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Biomedical subjects

R D White

Publications and source records attributed to R D White.

At least 73 records · Page 4Linked to original sources
PubMed1997

Improved retention of the EMS activation component (EMSAC) in adult CPR education.

This study was undertaken to determine whether using a model-telephone to simulate the emergency medical services activation component (EMSAC) during adult cardiopulmonary resuscitation (CPR) training practice would lead to better retention of this component during end-of-class assessment. In a prospective randomized manner, 233 medical professionals and lay-persons taking American Heart Association (AHA) CPR classes were evaluated for EMSAC retention during CPR skills performance at the end of class. During the assessment correct versus incorrect activation of EMS was noted. Subject response by age, exposure to previous CPR training, and medical professional or lay-person status was examined. Differences in results among instructors also were examined. Overall, those in the group using the model-telephone remembered to activate EMS correctly more frequently than those in the group not using the phone (69 vs 52%, P = 0.009). The < 30 age group was unaffected by the use of the phone (P = 0.85). The group between 30 and 50 years of age did significantly better with the use of the phone (P = 0.007), as did those 50 years of age and older (P = 0.03). Previous CPR training did not affect the response (P = 0.18). We conclude that use of the model-telephone improved EMSAC retention significantly overall except in the < 30 year-old age group. We recommend using the model-telephone in future adult CPR classes.

Adolescent↗
PubMed1997

Current concepts in cardiopulmonary resuscitation.

The "chain of survival" is important in the resuscitation of a patient who has had a cardiac arrest. The provision of Basic Life Support (BLS) and Advanced Cardiac Life Support (ACLS) is essential in this "chain of survival." Both BLS and ACLS have undergone several revisions since their initial inception. This article reviews (1) the current established and investigational issues of cardiopulmonary resuscitation, (2) the incidence and outcomes of anesthesia-related cardiac arrest, (3) the use of cardiopulmonary bypass in resuscitation, and (4) cerebral protection during and after resuscitation.

Anesthesia, General↗
PubMed1997

Early out-of-hospital experience with an impedance-compensating low-energy biphasic waveform automatic external defibrillator.

Impedance-compensating low-energy biphasic truncated exponential (BTE) waveforms are effective in transthoracic defibrillation of short-duration ventricular fibrillation (VF). However, the BTE waveform has not been examined in out-of-hospital cardiac arrest (OHCA) with patients in prolonged VF often associated with myocardial ischemia. The objective of this study was to evaluate the BTE waveform automatic external defibrillator (AED) in the out-of-hospital setting with long-duration VF. AEDs incorporating a 150-J BTE waveform were placed in 12 police squad cars and 4 paramedic-staffed advanced life support ambulances. AEDs were applied to arrested patients by first-arriving personnel, whether police or paramedics. Data were obtained from PC Data Cards within the AED. Defibrillation was defined as at least transient termination of VF. Ten patients, 64 +/- 14 years, were treated for VF with BTE shocks. Another 8 patients were in nonshockable rhythms and the AEDs, appropriately, did not advise a shock. Five of the 10 VF arrests were witnessed with a 911 call-to-shock time of 6.6 +/- 1.7 minutes. VF detection and defibrillation occurred in all 10 patients. Spontaneous circulation was restored in 3 of 5 witnessed arrest patients and 1 survived to discharge home. Fifty-one VF episodes were converted with 62 shocks. Presenting VF amplitude and rate were 0.43 +/- 0.22 (0.13-0.86) mV and 232 +/- 62 (122-353) beats/min, respectively, and defibrillation was achieved with the first shock in 7 of 10 patients. Including transient conversions, defibrillation occurred in 42 of 51 VF episodes (82%) with one BTE shock. Shock impedance was 85 +/- 10 (39-138) ohms. Delivered energy and peak voltage were 152 +/- 2 J and 1754 +/- 4 V, respectively. The average number of shocks per VF episode was 1.2 +/- 0.5 (1-3). More than one shock was needed in only 9 episodes; none required > 3 shocks to defibrillate. Impedance-compensating low-energy BTE waveforms terminated VF in OHCA patients with a conversion rate exceeding that of higher energy monophasic waveforms. VF was terminated in all patients, including those with high impedance.

Adult↗
PubMed1997

Low-energy impedance-compensating biphasic waveforms terminate ventricular fibrillation at high rates in victims of out-of-hospital cardiac arrest. LIFE Investigators.

INTRODUCTION: New automatic external defibrillators (AEDs), which are smaller, lighter, easier to use, and less costly make the goal of widespread AED deployment and early defibrillation for out-of-hospital cardiac arrest feasible. The objective of this study was to observe the performance of a low-energy impedance-compensating biphasic waveform in the out-of-hospital setting on 100 consecutive victims of sudden cardiac arrest. METHODS AND RESULTS: AEDs incorporating a 150-J impedance-compensating biphasic waveform were used by 12 EMS systems. Data were obtained from the AED PC card reporting system. Defibrillation was defined as conversion to an organized rhythm or to asystole. Endpoints included: defibrillation efficacy for ventricular fibrillation (VF); restoration of an organized rhythm at the time of patient transfer to an advanced life support (ALS) team or to the emergency department (ED); and time from AED power-on to first defibrillation. The AED correctly identified 44 of 100 patients presenting in VF as requiring a shock (100% sensitivity) and 56 of 100 patients not in VF as not requiring a shock (100% specificity). The time from 911 call to first shock delivery averaged 8.1 +/- 3.0 minutes. A single 150-J biphasic shock defibrillated the initial VF episode in 39 of 44 (89%) patients. The average time from power-on to first defibrillation was 25 +/- 17 seconds. At patient transfer to ALS or ED care, an organized rhythm was present in 34 of 44 (77%) patients presenting with VF. Asystole was present in 7 (16%) and VF in 3 (7%). CONCLUSIONS: Low-energy impedance-compensating biphasic waveforms terminate long-duration VF at high rates in out-of-hospital cardiac arrest. Use of this waveform allows AED device characteristics consistent with widespread AED deployment and early defibrillation.

Adult↗
PubMed1997

Intramural hematoma of the thoracic aorta: MR image findings and their prognostic implications.

PURPOSE: To evaluate magnetic resonance (MR) imaging findings of intramural hematoma of the thoracic aorta and their relationship to prognosis. MATERIALS AND METHODS: MR images of 22 patients with intramural hematoma of the thoracic aorta were reviewed retrospectively. Site, thickness, degree of mural involvement, and signal intensity on spin-echo (SE) and cine gradient-echo (GRE) images of the hematoma were noted. MR findings of patients who did and those who did not develop complications were compared. RESULTS: Hematoma site was the only MR finding that correlated significantly with patient outcome. Complication frequencies in four (80%) of five patients with hematoma of the ascending aorta (type A) and in two (12%) of 17 patients with hematoma of the descending aorta (type B) were significantly different (P = .009). There were moderately strong correlations between days after symptom onset and signal intensity of the hematoma on SE (r = 0.78) and GRE (r = 0.72) images. MR images of two of three patients who developed early-subacute complications showed signal intensity changes of the hematoma that were consistent with recurrent bleeding. CONCLUSION: Patients with MR findings consistent with type A intramural hematoma of the thoracic aorta should undergo surgery. In cases of type B intramural hematoma of the thoracic aorta, MR imaging can be useful for detecting complete resolution or impending complications of the hematoma.

Aged↗
PubMed1997

Tolerable life.

Explore the source record for details and available documents.

Decision Making↗
PubMed1997

Metabolism of the aryl hydrocarbon receptor agonist 3,3',4,4'-tetrachlorobiphenyl by the marine fish scup (Stenotomus chrysops) in vivo and in vitro.

The metabolism of the polychlorinated biphenyl congener 3,3',4,4'-tetrachlorobiphenyl (TCB) was examined in vitro and in vivo in the marine fish scup (Stenotomus chrysops). Untreated scup liver microsomes catalyzed metabolism of TCB with an estimated KM of 0.7 microM, at a rate < or = 0.13 pmol/min/mg. Metabolism was NADPH-dependent and inhibited by cytochrome c and CO, indicating cytochrome P450 (CYP) involvement. alpha-Naphthoflavone strongly inhibited microsomal TCB metabolism, and treatment of fish with CYP1A inducers increased the rates by approximately 2-fold, suggesting involvement of CYP1A. Scup were injected intraperitoneally with 0.1 or 5 mg TCB/kg and sampled on days 1-16 after treatment (after 3 days without food at each sampling). Concentrations of unmetabolized TCB in liver peaked on day 5 in low dose fish and on day 12 in high dose fish. In both groups the TCB content in the liver had declined 60% or more by day 16, suggesting depuration or redistribution from the liver. GC and MS revealed TCB and TCB metabolites in bile within 24 hr of treatment. The concentrations of TCB and metabolites in bile peaked at the same time that TCB concentrations peaked in the liver. The major metabolites were 5-hydroxy-3,3'4,4'-TCB (5-OH-TCB) and 4-hydroxy-3,3',5,4'-TCB (4-OH-TCB); 2-hydroxy-3,3',4,4'-TCB and 6-hydroxy-3,3',4,4'-TCB were minor metabolites. Animals given the high dose had much less 5-OH-TCB and much more parent TCB in bile than did fish given the low dose. Amounts of 4-OH-TCB in bile did not differ between doses. The reduced excretion of 5-OH-TCB coincided with a suppression of CYP1A in fish given the high dose, that did not occur in low dose fish, consistent with an involvement of CYP1A in TCB metabolism and particularly in formation of 5-OH-TCB. This study provides the first direct demonstration of 3,3',4,4'-TCB metabolism by fish. Data also indicate that these fish are able to eliminate TCB both as parent compound and as metabolites, despite a very slow rate of metabolism in vitro.

Animals↗
PubMed1997

Optimal access to- and response by-public and voluntary services, including the role of bystanders and family members, in cardiopulmonary resuscitation.

Victims of out-of-hospital cardiac arrest in most communities are not the beneficiaries of an optimal healthcare system response capable of providing survivors who live to hospital discharge. The public at large, including family members and bystander witnesses of cardiac arrest, must be expected to participate in this optimal response capability. The American Heart Association Chain of Survival defines the elements of a system capable of saving lives of victims of ventricular fibrillation cardiac arrest. Widespread dissemination of only the essential elements of life-saving steps, probably through media not yet used for this function, will be needed to reach the largest number of people possible. Emergency medical services systems need to devise innovative approaches to rapid provision of automated external defibrillation, in many cases no doubt outside the boundaries of traditional means of delivery of this intervention. Finally, it is likely that targeted responders among the public will be participants in a public access defibrillation approach to dealing with sudden cardiac death.

Cardiopulmonary Resuscitation↗
PubMed1996

Dynamic magnetic resonance imaging assessment of the effect of ventricular wall curvature on regional function in hypertrophic cardiomyopathy.

We hypothesized that contraction within the ventricular septum in hypertrophic cardiomyopathy (HC) may be related to its abnormal morphology because ventricular wall stress is related to wall curvature by the Laplace equation. To test this, we studied 17 HC patients with various septal morphologies using dynamic magnetic resonance imaging techniques. Short- and long-axis curvatures of the basal septal and basal lateral walls were determined on cine images as the reciprocal of the radius of the arc best fit to the endocardial contour, which was negative if the wall was convex to the cavity of the left ventricle. Endocardial and epicardial intramyocardial circumferential shortening (% circumferential shortening) was measured in the septal and lateral walls on basal short-axis myocardial tagging images. Septal walls were flatter in the short-axis plane and more convex toward the left ventricular cavity in the long-axis plane than lateral walls, as indicated by smaller short- and long-axis curvatures. Septal percent circumferential shortening was significantly lower than the lateral percent circumferential shortening, suggesting reduced septal contraction. Endocardial and epicardial percent circumferential shortening showed significant positive correlations with wall curvatures. Multiple stepwise linear regression analysis revealed that both short- and long-axis curvatures significantly contributed to percent circumferential shortening (r=0.87 for endocardial and r=0.70 for epicardial, both p<0.0001). In conclusion, wall curvature is related to wall function in HC; the more convex toward the left ventricular cavity the wall is, the less it contracts. Reduced contraction of the septum in HC may be partly due to its abnormal curvature.

Cardiomyopathy, Hypertrophic↗
PubMed1996

High discharge survival rate after out-of-hospital ventricular fibrillation with rapid defibrillation by police and paramedics.

STUDY OBJECTIVE: To assess outcome in patients with ventricular fibrillation (VF) treated by defibrillator-equipped police and emergency medical technician-paramedics in an advanced life support (ALS) emergency medical services (EMS) system. METHODS: We carried out a retrospective observational outcome study of all consecutive adult patients with atraumatic cardiac arrest treated from November 1990 through July 1995. The study was carried out in a city with a population of 76,865 in an area of 32.6 square miles. Central 911 dispatched police and an ALS ambulance simultaneously. Accurate intervals were obtained with the synchronization of all defibrillator clocks with the 911 dispatch clock. The personnel who arrived first delivered the initial shock. After shocks delivered by police, paramedics provided additional treatment if needed. Main outcome measures were time elapsed before delivery of the first shock, restoration of spontaneous circulation (ROSC), and survival to discharge home. RESULTS: Of 84 patients, 31 (37%) were first shocked by police. Thirteen of the 31 demonstrated ROSC, without need for ALS treatment. All 13 survived to discharge. The other 18 patients required ALS; 5 (27.7%) survived. Among the 53 patients first shocked by paramedics, 15 had ROSC after shocks only, and 14 survived. The other 38 needed ALS treatment; 9 survived. Call-to-shock time for all patients was less in the police group than in the paramedic group (5.6 versus 6.3 minutes, P = .038). For all patients, call-to-shock time was less in those with ROSC after shocks only than in those who needed ALS (5.4 versus 6.3 minutes, P = .011). Survival to discharge was 49% (41 of 84), with 18 of 31 (58%) in the police group and 23 of 53 (43%) in the paramedic group. Call-to-shock time for survivors was 5.8 minutes; it was 6.4 minutes for the nonsurvivors (P = .020). Neither ROSC nor discharge survival was significantly different between police and paramedic-shocked patients. ROSC after initial shock and call-to-shock time were major determinants of survival, whether the first shocks were administered by police or by paramedics. With ROSC after shocks only, 27 of 28 (96%) survived, whereas 14 of 56 (25%) needing ALS survived (P < .001). CONCLUSION: A high discharge-to-home survival rate was obtained with early defibrillation by both police and paramedics. When shocks resulted in ROSC, the overwhelming majority of patients survived (96%). Even brief time decreases (eg. 1 minute) in call-to-shock time increase the likelihood of ROSC from shocks only, with a consequent decrease in the need for ALS intervention. Short call-to-shock time and ROSC response to shocks only are major determinants of a high rate of survival after VF.

Adult↗
PubMed1996

Longitudinal study of free running exercise challenge: reproducibility.

The reproducibility of free running exercise challenge has been examined in an unselected population of 8-10 year olds. Using a standardised protocol, monthly exercise tests were performed on 143 children over one year. A positive test was defined using both a 15% and 20% fall in peak expiratory flow after exercise. The mean (95% confidence interval, CI) population frequency for a positive test at 15% fall was 14.9% (6.5 to 23.3) and coefficient of variation 24.6%. For a 20% fall, the mean (95% CI) population frequency was 7.9% (2.9 to 12.9) and coefficient of variation 27.8%. Seventy two (50.3%) of the children gave at least one positive response at 15% fall. Exercise testing is not reproducible in the community setting and should not be used as a screening test. Exercise data from epidemiological studies of asthma should be interpreted with caution.

Asthma↗
PubMed1996

"Black blood" T2-weighted inversion-recovery MR imaging of the heart.

PURPOSE: To develop a short-inversion-time inversion-recovery (STIR) magnetic resonance imaging pulse sequence for evaluating the myocardium that is relatively free of flow and motion artifact. MATERIALS AND METHODS: The authors implemented a breath-hold, cardiac-triggered STIR sequence with preparatory radio-frequency pulses to eliminate signal from flowing blood. A segmented rapid acquisition with relaxation enhancement (turbo spin echo) readout was used, with the inversion-recovery delay adjusted to null fat. The sequence was implemented at 1.0 and 1.5 T and tested in phantoms, five healthy volunteers, and three patients. RESULTS: Phantom studies confirmed the expected behavior of the sequence. In the volunteers, fat-suppressed images of the heart with STIR contrast were generated in a breath-hold period. Blood in the heart chambers was uniformly nulled, and motion artifacts were effectively suppressed. Focal high signal intensity consistent with edema was seen in two patients with acute myocardial infarction; in a third patient, a paracardiac mass was visualized and sharply demarcated relative to normal myocardium. CONCLUSION: Fast STIR imaging of the heart with effective suppression of flow and motion artifacts was implemented. The approach has much potential for high-contrast imaging in a variety of diseases affecting the heart and mediastinum.

Adult↗
PubMed1996

Left ventricular outflow tract obstruction in hypertrophic cardiomyopathy: presurgical and postsurgical evaluation by computed tomography magnetic resonance imaging.

Along with hypertrophy of the left ventricle (LV), hypertrophic cardiomyopathy (HC) is characterized by LV outflow tract (LVOT) obstruction, partly from systolic anterior motion (SAM) of the anterior mitral leaflet; if obstruction is significant, excision of excess subaortic septal myocardium may be indicated. In this study, the ability of computed tomography magnetic resonance imaging (Cine MRI) to provide information about LVOT obstruction was assessed in a series of 37 HC cases undergoing evaluation, including echocardiography (0 to 14 days before), for possible septal myectomy; in 4 cases, Cine MRI was used postsurgically (5 to 25 months after). Blinded to echocardiography results, 3 reviewers analyzed by consensus the Cine-MRI LVOT-long-axis image-loops for SAM grade (none, mild, severe) and "aorta:LVOT signal ratio" (intensity in descending aorta/intensity in LVOT at maximum systolic-flow disturbance). Resting LVOT flow velocities were separately determined using Doppler analysis, permitting differentiation between insignificant (< 30 mm Hg) and significant (< or = 30 mm Hg) gradients. With echocardiography, significant resting obstruction was found in 62% of cases, including 92% treated surgically. A significant association between SAM grade and obstruction was found; all cases with a SAM grade of none had insignificant ([-] predictive value: 100%) and most with a severe grade had significant ([+] predictive value: 78%) obstruction. Signal ratio in the absence of a significant gradient was significantly lower than in its presence; a significant linear relationship between aorta:LVOT signal ratio and resting gradient was found: LVOT gradient = ([2.9] x [signal ratio]) + 22.8. SAM grade did not contribute significantly in obstruction categorization when signal ratio was known. In all cases studied after surgery, SAM grade had decreased from severe to insignificant levels and aorta:LVOT signal ratio had been significantly reduced. Insights into the dynamic nature of the LVOT in HC patients can be provided by Cine MRI, either during their evaluation for surgery or after their septal myectomy.

Cardiomyopathy, Hypertrophic↗
PubMed1996

MR imaging of the thoracic aorta.

The evaluation and diagnosis of thoracic aortic disease using magnetic resonance imaging, including magnetic resonance angiography, is assuming an increasing role in clinical practice. Comparison with other modalities, including computed tomography and echocardiography, is discussed. Newer magnetic resonance imaging techniques, including 3-D breath-hold time-of-flight sequences are highlighted, as well as imaging strategies using standard magnetic resonance imaging techniques. Thoracic aortic disease entities covered include aneurysm, dissection, penetrating ulcers and intramural hematoma, aortitis and infection, tumors, and congenital aortic disease.

Aorta, Thoracic↗
PubMed1995

Custom CAD/CAM total temporomandibular joint reconstruction system: preliminary multicenter report.

PURPOSE: The purpose was to test the outcome of a custom computer assisted design/computer assisted manufactured (CAD/CAM) total temporomandibular joint (TMJ) reconstruction system. PATIENTS AND METHODS: There were 215 patients (13 males and 202 females); the average age at reconstruction was 40.9 +/- 10.3 years (range, 15 to 77 years). There were 363 joints placed, 296 bilateral and 67 unilateral. The patients had TMJ problems for an average of 10.3 +/- 7.0 years (range, 1 to 44 years), and had undergone a mean of 5.4 +/- 4.8 (range, 0 to 28) prior unsuccessful surgeries. Preoperative and postoperative data were collected for up to 48 months using a standardized data collection format. Subjective data related to pain, function of the lower jaw, and diet, were obtained using a visual analogue scale. Objective measures of mandibular range of motion were made directly on the patient preoperatively and postoperatively. RESULTS: Preliminary analysis of these data reveals a statistically significant decrease in pain, an increase in function, and improvement in diet (P < .0001) from the preoperative measurements to 1 and 2 years postoperatively. There was also improvement in mandibular vertical range of motion. The number of previous surgeries was a strong predictor of postoperative pain, function, and diet scores, as well as of maximal interincisal opening. A life table analysis of failures indicates good durability of the prosthesis over time. CONCLUSION: These preliminary data indicate that this custom CAD/CAM total TMJ reconstruction system seems to be useful in the treatment of the multiply operated, and/or anatomically mutilated TMJ.

Adolescent↗