chest expansion were evaluated and clinical efficiency was analyzed during CPT, compared to Pre-CPT and Post-CPT with Bloom table. The results showed a significant clinical improvement of expired tidal volume, reduction in dyspnea level, and increase in chest expansion.

Manikins With Human-Like Chest Properties—A New Tool for Chest Compression Research

Commercially available training manikins for cardiopulmonary resuscitation (CPR) do not accurately mimic the mechanical properties of human chests. This may limit the usefulness of CPR research performed on such manikins. This paper presents the construction of manikins with chest properties matching those measured in patients during an ongoing CPR. The chest stiffness and damping of 59 cardiac arrest patients was measured during out-of-hospital CPR, using a defibrillator with a compression sensor with built-in force sensor and accelerometer. A manikin with eight interchangeable chest force-depth profiles, representing the measured range of chest stiffness and the average damping of these patients, was then specified and constructed. The stiffness and damping of the manikins were verified using the same equipment and method as was used during data collection. Between 30 and 50 mm compression depth, the force-depth relationship of all eight manikins were found to be within +/-30 N of force or +/-2 mm of depth from the reference specifications derived from measurements on patients' chests. The average damping was also found to closely match the specified value.

Chest compressions by ambulance personnel on chests with variable stiffness: Abilities and attitudes

Quality of cardiopulmonary resuscitation (CPR) performed by professionals is reported to be substandard even with automated corrective feedback. We hypothesised that lack of quality is not due to physical capabilities. Eighty ambulance personnel from the same services where the quality of clinical CPR was investigated, performed two-rescuer CPR with similar corrective feedback for 5min on each of four manikins with different chest stiffness. The personnel also scored their agreement with statements on clinical CPR performance. All study subjects performed CPR well within Guidelines recommendations on all four manikins with mean compression depth 44+/-3mm, compression rate 101+/-3min(-1), and 7+/-2 ventilations per minute. Three quarters stated that during CPR on patients their personal sense of correct depth and force determined their performance. Fifty-five percent believed that too deep chest compressions could cause serious injury to the patient, and 39% that compressing to Guidelines recommended depth may often result in severe patient injury. A quarter felt that the potential benefits of compressing to the Guidelines depth could not justify the injuries it would cause. Breaking ribs made 54% feel very uncomfortable. Ambulance personnel were physically capable of consistently compressing to the Guidelines depth even on the stiffest chest. These laboratory results cannot be directly compared to the clinical out-of-hospital ALS situation, but strongly indicate that the inadequate chest compressions found in our clinical study were not due to lack of physical capability. We speculate that this may at least partly be explained by their fear of causing patient injury and trust in their own opinion of what is the correct compression depth and force in preference to the feedback.

Compression force–depth relationship during out-of-hospital cardiopulmonary resuscitation

Recent clinical studies reporting the high frequency of inadequate chest compression depth (<38 mm) during CPR, have prompted the question if adult human chest characteristics render it difficult to attain the recommended compression depth in certain patients. Using a specially designed monitor/defibrillator equipped with a sternal pad fitted with an accelerometer and a pressure sensor, compression force and depth was measured during CPR in 91 adult out-of-hospital cardiac arrest patients. There was a strong non-linear relationship between the force of compression and depth achieved. Mean applied force for all patients was 30.3+/-8.2 kg and mean absolute compression depth 42+/-8 mm. For 87 of 91 patients 38 mm compression depth was obtained with less than 50 kg. Stiffer chests were compressed more forcefully than softer chests (p<0.001), but softer chests were compressed more deeply than stiffer chests (p=0.001). The force needed to reach 38 mm compression depth (F38) and mean compression force were higher for males than for females: 29.8+/-14.5 kg versus 22.5+/-10.2 kg (p<0.02), and 32.0+/-8.3 kg versus 27.0+/-7.0 kg (p<0.01), respectively. There was no significant variation in F38 or compression depth with age, but a significant 1.5 kg mean decrease in applied force for each 10 years increase in age (p<0.05). Chest stiffness decreased significantly (p<0.0001) with an increasing number of compressions performed. Average residual force during decompression was 1.7+/-1.0 kg, corresponding to an average residual depth of 3+/-2 mm. In most out-of-hospital cardiac arrest victims adequate chest compression depth can be achieved by a force<50 kg, indicating that an average sized and fit rescuer should be able to perform effective CPR in most adult patients.

Movements of thoracic and abdominal compartments during ventilation at rest and during exercise.

The present investigation utilised simultaneous measurements of chest (Ch) and abdominal (Ab) circumferences and respiratory airflow to test the hypothesis that Ch circumferential expansion contributes proportionally little to tidal volume in the running Thoroughbred. During exercise, there were only small changes in Ch and Ab circumference and no increase with increasing tidal volume. At rest, walk and trot, the flow, Ch and Ab signals were in phase. However, during canter and gallop, the Ch and Ab changes were 180 degrees out of phase with each other and both were out of phase with airflow. In contrast to exercise, increase in ventilation at rest achieved by administration of lobeline resulted in a 4-6-fold increase in tidal volume; large excursions of the chest were always in phase with airflow. Furthermore, 3 horses showed an increase in chest circumference, demonstrating that chest stiffness per se does not preclude chest circumferential expansion. In conclusion, in the absence of significant increases in either Ch or Ab expansion during running, elongation of the thoracoabdominal segment may be the main determinant of tidal volume.