Cynthia A. Trowbridge

A randomized cross-over study of the quality of cardiopulmonary resuscitation among females performing 30:2 and hands-only cardiopulmonary resuscitation

BackgroundHands-Only cardiopulmonary resuscitation (CPR) is recommended for use on adult victims of witnessed out-of-hospital (OOH) sudden cardiac arrest or in instances where rescuers cannot perform ventilations while maintaining minimally interrupted quality compressions. Promotion of Hands-Only CPR should improve the incidence of bystander CPR and, subsequently, survival from OOH cardiac arrest; but, little is known about a rescuers ability to deliver continuous chest compressions of adequate rate and depth for periods typical of emergency services response time. This study evaluated chest compression rate and depth as subjects performed Hands-Only CPR for 10 minutes. For comparison purposes, each also performed chest compressions with ventilations (30:2) CPR. It also evaluated fatigue and changes in body biomechanics associated with each type of CPR.MethodsTwenty healthy female volunteers certified in basic life support performed Hands-Only CPR and 30:2 CPR on a manikin. A mixed model repeated measures cross-over design evaluated chest compression rate and depth, changes in fatigue (chest compression force, perceived exertion, and blood lactate level), and changes in electromyography and joint kinetics and kinematics.ResultsAll subjects completed 10 minutes of 30:2 CPR; but, only 17 completed 10 minutes of Hands-Only CPR. Rate, average depth, percentage at least 38 millimeters deep, and force of compressions were significantly lower in Hands-Only CPR than in 30:2 CPR. Rates were maintained; but, compression depth and force declined significantly from beginning to end CPR with most decrement occurring in the first two minutes. Perceived effort and joint torque changes were significantly greater in Hands-Only CPR. Performance was not influenced by age.ConclusionHands-Only CPR required greater effort and was harder to sustain than 30:2 CPR. It is not known whether the observed greater decrement in chest compression depth associated with Hands-Only CPR would offset the potential physiological benefit of having fewer interruptions in compressions during an actual resuscitation. The dramatic decrease in compression depth in the first two minutes reinforces current recommendations that rescuers take turns performing compressions, switching every two minutes or less. Further study is recommended to determine the impact of real-time feedback and dispatcher coaching on rescuer performance.

Effect of Diathermy on Muscle Temperature, Electromyography, and Mechanomyography

This study examined the effects of pulsed shortwave diathermy on intramuscular temperature, surface electromyography (EMG), and mechanomyography (MMG) of the vastus lateralis. Thirty‐five men were assigned to diathermy (n = 13), sham‐diathermy (n = 12), or control (n = 10) groups. Each subject performed isometric maximal voluntary contractions (MVCs) and incremental ramp contractions (10%–90% MVC) before and after treatment. Torque, intramuscular temperature, EMG, and MMG were recorded. Temperature for the diathermy group increased (P ≤ 0.05). MMG amplitude and instantaneous mean frequency (IMF) increased (P ≤ 0.05) during the MVCs with the greatest increases observed for the diathermy group. During ramp contractions, MMG amplitude and IMF increased at all percentages of MVC (10%–90%) for the diathermy group only (P ≤ 0.05). There were no changes in MVC torque, EMG amplitude, or IMF. Diathermy treatments may decrease musculotendinous stiffness, but not absolute strength or motor control strategies that influence force production. Muscle Nerve, 2008

A counterbalanced cross-over study of the effects of visual, auditory and no feedback on performance measures in a simulated cardiopulmonary resuscitation

BackgroundPrevious research has demonstrated that trained rescuers have difficulties achieving and maintaining the correct depth and rate of chest compressions during both in and out of hospital cardiopulmonary resuscitation (CPR). Feedback on rate and depth mitigate decline in performance quality but not completely with the residual performance decline attributed to rescuer fatigue. The purpose of this study was to examine the effects of feedback (none, auditory only and visual only) on the quality of CPR and rescuer fatigue.MethodsFifteen female volunteers performed 10 minutes of 30:2 CPR in each of three feedback conditions: none, auditory only, and visual only. Visual feedback was displayed continuously in graphic form. Auditory feedback was error correcting and provided by a voice assisted CPR manikin. CPR quality measures were collected using SkillReporter® software. Blood lactate (mmol/dl) and perceived exertion served as indices of fatigue. One-way and two way repeated measures analyses of variance were used with alpha set a priori at 0.05.ResultsVisual feedback yielded a greater percentage of correct compressions (78.1 ± 8.2%) than did auditory (65.4 ± 7.6%) or no feedback (44.5 ± 8.1%). Compression rate with auditory feedback (87.9 ± 0.5 compressions per minute) was less than it was with both visual and no feedback (p < 0.05). CPR performed with no feedback (39.2 ± 0.5 mm) yielded a shallower average depth of compression and a lower percentage (55 ± 8.9%) of compressions within the accepted 38-50 mm range than did auditory or visual feedback (p < 0.05). The duty cycle for auditory feedback (39.4 ± 1.6%) was less than it was with no feedback (p < 0.05). Auditory feedback produced lower lactate concentrations than did visual feedback (p < 0.05) but there were no differences in perceived exertion.ConclusionsIn this study feedback mitigated the negative effects of fatigue on CPR performance and visual feedback yielded better CPR performance than did no feedback or auditory feedback. The perfect confounding of sensory modality and periodicity of feedback (visual feedback provided continuously and auditory feedback provided to correct error) leaves unanswered the question of optimal form and timing of feedback.

Effects of Cold Modality Application With Static and Intermittent Pneumatic Compression on Tissue Temperature and Systemic Cardiovascular Responses

Background: In the therapeutic setting, cryotherapy with varying levels of intermittent cyclical compression often replaces an ice bag and elastic wrap. However, little is known about the cardiovascular strain and tissue temperature decreases associated with cooling and intermittent compression. Hypothesis: The authors hypothesized that higher levels of intermittent compression will result in greater reductions of tissue temperature and that all cold modalities will cause acute increases in cardiovascular strain. Design: Experimental crossover repeated measure design. Methods: Ten healthy subjects (23 ± 3 years) volunteered for 4 cryotherapy sessions (30-minute treatments with 30-minute passive recovery). Treatments included ice with elastic wrap and Game Ready (GR) with no, medium (5-50 mmHg), and high compression (5-75 mmHg). Throughout the experiment, oral, skin surface, and intramuscular quadriceps temperatures were measured along with mean arterial pressure, heart rate, rate pressure product, forearm blood flow, and forearm vascular conductance. Results: Mean arterial pressure increased up to 5 minutes (P < 0.05). Forearm blood flow and forearm vascular conductance decreased after baseline (P < 0.05), but there were no differences between treatments. Peak intramuscular changes from baseline were −14 ± 2°C (ice), −11 ± 6°C (GRHIGH), −10 ± 5°C (GRMED), and −7 ± 3°C (GRNO). Ice cooled the muscle the most, while GR with medium and high compression cooled more than GR without compression (P < 0.05). Conclusions: The application of cold and intermittent pneumatic compression using GR did not produce acute cardiovascular strain that exceeded the strain produced by standard ice bags/elastic wrap treatment. Greater temperature decreases are achieved with medium- and high-pressure settings when using the GR system. Clinical Relevance: Type of cold and amount of compression affect tissue cooling in healthy lean subjects. All tested cold modalities caused acute increases in cardiovascular strain; however, these increases are no more than what healthy subjects experience with the onset of exercise.