Cardiac injury markers in non-elite marathon runners.

An elevation of cardiac injury markers including creatinine kinase (CK), myoglobin (Myo) and cardiac troponin T (cTnT) has been observed in elite athletes following strenuous exercise. The mechanism and significance of this observation however have not been fully elucidated. The goals of this study were: 1) to determine whether these changes in biomarkers also occur in a large, heterogeneous group of non-elite athletes; and 2) to identify possible clinical or biochemical associations. We recruited 129 non-elite runners in 2006, 61 individuals who were taking part in the half (13.1 miles) marathon and 68 individuals participating in the full (26.2 miles) marathon. Demographic data and blood samples were collected for analysis of CK, Myo, cTnT, and Creatinine (Cr) levels within two hours of race start, at race completion, and 1-h post-race for both patient cohorts. In the 61 individuals (40 males, 40+/-12 yrs) completing the half marathon in a mean time of 150+/-20 min, 90.3%, 65.2%, and 30.6% of the subjects exhibited significant elevations in Myo, CK, and cTnT, respectively immediately post race and 100%, 74.9% and 45.9% in the same biomarkers one hour-post race. In the 68 individuals (44 males, 42+/-14 yrs) completing the full marathon in a mean time of 310+/-30 min, 95.3%, 70.2% and 35.7% exhibited significant elevations in Myo, CK and cTnT respectively immediately post race and 100%, 78.5% and 52.8% in the same biomarkers one hour-post race. The elevation in cTnT levels post-race were modestly associated with the time required to complete the race for the entire cohort of marathon runners. The serum levels of Cr, CK, and Myo post-race did not correlate however with age, sex, BMI, level of training, or prior marathon experience. Elevations of cardiac injury markers in non-elite athletes are extremely common following the completion of endurance events and correlate to the increased endurance time. Whether the increase in the levels of these enzymes represents true myocardial injury or a result of the release of cTnT from the myocytes requires further investigation.

Biologically variable ventilation prevents deterioration of gas exchange during prolonged anaesthesia.

We have studied the time course of changes in gas exchange and respiratory mechanics using two different modes of ventilation during 7 h of isoflurane anaesthesia in pigs. One group received conventional control mode ventilation (CV). The other group received biologically variable ventilation (BVV) which simulates the breath-to-breath variation in ventilatory frequency (f) that characterizes normal spontaneous ventilation. After baseline measurements with CV, animals were allocated randomly to either CV or BVV (FIO2 1.0 with 1.5% end-tidal isoflurane). With BVV, there were 376 changes in f and tidal volume (VT) over 25.1 min. Ventilation was continued over the next 7 h and blood gases and respiratory mechanics were measured every 60 min. The modulation file used to control the ventilator for BVV used an inverse power law frequency distribution (I/fa with a = 2.3 +/- 0.3). After 7 h, at a similar delivered minute ventilation, significantly greater PaO2 (mean 72.3 (SD 4.0) vs 63.5 (6.5) kPa) and respiratory system compliance (1.08 (0.08) vs 0.92 (0.16) ml cm H2O-1 kg-1) and lower PaCO2 (6.5 (0.7) vs 8.7 (1.5) kPa) and shunt fraction (7.2 (2.7)% vs 12.3 (6.2)%) were seen with BVV, with no significant difference in peak airway pressure (16.3 (1.2) vs 15.3 (3.7) cm H2O). A deterioration in gas exchange and respiratory mechanics was seen with conventional control mode ventilation but not with BVV in this experimental model of prolonged anaesthesia.

Biologically variable pulsation improves jugular venous oxygen saturation during rewarming.

BACKGROUND: Conventional pulsatile (CP) roller pump cardiopulmonary bypass (CPB) was compared to computer controlled biologically variable pulsatile (BVP) bypass designed to return beat-to-beat variability in rate and pressure with superimposed respiratory rhythms. Jugular venous O2 saturation (SjvO2) below 50% during rewarming from hypothermia was compared for the two bypass techniques. A SjvO2 less than 50% during rewarming is correlated with cognitive dysfunction in humans. METHODS: Pigs were placed on CPB for 3 hours using a membrane oxygenator with alpha-stat acid base management and arterial filtration. After apulsatile normothermic CPB was initiated, animals were randomized to CP (n = 8) or BVP (roller pump speed adjusted by an average of 2.9 voltage output modulations/second; n = 8), then cooled to a nasopharyngeal temperature of 28 degrees C. During rewarming to stable normothermia, SjvO2 was measured at 5 minute intervals. The mean and cumulative area for SjvO2 less than 50% was determined. RESULTS: No between group difference in temperature existed during hypothermic CPB or during rewarming. Mean arterial pressure, arterial partial pressure O2, and arterial partial pressure CO2 did not differ between groups. The hemoglobin concentration was within 0.4 g/dL between groups at all time periods. The range of systolic pressure was greater with BVP (41 +/- 18 mm Hg) than with CP (12 +/- 4 mm Hg). A greater mean and cumulative area under the curve for SjvO2 less than 50% was seen with CP (82 +/- 96 versus 3.6% +/- 7.3% x min, p = 0.004; and 983 +/- 1158 versus 42% +/- 87% x min; p = 0.004, Wilcoxon 2-sample test). CONCLUSIONS: Computer-controlled BVP resulted in significantly greater SjvO2 during rewarming from hypothermic CPB. Both mean and cumulative area under the curve for SjvO2 less than 50% exceeded a ratio of 20 to 1 for CP versus BVP. Cerebral oxygenation is better preserved during rewarming from moderate hypothermia with bypass that returns biological variability to the flow pattern.

Impaired hepatic extraction and increased splanchnic production contribute to lactic acidosis in canine sepsis.

In septic shock, the extent to which lactic acidosis (LA) is a consequence of splanchnic lactate overproduction (SLP) or impaired hepatic lactate extraction (HLE) is not clear. We examined SLP and HLE in E. coli sepsis in dogs. We further determined the effects of vasopressor treatments, which included phenylephrine, dopamine, norepinephrine, and a combination of dobutamine and norepinephrine treatment, on SLP and HLE in respective groups. The animals were studied while anesthetized and ventilated. During sepsis, SLP increased as compared with presepsis (-0.017 versus 0.07 mmol/min, p < 0.05), but this increase could not be explained by reduced splanchnic oxygen delivery (SOD). During sepsis, HLE increased as compared with baseline (0.8 versus 8%, p < 0.05), but was significantly lower than that found during lactic acid loading in nonseptic dogs. None of the vasopressor treatments had a detrimental effect on SLP. These results indicate that LA in sepsis occurs secondary to an increase in splanchnic lactate production that is not related to reduced splanchnic oxygen delivery, as well as to a decrease in hepatic lactate extraction. Effects of different vasoactive agents did not alter either splanchnic lactate production or hepatic lactate extraction in this sepsis model.

Ethical and practical considerations of withdrawal of treatment in the intensive care unit.

PURPOSE: To discuss the medical, ethical and legal basis of decisions to discontinue life-support therapy in the adult intensive care unit (ICU), and to provide practical guidelines for the discontinuation of life support therapy. SOURCE: Relevant articles were retrieved through Medline (1991-present; terms: ethics, life support discontinuation, double effect, beneficence, non-maleficence). Other sources include legal references, and personal files. PRINCIPAL FINDINGS: Understanding the legal and ethical principles of autonomy, beneficence, non-maleficence and double effect are crucial when withdrawing life support therapy. The law respects a competent patient's right to direct his/her healthcare but does not uphold his/her right to demand futile care. Surrogate decision makers can be used when the patient is incompetent, provided they are acting in the patient's best interest. Euthanasia is illegal and the distinction between discontinuation of therapy and euthanasia is legally clear. Skillful administration of palliative therapy cannot be construed as euthanasia when the aforementioned ethical principals are respected. The various practical methods of discontinuing therapy are discussed. Every ICU should develop its own guidelines and a checklist to help caregivers during this difficult time. Caregivers must anticipate the mechanism of death and direct interventions at the symptoms that are likely to cause discomfort. Drugs and dosages must be individualized, and depend on the underlying disease, anticipated mechanism of death, and the patient's pharmacological history. When prescribing a drug, the intention should be clear. CONCLUSIONS: Appropriate discontinuation of therapy in the ICU allows patients a dignified and comfortable death.

Histamine H3 activation depresses cardiac function in experimental sepsis.

In the heart, histamine (H3) receptors may function as inhibitory presynaptic receptors that decrease adrenergic norepinephrine release in conditions of enhanced sympathetic neural activity. We hypothesized that H3-receptor blockade might improve cardiovascular function in sepsis. In a canine model of Escherichia coli sepsis, we found that H3-receptor blockade increased cardiac output (3.6 to 5.3 l/min, P < 0.05), systemic blood pressure (mean 76 to 96 mmHg, P < 0.05), and left ventricular contractility compared with pretreatment values. Plasma histamine concentrations increased modestly in the H3-blocker-sepsis group compared with values obtained in a nonsepsis-time-control group. In an in vitro preparation, histamine H3 activation could be identified under conditions of septic plasma. We conclude that activation of H3 receptors may contribute to cardiovascular collapse in sepsis.

Localization of a presumed catecholamine-secreting glomus tumor by 123I-metaiodobenzyl guanidine (MIBG) single photon emission computed tomography (SPECT) scanning.

We present an unusual case of a 41-year-old woman with a known glomus tumor, an adrenal mass, hypertension, and elevated catecholamines. The glomus tumor was shown to be the site of excessive catecholamine production in what we believe to be one of the few descriptions of 123I-metaiodobenzylguanidine (MIBG) scanning for this uncommon tumor. The diagnostic difficulties of such a case are discussed. A literature review of catecholamine-secreting glomus tumors and a systematic approach to catecholamine-secreting tumor localization in such patients is presented. Therapeutic options of surgery, radiation therapy, and embolization are reviewed. We conclude that the management of patients with functioning glomus tumors needs to be individualized. A careful, systematic approach is required if needless surgery is to be avoided. Further, the use of 123I-MIBG scanning deserves consideration to help localize catecholamine production in such patients.

Changes in hippocampal monoamine concentration following halothane anesthesia and concussion.

The concentration of norepinephrine in the hippocampus of rats anesthetized with halothane (Wyeth-Ayerst, Philadelphia, Pa) is found to be markedly increased, presumably due to the stress of handling and administering the anesthetic. This increased norepinephrine concentration persists for about 50 minutes but is obliterated when the anesthetized rat is concussed. This 50-minute period corresponds to the time it takes for a rat (or human), comatose for 1-2 seconds following concussion, to regain normal memory. No changes in 3,4-dihydroxybenzene-acetic acid (DOPAC), 3-(3,4-dihydroxyphenyl) alanine (L-DOPA), and 3,4-dihydroxybenzylamine (DHBA) were noted. 5-Hydroxy indole acetic acid (HIAA) showed a depression at 5 minutes and again at 30 minutes, changes that were consistent but not considered statistically significant.