Achieving Carnot efficiency in a finite-power Brownian Carnot cycle with arbitrary temperature difference.

Achieving the Carnot efficiency at finite power is a challenging problem in heat engines due to the trade-off relation between efficiency and power that holds for general heat engines. It is pointed out that the Carnot efficiency at finite power may be achievable in the vanishing limit of the relaxation times of a system without breaking the trade-off relation. However, any explicit model of heat engines that realizes this scenario for arbitrary temperature difference has not been proposed. Here, we investigate an underdamped Brownian Carnot cycle where the finite-time adiabatic processes connecting the isothermal processes are tactically adopted. We show that in the vanishing limit of the relaxation times in the above cycle, the compatibility of the Carnot efficiency and finite power is achievable for arbitrary temperature difference. This is theoretically explained based on the trade-off relation derived for our cycle, which is also confirmed by numerical simulations.

Compatibility of Carnot efficiency with finite power in an underdamped Brownian Carnot cycle in small temperature-difference regime.

We study the possibility of achieving the Carnot efficiency in a finite-power underdamped Brownian Carnot cycle. Recently, it was reported that the Carnot efficiency is achievable in a general class of finite-power Carnot cycles in the vanishing limit of the relaxation times. Thus, it may be interesting to clarify how the efficiency and power depend on the relaxation times by using a specific model. By evaluating the heat-leakage effect intrinsic in the underdamped dynamics with the instantaneous adiabatic processes, we demonstrate that the compatibility of the Carnot efficiency and finite power is achieved in the vanishing limit of the relaxation times in the small temperature-difference regime. Furthermore, we show that this result is consistent with a trade-off relation between power and efficiency by explicitly deriving the relation of our cycle in terms of the relaxation times.

Differential effects of propofol and sevoflurane on QT interval during anesthetic induction.

There have been conflicting reports on whether propofol prolongs, shortens, or does not change QT interval. The aim of this study was to determine the effect of target-controlled infusion (TCI) of propofol on heart rate-corrected QT (QTc) interval during anesthetic induction. We examined 50 patients undergoing lumbar spine surgery. Patients received 3 µg/kg of fentanyl and were randomly allocated to one of the following 2 groups. Group S patients received 5 mg/kg of thiamylal followed by sevoflurane, 5 % at the inhaled concentration. Group P patients received propofol using TCI system at 5 µg/mL for 2 min followed by 3 µg/mL. Tracheal intubation was performed after vecuronium administration. Heart rate (HR), mean arterial pressure (MAP), bispectral index score (BIS), and QTc interval in 12-lead electrocardiogram were recorded at the following time points: just before fentanyl administration (T1), 2 min after fentanyl injection (T2), 1 min after thiamylal injection or 2 min after the start of TCI (T3), just before intubation (T4), and 2 min after intubation (T5). BIS and MAP significantly decreased after anesthetic induction in both groups. HR decreased after anesthetic induction and recovered after tracheal intubation in group P, whereas it did changed in group S throughout the study period. QTc interval was shortened at T3 and T4 in group P, but prolonged at T3, T4, and T5 in group S, as compared with T1. Propofol TCI shortens QTc interval, whereas sevoflurane prolongs QTc interval during anesthetic induction.

Comparison between propofol and dexmedetomidine in postoperative sedation after extensive cervical spine surgery.

PURPOSE: Patients undergoing extensive cervical spine surgery (ECSS) occasionally require emergency reintubation due to postoperative airway complications. To avoid it, an endotracheal tube is retained in patients maintained under sedation overnight. This study was conducted to determine whether dexmedetomidine would be superior in sedative effects to propofol for postoperative sedation after ECSS. METHODS: We studied 32 consecutive patients undergoing ECSS who required prophylactic intubation postoperatively under sedation overnight. The patients were randomly divided into two groups. Group D (n = 16) received dexmedetomidine 0.1 µg/kg/min for 10 min as a loading dose, followed by a continuous infusion at 0.4 µg/kg/h. Group P (n = 16) received propofol 0.1 mg/kg/min for 10 min as a loading dose, followed by a continuous infusion at 1 mg/kg/h. All patients received analgesia with buprenorphine. Ramsay sedation scale, extremity movement, and pain intensity were recorded every 2 h. Dexmedetomidine and propofol dosages were adjusted to maintain a desired sedation level. Nursing staff adjusted dopamine to maintain systolic blood pressure >100 mmHg and administered atropine when the heart rate was <50 bpm. RESULTS: The proportions of adequate sedation level, movement, and pain status were similar between groups. In group D, heart rates were lower, frequency of atropine use was greater, and dopamine dose was higher than in group P. CONCLUSION: Both sedatives are efficacious after ECSS; however, dexmedetomidine decreased heart rate and required higher dose of dopamine.

[Relationship between magnesium concentration in cerebrospinal fluid and delayed cerebral ischemia in patients with aneurysmal subarachnoid hemorrhage].

BACKGROUND: The present study was conducted to determine the relationship between magnesium concentration in cerebrospinal fluid (CSF) and delayed cerebral ischemia (DCI) in patients with subarachnoid hemorrhage (SAH). METHODS: We studied 39 consecutive patients undergoing surgery after SAH. A spinal drainage catheter was inserted into the lower lumbar vertebrae before surgery. CSF was then sampled and the magnesium concentration measured. General clinical data, Hunt-Hess (H-H) grade and Fisher grade, aneurysm size and site, intracerebral and intraventricular hemorrhage, and blood glucose levels were all recorded on admission. At the same time, the Glasgow coma scale (GCS) score was calculated. Outcomes were assessed using the Glasgow outcome scale at discharge. DCI was defined as a two-point decrease in the GCS score and/or focal deficit, and was confirmed by cerebral angiography. The recorded values were expressed as the median (interquartile range). RESULTS: Of the 39 patients, 23 (59%) had DCI. The magnesium concentration in the DCI cases was 2.8 (2.7 and 2.9) mg x dl(-1), which was significantly lower than that in the non-DCI cases, i. e., 2.9 (2.8 and 3.0) mg x dl(-1) (P < 0.05). There were no significant differences in the other factors. CONCLUSIONS: The results indicate that preoperative hypomagnesemia within the CSF might play a role in the development of DCI in patients with SAH; however, further studies will be necessary to confirm this observation.

QTc interval and neurological outcomes in aneurysmal subarachnoid hemorrhage.

BACKGROUND: Prolonged heart rate-corrected QT (QTc) interval is frequently observed in subarachnoid hemorrhage (SAH). This study was conducted to determine the relationship between QTc interval and neurological outcome during the acute posthemorrhagic period after aneurysmal SAH. METHODS: We studied 71 patients undergoing surgery who were admitted within 24 h after the onset of aneurysmal SAH. Standard 12-lead electrocardiography was performed on admission (T1) and at 1 and 7 days after operation (T2 and T3). QT intervals were corrected by heart rate according to the Fridericia formula. The Glasgow Coma Scale (GCS) score was calculated over the period T1-T3. Neurological outcome was assessed using the Glasgow Outcome Scale at hospital discharge. RESULTS: Among the 71 patients, 31 had an unfavorable neurological outcome. Although QTc interval prolongation improved in patients with a good outcome, QTc interval prolongation continued in patients with an unfavorable outcome. The areas under the receiver-operator characteristic curves showed that the QTc and GCS score at T3, and the Hunt and Hess grade were significant predictors of an unfavorable neurological outcome. The threshold value, sensitivity, and specificity for the QTc at T3 were 448 ms, 73% [95% confidence interval (CI), 68-78], and 93% (95% CI, 90-96), respectively. CONCLUSION: This study confirms that QTc interval prolongation continues in the SAH patients with an unfavorable outcome but that QTc interval prolongation improves in patients with a good outcome, suggesting that a QTc interval of more than 448 ms at 7 days after operation is a predictor of neurological outcome after SAH.

Admission microalbuminuria and neurologic outcomes in intensive care unit patients with spontaneous intracerebral hemorrhage.

This study was performed to determine the prevalence and the prognostic significance of microalbuminuria in patients admitted to intensive care unit (ICU) after spontaneous intracerebral hemorrhage (ICH). From May 2004 to April 2006, we studied 59 consecutive ICH patients verified using computed tomography and admitted to our ICU within a day after stroke. General clinical, neurologic data, and Glasgow Coma Scale (GCS) were recorded at admission to ICU. Urine was collected at admission to ICU for measuring the urinary microalbumin/creatinine ratio. At hospital discharge, neurologic outcome was assessed using Glasgow Outcome Scale. Among 59 patients, 37 (63%) had unfavorable neurologic outcomes (death, persistent vegetative state, and severe disability). The prevalence rate of microalbuminuria was 85% [95% confidence interval (CI), 76-94]. The areas under the receiver operator characteristic curves showed that the urinary microalbumin/creatinine ratio [0.81 (95% CI, 0.70-0.92)] and the GCS score [0.78 (95% CI, 0.66-0.90)] at admission were significant predictors of unfavorable neurologic outcome at hospital discharge. The threshold value, sensitivity, specificity, and likelihood ratio for the urinary microalbumin/creatinine ratio were 200 mg/g, 51% (95% CI, 39-64), 96% (95% CI, 90-100), and 11.3 (95% CI, 7.9-16.0); and those for the GCS score were 11, 46% (95% CI, 36-61), 96% (95% CI, 90-100), and 10.1 (95% CI, 7.2-14.1), respectively. This study confirmed a high prevalence of microalbuminuria in ICH patients in ICU, and suggested that the urinary microalbumin/creatinine ratio >200 mg/g was comparable to the GCS score <11 at admission to the ICU with regard to its prognostic characteristics after ICH.

Effects of traditional "Juci" (contralateral acupuncture) on orofacial nociceptive behavior in the rat.

PURPOSE: "Juci", one of the traditional acupuncture techniques, means contralateral acupuncture; i.e., implanting a needle into an acupoint to treat a given disease or disorder, but on the side of the body opposite to the diseased side. The aim of this study was: (1) to assess acupuncture effects on formalin-induced nociceptive behavior in the orofacial region in the rat, and (2) to evaluate the efficacy of Juci in the orofacial formalin test. METHODS: Forty-four adult male Wistar rats were used in the present study. A 1.0% formalin solution (25 microl s.c., diluted in saline) was injected into the right upper lip. The rats were randomly assigned to five groups. (1) The control group (n = 9), which received formalin injection without acupuncture pretreatment; (2) the ipsilateral Ho-ku (see note below) acupuncture group (n = 10); (3) the contralateral Ho-ku acupuncture group (n = 11); (4) the acupuncture plus naloxone group (n = 9), where intraperitoneal naloxone (1.0 mgxkg(-1)) was injected immediately before acupuncture pretreatment; and (5) the sham acupuncture group (n = 5). "Ho-ku" is the term used for the "Large Intestine 4" acupoint, located between the first and second metacarpal bones. RESULTS: The injection of formalin produced the characteristic biphasic behavioral response. Acupuncture significantly inhibited the response in the early and late phases. Naloxone significantly reversed these effects. There were no statistically significant differences between the ipsilateral and Juci acupuncture groups. Sham acupuncture did not exert any significant effect on the formalin-induced behavior. CONCLUSION: Our results showed that the degree of effectiveness of Juci was similar to that of the ipsilateral acupuncture technique. Therefore, the Juci technique is also useful for the treatment of orofacial pain.

Quantitative analysis of the relationship between sedation and resting energy expenditure in postoperative patients.

OBJECTIVE: To analyze quantitatively the relationship between sedation and resting energy expenditure or oxygen consumption in postoperative patients. DESIGN: A prospective, clinical study. SETTING: An eight-bed intensive care unit at a university hospital. PATIENTS: Thirty-two postoperative patients undergoing either esophagectomy or surgery of malignant tumors of the head and neck who required mechanical ventilation and sedation for > or = 2 days postoperatively. INTERVENTIONS: None. MEASUREMENTS AND MAIN RESULTS: A total of 133 metabolic measurements were performed. Ramsay sedation scale (RSS), body temperature, and the dose of midazolam were evaluated at the time of the metabolic cart study. All patients received analgesia with buprenorphine at a fixed dose of 0.625 microg x kg(-1) x hr(-1) continuously. Midazolam was used for induction and maintenance of intravenous sedation after admission to the intensive care unit. The initial dose was 0.04 mg x kg(-1) x hr(-1) and was adjusted to achieve a desired depth of sedation at 3, 4, or 5 on the RSS every 4 hrs. The degree of sedation was classified into three states: light sedation (RSS 2-3; n = 49), moderate sedation (RSS 4; n = 39), and heavy sedation (RSS 5-6; n = 45). RESULTS: With increasing the depth of sedation, oxygen consumption index (mL x min(-1) x m(-2)), resting energy expenditure index (REEI; kcal x day(-1) x m(-2)), and REE/basal energy expenditure (BEE) decreased significantly. Oxygen consumption index (mean +/- SD), REEI, and REE/BEE were 151 +/- 18, 1032 +/- 120, and 1.29 +/- 0.17 in the light sedation, 139 +/- 22, 947 +/- 143, and 1.20 +/- 0.16 in the moderate sedation, and 125 +/- 16, 865 +/- 105, and 1.13 +/- 0.12 in the heavy sedation, respectively. CONCLUSION: An increase in the depth of sedation progressively decreases in oxygen consumption index and REEI in postoperative patients.