Lower Core Temperature Research Articles

Experimental investigations of coaxial injectors in a laboratory-scale rocket combustor

An investigation is performed through experiments of a laboratory-scale optically accessible combustor equipped with a single-element shear coaxial injector. Various optical diagnostics approaches, such as hydroxyl (OH) planar laser-induced fluorescence (OH-PLIF), high-speed imaging and infrared imaging, are simultaneously used to determine the OH radical spatial distribution, flame instantaneous fluctuations, and temperature fields outside the combustor nozzle. This study emphasizes the combustion characteristics and flame stabilizations of two propellant combinations under the same thrust level, including gaseous hydrogen/gaseous oxygen (GH2/GO2) and gaseous methane/gaseous oxygen (GCH4/GO2). Moreover, to validate a pressure-scaling criterion, different pressure conditions are also considered. Based on the results of the high-speed and OH-PLIF images, combustion similarities are evident under different chamber pressures for each propellant couple. The two kinds of flame are seen to be stabilized in the vicinity of the oxidizer injector lip but the anchor region in the GCH4/GH2 cases is found to change dynamically near the lip. The lift-off GCH4/GO2 flame exhibits evident unsteady combustion phenomenon in the combustor. Experimental data indicates that GCH4/GO2 flame stabilization is hard to achieve compared to the GH2/GO2 flame. Furthermore, the GCH4/GO2 flame has a greater heat releasing intensity and gentler reaction zone distribution. This indicates that relative to the GH2/GO2 flame, the GCH4/GO2 flame causes major issues with regard to heat protection of the inner wall in the combustor. Meanwhile, according to the infrared images, the GCH4/GO2 plume has a lower outlet core temperature and larger temperature gradient, which is an advantage for employment in future space engines. This study, identifying preliminary behavior differences between the GH2/GO2 and GCH4/GO2 flames, will be applicable for future engine design.

Evaluation of 2 Heat-Mitigation Methods in Army Trainees.

Heat injury is a significant threat to military trainees. Different methods of heat mitigation are in use across military units. Mist fans are 1 of several methods used in the hot and humid climate of Fort Benning, Georgia. To determine if (1) the mist fan or the cooling towel effectively lowered participant core temperature in the humid environment found at Fort Benning and (2) the mist fan or the cooling towel presented additional physiologic or safety benefits or detriments when used in this environment. Randomized controlled clinical trial. Laboratory environmental chamber. Thirty-five physically active men aged 19 to 35 years. (1) Mist fan, (2) commercial cooling towel, (3) passive-cooling (no intervention) control. All treatments lasted 20 minutes. Participants ran on a treadmill at 60% V̇o2max. Rectal core temperature, heart rate, thermal comfort, perceived temperature, perceived wetness, and blood pressure. Average core temperature increased during 20 minutes of cooling (F1,28 = 64.76, P < .001, ηp2 = 0.70), regardless of group (F1,28 = 3.41, P = .08, ηp2 = 0.11) or condition (F1,28 < 1.0). Core temperature, heart rate, and blood pressure did not differ among the 3 conditions. Perceived temperature during 20 minutes of cooling decreased (F1,30 = 141.19, P < .001, ηp2 = 0.83) regardless of group or condition. Perceived temperature was lower with the mist-fan treatment than with the control treatment (F1,15 = 7.38, P = .02, ηp2 = 0.32). The mist-fan group perceived themselves to be cooler even at elevated core temperatures. The mist fan and cooling towel were both ineffective at lowering core temperature. Core temperature continued to increase after exercise in all groups. The mist fan produced feelings of coolness while the core temperature remained elevated, possibly increasing the risk of heat illness.

The Impact of Residual Neuromuscular Blockade, Oversedation, and Hypothermia on Adverse Respiratory Events in a Postanesthetic Care Unit: A Prospective Study of Prevalence, Predictors, and Outcomes.

Residual neuromuscular blockade (RNMB) has been linked to adverse respiratory events (AREs) in the postanesthetic care unit (PACU). However, these events are often not attributed to RNMB by anesthesiologists because they may also be precipitated by other factors including obstructive sleep apnea, opioids, or hypnotic agents. Many anesthesiologists believe RNMB occurs infrequently and is rarely associated with adverse outcomes. This study evaluated the prevalence and predictors of RNMB and AREs. This prospective cohort study included 599 adult patients undergoing general anesthesia who received neuromuscular blocking agents. Baseline demographic, surgical, and anesthetic variables were collected. RNMB was defined as a train-of-four ratio below 0.90 measured by electromyography on admission to the PACU. AREs were defined based on the modified Murphy's criteria. RNMB was present in 186 patients (31% [95% confidence interval (CI), 27%-35%]) on admission to the PACU. One or more AREs were experienced by 97 patients (16% [95% CI 13-19]). AREs were more frequent in patients with RNMB (21% vs 14%, P = .033). RNMB was significantly associated with age (adjusted relative risk [RR], 1.17 [95% CI, 1.06-1.29] per 10-year increase), type of operation (adjusted RR, 0.59 [95% CI, 0.34-0.99] for laparoscopic surgery compared with open abdominal surgery), and duration of operation (adjusted RR, 0.59 [95% CI, 0.39-0.86] for ≥90 minutes compared with <90 minutes). Using multivariate logistic regression, AREs were found to be independently associated with decreased level of consciousness (adjusted RR, 4.76 [95% CI, 1.49-6.76] for unrousable/unconscious compared with alert/awake) and lower core temperature (adjusted RR, 1.43 [95% CI, 1.04-1.92] per 1°C decrease). Although univariate analysis found a significant association between AREs and RNMB, the significance became borderline after adjusting for other covariates (adjusted RR, 1.46 [95% CI, 0.99-2.08]). The prevalence of RNMB in the PACU was >30%. Older age, open abdominal surgery, and duration of operation <90 minutes were associated with increased risk of RNMB in our patients. Our RR estimate for AREs was highest for depressed level of consciousness. When AREs occur in the PACU, potentially preventable causes including RNMB, hypothermia, and reduced level of consciousness should be readily identified and treated appropriately. Delaying extubation until the patient is awake and responsive may reduce AREs.

Outcome After Rewarming From Accidental Hypothermia by Use of Extracorporeal Circulation

Accidental hypothermia with arrested circulation remains a condition associated with high mortality. In our institution, extracorporeal circulation (ECC) rewarming has been the cornerstone in treating such patients since 1987. We here explore characteristics and outcomes of this treatment, to identify significant merits and challenges from 3 decades of experience in ECC rewarming. Sixty-nine patients rewarmed by ECC during the period from December 1987 to December 2015 were analyzed. One patient was excluded from the analyses because of combined traumatic cerebral injury. The analysis was focused on patient characteristics, treatment procedures, and outcomes were focused. Survivors were evaluated according to the cerebral performance categories scale. Simple statistics with nonparametric tests and χ2 tests were used. Median value and range are reported. Median age was 30 years (minimum 1.5, maximum 76), and the cause of accidental hypothermia was cold exposure (27.9%), avalanche (5.9%), and immersion/submersion accidents (66.2%). Eighteen patients survived (26.5%). The survival rate did not improve during the years. Survivors had lower serum potassium (p= 0.002), higher pH (p= 0.03), lower core temperature (p= 0.02), and shorter cardiopulmonary resuscitation time (p= 0.001), but ranges were wide. Although suspected primary hypoxia and hypothermia were associated with lower survival, we observed a 10.5% survival of these victims. Sixteen survivors had good outcome (cerebral performance category 1 or 2), whereas 2 patients with suspected primary hypoxia survived with severe cerebral disability (cerebral performance category 3). Despite extended experience with ECC rewarming, improved handling strategies, and intensive care, no overall improvement in survival was observed. Good outcome was observed even among patients with a dismal prognosis.

Accidental hypothermia: factors related to long-term hospitalization. A retrospective study from northern Finland.

Accidental hypothermia has a low incidence, but is associated with a high mortality rate. Knowledge about concomitant factors, complications, and length of hospital stay is limited. A retrospective cohort study on patients with accidental hypothermia admitted to Oulu University Hospital in Finland, over a 5-year period. Patients were categorized as short-stay patients (7days or less) and long-stay patients (more than 7days) according to their length of stay in hospital. From a total of 105 patients, 67 patients were included in the analyses. Alcohol abuse was the most common concomitant factor (54%). Median length of hospital stay was 4days, and 16 patients (24%) stayed in hospital over 7days (median 15days). Thirty-day mortality was low (14/105, 13%). Patients with long-term hospitalization had a lower initial temperature (28.4 versus 31.2°C, p=0.011), a lower level of consciousness (GCS score 8.4 versus 12.8, p=0.003), more severe acidosis (pH 7.08 versus 7.28, p=0.005, and lactate 7.2 versus 3.9, p=0.043), and a lower level of platelets (183 versus 242, p=0.041) on admission compared with short-stay patients. Thirty-six patients (54%) had at least one complication, and this prolonged median hospital treatment for 2.5days (p<0.001). Alcohol is the most common concomitant factor and every fourth patient spends more than 7days in hospital. Long-term hospitalization is related to a lower core temperature, lower consciousness, more severe lactic acidosis, lower platelet level and infections, rhabdomyolysis, and renal failure.

Involvement of Central Endothelin ETA and Cannabinoid CB1 Receptors and Arginine Vasopressin Release in Sepsis Induced by Cecal Ligation and Puncture in Rats.

We previously reported that endothelin-1 (ET-1) reduced the frequency of spontaneous excitatory currents in vasopressinergic magnocellular cells through the activation of endothelin ETA receptors in rat brain slices. This effect was abolished by a cannabinoid CB1 receptor antagonist, suggesting the involvement of endocannabinoids. The present study investigated whether the blockade of ETA or CB1 receptors during the phase of increased levels of ET-1 after severe sepsis increases the survival rate of animals concomitantly with an increase in plasma arginine vasopressin (AVP) levels. Sepsis was induced in male Wistar rats by cecal ligation and puncture (CLP). Treatment with the CB1 receptor antagonist rimonabant (Rim; 10 and 20 mg/kg, orally) 4 h after CLP (three punctures) significantly increased the survival rate compared with the CLP per vehicle group. Intracerebroventricular treatment with the ETA receptor antagonist BQ123 (100 pmol) or with Rim (2 μg) 4 and 8 h after CLP but not the ETB receptor antagonist BQ788 (100 pmol), also significantly improved the survival rate. Sham-operated and CLP animals that were treated with Rim had significantly lower core temperature than CLP animals. However, oral treatment with Rim did not change bacterial count in the peritoneal exudate, neutrophil migration to the peritoneal cavity, leucopenia or increased plasma interleukin-6 levels induced by CLP. Both Rim and BQ123 also increased AVP levels 12 h after CLP. The blockade of central CB1 and ETA receptors in the late phase of sepsis increased the survival rate, reduced body temperature and increased the circulating AVP levels.

Laser-diode pumped glass-clad Ti:sapphire crystal fiber laser.

Efficient glass-clad crystal fiber (CF) lasers were demonstrated using a Ti:sapphire crystalline core as the gain medium. With a core diameter of 18 μm, the laser diode (LD) pump source can be effectively coupled and guided throughout the crystal fiber for a low threshold and high slope efficiency laser operation. The advantage of high heat dissipation efficiency of the fiber structure can be derived from the low core temperature rising measurement (i.e., 17 K/W) with passive cooling. At an output transmittance of 23%, the lowest absorbed threshold of 118.2 mW and highest slope efficiency of 29.6% were achieved, with linear laser polarization.

Comprehensive evaluation of the linear stability of Alfvén eigenmodes driven by alpha particles in an ITER baseline scenario

The linear stability of Alfvén eigenmodes in the presence of fusion-born alpha particles is thoroughly assessed for two variants of an ITER baseline scenario, which differ significantly in their core and pedestal temperatures. A systematic approach based on CASTOR-K (Borba and Kerner 1999 J. Comput. Phys. 153 101; Nabais et al 2015 Plasma Sci. Technol. 17 89) is used that considers all possible eigenmodes for a given magnetic equilibrium and determines their growth rates due to alpha-particle drive and Landau damping on fuel ions, helium ashes and electrons. It is found that the fastest growing instabilities in the aforementioned ITER scenario are core-localized, low-shear toroidal Alfvén eigenmodes. The largest growth-rates occur in the scenario variant with higher core temperatures, which has the highest alpha-particle density and density gradient, for eigenmodes with toroidal mode numbers . Although these eigenmodes suffer significant radiative damping, which is also evaluated, their growth rates remain larger than those of the most unstable eigenmodes found in the variant of the ITER baseline scenario with lower core temperatures, which have and are not affected by radiative damping.

Problems and Pitfalls of Qualification for Extracorporeal Rewarming in Severe Accidental Hypothermia.

When establishing the Severe Hypothermia Treatment Centre, certain problems and pitfalls regarding the qualification for extracorporeal rewarming were encountered. The authors shared their experience and opened a discussion with other centers that deal with severe, accidental hypothermia. Retrospective analysis of medical records of all patients examined by the hypothermia coordinator. Patients consulted and treated by the Severe Hypothermia Treatment Centre. Patients who underwent accidental hypothermia. From July 2013 until January 2016, hypothermia coordinators at the Severe Hypothermia Treatment Centre examined the cases of 152 hypothermic patients. Of those cases, 127 patients were subjected to noninvasive rewarming in referral hospitals and 25 were accepted to the center for extracorporeal rewarming. Difficulties that deferred or delayed the implementation of extracorporeal membrane oxygen rewarming were identified and addressed, including low platelet/red blood count, intraperitoneal fluid of unknown origin, abnormal results of head computed tomography, extremes of age, bleeding from the external auditory meatus, inaccuracy of infrared-based thermometers, iatrogenic trauma to the femoral vessels, chronic/terminal comorbidities, poisonings, pregnancy, hypoglycemia, hemodynamic stability despite severe hypothermia, and decontamination protocol. The problems discussed may delay the use of extracorporeal membrane oxygen rewarming in hypothermic patients but should not discourage medical teams from the implementation of extracorporeal rewarming. The prognosis for severe hypothermia is favorable, even with a long resuscitation time and low core temperatures.

Prevalence and risk factors for central diabetes insipidus in cardiac arrest survivor treated with targeted temperature management

PurposeCentral diabetes insipidus (CDI) is a marker of severe brain injury. Here we aimed to investigate the prevalence and risk factors of CDI in cardiac arrest survivors treated with targeted temperature management (TTM). MethodsThis retrospective observational study included consecutive adult cardiac arrest survivors treated with TTM between 2008 and 2014. Central diabetes insipidus was confirmed if all of the following criteria were met: urine volume >50 cc kg−1 d−1, serum osmolarity >300 mmol/L, urine osmolarity <300 mmol/L, and serum sodium >145 mEq/L. The primary outcome was the incidence of CDI. ResultsOf the 385 included patients, 45 (11.7%) had confirmed central CDI. Univariate analysis showed that younger age, nonwitness of collapse, nonshockable rhythm, a high incidence of asphyxia arrest, longer downtime, and lower initial core temperature were associated with CDI development. Patients with CDI had a higher incidence of poor neurologic outcomes at discharge and higher in-hospital mortality rate (20/45 vs 76/340, P= .001) as well as 180-day mortality (44/45 vs 174/340, P< .001). Multivariate analysis revealed that age (odds ratio [OR], 0.963; 95% confidence interval [CI], 0.942-0.984), shockable rhythm (OR, 0.077; 95% CI, 0.009-0.662), downtime (OR, 1.025; 95% CI, 1.006-1.044), and asphyxia etiology (OR, 6.815; 95% CI, 2.457-18.899) were independently associated with CDI development. ConclusionCentral diabetes insipidus developed in 12% of cardiac arrest survivors treated with TTM, and those with CDI showed poor neurologic outcomes and high mortality rates. Younger age, nonshockable rhythm, long downtime, and asphyxia arrest were significant risk factors for development of CDI.

The Clinical Role of Intraoperative Core Temperature in Free Tissue Transfer.

Lengthy microvascular procedures carry hypothermia risk, yet limited published data evaluate the overall impact of core temperature on patient and flap morbidity. Although hypothermia may contribute to complications, warming measures are challenged by conflicting reports of intraoperative hypothermia improving anastomotic patency. A retrospective review included all free flaps performed by plastic surgeons at an academic medical center from December 2005 to December 2010. Intraoperative core temperatures were measured by esophageal probe, and median values recorded over 5-minute intervals yielded a case mean (Tavg), maximum (Tmax), and nadir (Tmin). Outcomes included flap failure, pedicle thrombosis, recipient site infection and complications associated with patient, and flap morbidity. Analysis used Student t test, Fisher exact test, Probit, and logistic regression. Of 156 consecutive free tissue transfers, the median Tavg, Tmax, and Tmin were 36.5°C, 37.1°C, and 35.8°C, respectively. The flap failure rate was 7.7% (12/156) and pedicle thrombosis occurred in 9 (6%) cases. Core temperatures did not associate with overall flap failure or pedicle thrombosis but recipient site infection occurred in 21 (13%) patients who had significantly lower mean core temperatures (Tavg=36.0°C, P<0.01). Lower Tavg and Tmax significantly predicted recipient site infection (P<0.01 and P<0.05, respectively). Cut-point analysis revealed significant increases in recipient site infection risk at Tavg less than 37.0°C (P=0.026) and Tmin less than or equal to 34.5°C (P=0.020). Intraoperative hypothermia posed significant risk of flap infection with no benefit to anastomotic patency in free tissue transfer.

Effect of the intensity of cooking methods on the nutritional and physical properties of potato tubers

The different intensities of common culinary techniques (boiling, baking and microwaving) produce several changes that reduce the nutritional and physical properties of potatoes. This study evaluated the effect of those cooking methods on the quality of commercial potato tubers (Agata, Kennebec, Caesar and Red Pontiac). The higher weight losses were obtained for baking, but the potato softening depended on the cultivar. Color losses were independent of the intensity of the treatment; however, microwaving promoted a prompt starch gelatinization with respect to the other methods. The resistant starch retention of baking and microwaving was higher than that of boiling, and the maximum retention of bioactive compounds was obtained with the lower core temperature during boiling, as well as higher temperature and shorter baking time and the lower power and longer microwaving time. Principal component analysis revealed significant relationships between the instrumental and functional properties of cooked potatoes.

Systemic Administration of the TRPV3 Ion Channel Agonist Carvacrol Induces Hypothermia in Conscious Rodents.

Therapeutic hypothermia is a promising new strategy for neuroprotection. However, the methods for safe and effective hypothermia induction in conscious patients are lacking. The current study explored the Transient Receptor Potential Vanilloid 3 (TRPV3) channel activation by the agonist carvacrol as a potential hypothermic strategy. It was found that carvacrol lowers core temperature after intraperitoneal and intravenous administration in mice and rats. However, the hypothermic effect at safe doses was modest, while higher intravenous doses of carvacrol induced a pronounced drop in blood pressure and substantial toxicity. Experiments on the mechanism of the hypothermic effect in mice revealed that it was associated with a decrease in whole-body heat generation, but not with a change in cold-seeking behaviors. In addition, the hypothermic effect was lost at cold ambient temperature. Our findings suggest that although TRPV3 agonism induces hypothermia in rodents, it may have a limited potential as a novel pharmacological method for induction of hypothermia in conscious patients due to suboptimal effectiveness and high toxicity.

Approaches to optimization of core reactivity coefficirnts for the “MASTER” heat supply reactor

After increasing the power output of heat supply reactor «MASTER» by insertion of the annular channel with coolant, feedback coefficients are deteriorated. Thereby, there was need to find ways for changing reactivity coefficients in new reactor design and at the same time to save natural circulation, low core pressure and outlet core temperature of coolant. Reactivity coefficients have been calculated depending on width and locations radius of annular coolant channel at once to fuel enrichment. Neutron-physical code WIMS-D4 was used as calculation tool. The results showed that the feedback coefficients optimum can be achieved by reducing of annular channel width and increasing of fuel enrichment. At the same time reactivity coefficients are insensitive to location of annular coolant channel radius changes. Restrictions for fuel enrichment (IAEA requirements) coupled with geometry restrictions of annular channel listed above (impossible to remove the thermal power or significant increasing of heat exchangers height) have shown that prospect of feedbacks improving via width and location of annular channel is used up. Possible improvements can be achieved by changing type of burnable poison and neutron spectrum.

Change in body surface temperature as an ancillary measurement to motor evoked potentials.

Experimental study. To study the role of surface temperature as an adjunct to motor evoked potentials (MEPs) in rabbit spinal cord injury (SCI) model. Department of Orthopedics, Korea University Guro Hospital, Seoul, Korea. Rabbits (n =18) were divided into Complete (n = 9) and Incomplete (n = 9) SCI groups. Complete SCI was defined as being non-responsive to a wake-up test with loss of MEPs after transection of spinal cord. Incomplete SCI was defined as being responsive to a wake-up test with significant attenuation (⩾ 80%) of MEPs after impaction on spinal cord. Surface temperature of upper and lower extremities, core temperature and MEPs signals were checked before, during and after SCI for 20 min. A wake-up test was conducted and spinal cord was histologicaly evaluated. Experimental conditions between the two groups were statistically similar (P > 0.005 for all values). After SCI, upper extremity temperatures did not change in either group (P > 0.005); however, the surface temperature of the lower extremities in the Complete SCI Group elevated to 1.7 ± 0.5°C in comparison to 0.5 ± 0.1°C in the Incomplete SCI Group (P < 0.001). The scores of wake-up test in the Incomplete SCI Group were significantly different from that of the Complete SCI Group (P < 0.001), while white and gray matter damage was variable on histology. Monitoring of changes of body surface temperature of the lower extremities can be potentially used to identify the completeness of SCI in a rabbit model.

Risk factors associated with intraoperatively acquired pressure ulcers in the park-bench position: a retrospective study.

Patients undergoing surgery in the park-bench position are at high risk of developing intraoperatively acquired pressure ulcers (IAPUs). The purpose was to examine retrospectively risk factors associated with IAPUs in the park-bench position. This study was conducted at a general hospital during the period of September 2010 to September 2012. Twenty-one potential risk factors were evaluated using data obtained from the hospital database. IAPUs developed in 30 of 277 patients (11%). Perspiration was statistically found to be independently associated with IAPUs [OR 3·09, 95% confidence interval (Cl) 1.07-8·58, P = 0·037]. A length of surgery of more than 6 hours was identified to be likely associated with IAPUs (OR 2·64, 95% Cl 0·84-9·08, P = 0·095) compared with less than 6 hours. Furthermore, there was an interaction between the length of surgery and the core temperature; that is, when the length of surgery was more than 6 hours, a core temperature of more than 38·1°C at the end of surgery had a higher odds ratio (8·45, 95% Cl 3·04-27·46, P < 0·001) than that at a lower core temperature (3·20, 95% Cl 1·23-8·78, P = 0·017). These results suggest that perspiration and core temperature are preventable causative factors of pressure ulcers, even under conditions of prolonged surgery in the park-bench position.

Neurokinin 3 Receptor-Expressing Neurons in the Median Preoptic Nucleus Modulate Heat-Dissipation Effectors in the Female Rat.

KNDy neurons facilitate tail skin vasodilation and modulate the effects of estradiol on thermoregulation. We hypothesize that KNDy neurons influence cutaneous vasodilation via projections to neurons in the median preoptic nucleus (MnPO) that express the neurokinin 3 receptor (NK3R). In support of this hypothesis, focal microinjections of senktide, an NK3R agonist, into the MnPO lowers core temperature (TCORE) in the female rat. To further study the role of MnPO NK3R neurons in thermoregulation, these neurons were specifically ablated using a conjugate of a selective NK3R agonist and saporin (NK3-SAP). NK3-SAP or blank-SAP (control) was injected into the MnPO/medial septum. Tail skin temperature (TSKIN) and TCORE were measured in ovariectomized rats exposed to 3 ambient temperatures (TAMBIENT) before and after estradiol-17β (E2) treatment. Before killing, we injected senktide (sc), monitored TCORE for 70 minutes, and harvested brains for Fos immunohistochemistry. Ablation of MnPO NK3R neurons lowered TSKIN at neutral and subneutral TAMBIENT regardless of E2 treatment. However, ablation did not prevent the effects of E2 on TCORE and TSKIN. In control rats, senktide injections induced hypothermia with numerous Fos-immunoreactive cells in the MnPO. In contrast, in NK3-SAP rats, senktide did not alter TCORE and minimal Fos-immunoreactive neurons were identified in the MnPO. These data show that NK3R neurons in the MnPO are required for the hypothermic effects of senktide but not for the E2 modulation of thermoregulation. The lower TSKIN in NK3-SAP-injected rats suggests that MnPO NK3R neurons, like KNDy neurons, facilitate cutaneous vasodilation, an important heat-dissipation effector.

The effect of star-spots on the ages of low-mass stars determined from the lithium depletion boundary

In a coeval group of low-mass stars, the luminosity of the sharp transition between stars that retain their initial lithium and those at slightly higher masses in which Li has been depleted by nuclear reactions, the lithium depletion boundary (LDB), has been advanced as an almost model-independent means of establishing an age scale for young stars. Here we construct polytropic models of contracting pre-main sequence stars (PMS) that have cool, magnetic starspots blocking a fraction $\beta$ of their photospheric flux. Starspots slow the descent along Hayashi tracks, leading to lower core temperatures and less Li destruction at a given mass and age. The age, $\tau_{\rm LDB}$, determined from the luminosity of the LDB, $L_{\rm LDB}$, is increased by a factor $(1-\beta)^{-E}$ compared to that inferred from unspotted models, where $E \simeq 1 + d\log \tau_{\rm LDB}/d \log L_{\rm LDB}$ and has a value $\sim 0.5$ at ages $< 80$ Myr, decreasing to $\sim 0.3$ for older stars. Spotted stars have virtually the same relationship between K-band bolometric correction and colour as unspotted stars, so this relationship applies equally to ages inferred from the absolute K magnitude of the LDB. Low-mass PMS stars do have starspots, but the appropriate value of $\beta$ is highly uncertain with a probable range of $0.1 < \beta < 0.4$. For the smaller $\beta$ values our result suggests a modest systematic increase in LDB ages that is comparable with the maximum levels of theoretical uncertainty previously claimed for the technique. The largest $\beta$ values would however increase LDB ages by 20-30 per cent and demand a re-evaluation of other age estimation techniques calibrated using LDB ages.

Milrinone ameliorates cardiac mechanical dysfunction after hypothermia in an intact rat model

BackgroundRewarming from hypothermia is often complicated by cardiac dysfunction, characterized by substantial reduction in stroke volume. Previously we have reported that inotropic agents, working via cardiac β-receptor agonism may exert serious side effects when applied to treat cardiac contractile dysfunction during rewarming. In this study we tested whether Milrinone, a phosphodiesterase III inhibitor, is able to ameliorate such dysfunction when given during rewarming. MethodsA rat model designed for circulatory studies during experimental hypothermia with cooling to a core temperature of 15°C, stable hypothermia at this temperature for 3h and subsequent rewarming was used, with a total of 3 groups: (1) a normothermic group receiving Milrinone, (2) a hypothermic group receiving Milrinone the last hour of hypothermia and during rewarming, and (3) a hypothermic saline control group. Hemodynamic function was monitored using a conductance catheter introduced to the left ventricle. ResultsAfter rewarming from 15°C, stroke volume and cardiac output returned to within baseline values in Milrinone treated animals, while these variables were significantly reduced in saline controls. ConclusionsMilrinone ameliorated cardiac dysfunction during rewarming from 15°C. The present results suggest that at low core temperatures and during rewarming from such temperatures, pharmacologic efforts to support cardiovascular function is better achieved by substances preventing cyclic AMP breakdown rather than increasing its formation via β-receptor stimulation.

Biomarkers of cerebral injury in cardiac surgery.

The present study aims to reveal the changing patterns of cerebral biomarkers and the underlying predictive factors as a consequence of cardiac surgery. Literature retrieval of articles on S100 and S100B of recent 20 years were made in the MEDLINE database, Highwire Press and Google search. Quantitative data of S100 and S100B along with neuron-specific enolase were carefully screened, collected and statistically analyzed. The biomarkers appeared earlier and lasted longer in the cerebrospinal fluid than in the serum. All three biomarkers exhibited a similar kinetic trend in the bloodstream, reaching a peak value at the end of cardiopulmonary bypass (CPB). In adults, serum biomarkers may recover to normal earlier than in pediatrics undergoing a cardiac surgery. The patients undergoing off-pump surgery had the minimal elevations of cerebral biomarkers comparing to all other cardiac surgeries under CPB, low core temperature and/or hypothermic circulatory arrest. In patients with pre- or postoperative neurological disorders, the biomarkers in the serum elevated even before operation and persisted longer time than those without neurological disorders. The serum concentrations of the biomarkers showed direct correlation with CPB duration and core temperature. Cardiac operations may lead to cerebral damage and blood-brain barrier changes, as a consequence of CPB and low core temperature. The cerebral biomarkers including S100, S100B and neuron-specific enolase may precisely reflect the cerebral damages in cardiac surgery. Attention has to be paid to the attenuations of cerebral damage by modifying the surgical conditions of CPB and core temperature.