Nonlinear dynamics of heart rate variability during experimental hemorrhage in ketamine-anesthetized rats.

Indexes of heart rate variability (HRV) based on linear stochastic models are independent risk factors for arrhythmic death (AD). An index based on a nonlinear deterministic model, a reduction in the point correlation dimension (PD2i), has been shown in both animal and human studies to have a higher sensitivity and specificity for predicting AD. Dimensional reduction subsequent to transient ischemia was examined previously in a simple model system, the intrinsic nervous system of the isolated rabbit heart. The present study presents a new model system in which the higher cerebral centers are blocked chemically (ketamine inhibition of N-methyl-D-aspartate receptors) and the system is perturbed over a longer 15-min interval by continuous hemorrhage. The hypothesis tested was that dimensional reduction would again be evoked, but in association with a more complex relationship between the system variables. The hypothesis was supported, and we interpret the greater response complexity to result from the larger autonomic superstructure attached to the heart. The complexities observed in the nonlinear heartbeat dynamics constitute a new genre of autonomic response, one clearly distinct from a hardwired reflex or a cerebrally determined defensive reaction

Adenosine A1 antagonism attenuates atropine-resistant hypoxic bradycardia in rats

Objectives: To test the following hypotheses: Hypoxia induces bradycardia and hemodynamic compromise that are resistant to atropine but responsive to selective antagonism of the adenosine A1 receptor (A1AdoR). The mechanism for such attenuation is independent of the vagus nerve. Methods: Ten minutes after sham or actual bilateral cervical vagotomy, paralyzed ventilated rats were made hypoxic (5% fractional inspired oxygen, continued until death). Five minutes after beginning hypoxia, intravenous treatment with BG-9719, a selective A1AdoR antagonist (0.1 mg/kg); atropine (0.1 mg/kg); BG-9719 vehicle; or saline was initiated. These drug doses were based on pilot studies. Of the eight treatment groups (eight possible combinations of vagotomy status and drug/vehicle treatment), n = 8 in all except nonvagotomized, vehicle-treated rats (where n = 7). Results: Heart rate and left ventricular contractility decreased rapidly with hypoxia. Atropine had minimal effects in prolonging survival (from mean ± SEM of 15.5 ± 2.1 minutes to 20.2 ± 2.5 minutes, p = 0.94) and attenuating posthypoxic decreases in heart rate (p = 0.89) and contractility (p = 0.83) compared with saline. BG-9719 prolonged survival, however, from 14.4 ± 1.9 minutes (with vehicle treatment) to 37.2 ± 6.8 minutes (p \u3c 0.001). Survival, heart rate, and contractility were preserved with BG-9719 compared with atropine and vehicle (p \u3c 0.05, all comparisons). Vagotomy prevented the effects of BG-9719 on survival prolongation (p = 0.003), heart rate (p = 0.01), and contractility (p \u3c 0.001) but did not affect those outcomes in saline-treated rats. Conclusions: Survival, heart rate, and contractility were better preserved with BG-9719 than atropine. A1AdoR selective antagonism, possibly because of its multiple mechanisms for attenuating hypoxic cardiac insufficiency, resulted in better hemodynamic and clinical outcomes. That attenuation seems to have a component of vagal mediation

What is gross hematuria? Correlation of subjective and objective assessment

Background: Gross hematuria is a screening test used to help determine the need for radiographic evaluation in patients with blunt trauma. This subjective assessment has not been compared with objective measures, nor has interrater reliability been described. Methods: We performed a prospective, randomized, controlled study to determine the ability of clinicians to assess gross hematuria. Clinicians were asked to assess samples containing various concentrations of blood diluted in urine for the presence of gross hematuria. Results: Gross hematuria was recognized by more than 95% of clinicians only when samples contained more than 3,500 red blood cells per high-power field. Clinicians\u27 interpretations were independent of profession, specialty, and level of training (p \u3e 0.08). Conclusion: Clinicians demonstrate poor sensitivity and interrater reliability identifying gross hematuria by inspection. Clinical studies correlating degrees of hematuria to the need for genitourinary diagnostic evaluation should report both subjective and objective measures to identify a threshold value predictive of renal injury

Use of ultrasound to determine need for laparotomy in trauma patients.

STUDY OBJECTIVE: To determine whether abdominal ultrasound can be used routinely as the primary screening test to identify the need for laparotomy in trauma patients. METHODS: Ultrasound was used at a Level II trauma center as a primary screening test for evaluation of intraabdominal injury. We reviewed the charts of all patients from trauma codes presenting between January 1, 1991, and December 31, 1993, to determine the results of abdominal ultrasound evaluation and to learn whether laparotomy was required. RESULTS: A total of 2,013 trauma patients presented during the study interval. Ultrasound was performed in 1,631 patients as the primary screening test for abdominal injury (mean time after arrival, 22.9 minutes), abdominal computed tomography (CT) was performed as the primary screen on 8 (mean time, 68.6 minutes), and 93 patients underwent both ultrasound and CT of the abdomen. Of 86 patients requiring laparotomy who were screened by ultrasound, 80 had positive diagnostic findings, for a sensitivity of 93.0%. Of the 1,545 ultrasound-screened patients who did not require laparotomy, 1,390 had negative findings, for a specificity of 90.0%. None of the patients with negative ultrasound results died or sustained identifiable mortality as a consequence of their negative scans. CONCLUSION: Ultrasound is a sensitive and specific test with which to evaluate trauma patients for abdominal injury requiring surgery. Routine abdominal ultrasound can be performed at the bedside in the emergency department as a timely, noninvasive diagnostic test. This use of a screening abdominal ultrasound examination can improve clinical decision-making for the use of emergency laparotomy. Ultrasound may be a better alternative to CT or diagnostic peritoneal lavage for the initial screening evaluation of abdominal trauma