Biomedical subjects

Richard L Summers

Publications and source records attributed to Richard L Summers.

10 recordsLinked to original sources

PubMed2006

Computer systems analysis of spaceflight induced changes in left ventricular mass.

Circulatory adaptations resulting in postflight orthostasis have frequently been observed in response to space travel. It has been postulated that a decrement in left ventricular mass (LVM) found after microgravity exposure may be the central component in this cardiovascular deconditioning. However, a physiologic mechanism responsible for these changes in the myocardium has not been determined. In this study, we examined the sequential alterations in echocardiographic measured LVM from preflight to landing day and 3 days into the postflight recovery period. In a previous study in returning astronauts we found a comparative 9.1% reduction in postflight LVM that returned to preflight values by the third day of recovery. This data was further evaluated in a systems analysis approach using a well-established advanced computer model of circulatory functioning. The computer model incorporates the physiologic responses to changes in pressures, flows and hydraulics within the circulatory system as affected by gravitational forces. Myocardial muscle progression to atrophy or hypertrophy in reaction to the circulatory load conditions is also included in the model. The integrative computer analysis suggests that these variations in LVM could be explained by simple fluid shifts known to occur during spaceflight and can reverse within a few days after reentry into earth's gravity. According to model predictions, the reductions in LVM found upon exposure to microgravity are a result of a contraction of the myocardial interstitial fluid space secondary to a loss in the plasma volume. This hypothesis was additionally supported by the published ground-based study in which we followed the alterations in LVM and plasma volume in normal subjects in which hypovolemia was induced by simple dehydration. In the hypovolemic state, plasma volume was reduced in these subjects and was significantly correlated with echocardiographic measurements of LVM. Based on these experimental findings and the performance of the computer systems analysis it appears that reductions in LVM observed after spaceflight may be secondary to fluid exchanges produced by common physiologic mechanisms. Reductions in LVM observed after microgravity exposure have been previously postulated to be a central component of spaceflight-induced cardiovascular deconditioning. However, a recent study has demonstrated a return of astronauts' LVM to preflight values by the third day after landing through uncertain mechanisms. A systems analysis approach using computer simulation techniques allows for a dissection of the complex physiologic control processes and a more detailed examination of the phenomena. From the simulation studies and computer analysis it appears that microgravity induced reductions in LVM may be explained by considering physiologic fluid exchanges rather than cardiac muscle atrophy.

Adult↗

PubMed2006

Impact of impedance cardiography on diagnosis and therapy of emergent dyspnea: the ED-IMPACT trial.

BACKGROUND: Dyspnea is one of the most common emergency department (ED) symptoms, but early diagnosis and treatment are challenging because of multiple potential causes. Impedance cardiography (ICG) is a noninvasive method to measure hemodynamics that may assist in early ED decision making. OBJECTIVES: To determine the rate of change in working diagnosis and initial treatment plan by adding ICG data during the course of ED clinical evaluation of elder patients presenting with dyspnea. METHODS: The authors studied a convenience sample of dyspneic patients 65 years and older who were presenting to the EDs of two urban academic centers. The attending emergency physician was initially blinded to the ICG data, which was collected by research staff not involved in patient care. At initial ED presentation, after history and physical but before central lab or radiograph data were returned, the attending ED physician completed a case report form documenting diagnosis and treatment plan. The physician then was shown the ICG data and the same information was again recorded. Pre- and post-ICG differences were analyzed. RESULTS: Eighty-nine patients were enrolled, with a mean age of 74.8 +/- 7.0 years; 52 (58%) were African American, 42 (47%) were male. Congestive heart failure and chronic obstructive pulmonary disease were the most common final diagnoses, occurring in 43 (48%), and 20 (22%), respectively. ICG data changed the working diagnosis in 12 (13%; 95% CI = 7% to 22%) and medications administered in 35 (39%; 95% CI = 29% to 50%). CONCLUSIONS: Impedance cardiography data result in significant changes in ED physician diagnosis and therapeutic plan during the evaluation of dyspneic patients 65 years and older.

Aged↗

PubMed2006

The impact of emergency department structure and care processes in delivering care for non-ST-segment elevation acute coronary syndromes.

BACKGROUND: We sought to assess the influence of emergency department (ED) structure and care processes on adherence to practice guidelines for the treatment of patients with non-ST-segment elevation acute coronary syndromes. METHODS: We surveyed emergency physicians and nurses from 316 hospitals participating in the CRUSADE Quality Improvement Initiative and used multivariable modeling to correlate ED-specific characteristics with guidelines adherence. RESULTS: Factors that were significantly associated with improved guidelines adherence included collaboration between emergency physicians and hospital administration, northeast region, adequate nursing support, use of locum tenens physicians, an independent ED (not a division of another clinical department), and use of a care algorithm for acute coronary syndromes. CONCLUSIONS: Quality improvement strategies that have the full support of hospital administration, focus on increasing collaboration between emergency physicians and other health care providers, and specified protocol-driven management algorithm may be the most successful methods for improving the care and outcomes of patients with non-ST-segment elevation acute coronary syndromes.

Acute Disease↗

PubMed2005

Mechanism of spaceflight-induced changes in left ventricular mass.

Decrements in left ventricular (LV) mass observed after microgravity exposure have been previously postulated to be a central component of spaceflight-induced cardiovascular deconditioning. In this study, echocardiographic measurements of LV mass in astronauts demonstrated a comparative 9.1% reduction in postflight LV mass that returned to preflight values by the third day of recovery. A ground-based study in normal subjects determined that these pre- to postflight LV mass changes could be reproduced by simple dehydration. Reductions in LV mass observed immediately after spaceflight may be secondary to simple physiologic fluid exchanges.

Adult↗

PubMed2005

Emergencies in space.

Manned spaceflight is inherently risky and results in unique problems from a trauma and medical perspective. Emergency care under these special physiologic and environmental conditions calls for novel techniques for diagnosis and therapy.

Aerospace Medicine↗

PubMed2004

Certified mail fails to reach an Emergency Department population.

The objective of this study was to determine if correspondence sent by regular mail would be delivered more often than correspondence sent by certified mail. Correspondence was prospectively randomized and mailed by United States Postal Service using either regular mail service or certified mail service. Mailings were analyzed based on patient demographic information, whether or not mail was returned, and the reason for the return. Certified mail was sent to 145 patients; 58 (40%) of the mailings were returned. Wrong addresses accounted for only 23 (16%) of these, whereas the addressee never claimed 35 (24%). Regular mail was sent to 126 patients, and 19 (15%) of the letters were returned. Wrong addresses accounted for 18 (14%) of these letters, and only 1 (1%) was refused for delivery. In conclusion, when compared with certified mail, regular mail is a more effective means of reaching patients with follow-up information after an Emergency Department visit.

Correspondence as Topic↗

PubMed2003

Effect of a delta receptor agonist on duration of survival during hemorrhagic shock.

OBJECTIVES: Selective delta receptor agonists have been shown to stabilize membrane physiologic processes, reduce metabolic rates, and provide protection against ischemic insults through K(ATP) channel opening in a variety of organ beds. However, their potential for affecting outcomes in states of generalized ischemia has not been explored. The authors examined the effect of the nonselective delta receptor agonist, DADLE (D-Ala2-Leu5-enkephalin), on hemodynamic stability and duration of survival in an animal model of severe hemorrhagic shock. METHODS: Conscious Sprague Dawley rats with indwelling catheters were hemorrhaged at a rate of 3.25 mL/100 grams over 20 minutes after half of the group received 1% DADLE (1 mg/kg IV). Following the hemorrhage, all rats were continuously monitored for heart rate (HR), mean arterial pressure (MAP), and life signs for up to three hours (death defined as apnea, systolic blood pressure < 30 mm Hg without pulsations, and electroencephalographic silence). Survival rates and hemodynamic trends were compared between the control and DADLE-treated groups. RESULTS: In the 14 rats studied (8 DADLE; 6 controls), initial hemorrhage resulted in similar hemodynamic shock (average MAP fall: 118 to 59 vs 119 to 55 mm Hg). Analysis of survival at 3.5 hours revealed statistically significant differences between the control and DADLE groups. While 50% of the DADLE group survived past the three hours, no control animals were still alive at the end of the experimental period. The MAP trended downward and the HR increased for the control group, but all hemodynamic parameters stabilized in the rats treated with DADLE. CONCLUSIONS: Most current strategies for treating shock focus on the supply side of resuscitation. The coordinated various actions of DADLE have the potential to work in concert in the intact organism to improve overall survival during severe hemorrhagic shock. In an animal model of severe hemorrhagic shock, there was improvement in hemodynamic stability and a prolonged survival with DADLE treatment. Physiologic manipulation with DADLE appears to be a way to improve survival during shock with possible clinical implications.

Animals↗

PubMed2003

Bench to bedside: electrophysiologic and clinical principles of noninvasive hemodynamic monitoring using impedance cardiography.

The evaluation of the hemodynamic state of the severely ill patient is a common problem in emergency medicine. While conventional vital signs offer some insight into delineating the circulatory pathophysiology, it is often impossible to determine the true clinical state from an analysis of blood pressure and heart rate alone. Cardiac output measurements by thermodilution have been the criterion standard for the evaluation of hemodynamics. However, this technology is invasive, expensive, time-consuming, and impractical for most emergency department environments. Impedance cardiography (ICG) is a noninvasive method of obtaining continuous measurements of hemodynamic data such as cardiac output that requires little technical expertise. ICG technology was first developed by NASA in the 1960s and is based on the idea that the human thorax is electrically a nonhomogeneous, bulk conductor. Variation in the impedance to flow of a high-frequency, low-magnitude alternating current across the thorax results in the generation of a measured waveform from which stroke volume can be calculated by a modification of the pulse contour method. To adequately judge the possible role of this technology in the practice of emergency medicine, it is important to have a sufficient understanding of the basic scientific principles involved as well as the clinical validity and limitations of the technique.

Cardiac Output↗

PubMed2002

Blunt trauma in the obstetric patient: monitoring practices in the ED.

This study was undertaken to determine the usually used approach to fetal monitoring in the emergency department (ED) of the less severely injured obstetric patient who has sustained blunt trauma. A written survey was sent to clinical directors of teaching programs in emergency medicine (EM) with inquiries on the usual way of monitoring, what studies were performed, and the usual disposition of the less-injured obstetric patient. From the 112 teaching programs surveyed in early 1996, there were 87 responses (78%). Seventy-eight percent of programs generally have fetal monitoring performed for 2 to 4 hours in obstetric trauma patients when the trauma is more than minor extremity injury. In 68%, fetal monitoring was not performed in the ED from the time of the initial assessment of fetal heart tones until the mother went to an obstetric area even though the average estimated time to radiographically clear a cervical spine was 36 minutes. In 92% of programs residents are taught cardiotocographic changes indicative of fetal distress but only 15% have such monitoring equipment in their department. However, 51% do have sonographic equipment in their department. Given a patient with a viable fetus who has no abdominal pain, 46% routinely use fetal monitoring if the mechanism is a simple fall whereas 92% use monitoring only if the mechanism is a rollover motor vehicle collision or a strike to the abdomen. It is generally recognized that fetal distress may occur subtly without overt clinical signs and that obstetric area monitoring for a period of several hours should take place. However, most teaching programs do not institute continuous fetal monitoring during the first 30 to 60 minutes that the mother is undergoing her work-up even though residents are taught such monitoring.

Abdominal Pain↗

PubMedDate not supplied

Use of noninvasive hemodynamics to aid decision making in the initiation and titration of neurohormonal agents.

Angiotensin-converting enzyme inhibitors, beta adrenergic blockers, and nesiritide are pharmacologic agents for heart failure with both short- and long-term neurohormonal and hemodynamic effects. Angiotensin-converting enzyme inhibitors and beta adrenergic blockers reduce morbidity and mortality in chronic heart failure. Higher doses may result in better outcomes than lower doses, but concern about hemodynamic tolerance is a major barrier to the initiation and up-titration of these agents. Nesiritide is a newer neurohormonal agent with proven efficacy and safety for use in decompensated heart failure, but appropriate patient selection has been challenging for clinicians. Like vasodilators, nesiritide may be underutilized in heart failure treatment. Impedance cardiography is a newer, noninvasive monitoring technology that can accurately measure hemodynamic parameters. Impedance cardiography is being used with increasing frequency by clinicians to guide therapy in patients with heart failure and has been proposed in heart failure treatment algorithms. Three case reports are presented to illustrate how hemodynamic data using impedance cardiography can be utilized in the initiation and titration of neurohormonal agents.

Adrenergic beta-Antagonists↗