The influence of glucose load on metabolism during minor surgery using remifentanil-induced anesthesia.

BACKGROUND: During perioperative fasting, lipid metabolism gradually increases, resulting in free fatty acids (FFA) and/or ketone bodies. Suppression of surgical stress by remifentanil may allow the safe administration of glucose infusions, avoiding both hyperglycemia and ketogenesis. The effects of glucose infusion on glucose and lipid metabolism were therefore investigated in patients undergoing minor surgery with remifentanil anesthesia. METHODS: Thirty-four patients were randomized 1 : 1 to receive no glucose (0G group) or low-dose glucose (0.1 g/kg/h for 1 h followed by 0.05 g/kg/h for 1 h; LG group). The concentrations of glucose, adrenocorticotropic hormone (ACTH), 3-methylhistidine (3-MH), insulin, cortisol, FFA, creatinine (Cr), and ketone bodies were measured before anesthetic induction, 1 and 2 h after glucose infusion, at the end of surgery, and the next morning. RESULTS: The concentrations of cortisol and ACTH decreased during surgery in both groups when compared with the concentrations before anesthesia and at the end of surgery (P < 0.05). Glucose and insulin concentrations were significantly higher in the LG than in the 0G group at 1 and 2 h after infusion. No patient experienced hyperglycemia. The concentrations of FFA and ketone bodies were lower in the LG than in the 0G group during surgery, but there were no significant between group differences in 3-MH/Cr. CONCLUSION: Infusion of low-dose glucose attenuated fat catabolism without causing hyperglycemia, indicating that infusion of low-dose glucose during remifentanil-induced anesthesia may be safe for patients.

Estimation of radiative heat transfer using a geometric human model.

In order to provide a detailed estimate of radiative heat transfer between a human body and its surrounding environment, we have developed a geometric model of a human form and an algorithm. The model closely resembles the actual shape of a human body and is composed of small quadrilateral surfaces. Dealing with an object or a space with an arbitrary shape, the developed algorithm can judge efficiently whether there is an obstruction between a pair of surfaces. As a result, the angle factors between a pair of surfaces that only occur during radiative heat transfer can be defined. The distribution of the radiative heat transfer rates shows the characteristics of body shape and variations in posture.

A method for measurement of water temperature in micro-region using near infrared light.

We have proposed a method for non-invasively measuring the temperature changes of water in a micro-region using near infrared (NIR) light. The goal of this study is to measure the temperature changes of biological cells or tissues. This method is on the basis of the phenomenon that the NIR absorption spectrum of water depends on temperature. First, in order to confirm whether a right irradiation for the temperature measurement itself affects the water temperature, we calculated the temperature rise caused by the optical absorption. Next, absorbance spectra in the wavelength range of 1300 - 2000 nm of water with a thickness of 100 and 500 m were measured by a micro-spectrometer. The measured spectra with temperature-dependence were calibrated using a regression analysis. The standard error of calibration was 0.6 C for 100 m-thickness.

Micro-thermocouple probe for measurement of cellular thermal responses.

We have produced micro-thermocouple probes for the measurement of cellular thermal responses. Cells generate heat with their metabolisms and more heat with reactions to a certain physical or chemical stimulation. Therefore, the analysis of the cellular thermal responses would provide new physiological information. However, a real-time thermal measurement technique on a target of a single cell has not been established. In this study, glass micropipettes, which are widely used in bioengineering and medicine, are used for the base of the thermocouple probes. Using microfabrication techniques, the junction of two different metal films is formed at the micropipette tip with a diameter of 1 μm. This probe can inject a chemical substance into a cell and to detect its subsequent temperature changes simultaneously.

Development of a new algorithm for heat transfer equation in the human body and its applications.

A computer program has been developed for the numerical analysis of thermal conditions within the human body. In this study, a cylindrical model, which consists of internal multi-layers, is adapted for the segment of the human body. For the present concentric cylindrical model we developed a new numerical solution method using a linear combination of the modified Bessel functions. By using the present computer program the internal tissue temperatures, heat fluxes and blood temperatures of the thigh, crus and foot segments are calculated. This paper describes a new algorithm solving heat transfer equation in the human body and the example of calculated results of the combination of thigh, crus and foot segments. The calculated results show the local characteristics of each segment in the human body.

Diamond-like carbon coating on micropipettes.

Based on glass micropipettes which are widely used in bioengineering and medicine, various microsensor probes could be produced by recent microfabrication techniques. Conductive surfaces of these sensor probes mostly need electrical insulating films coated on them, but it has been difficult to coat a high-quality and strong insulating film on a microacute probe such as a micropipette, especially on its tip. Therefore, we have employed diamond-like carbon (DLC) as an insulating film and developed a DLC coating method based on plasma chemical vapor deposition method. In the deposition apparatus, the cathode is the micropipette itself and the anode is a mesh cylinder with a central focus on the micropipette. In order to prevent the growing films from transformation due to high temperature at the tip, the voltage between the pair of electrodes is impressed intermittently. Raman spectrum and electrical resistivity measured here indicate that the deposited film is DLC and it can be worked well as an insulating film. The DLC coating method could be useful in microprobe fabrications.

Inflammatory cells and the epithelium. Mast cell/nerve interactions in the lung in vitro and in vivo.

A hypothesis is presented that mast cells in and below the epithelium of the respiratory tract show functional association with nerves to form a homeostatic regulatory unit. During inflammation, mast cells may arise in situ as well as by infiltration because epithelium contains both mast cell precursors and produces factors that support their growth in vitro. Structural studies show that mast cells associate with nerves in the lung. Using a tissue culture model, we showed that sympathetic nerves formed lasting contacts with rat basophilic leukemia (RBL) cells. Electrophysiologic studies showed that nerve contact increases RBL membrane conductance, which can be mimicked by exogenous substance P (SP). Experiments with sensitized rat tracheal mucosa in Ussing chambers showed functional evidence of interaction of mast cells with SP-containing nerves: changes in short circuit current caused by antigen were blocked by the mast cell stabilizer doxantrazole and reduced by 50% by neonatal pretreatment with capsaicin. Experiments in vivo showed that lung clearance of the aerosol probe 99mTc-DTPA was increased by antigen challenge in sensitized rats. This was blocked by neonatal capsaicin treatment, again implicating SP-containing nerves. Therefore, we conclude that the functional association of mast cells with nerves is an important mechanism in regulating the local epithelial environment.