Biomedical subjects

R L Summers

Publications and source records attributed to R L Summers.

At least 19 recordsLinked to original sources

PubMed2002

Effect of the initiation of noninvasive bi-level positive airway pressure on haemodynamic stability.

Noninvasive ventilation using noninvasive bilevel positive airway pressure (Bi-PAP) has been shown to be an effective means of improving oxygenation and respiratory status in patients with obstructive pulmonary disease (COPD) and acute congestive heart failure (CHF). However, it is uncertain what effects this positive airway pressure has on the haemodynamic condition of these patients. This study examines the acute changes in basic circulatory parameters with the initiation of Bi-PAP. Noninvasive measurements of the heart rate, systolic and diastolic arterial pressure, cardiac index, total peripheral resistance, ventricular ejection time, and total diastolic time were determined by impedance cardiography before and after the institution of Bi-PAP (pressures 15/5) in a group of healthy volunteers. In a collateral study, the same measurements were made in COPD patients in whom Bi-PAP was initiated for therapeutic reasons. Changes in the haemodynamic parameters were analysed using a paired t-test (p < 0.05). In the 12 healthy volunteers studied there were no significant differences in any of the haemodynamic parameters measured (average cardiac index: 2.75 +/- 0.78) over a period of 15 minutes after the placement of Bi-PAP. Similar results for most haemodynamic parameters were found in the 7 COPD patients with imminent respiratory failure (average respiratory rate 24.8 +/- 3.2) when Bi-PAP was utilized with the exception of significant but small increases in the cardiac index, stroke volume and oxygen saturation (p<0.05). While Bi-PAP is frequently used in the treatment of patients with acute respiratory failure, little is known about its effect on haemodynamics. This study suggests that the effects of the initiation of Bi-PAP on the general circulation and cardiac output may be of minor relevance.

Adult↗

PubMed2002

Computer systems analysis of the cardiovascular mechanisms of reentry orthostasis in astronauts.

Reentry orthostasis secondary to a prolonged exposure to microgravity is a common problem among astronauts. However, the physiologic mechanisms are poorly understood due to the many control systems involved. In this study an advanced computer model of cardiovascular functioning was employed in a systems analysis approach to clarify the relative importance of some of the adaptive physiologic processes engaged when humans return from space. After simulation of the conditions of zero gravity for one month, the model predicted that the change in capacitance of the lower extremity veins resulting from a loss of external fluid forces in the dehydrated extracellular compartment was the dominant mechanism associated with reentry orthostasis. This condition appears accentuated in women due to their inherent lower center of gravity and proportionately larger mass in the lower extremities.

Adaptation, Physiological↗

PubMed2001

Benign paroxysmal positional vertigo: diagnosis and treatment in the emergency department--a review of the literature and discussion of canalith-repositioning maneuvers.

Dizziness is a frequent presenting complaint in emergency department patients. Although seen in patients of all ages, it is more prevalent in patients older than 50 years of age. Vertigo represents a subset of dizziness and is defined as an illusion of movement, usually rotational, of the patient or the patient's surroundings. The illusion of motion may be of oneself (subjective vertigo) or of external objects (objective vertigo). The emergency physician should consider a large differential in the evaluation of vertigo with special attention to whether the vertigo is central or peripheral in origin.

Emergency Service, Hospital↗

PubMed2001

Association of atypical chest pain presentations by African Americans and the lack of utilization of reperfusion therapy.

OBJECTIVE: One possible factor resulting in delays in using reperfusion therapy in patients with acute myocardial infarction (AMI) is the failure to recognize cardiac symptomatology early in certain subgroups of patients. These patients may undergo extensive evaluation for gastrointestinal or musculoskeletal complaints before it is recognized that they are suffering from an AMI. METHODS: The records of patients (52% Black and 48% White; 49% male and 51% female) presenting to an urban teaching hospital with enzyme documented myocardial infarctions were retrospectively examined for traditional elements of atypia in their initial chest pain descriptions to the emergency department (ED). The rate of reperfusion therapy utilization was also determined for this group. RESULTS: Of the patients meeting the study criteria (166 total), 43% were found to have atypical elements in the character of their pain description. This high prevalence of atypia also coincided with a low reperfusion intervention rate of 38%. In examining the subgroups, it appears that African Americans and women had the highest rates of atypical pain (56% and 46%, respectively) while also having the lowest utilization rates for reperfusion therapies (31% and 33%, respectively). This compares to rates of 48% for Whites and 60% for White males who had more typical chest pain. CONCLUSIONS: While no direct correlation can be drawn from the data, it has been suggested that atypical presentations may result in early failure to recognize myocardial infarction and cause delay in or prevent appropriate therapy. It is thought that chest pain should be de-emphasized as a part of the indication criteria for thrombolytics and emergent angioplasty.

Adult↗

PubMed2000

Detection of isopropyl alcohol in a patient with diabetic ketoacidosis.

A 29-year-old man presented to the Emergency Department with acute mental status changes. He was unable to give a history. He was found to be in diabetic ketoacidosis, although his family reported no prior history of diabetes. A toxic exposure work-up revealed the presence of isopropyl alcohol in the patient's blood. His condition improved with treatment of the ketoacidosis, and he subsequently denied any exposure to isopropyl alcohol prior to presentation to the hospital. This case provides further support to a growing body of evidence that the detection of isopropyl alcohol may not represent an acute ingestion but, rather, a byproduct of acetone metabolism in certain disease states.

2-Propanol↗

PubMed2000

Noninvasive estimation of the end systolic pressure-volume relationship using impedance cardiography.

PURPOSE: Traditional measures of cardiac contractility such as dp/dt and ejection fraction has been noted to be sensitive to preload and afterload conditions. The end systolic pressure-volume relationship of the left ventricle (ESPVR, Suga Index or Emax) has been found to be the best load independent measure of the cardiac contractile state. However, determination of the ESPVR requires very highly invasive procedures. Impedance cardiography (IC) is a reliable noninvasive method for calculating stroke volume and may also be useful for estimating the end systolic volume. METHODS: An equation was derived using the systolic time intervals (PEP = pre-ejection period, LVET = left ventricular ejection time) and determined stroke volume (SV) as calculated from the impedance cardiograph to estimate the end systolic volume of the left ventricle. Likewise, and systolic pressure (ESP) was estimated from brachial cuff pressures using a previously published method. The resulting ESPVR was then calculated from tracings recorded in healthy normal subjects and compared to those obtained from patients in decompensated congestive heart failure (ejection fraction < 30% by echocardiogram) using the standard t test (p < 0.05). RESULTS: Using the derived equation (ESPVR = ESP/(SV/(1.125-1.25(PEP/LVET)) - SV), the ESPVR for the normal group of 6 averaged 2.72 +/- 0.71 and was significantly different from the 1.04 +/- 0.45 found in 6 patients with known systolic dysfunction. In a further test of the method, 15 patients who received concurrent echocardiographic and IC evaluations were found to have calculated ESPVR values that significantly correlated with determined ejection fractions (r = 0.83, p < 0.01). CONCLUSIONS: A noninvasive method for estimating the ESPVR that differentiates the myocardial contractile state in the clinically setting was derived using parameters obtained from IC. While further studies are needed to correlate this new equation with invasive measurements, this method has the potential for easily estimating load independent contractility in patients with cardiac dysfunction.

Adult↗

PubMed1999

Cervical collar-induced changes in intracranial pressure.

Placement of a protective cervical collar is common in cases of acute head trauma. However, the effect of this collar on intracranial pressure is uncertain. This prospective study examined the change in measured cerebrospinal fluid pressure (CSFP) after the application of a rigid Philadelphia collar in 20 adult patients undergoing lumbar puncture. CSFP averaged 176.8 mm H2O initially and increased to an average of 201.5 mm H2O after collar placement (range 0 to 120). Although this difference of 24.8 mm H2O is statistically significant (P = .001), it is uncertain if this would be clinically important. Nonetheless, this small increment in pressure could be significant in patients who already have an elevated intracranial pressure.

Adult↗

PubMed1999

Effect of nebulized albuterol on circulating leukocyte counts in normal subjects.

Nebulized beta 2-receptor agonists may cause neutrophil demargination and result in misleading total circulating leukocyte counts (WBCs) in patients with acute bronchospasm. Varying underlying adrenergic stimulation in these patients also makes interpretation of these data difficult. This study examined the direct effect of these agents on the measured WBCs of healthy adults without evidence of bronchospasm or illness. A prospective, blinded, randomized study of 30 healthy volunteers (aged 18-50 years) was performed in a controlled environment. Subjects were excluded if they were pregnant, had a known underlying medical disorder or have had a prior reaction to albuterol or similar medications. Participants in the study were given either a nebulized albuterol treatment or nebulized normal saline (control group). Leukocyte counts were then obtained before and after treatments. Paired data were analysed using a one-tailed t-test while considering an increase of 40% in WBCs to be significant, P = 0.05, and beta = 0.10. Mean leukocyte counts were 5.9 (+/- 1.2) before treatment as compared to 6.0 (+/- 1.3) after albuterol nebulization. Using the coefficient of variance of WBCs in normal humans as c. 50% (6000 +/- 3000 cells mm-1) we were unable to demonstrate a significant difference in variation in post-nebulized leukocyte counts between the control group and the nebulized albuterol group. While there is concern that the treatment of patients experiencing acute bronchospasm with beta 2 agonists may result in factitious elevations in peripheral leukocyte counts, were found no direct effect of these agents on measured counts in normal subjects.

Adolescent↗

PubMed1999

Prevalence of atypical chest pain descriptions in a population from the southern United States.

INTRODUCTION: The character of chest pain (CP) is a major factor determining triage and admission for patients presenting to the emergency department (ED). Previous studies have found atypical descriptions in as little as 10-15% of patients with true myocardial ischemic pain. Atypical descriptions may be more prevalent in the Deep South of the United States because of cultural differences in the semantic description of pain. METHODS: A retrospective study of patients presenting to the ED of a southern U.S. urban hospital with enzyme-documented myocardial infarction was conducted to determine the prevalence of atypical CP descriptions. A multivariate analysis of those patients with atypical pain descriptions was conducted to determine the independent demographic factors associated with these descriptions. RESULTS: In a total of 77 subjects (56% black; 44% white) meeting the study criteria, 43% were found to have atypical elements in the character of their CP descriptions. Only the black race demographic was found to be significantly correlated with the atypical descriptions. The use of the descriptive term "sharp" accounted for nearly half of the atypical presentations. CONCLUSION: Regional differences in the description of the character of CP may result in misleading portrayals of ischemic heart disease in southern U.S. populations. These differences are associated with a higher prevalence of atypical CP because of semantic distinctions, such as the use of the term "sharp" as a descriptor of acuity rather than character or quality.

Adult↗

PubMed1999

Diagnostic uses for thoracic electrical bioimpedance in the emergency department: clinical case series.

Differentiation of the central haemodynamic state is often critical during acute resuscitation. A clinical case series is presented in which the use of thoracic electrical bioimpedance (TEB) was pivotal in the diagnostic determination of the pathophysiology. This new technology allows the emergency physician to rapidly determine cardiac output, total peripheral resistance and myocardial contractility. The inexpensive and non-invasive nature of the TEB measurement makes cardiac output determination a potential 'sixth' vital sign for the evaluation of the emergent patient.

Adult↗

PubMed1999

Assessment of the "scholarly project" requirement for emergency medicine residents: report of the SAEM Research Directors' workshop. SAEM Research Directors' Interest Group.

OBJECTIVES: Differences in interpretation of the residency review committee (RRC) directive concerning resident scholarly activity have resulted in inconsistencies in the practical fulfillment of this responsibility among the various training programs in emergency medicine. During a workshop organized by the SAEM Research Directors' Interest Group (RDIG), a consensus statement was developed regarding the scope, definition, and purpose of the scholarly project requirement. METHODS: During the workshop, the NIH model of consensus building was used to develop statements pertaining to specific questions of the goals, definition, and endpoints of the scholarly project. The program consisted of an overview of the history and issues related to the scholarly project and presentations of varying viewpoints from interested parties. A final consensus of answers to the defined questions was then developed by the workshop participants during roundtable discussions and further refined through interactive debate using the RDIG e-mail list server. RESULTS: By consensus it was agreed that the primary role of the scholarly project is to instruct residents in the process of scientific inquiry, to teach problem-solving skills, and to expose the resident to the mechanics of research. To realize these goals, the project should include the general elements of hypothesis formulation, data collection, analytic thinking, and interpretation of results. It was also thought that these elements should be documented in some written form with a literature review. CONCLUSIONS: While each residency program must implement the RRC residency requirements in a manner that best suits the needs and culture of its individual environment, a concurrence of definition and approach to satisfying the scholarly project requirement would provide better consistency in resident training. Guidelines developed by consensus during the SAEM RDIG workshop may serve as a general recipe that can be used to fulfill the goals of the scholarly project and the spirit of the RRC directive.

Decision Making↗

PubMed1999

Differentiating systolic from diastolic heart failure using impedance cardiography.

OBJECTIVE: Differentiating systolic from diastolic congestive heart failure (CHF) is often difficult in the ED. Impedance cardiography (IC) allows for the noninvasive evaluation of systolic function and measurement of diastolic time intervals. This study was designed to assess the ability of IC to accurately measure isovolumic relaxation time (IVRT) and determine relative cardiac contractility, thereby differentiating systolic from diastolic mechanisms in acute CHF. METHODS: In an evaluation of the technique, the average differences in the diastolic time intervals measured in normal subjects by both IC tracings and phonocardiography were compared. Likewise, the average Heather index (HI) of patients with known systolic dysfunction (ejection fraction < 30% by echo-cardiography) was compared with the mean HI measured in the normal subjects. In a retrospective analysis, the clinical performance of the method was examined by extracting the values of IVRT and HI from IC tracings of patients presenting with CHF. The determined IVRT and HI values were then correlated to clinical markers for diastolic and systolic dysfunction. RESULTS: Analysis of 280 IC tracings in eight healthy volunteers revealed an average difference of 0.0075 seconds (95% CI = -0.0067 to 0.0217) when IVRT intervals measured by phonocardiography and IC are compared. The HI in this normal group averaged 14.2 (95% CI = 9.4 to 19.0), contrasting to the much lower value of 2.8 (95% CI = 1.98 to 3.62) seen in eight subjects with documented systolic dysfunction. In 26 patients with decompensated CHF, there was a close correlation (r = 0.81) of the measured IVRT to left ventricular hypertrophy by voltage criteria and while a fall in the HI was correlated with intravascular volume expansion. Though there was considerable overlap (46%) in mechanisms of CHF, 35% of the patients were found to have only systolic dysfunction (HI < 5 and IVRT < 0.125), while 19% had a predominantly diastolic etiology (IVRT > 0.125 and HI > 5) for their failure. CONCLUSION: IC measures of contractility and diastolic time intervals are a potentially effective method for differentiating the dominant mechanisms of CHF in the emergent setting and categorizing CHF patients into different subsets.

Acute Disease↗

PubMed1999

Diastolic compliance is reduced in obese rabbits.

Obesity often leads to symptoms of cardiopulmonary congestion associated with normal systolic but abnormal diastolic function. This study analyzed alterations in passive diastolic compliance in obesity using the rabbit model. New Zealand White rabbits were fed a normal (n=8) or 10% added fat diet (n=8). After 12 weeks, rabbits fed the high fat diet developed obesity (5.34+/-0.11 versus 3.68+/-0. 04 kg, P</=0.05) and left ventricular hypertrophy (1.37+/-0.07 versus 0.98+/-0.03 g dry weight, P</=0.05). Compliance was assessed with the isolated heart preparation by analyzing the passive end-diastolic left ventricular pressure-volume relationship. The pressure-volume relation was fit to an exponential function by regression analysis; results showed that the modulus of stiffness was greater in obese than in lean rabbits (1.21+/-0.16 versus 0. 83+/-0.05, P</=0.05), indicating that diastolic compliance was reduced. Computer simulation analyses suggested that an isolated reduction in diastolic compliance may contribute to elevated cardiac filling pressures and exercise intolerance. These data suggest that diastolic compliance is reduced early in the development of obesity and may be an important component in the reduction of cardiac reserve in obesity.

Animals↗

PubMed1998

Effect of routine pulse oximetry measurements on ED triage classification.

Pulse oximetry is commonly used to rapidly determine oxygen saturation and is incorporated in emergency triage as a screening for potential cardiopulmonary complications. This study examined the effect of routine pulse oximetry measurements on emergency department (ED) triage classification. Using a portable pulse oximeter, oxygen saturation of 1,235 adults presenting to a university-based, urban ED was obtained and each patient was assigned a classification of severity based on a standard 1-to-4 scale before and after the measurement. According to data obtained, a small but statistically significant group (2.8%) benefitted from the routine use of pulse oximetry in an emergency triage system and only 40% of these patients required admission or extended care. Although this group is small in number, the potential consequences of missing a hypoxic condition could be devastating for the individual patient. Since pulse oximetry is presently an inexpensive technology, it would seem to be a worthwhile screening tool for emergency triage.

Adult↗

PubMed1998

Computer simulation studies and the scientific method.

The scientific method is the formal procedure for all acceptable scientific endeavors. With this methodology, there is a continual interaction between theory, in the form of an hypothesis, and objective, experimental analysis. There is a new step in the scientific method that involves the use of computer models and simulation studies. When computer models are incorporated into hypothesis formulation, they can be used in simulation studies to test ideas before they are tried experimentally. An iterative feedback between these tests and current ideas allows for a preliminary refinement of hypotheses and development of more intelligent research protocols. In this way, computer simulation studies can serve as an intermediate step in the scientific method, reducing the number of animals used in biomedical experimentation. In this article we also explore other ways that computer simulation studies could limit the use of animals in biomedical research and education.

Journal Article↗

PubMed1998

Injuries sustained during competitive white-water paddling: a survey of athletes in the 1996 Olympic trials.

To examine injury prevalence in competitive paddlers, a cross-sectional, retrospective, written survey of the athletes competing in the four regional Olympic canoe and kayak qualifying races for the United States Canoe and Kayak Team was conducted in the spring of 1996. A total of 375 questionnaires were distributed, of which 54 were completed and returned. Results were reported as the percentage of total injuries. A composite of 271 separate injuries was reported by kayakers during their careers. While 56% of the injuries occurred during training, 40% happened during recreation and 4% during competition. The most frequent injuries were sprains (32%), tendonitis (20%), and chronic musculoskeletal pain (14%). Simple bruises (9%) and infections (8%) occurred with moderate frequency, while severe injuries, such as dislocations (3%) and lacerations (2%), were even less common. About 10% of the paddlers noted a near-drowning event during their careers. Of the injuries noted, 70% were reported as recurrent or chronic. Treatment included rest (37%), physical therapy (23%), medical intervention (34%), and surgical intervention (6%). White-water paddling of canoes and kayaks is a potentially dangerous sport, and competitive paddlers frequently suffer a range of injuries. Most injuries occurred during training; however, the short intense work of racing produced a greater frequency of injuries.

Adult↗

PubMed1998

Role of technetium-99m sestamibi myocardial imaging in the emergency department evaluation of chest pain.

The use of technetium-99m sestamibi myocardial imaging is rapidly becoming a state of the art methodology for the emergency department evaluation of patients with chest pain. The following case report represents the first emergency department sestamibi scan ordered at the University of Mississippi Medical Center and is used to discuss the logistics and indications for such tests. A general guideline for ordering sestamibi scans has been developed for use in the emergency department.

Adult↗

PubMed1997

Theoretical analysis of the mechanisms of chronic hyperinsulinemia.

Steady-state insulin resistance results in a fasting hyperinsulinemia and is a common feature of type II diabetes mellitus and obesity. In this study, a systems analysis approach was used to study glucose homeostasis which is considered as the dynamic balance between glucose release by the liver and its uptake by the peripheral tissues as regulated by insulin and glucagon. A series of computer simulation studies were performed utilizing a mathematical model of glucose homeostasis. The purpose of the study was to better understand the factors which control glucose balance and to ascertain their relative importance in the development of steady state, fasting hyperinsulinemia. When peripheral cellular insulin receptors which regulate glucose uptake were reduced to 25% of normal, the steady state plasma insulin concentration showed little change from the basal level of 8 microU/ml. When insulin receptors in the liver were also reduced to 25% of normal, the steady state insulin concentration increased from the basal levels to 32 microU/ml. Reducing pancreatic alpha cell insulin receptors to 25% of normal further increased the hyperinsulinemia to 80 microU/ml. Hence, this study suggests that the liver and its release of glucose, as controlled by insulin and glucagon, plays a central role in the development of a steady-state insulin resistance and hyperinsulinemia.

Adult↗