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Biomedical subjects

W D Weaver

Publications and source records attributed to W D Weaver.

At least 145 records · Page 8Linked to original sources
PubMed1990

The potential for prehospital thrombolytic therapy.

Several large trials of thrombolytic therapy have shown that treatment initiated in the first 1 or 2 hours following the onset of symptoms of acute myocardial infarction (AMI) is more effective than therapy started later in the course of illness. From our experience in three thrombolytic trials we concluded it would be difficult to reduce the total time from symptom onset to therapy without a major change in patient management. To accomplish this goal we have initiated MITI (Myocardial Infarction Triage and Intervention Project), a program for the prehospital diagnosis of AMI using specially trained paramedics, a checklist to establish eligibility for and contraindications to thrombolytic therapy, and a portable, battery-powered 12-lead electrocardiography (ECG) cellular telephone system that allows an electrocardiographic diagnosis to be made remotely by an emergency department physician. In the feasibility phase of MITI, 2,472 patients with chest pain of presumed cardiac origin were evaluated; 677 (27%) met the rigorous history and physical exam inclusion and exclusion criteria for potential thrombolytic therapy and had an ECG performed in the field. Of these ECGs, 522 were transmitted successfully by cellular telephone to a base station physician. Of the 522 patients, 107 had ST-segment elevation and met our criteria for initiation of thrombolytic therapy. Of the 2,472 patients with chest pain evaluated by the emergency medical technicians, 453 (18%) were diagnosed with AMI during hospitalization. Of these AMI patients, only 105 (23%) met the clinical examination and ECG criteria for pre-hospital thrombolytic therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

Emergency Medical Service Communication Systems↗
PubMed1989

Potential use of thrombolytic therapy before hospitalization.

Three trials of thrombolytic therapy in myocardial infarction (MI) up to 12 hours after symptom onset were conducted to measure the mean time from onset of chest pain to hospital arrival, and mean time to therapy. The trials, using intracoronary streptokinase, intravenous streptokinase and tissue plasminogen activator (t-PA), indicated a progressive shortening of time between symptom onset and hospital arrival. The Seattle Myocardial Infarction, Triage and Intervention (MITI) trial is evaluating the safety and efficacy of thrombolytic therapy initiated by paramedics in the prehospital setting. Phase I of the trial indicates that one-half of the patients would receive prehospital therapy in the field within the first hour of symptoms, substantially sooner than what can be achieved in the hospital. Phase II of MITI, in a nonrandomized trial, will compare the use of intravenous t-PA in the field with t-PA administered in the emergency department.

Ambulatory Care↗
PubMed1989

Emergency medical care requirements for large public assemblies and a new strategy for managing cardiac arrest in this setting.

During the 1986 World's Exposition held in Vancouver, British Columbia, the types and frequencies of emergency medical problems were assessed. The average number of patients seeking care was 3.93 +/- 0.95 per 1,000 visitors (daily range, 1.94 to 6.8). Patient loads were linearly related to gate attendance, but the correlation was imperfect (P less than .001, r = .63). Only 4.4% of patients evaluated on site by nurses and paramedics were referred for additional testing and treatment: of these patients, 30% had suspected serious musculoskeletal injury, 16% had abdominal pain, and 25% had complaints of chest pain, dizziness, or loss of consciousness. Lay employees (security personnel) were trained to use automatic external defibrillators. There were six cardiac arrests (0.3 per million visitors). Two patients collapsed with ventricular fibrillation, were defibrillated by lay personnel, quickly regained consciousness, and survived. The other arrests were associated with asystole or electromechanical dissociation; no shocks were inappropriately given, and all four died. We conclude that four of every 1,000 persons at this assembly sought emergency medical care, that 95% of the problems seen were minor with few requiring physician skills, and that the automatic external defibrillator was suited for this setting and could be used by lay responders to provide early definitive treatment.

Adolescent↗
PubMed1988

Use of the automatic external defibrillator in the management of out-of-hospital cardiac arrest.

The automatic external defibrillator is a simple device that can be used by nonprofessional rescuers to treat cardiac arrest. In 1287 consecutive patients with out-of-hospital cardiac arrest, we assessed the results of initial treatment with this device by firefighters who arrived first at the scene, as compared with the results of standard defibrillation administered by paramedics who arrived slightly after the firefighters. Of 276 patients who were initially treated by firefighters using the automatic defibrillator, 84 (30 percent) survived to hospital discharge (expected rate according to a logistic model, 17 percent; P less than 0.001), as compared with 44 (19 percent) of 228 patients when fire-fighters delivered only basic cardiopulmonary resuscitation and the first defibrillation was performed after the arrival of the paramedic team. Few patients with conditions other than ventricular fibrillation survived. In a multivariate analysis of characteristics that influenced survival after ventricular fibrillation, a better survival rate was related to a witnessed collapse (odds ratio, 3.9; 95 percent confidence interval, 2.0 to 7.6), younger age (odds ratio, 1.2; 95 percent confidence interval, 1.0 to 1.4), the presence of "coarse" (higher-amplitude) fibrillation (odds ratio, 4.2; 95 percent confidence interval, 1.6 to 11.0), a shorter response time for paramedics (odds ratio, 1.4; 95 percent confidence interval, 1.0 to 2.1), and initial treatment by firefighters using an automatic external defibrillator (odds ratio, 1.8; 95 percent confidence interval, 1.1 to 2.9). These findings support the widespread use of the automatic external defibrillator as an important part of the treatment of out-of-hospital cardiac arrest, although the overall impact of the use of this device on community survival rates is still uncertain.

Aged↗
PubMed1988

Hemodynamics in humans during conventional and experimental methods of cardiopulmonary resuscitation.

High-fidelity hemodynamic recordings of aortic and right atrial pressures and the coronary perfusion gradient (the difference between aortic and atrial pressure) were made in nine patients during cardiopulmonary resuscitation (CPR). Findings during conventional manual CPR were compared with those during high-impulse CPR (rate, 120 cycles/min with a shorter compression:relaxation ratio) as well as during pneumatic vest CPR with and without simultaneous ventilation and abdominal binding. Aortic peak pressure during conventional CPR averaged 61 +/- 29 mm Hg but varied widely (range, 39-126 mm Hg) among patients. Although the magnitude of improvement was modest, the high-impulse method was the only technique tested that significantly elevated both aortic peak pressure and the coronary perfusion gradient during cardiac arrest. During conventional CPR, aortic pressure rose from 61 +/- 29 to 80 +/- 39 mm Hg during high-impulse CPR, and the gradient rose from 9 +/- 11 to 14 +/- 15 mm Hg, respectively; p less than 0.01. The pneumatic vest method significantly improved peak aortic pressure but not the coronary perfusion gradient. Simultaneous ventilation and chest compression created high end-expiratory pressure and lowered the coronary perfusion gradient. Abdominal binding had no significant hemodynamic effects. This evaluation of experimental resuscitation methods in humans shows that the high-impulse chest compression method augments aortic pressure over levels achieved during conventional CPR methods; however, the improvement in pressure is modest and may not be clinically important. Simultaneous ventilation as well as abdominal binding during CPR were associated with no benefit; in fact, simultaneous ventilation appears to adversely affect cardiac perfusion and, therefore, should not be used during clinical resuscitation.

Aorta↗
PubMed1988

Effect of heat stress early in life on mortality of broilers exposed to high environmental temperatures just prior to marketing.

A study was conducted to investigate the effects of heat stress during the 1st wk of life on subsequent mortality resulting from exposure to high environmental temperature and feed restriction just prior to marketing of broiler cockerels. Birds were raised under standard husbandry procedures except that at 5 days of age, half the broilers were heat stressed by exposure to an environmental temperature ranging from 35.0 to 37.8 C for 24 h while the remaining birds were held at 29.4 C. At 44 and 45 days of age, half the unstressed controls and half the birds stressed at 5 days of age were exposed to temperatures ranging from 35.0 to 37.8 C for 8 h/day. In a factorial arrangement of treatments, the effect of restricting feed for 8 h/day on Days 43, 44, and 45 was also examined. Exposing birds to high environmental temperatures at 5 days of age resulted in a significant decrease in mortality when birds were exposed to a high environmental temperature later in life. In addition, feed efficiency was improved significantly in early heat-stressed birds whereas body weight and body weight gain were not affected. Feed restriction had no significant effect on mortality, body weight, or feed efficiency. It appears, therefore, that exposing broiler cockerels to mild heat stress for 24 h at 5 days of age can significantly decrease mortality resulting from high environmental temperature later in life.

Animals↗
PubMed1988

Effects of feeder space on body weight uniformity of broiler breeder pullets during an alternate day feeding program.

The effect of feeder space on body weight uniformity of adolescent broiler breeder females during a feed restriction program was evaluated. From 2 to 20 wk of age, broiler breeder pullets were fed a starter/developer diet containing 16.0% protein and 2,944 kcal ME/kg feed. Feed allocations, predicated on mean pen body weight, were fed on an every other day basis. Feeder space was 45 or 90% of that recommended for use with a feed restriction program. The mortality, feed efficiency and body weight uniformity data all support the hypothesis that it is not necessary to provide enough feeder space to enable all birds to eat simultaneously. Broiler breeder pullets provided only 45% of the recommended feeder space responded as well as, or better than, those given 90% of the recommended feeder space.

Animal Husbandry↗
PubMed1987

Automatic external defibrillators: importance of field testing to evaluate performance.

A new automatic external defibrillator was tested first against a tape-recorded data base of rhythms and then during use by first-responding fire fighters in a tiered emergency system. The sensitivity for correctly classifying ventricular fibrillation and ventricular tachycardia was substantially less during clinical testing in 298 patients than would have been predicted from preclinical results: 52% of ventricular fibrillation analyses in patients were correctly classified versus 88% of episodes in the data base, and 22 versus 86%, respectively, for ventricular tachycardia (p less than 0.001). The detection algorithm was modified and evaluated further in another 322 patients. The modified detector performed substantially better than did the one that had been designed from prerecorded rhythms: with its use, 118 (94%) of 125 patients in ventricular fibrillation were counter-shocked compared with 91 (77%) of 118 similar patients with use of the initial algorithm (p less than 0.001). No inappropriate shocks were delivered. This improvement resulted in a shorter time to first shock (p less than 0.01) and more shocks being delivered for persistent or recurrent episodes of ventricular fibrillation (p less than 0.05). Of 620 patients treated with the automatic defibrillator, 243 (39%) had ventricular fibrillation; 57 (23%) of the 243 regained pulse and blood pressure before paramedics arrived, 141 (58%) were admitted to hospital and 71 (29%) were discharged.(ABSTRACT TRUNCATED AT 250 WORDS)

Algorithms↗
PubMed1987

CPR training for patients' families: do physicians recommend it?

All Seattle-area cardiologists and 25 per cent of selected other physicians were queried by mail to determine whether they recommended CPR (cardiopulmonary resuscitation) training for families of their patients. Two-thirds reported that they advocated training for some patients' families, but only 52 per cent of cardiologists and 37 per cent of the others did so for families of at least half of the patients considered at risk. Physicians who had performed out-of-hospital CPR or had received advanced or recent training were more likely to recommend instruction.

Attitude of Health Personnel↗
PubMed1986

Cardiac arrest treated with a new automatic external defibrillator by out-of-hospital first responders.

Two hundred sixty patients in cardiac arrest were treated with an automatic external defibrillator by first-responding firefighters before arrival of paramedics. On average, first responders arrived 5 minutes before paramedics. Of 118 patients with ventricular fibrillation, 91 (77%) were administered shocks, 21 (23%) of whom had return of pulse and blood pressure by the time paramedics arrived. Fifty-six (62%) were admitted to the hospital and 30 (33%) survived. The survival rate for all 118 victims discovered with ventricular fibrillation was 27%. The device correctly classified the initial and all subsequent rhythms in 92 patients with asystole, 46 with electromechanical dissociation, and 22 others with presumed respiratory arrest; it did not deliver any inappropriate shocks to patients or to the rescuers using the device. An automatic external defibrillator can be used by first responders as an adjunct to basic life support, and its use may improve survival by shortening the time to defibrillation.

Allied Health Personnel↗
PubMed1986

Considerations for improving survival from out-of-hospital cardiac arrest.

Since the implementation of a paramedic system in Seattle, yearly survival rates from out-of-hospital cardiac arrest due to ventricular fibrillation have averaged 25% without any significant increase over the years. Outcome for cardiac arrest associated with other rhythms has been poor: when asystole was the first rhythm recorded, only 1% of patients survived; when electromechanical dissociation was initially present, only 6% survived. For cases of electromechanical dissociation, neither the type of rhythm nor the rate appear to influence outcome. Survival from ventricular fibrillation can be improved by shortening the delay to initiation of CPR and to defibrillation. When outcome in 244 witnessed arrests was related to the times to beginning CPR and to initial defibrillation, mortality increased 3% each minute until CPR was begun and 4% a minute until the first shock was delivered. New strategies that minimize delays appear to have the greatest promise for improving survival after cardiac arrest.

Ambulances↗
PubMed1986

Exercise: a risk for sudden death in patients with coronary heart disease.

Although sudden arrhythmic death is usually unrelated to exertion, there is more than anecdotal evidence that strenuous exercise in patients with coronary heart disease carries an additional risk for sudden death. When cardiac arrest has been observed after exercise stress testing or within seconds after collapse associated with exertion, ventricular fibrillation has usually been present and has responded to the prompt application of a defibrillatory shock. Exertion-related cardiac arrest is typically a "primary" arrhythmic event not due to acute myocardial infarction. As estimated here, the additional risk of exercise for cardiac arrest may be more than 100-fold during or after a few minutes of vigorous exertion.

Adult↗
PubMed1986

Factors influencing survival after out-of-hospital cardiac arrest.

Survival to hospital discharge was related to the clinical history and emergency care system factors in 285 patients with witnessed cardiac arrest due to ventricular fibrillation. Only the emergency care factors were associated with differences in outcome. Both the period from collapse until initiation of basic life support and the duration of basic life support before delivery of the first defibrillatory shock were shorter in patients who survived compared with those who died (3.6 +/- 2.5 versus 6.1 +/- 3.3 minutes and 4.3 +/- 3.3 versus 7.3 +/- 4.2 minutes; p less than 0.05). A linear regression model based on emergency response times for 942 patients discovered in ventricular fibrillation was used to estimate expected survival rates if the first-responding rescuers, in addition to paramedics, had been equipped and trained to defibrillate. Expected survival rates were higher with early defibrillation (38 +/- 3%; 95% confidence limits) than the observed rate (28 +/- 3%). Because outcome from cardiac arrest is primarily influenced by delays in providing cardiopulmonary resuscitation and defibrillation, factors affecting response time should be carefully examined by all emergency care systems.

Aged↗
PubMed1986

Influence of hatcher holding times on several physiological parameters associated with the immune system of chickens.

Two experiments were conducted with broiler chicks to study the effects of posthatch holding time in the incubator on physiological and disease parameters. In each experiment, half of the chicks were removed shortly after hatching and half of the chicks were allowed to remain in the hatcher for an additional 30 hr. Bursa weights, hematocrits, total plasma protein, and blood glucose concentrations were measured at various times up to 35 and 28 days of age in Experiments 1 and 2, respectively. In addition, chicks hatched from eggs with one of two specific gravities (less than or equal to 1.065 and greater than or equal to 1.075) were tested in the second experiment. Spleen weights, heterophil:lymphocyte ratios and the influence of an aerosol Newcastle disease-Mycoplasma gallisepticum vaccine challenge were also measured in the second experiment. In Experiment 1, when chicks were held in the hatcher for an additional 30 hr, bursa weights were reduced through 8 days of age; however, they were significantly heavier by 21 days of age. In Experiment 2, both bursa and spleen weights were significantly reduced through 14 days of age when chicks were held in the incubator. Total plasma protein and glucose concentrations, hematocrits, and heterophil:lymphocyte ratios were all significantly higher for chicks held in the incubator. Chicks held in the incubator and then exposed to an aerosol vaccine challenge at 1 day of age had a significantly greater percentage of air sac lesions and the lesions were more severe at 28 days of age. Egg specific gravity had no influence on any of the parameters measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Calcium-channel blockers and advanced cardiac life support.

Calcium channel-blocking drugs have potent antiarrhythmic and antianginal effects and in addition may reduce the extent of cellular injury after anoxia/ischemia. Verapamil is the treatment of choice (90% effective) for uncomplicated episodes of paroxysmal supraventricular tachycardia. All three calcium-channel blockers available, diltiazem, nifedipine, and verapamil, can reduce the frequency of angina occurring both at rest and with exertion. Calcium may mediate several cytotoxic events during the reperfusion period after prolonged ischemia that lead to irreversible cell injury. There is experimental evidence that calcium-channel blockers may reduce the cellular influx of calcium after ischemia and reperfusion, and thereby attenuate cerebral and myocardial injury, although most studies have failed to show benefit of treatment unless the drug is administered before the onset of ischemia. Most trials using calcium-channel blockers in the setting of acute myocardial infarction have failed to show a benefit of treatment. The safety and efficacy of calcium-channel blockers have yet to be shown in controlled studies of human resuscitation, although the potential for such treatment, if it is effective in attenuating myocardial cerebral cellular injury, could be enormous.

Brain Ischemia↗