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Biomedical subjects

G A Ewy

Publications and source records attributed to G A Ewy.

At least 19 recordsLinked to original sources
PubMed1995

Bystander cardiopulmonary resuscitation. Concerns about mouth-to-mouth contact.

BACKGROUND: Bystander cardiopulmonary resuscitation (CPR) is performed on only a small percentage of patients who suffer cardiac arrest. We conducted a study to elucidate attitudes toward and potential obstacles to performance of bystander CPR. METHODS: Attitude survey of 975 people on the University Heart Center, University of Arizona, Tucson, mailing list. Participants were asked about their willingness to perform CPR under four conditions, with varying relationships (stranger vs relative or friend) and CPR techniques (chest compressions plus mouth-to-mouth ventilation [CC+V] vs chest compressions alone [CC]). RESULTS: Participants rated willingness to perform CPR and concern about disease transmission. Both relationship and CPR technique affected willingness to respond. Only 15% would "definitely" provide CC+V with strangers compared with 68% who would "definitely" perform CC. Even with relatives or friends, only 74% would "definitely" provide CC+V compared with 88% who would "definitely" provide CC. Eighty-two percent of participants were at least "moderately" concerned about disease transmission. CONCLUSION: Concerns regarding mouth-to-mouth ventilation appear to create substantial barriers to performance of bystander CPR. Intensified educational efforts and investigations of new approaches to bystander CPR are warranted.

Adult↗
PubMed1995

Multimedia computer-assisted instruction in cardiology.

BACKGROUND: Medical education faces problems caused by increasing restraints on resources. A multicenter consortium combined simulation and multimedia computer-assisted instruction (MCAI) to develop unique interactive teaching programs that can address a number of these problems. We describe the consortium, the MCAI system, the programs, and a multicenter evaluation of technical and educational performance. METHODS: The MCAI system uses computer-controlled access to full-screen, full-motion, and full-color laser disc video in combination with digitized sound, images, and graphics stored on removable media. The Socratic teaching method enhances interaction and guides learners through the patient's history, cardiovascular physical examination, laboratory evaluation, and therapy. Self-instruction and instructor-led modes of function are possible. The first five programs, based on simulations of specific cardiology problems, were distributed to four medical centers. Questionnaires evaluated technical function and medical student opinions, while behaviors and scores were automatically tracked and tabulated by program administration software. RESULTS: The MCAI system functioned reliably and accurately in all modes and at all sites. The programs were highly rated. Student ratings, scores, and behaviors were independent of institution and mode of use. CONCLUSION: A multicenter educational consortium developed a system to produce unique, sophisticated MCAI programs in cardiology. Both system and programs functioned reliably at four institutions and were highly rated by fourth-year medical students. With this enthusiastic reception, the economies and strengths associated with MCAI make it an attractive solution to a number of problem areas, and it will likely play an increasingly important role.

Cardiology↗
PubMed1995

The need for ventilatory support during bystander CPR.

STUDY OBJECTIVE: To compare CPR with chest compressions plus ventilatory support (CC+V) and chest compressions alone (CC). DESIGN: Prospective, randomized study. SETTING: Research laboratory. INTERVENTIONS: After 2 minutes of ventricular fibrillation, 18 domestic swine (20 to 35 kg) were treated first with CC or CC+V for 10 minutes, then with standard advanced cardiac life support. RESULTS: Hemodynamics, survival, and neurologic outcome were determined. All 8 swine subjected to CC+V and all 10 subjected to CC showed return of spontaneous circulation. One animal in each group died within 1 hour. Seven of 8 animals in the CC+V group survived for 24 and 48 hours, compared with 9 of 10 CC animals at 24 hours and 8 of 10 at 48 hours. All 48-hour survivors were neurologically normal. CONCLUSION: In this experimental model of bystander CPR, we could not detect a difference in hemodynamics, 48-hour survival, or neurologic outcome when CPR was applied with and without ventilatory support.

Animals↗
PubMed1995

Chest compression and ventilation rates during cardiopulmonary resuscitation: the effects of audible tone guidance.

OBJECTIVES: To determine: 1) whether chest compressions during CPR are being performed according to American Heart Association (AHA) guidelines during cardiac arrest; and 2) the effect of an audio prompt to guide chest compressions on compliance with AHA guidelines and hemodynamic parameters associated with successful resuscitation. METHODS: An observational clinical report and laboratory study was conducted. A research observer responded to a convenience sample of cardiac arrests within a 300-bed hospital and counted the rate of chest compressions and ventilations during CPR. To evaluate the effect of an audio prompt on CPR, health care providers performed chest compression without guidance using a porcine cardiac arrest model for 1 minute, followed by a second minute in which audio guidance was added. Chest compression rates, arterial and venous blood pressures, end-tidal CO2 (ETCO2) levels, and coronary perfusion pressures were measured and compared for the two periods. RESULTS: Twelve in-hospital cardiac arrests were observed in the clinical part of the study. Only two of 12 patients had chest compressions performed within AHA guidelines. No patient had respirations performed within AHA guidelines. In the laboratory, 41 volunteers were tested, with 66% performing chest compressions outside the AHA standards for compression rate without audible tone guidance. With guided chest compressions, the mean (+/- SD) chest compression rate increased from 74 +/- 22 to 100 +/- 3/min (p < 0.01). End-tidal CO2 levels increased from 15 +/- 7 to 17 +/- 7 torr (p < 0.01). Coronary perfusion pressure increased minimally with audible tone-guided chest compressions. CONCLUSIONS: The majority of Basic Cardiac Life Support--certified health care professionals did not perform CPR according to AHA-recommended guidelines. The use of audible tones to guide chest compression resulted in significantly higher chest compression rates and ETCO2 levels.

American Heart Association↗
PubMed1992

Case and survival definitions in out-of-hospital cardiac arrest. Effect on survival rate calculation.

OBJECTIVE: To determine the effect of different case and survival definitions of out-of-hospital cardiac arrest on survival rate calculations. DESIGN: A 22-month case series of nontraumatic, out-of-hospital cardiac arrests. SETTING: Southwestern city (population, 400,000; area, 390 km2) with a two-tiered emergency response system consisting of emergency medical technicians and paramedics. PATIENTS: A consecutive sample of 372 patients found without palpable pulse of spontaneous respiration. MAIN OUTCOME MEASURES: Survival rate after cardiac arrest was calculated using three case definitions of arrest and two definitions of survival. RESULTS: Twenty percent of all patients survived to hospital admission and 6% survived to hospital discharge. Twenty-six percent of adults whose collapse was witnessed survived to hospital admission, and 10% survived to hospital discharge. Patients whose collapse was witnessed and who experienced initial ventricular fibrillation survived to hospital admission in 38% and to hospital discharge in 15% of cases. CONCLUSIONS: The survival rate after out-of-hospital cardiac arrest varies widely depending on the case and survival definitions selected. To facilitate intersystem comparison and assessment of interventions designed to improve outcome, the Utstein Consensus Conference recommended that case and survival definitions should be adopted by all prehospital emergency systems.

Aged↗
PubMed1992

Minimal coronary stenoses and left ventricular blood flow during CPR.

STUDY OBJECTIVE: To assess the effect of a 33% coronary stenosis on myocardial blood flow during normal sinus rhythm and CPR. DESIGN: Prospective, before and after cardiac arrest and CPR; before and after creation of a 33% stenosis. SETTING: The University of Arizona Resuscitation Research Laboratory. SUBJECTS: Ten domestic closed-chest swine with patent coronary stenoses. INTERVENTIONS: A Teflon cylinder was placed in the mid-left anterior descending coronary artery to create a 33% stenosis. Myocardial blood flow was measured with colored microspheres both proximal and distal to the stenosis during normal sinus rhythm and during CPR. MEASUREMENTS AND MAIN RESULTS: During normal sinus rhythm, the stenosis did not alter the amount of myocardial blood flow distribution or quantity. Proximal to the stenosis the endocardial/epicardial flow ratio was 1.49 +/- 0.33, and distal to the stenosis it was 1.50 +/- 0.50. Likewise, during normal sinus rhythm, blood flow proximal and distal to the stenosis did not differ for either the epicardium (79 +/- 9 versus 66 +/- 13 mL/min/100 g) or the endocardium (111 +/- 27 versus 83 +/- 19 mL/min/100 g). However, the distribution of myocardial blood flow was markedly altered during CPR. The resultant endocardial/epicardial flow ratios were significantly less than during normal sinus rhythm, 0.49 +/- 0.11 (three minutes of CPR) and 0.74 +/- 0.07 (eight minutes of CPR) proximal to the stenosis and 0.39 +/- 0.15 (three minutes of CPR) and 0.49 +/- 0.14 (eight minutes of CPR) distal to the stenosis (P less than .05 versus normal sinus rhythm). In the presence of a 33% mid-left anterior descending coronary artery stenosis, endocardial blood flow at eight minutes of CPR was significantly lower distal to the stenosis compared with proximal to the stenosis (23 +/- 7 mL/min/100 g versus 74 +/- 18 mL/min/100 g; P less than .02). CONCLUSION: Minimal coronary lesions that do not diminish myocardial perfusion during normal physiologic conditions appear to significantly decrease subendocardial blood flow during cardiac arrest and CPR.

Animals↗
PubMed1992

Clinical significance of early vs late hypotensive blood pressure response to treadmill exercise.

BACKGROUND: It is generally believed that exercise-induced hypotension is the result of severe left-main or triple-vessel disease. Since this is not invariably so, and since most studies were performed in male populations, this study was done to determine the frequency of, and the significance of, exercise-induced hypotension in a more general population. METHODS: The treadmill exercise tests of 4850 consecutive patients performed at a university medical center over a period of 7.5 years were reviewed. To identify patients for further analysis, a hypotensive blood pressure response was initially defined (1) as a progressive fall in systolic blood pressure, (2) as a failure of the systolic blood pressure to rise more than 5 mm Hg during exercise, or (3) as an initial rise followed by a fall below the resting standing systolic blood pressure. RESULTS: The incidence of exercise-induced hypotension so defined was less than 2%. Exercise-induced hypotension occurred in two patterns. An early hypotension response was defined as a fall in systolic blood pressure of more than 10 mm Hg, associated with symptoms or ST-segment depression, during the first 5 minutes of exercise or as a progressive fall in systolic blood pressure of at least 20 mm Hg. The majority of patients (nine of 10) with an early hypotensive response had severe coronary artery disease. The late hypotension pattern was characterized by an initial rise, followed by a fall in the systolic blood pressure with continued exercise. Only half of the patients with this pattern had significant coronary artery disease, and half of the patients had other causes for exercise-induced hypotension. A late hypotensive response was six times more frequent than an early hypotensive response. CONCLUSIONS: This study identified two patterns of exercise-induced hypotension. Early, almost always due to severe coronary artery disease, and late, six times more common than early in which only half were due to coronary artery disease. Causes of a late hypotensive response to exercise that were not due to severe coronary artery disease included valvular heart disease, orthostatic hypotension, cardiomyopathy, idiopathic causes, and drugs. Drugs that contributed to a late exercise-induced hypotension response were diuretics, vasodilators, and negative inotropic agents.

Blood Pressure↗
PubMed1992

A study of chest compression rates during cardiopulmonary resuscitation in humans. The importance of rate-directed chest compressions.

A prospective, cross-over trial was performed comparing two different rates of precordial compression using end-tidal carbon dioxide as an indicator of the efficacy of cardiopulmonary resuscitation in 23 adult patients. A second purpose of this study was to determine the effect of audio-prompted, rate-directed chest compressions on the end-tidal carbon dioxide concentrations during cardiopulmonary resuscitation. Patients with cardiac arrest received external chest compressions, initially in the usual fashion without rate direction and then with rhythmic audiotones for rate direction at either 80 compressions per minute or 120 compressions per minute. Nineteen of 23 patients had higher end-tidal carbon dioxide levels at the compression rate of 120 per minute. The mean end-tidal carbon dioxide level during compressions of 120 per minute was 15.0 +/- 1.8 mm Hg, slightly but significantly higher than the mean level of 13.0 +/- 1.8 mm Hg at a compression rate of 80 per minute. However, end-tidal carbon dioxide levels increased rather dramatically when audiotones were used to guide the rate of chest compressions. Mean end-tidal carbon dioxide concentration was 8.7 +/- 1.2 mm Hg during standard cardiopulmonary resuscitation immediately before audio-prompted, rate-directed chest compression and increased to 14.0 +/- 1.3 mm Hg after the first 60 seconds of audible tones directing compressions. Using end-tidal carbon dioxide as an indicator of cardiopulmonary resuscitation efficacy, we conclude that audible rate guidance during chest compressions may improve cardiopulmonary resuscitation performance.

Aged↗
PubMed1991

Limitations of open-chest cardiac massage after prolonged, untreated cardiac arrest in dogs.

STUDY OBJECTIVES: Open-chest cardiac massage is an effective method of resuscitation if instituted within 15 minutes of normothermic cardiac arrest that has failed to respond to ongoing closed-chest CPR efforts. The usefulness of invasive forms of CPR after various periods of untreated cardiac arrest is less certain. This study was performed to determine the effectiveness of open-chest resuscitation after prolonged periods of untreated cardiac arrest. SETTING AND DESIGN: Prospective, controlled laboratory investigation using an animal model of cardiac arrest. Open-chest cardiac massage initially was compared to standard closed-chest compression CPR. The efficacy of open-chest CPR then was evaluated after ten and 40 minutes of untreated ventricular fibrillation. TYPE OF PARTICIPANTS: Twenty mongrel dogs (24 +/- 1 kg). MEASUREMENTS AND MAIN RESULTS: After 20 minutes of untreated ventricular fibrillation, open-chest resuscitation was significantly better than closed-chest efforts for the production of coronary perfusion pressure (58 +/- 14 vs 2 +/- 1 mm Hg; P less than .05) and initial resuscitation success (five of five vs one of five; P less than .03). Open-chest cardiac massage was equally effective for initial resuscitation if begun after ten or 20 minutes of untreated ventricular fibrillation (five of five vs five of five), but if untreated ventricular fibrillation continued for 40 minutes prior to instituting open-chest massage, no resuscitation benefit was found (none of five; P less than .005). There were marked differences in 24-hour survival depending on the length of time untreated cardiac arrest continued prior to instituting open-chest resuscitation efforts. After 20 minutes of ventricular fibrillation, initial resuscitation was successful with open-chest massage, but long-term survival was poor. CONCLUSION: Open-chest cardiac massage did not produce long-term survival if untreated cardiac arrest persisted for 20 or more minutes prior to invasive resuscitation efforts.

Animals↗
PubMed1991

The effect of bicarbonate on resuscitation from cardiac arrest.

STUDY OBJECTIVES: This study attempted to determine the effect of bicarbonate administration on resuscitation in a porcine model of prolonged cardiac arrest. DESIGN: After instrumentation, 26 swine were subjected to ventricular fibrillation for 15 minutes (16 animals) or 20 minutes (ten animals) with no resuscitative efforts. INTERVENTIONS: Resuscitation attempts with open-chest cardiac massage and epinephrine were used in all animals after the arrest period. The experimental group was given sodium bicarbonate (3 mEq/kg), and the control group received 3% saline (5 mL/kg) at the initiation of cardiac massage. MEASUREMENTS: Resuscitation success, hemodynamics, and arterial and mixed venous gases were compared in the bicarbonate and hypertonic saline-treated groups. RESULTS: There was no difference in resuscitation rates between bicarbonate and nonbicarbonate-treated swine. After 15 minutes of ventricular fibrillation, six of eight bicarbonate-treated swine were resuscitated successfully compared with five of eight hypertonic saline-treated animals. None of the five bicarbonate-treated or five hypertonic saline-treated swine that underwent 20 minutes of ventricular fibrillation were resuscitated. The arterial and mixed venous pH values were significantly different in the bicarbonate-treated animals from values in the control group. There was no difference in systolic or diastolic blood pressures or myocardial perfusion pressure between the bicarbonate and hypertonic saline-treated animals. CONCLUSION: Despite correlation of arterial and venous acidemia, the use of sodium bicarbonate did not improve resuscitation from prolonged cardiac arrest.

Animals↗
PubMed1990

The effect of coronary artery lesions on the relationship between coronary perfusion pressure and myocardial blood flow during cardiopulmonary resuscitation in pigs.

In subjects without coronary disease, coronary perfusion pressure generated with closed-chest cardiopulmonary resuscitation (CPR) bears a direct relationship to myocardial blood flow. The effect of coronary lesions on this relationship was studied in an experimental porcine model not requiring thoracotomy. Coronary stenoses (a 50% reduction in coronary cross-sectional area) or total coronary occlusions were created by percutaneous, transarterial catheter placement of a Teflon cylinder in the left anterior descending artery of 21 swine (30 to 60 kg). Coronary perfusion pressure, defined as the aortic diastolic pressure minus right atrial diastolic pressure, was correlated with myocardial blood flow measured with nonradioactive, colored microspheres during external chest compression CPR. Complete occlusion of the left anterior coronary artery resulted in essentially no CPR-generated blood flow to the anterior myocardium distal to the site of occlusion. Coronary perfusion pressure showed a positive correlation with myocardial blood flow above the area of occlusion (r = 0.783; p less than 0.01) but did not correlate with myocardial blood flow below the occlusion site (r = 0.239). In the presence of a patent coronary artery stenosis, coronary perfusion pressure correlated with myocardial blood flow both above (r = 0.841; p less than 0.001) and below (r = 0.508; p less than 0.05) the stenosis. During closed-chest CPR producing coronary perfusion pressures between 30 and 60 mm Hg, anterior myocardial blood flow was 109 +/- 16 ml/min/100 gm above a patent stenosis and 66 +/- 13 ml/min/100 gm below the stenosis (p less than 0.005). Over a wide range of coronary perfusion pressures, myocardial blood flow below a coronary lesion was significantly less than that above the lesion. Coronary occlusions and stenoses can substantially affect the amount of CPR-generated coronary perfusion pressure needed to produce distal myocardial blood flow.

Animals↗
PubMed1990

Depletion of myocardial adenosine triphosphate during prolonged untreated ventricular fibrillation: effect on defibrillation success.

We studied left ventricular endomyocardial adenosine triphosphate levels in 13 large mongrel dogs before and during ventricular fibrillation induced cardiac arrest to assess whether myocardial adenosine triphosphate content could predict successful cardiopulmonary resuscitation. Endomyocardial biopsies were performed during sinus rhythm (control), after 15 min of ventricular fibrillation or 10 min of ventricular fibrillation and 5 min of open chest cardiopulmonary resuscitation, after 20 min of ventricular fibrillation and 10 min of open chest cardiopulmonary resuscitation and after 40 min ventricular fibrillation and 15-20 min open chest cardiopulmonary resuscitation. Myocardial adenosine triphosphate was measured utilizing a bioluminescence method adapted for use with endomyocardial biopsies and normalized to protein content. Left ventricular endomyocardial adenosine triphosphate content fell significantly over time from a control level of 8.88 +/- 0.9 micrograms/mg protein to 5.73 +/- 0.5 micrograms/mg protein at 15 min of cardiac arrest, to 3.4 +/- 0.4 micrograms/mg protein after 30 min of cardiac arrest and to 1.98 +/- 0.3 micrograms/mg protein after 60 min of cardiac arrest (P less than 0.001). Adenosine triphosphate levels were significantly different between animals that received 10 min of ventricular fibrillation and successful open chest cardiopulmonary resuscitation and those that received 40 min of ventricular fibrillation and unsuccessful open chest cardiopulmonary resuscitation (4.35 +/- 0.48 vs. 2.11 +/- 0.43 micrograms/mg protein; P less than 0.025).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1990

The mechanism of blood flow during closed chest cardiac massage in humans: transesophageal echocardiographic observations.

Despite years of research, the mechanism of forward blood flow during closed chest cardiac massage remains controversial. Two theories have been suggested: the cardiac pump theory and the thoracic pump theory. Transesophageal echocardiography offers a new approach for study of the flows and cardiac morphologic features during chest compressions in humans. Case reports are presented to illustrate the use of transesophageal echocardiography during cardiopulmonary resuscitation. The findings included right and left ventricular compression, closure of the mitral valve during compression, opening of the mitral valve during the release phase, and atrioventricular valvular regurgitation during compression, indicating a positive ventricular-to-atrial pressure gradient. These findings suggest that direct cardiac compression was the predominant mechanism of forward blood flow during cardiopulmonary resuscitation in these patients. An understanding of the actual mechanisms involved is necessary if improved cardiopulmonary resuscitative techniques or adjuncts are to be rationally developed for enhancing the outcome of resuscitation.

Aged↗
PubMed1990

The role of bicarbonate and fluid loading in improving resuscitation from prolonged cardiac arrest with rapid manual chest compression CPR.

Rapid manual chest compression (120 compressions/min) CPR has been shown to improve hemodynamics and survival when compared with standard CPR (60 compressions/min) in a canine model of prolonged cardiac arrest. The study showing improved survival with rapid manual CPR empirically included treatment with bicarbonate and initial fluid loading. To determine the role of bicarbonate and fluid loading in the success of rapid manual chest compression CPR, 31 mongrel dogs were studied. After instrumentation with micromanometer-tipped catheters to measure aortic and right atrial pressures, the animals were assigned sequentially to three treatment groups. Group A underwent rapid manual chest compressions at 120 compressions/min, bicarbonate treatment, and initial fluid loading. Group B underwent rapid manual compressions at 120 compressions/min without bicarbonate or fluid loading. Group C underwent standard CPR at 80 compressions/min with bicarbonate and fluid loading. After 30 minutes of ventricular fibrillation, defibrillation was attempted. Seven of 11 dogs in group A survived 24 hours. None of the animals in group B resuscitated or survived. Three of the ten dogs in group C survived 24 hours. Survival with rapid manual CPR without bicarbonate and initial fluid loading was significantly less than when these interventions were used (P less than .01). To examine the separate contribution of bicarbonate and fluid therapy, two additional groups of animals were studied. Fourteen animals (group D) received rapid manual CPR with bicarbonate therapy, and 12 (group E) received rapid manual CPR with fluid loading only.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗