Master of Science (MSc)
Faculty of Science
Dr. Diane Gregory
She was my supervisor for my master's thesis. She guided me throughout the program and instructed me on the use of equipment and processes of performing research. She played a critical role in revising and improving the quality of my thesis document, as well as helping me grow throughout the two-year program.
Background: The current American Heart Association (AHA) standard cardiopulmonary resuscitation (CPR) is performed with a compression-ventilation ratio of 30:2 (standard CPR), meaning 30 compressions are applied to the chest followed by the administration of two breaths to the victim. Some evidence has shown that performing continuous chest compressions rather than standard CPR with breaks in chest compressions for administering breaths, may increase survival rates after cardiac arrest. Cont-CPR has been shown to be very fatiguing in nature, with a significant drop in chest compression force within the first two minutes of CPR. The purpose of this study was to examine and compare the biomechanical demand of individuals performing cont-CPR and standard CPR under timing conditions that are representative of a three-person rescue team.
Methodology: Fifteen individuals (ten emergency responders, five civilians) performed two sets of CPR trials; one set was performed using standard CPR (30:2) and the other set using cont-CPR. The order in which these CPR types were presented to each participant was randomized. The first set of trials comprised of three two-minute periods of CPR administration, during which the chest compressions were performed on a force transducer that was placed over the sternum of a CPR mannequin. In between each two-minute trial, the participants were given four minutes of rest (to simulate a three-person rescue team). After the third CPR trial, the participants were given 30 minutes of rest before repeating the complete procedure performing the second type of CPR. Immediately prior to, and immediately after, completing each set of CPR trials (standard and cont-CPR), participants were instructed to fill out ratings of perceived exertion and discomfort scales (RPE and RPD, respectively) as well as perform a static back extensor test to evaluate low back muscular fatigue. During the CPR trials, the following measures were collected: 1) Electromyography (EMG) data collected from four trunk muscles and two upper extremity muscles; 2) low back flexion using electromagnetic motion sensors; and, 3) chest compression force using a force transducer placed on the sternum of a CPR mannequin.
Results and Discussion: Chest compression force decreased significantly over the two minute standard and cont-CPR trials evident by a significant main effect of time (p<0.0001). There was also a significant interaction between CPR type and time (p=0.011) with regards to chest compression force. During the cont-CPR trials, chest compression force began to decrease immediately, whereas during the standard CPR trials, chest compression force was maintained relatively constant for the first 40 seconds, and subsequently began to decrease at a similar rate to the cont-CPR condition. Therefore, the overall drop in chest compression force was larger for the cont-CPR trials compared to the standard CPR trials. The amount of chest compression force varied greatly between the emergency responders and the civilians such that the majority of emergency responders were able to perform effective chest compressions (i.e. reach a level of chest compression force shown to be high enough to create blood flow) and many exceeded the maximum recommended chest compression force, regardless of CPR type. Contrary, most civilians were not able to sustain enough chest compression force throughout the two minute trials to maintain effective chest compressions. This has implications in both groups of individuals (emergency responders and civilians) as too much chest compression force may cause emergency responders to fatigue quickly and not be able to perform effective compressions, while too low of chest compression force may not effectively circulate blood in the victim’s body.
Significant increases in left and right lumbar erector spinae (LES) muscle activation over the two minutes of CPR, regardless of the type of CPR, were also observed in the current study (p=.025 and p=.040, respectively). These increases may be due to increased demand to maintain a flexed posture during the performance of CPR. It is not likely that the increased amplitude of activation in the erector spinae muscles was due to fatigue as a decrease in the median power frequency was not observed following the CPR trials for either left or right LES (p=.412 and p=.549, respectively).
In the upper extremity, a shift in muscle activation was observed from the triceps brachii (TB) to the pectoralis major (PM). Specifically, a decrease in activation of the left TB (p=.022) was observed over time with a subsequent increase in activation of the left PM (p=.002). This finding suggests that the PM may have compensated for decreased force output from the TB likely as a result of fatigue. No differences in lumbar spine flexion were observed over time (p=.685) or between CPR conditions (p=.477).
Last, a significant increase in all the RPD variables and RPE scores was observed regardless of CPR type, which emphasized the exhausting nature of performing CPR.
Conclusion: The results of this study demonstrated that the performance of CPR over two minute bouts is fatiguing, regardless of CPR type. However, performing cont-CPR displayed an immediate and greater drop in chest compression force compared to standard CPR. This result may indicate a psychophysical aspect of performing cont-CPR compared to standard CPR. The very high chest compression force production from the emergency responders, along with the low chest compression force from the civilians, both pose their own problems that need to be addressed. If the AHA CPR guidelines are amended to perform cont-CPR rather than the current standard CPR, it is suggested that during a multi-person rescue, the duration of CPR administration should be shortened to less than two minutes; ideally one or one and a half minutes for each rescuer rotation to help prevent fatigue.
Dainty, Richard Scott, "Investigation of low back and shoulder demand during cardiopulmonary resuscitation: the effect of different compression-ventilation ratios" (2015). Theses and Dissertations (Comprehensive). 1700.