Changes In Blood Temperature Research Articles

Analysis of entropy generation and Brownian motion for the pulsatile flow of Herschel–Bulkley fluid in a diseased curved artery

The influence of Thermophoresis and Brownian motion on the pulsing flow of nano-fluid (blood) through a curved artery with stenosis and post-stenotic dilatation in its interior is investigated numerically. The Herschel-Bulkley model of fluid dynamics accurately represents the fluid's rheology. By applying the mild stenosis condition, the highly coupled momentum, energy, and mass concentration equations can be modelled and reduced. Explicit finite differences methods are used to discretize and solve the non-dimensionalized governing equations associated with the boundary condition. Entropy creation in blood flow due to loss and magnetohydrodynamic processes is also investigated. Graphs and discussions of the effects of changing pertinent geometric and rheological factors on key flow characteristics, such as temperature, velocity, and mass concentration, are provided. Because of the small changes in blood temperature and mass concentration caused by the artery's curvature, it is observed that the radius of the curved channel has a significant impact on blood velocity. An increase in Brownian motion also resulted in a drop in the nano-temperature, a fluid's but the thermophoresis parameter exhibited the reverse behavior.

Extravascular Cooling of Blood Using a Concentrated Thermoelectric Cooling Probe

Abstract Thermal therapies have strong potential for improving outcomes for patients suffering from cardiac arrest, neonatal hypoxic-ischemic encephalopathy, or medically refractory intracranial hypertension. We propose a novel tool to manipulate blood temperature through extravascular thermoelectric heat exchange of blood vessel walls and flowing blood. This tool is a concentrated cooling probe with several thermoelectric units combined to focus cooling at the application site. Using this tool, we aim to achieve desired levels of temperature control and potentially reduce complications associated with traditional intravascular or systemic thermal therapies. Leveraging the feedback control, speed, and reversible operation of thermoelectric cooling modules, the device can adapt to cool or heat as desired. Preclinical testing on rodent models confirmed rapid, significant reduction of intravenous jugular blood temperature when a prototype device was brought in contact with the left carotid artery (change in blood temperature of −4.74 ± 2.9 °C/h and −4.29 ± 1.64 °C/h for 0 °C and −5 °C cooling trials, respectively). Declines in rectal temperature were also noted, but at lesser magnitudes than for jugular blood (0 °C: −3.09 ± 1.29 °C/h; −5 °C: −2.04 ± 1.08 °C/h), indicating proof-of-concept of thermoelectric extravascular blood cooling within a relatively localized region of the body. With further improvements in the technique, there is potential for selective organ cooling via a reduction in the temperature of flowing blood.

A thermoregulation model for whole body cooling hypothermia

This paper presents a thermoregulation model based on the finite element method to perform numerical analyses of brain cooling procedures as a contribution to the investigation on the use of therapeutic hypothermia after ischemia in adults. The use of computational methods can aid clinicians to observe body temperature using different cooling methods without the need of invasive techniques, and can thus be a valuable tool to assist clinical trials simulating different cooling options that can be used for treatment. In this work, we developed a finite element method (FEM) package using isoparametric linear three-dimensional elements which is applied to the solution of the continuum bioheat Pennes equation. Blood temperature changes were considered using a blood pool approach and a lumped analysis for intravascular catheter methods of blood cooling. Some analyses are performed using a three-dimensional mesh based on a complex geometry obtained from computed tomography medical images, considering a cooling blanket and an intravascular catheter. A comparison is made between the results obtained with the two techniques and the effects of each case in brain temperature reduction in a required period of time, maintenance of body temperature at moderate hypothermia levels and gradual rewarming.

A thermoregulation model for hypothermic treatment of neonates

This paper presents a thermoregulation finite element model (FEM) to simulate hypothermia procedures for the treatment of encephalopathy hypoxic-ischemia (EHI) in neonates, a dangerous ischemic condition that can cause neurological damages and even death. Therapeutic hypothermia is the only recommended technique to reduce sequels caused by EHI in neonates; intervention with moderate cooling for neural rescue in newborns with hypoxic-ischemic brain injury is the culmination of a series of clinical research studies spanning decades. However, the direct monitoring of brain cooling is difficult and can lead to additional tissue damage. Therefore, the measurement of efficiency during clinical trials of hypothermia treatment is still challenging. The use of computational methods can aid clinicians to observe the continuous temperature of tissues and organs during cooling procedures without the need for invasive techniques, and can thus be a valuable tool to assist clinical trials simulating different cooling options that can be used for treatment. The use of low cost methods such as cooling blankets can open the possibility of using brain cooling techniques in hospitals and clinics that cannot currently afford the available expensive equipment and techniques. In this work, we developed a FEM package using isoparametric linear three-dimensional elements which is applied to the solution of the continuum bioheat Pennes equation. Blood temperature changes were considered using a blood pool approach. The results of the FEM model were compared to those obtained through the implementation of a user-defined function (UDF) in the commercial finite volume software FLUENT and validated with experimental tests. Numerical analyses were performed using a three-dimensional mesh based on a complex geometry obtained from MRI scan medical images.

Pharmacologically induced hypothermia with cannabinoid receptor agonist WIN55, 212-2 after cardiopulmonary resuscitation*

To investigate whether hypothermia could be induced pharmacologically after resuscitation with the cannabinoid CB1/CB2 receptor agonist in a rat model and its effects on outcomes of cardiopulmonary resuscitation. Prospective, randomized, placebo-controlled experimental study. University-affiliated animal research laboratory. Ten healthy male Sprague-Dawley rats. Ventricular fibrillation was induced and untreated for 6 mins. Defibrillation was attempted after 8 mins of cardiopulmonary resuscitation. Thirty minutes after resuscitation, animals were randomized to receive either WIN55, 212-2 (1.0 mg/kg/hr) or vehicle placebo (1.4 mL/kg/hr) for 6 hrs. Before infusion, the temperature was maintained at 37°C in all the animals with the help of a heating lamp. The same temperature environment was maintained for both groups after infusion. Hemodynamic measurements and cardiac output, ejection fraction, and myocardial performance index were measured at baseline and hourly for 6 hrs after resuscitation. Survival time up to 72 hrs was observed. Blood temperature decreased progressively after infusion of WIN55, 212-2 from 37°C to 34°C 4 hrs after resuscitation. There was no significant change in blood temperature after 6 hrs of placebo infusion of the same volume and same infusate temperature. Significantly better postresuscitation myocardial function and longer durations of survival were observed in WIN55, 212-2-treated animals. The selective cannabinoid agonist, WIN55, 212-2, produced a significant reduction in blood temperature and improved postresuscitation myocardial functions and survival after cardiopulmonary resuscitation. The study results may provide a further option for early and effective induction of therapeutic hypothermia in settings of cardiopulmonary resuscitation.

Bolus Cardiac Output and Accuracy in Therapeutic Hypothermia

Bolus Cardiac Output and Accuracy in Therapeutic Hypothermia

Monitoring preload during liver transplantation

Liver transplantation is associated with major shifts incentral blood volume; therefore, monitoring preload is es-sential. Filling pressures (central venous pressure or pul-monary artery occlusion pressure) do not reflect preload[right ventricular end-diastolic volume (RVEDV) or leftventricular end-diastolic volume (LVEDV)] well becausethese pressures are affected not just by preload but alsoby changes in compliance of the heart. These compliancechanges can be quite significant because of the changesin chest volume that are the result of surgical retractionand variable pressure on the diaphragm. Then, what arethe alternative methods of preload monitoring in the op-erating room? There are only two: thermodilution deter-mination of RVEDV and transesophageal echocardio-graphic estimation of RVEDV and LVEDV. Each of thesetechniques has advantages and disadvantages.The clinical determination of the right ventricularejection fraction (RVEF) and RVEDV became possible inthe early 1980s when American Edwards Laboratoriesmarketed a pulmonary artery catheter with a fast-re-sponse thermistor and an accompanying computer.That technology was based on intermittent injection ofa cold solution as a dye, and the principle of conserva-tion of energy allowed the calculation of RVEF and rightventricular volumes.

The Effect of Temperature and Aprotinin During Cardiopulmonary Bypass on Three Different Methods of Activated Clotting Time Measurement

The activated clotting time (ACT) is used frequently for monitoring blood anticoagulant response with heparin before, during, and after cardiopulmonary bypass (CPB). Many cardiac procedures involving CPB require reduction of the patient’s blood temperature and use of the serine protease inhibitor, aprotinin. Three different methods of ACT measurement were compared to show the effects of different CPB temperatures and the presence of aprotinin. A total of 42 patients were included in the study: 14 received CPB at 28°C, 14 received CPB at 32°C, and 14 normothermic (37°C) CPB. Within each temperature group, seven received aprotinin. The ACT in each group of patients was measured by a celite activator (C-ACT), a kaolin activator (K-ACT), and a celite, kaolin and glass activator (MAX-ACT). All three methods of ACT measurement showed significant increases (p< .05) in clotting times at hypothermic CPB compared with normothermic groups. During heparinization the C-ACT was significantly increased (p< .05) in the presence of aprotinin. Comparability between the 3 ACT measurement methods showed a very high correlation between C-ACT and K-ACT clotting times (R2= .8962), and slightly lower correlation between MAX-ACT and C-ACT (R2= .7780), and MAX-ACT and K-ACT (R2= .7827). All ACT measurements are affected by changes in blood temperature. The C-ACT measurement is prolonged with aprotinin, whereas the MAX-ACT and K-ACT method of measurement in the presence of aprotinin are not significantly altered. It appears that the MAX-ACT produces lower values and may necessitate additional heparin therapy for ACT target values considered safe during CPB. Further study is required from these additional findings.

Measuring Cardiac Output: Intermittent Bolus Thermodilution Method

cialist in the cardiac care unit and cardiac observation unit at UCLA Medical Center and is an assistant professor of nursing at the UCLA School of Nursing, Los Angeles, Calif. by a computer and converted into a measurement of cardiac output. Cardiac output is inversely proportional to the area under the curve. The normal cardiac output curve has a rapid smooth upstroke and a gradual downstroke (Figure 1). A small area under the curve indicates a high cardiac output. The faster blood flows through the heart, the earlier the peak and sharper the drop, because the catheter senses temperature change over a short period. A low cardiac output results in a larger area under the curve. When blood flows slowly (low cardiac output), the area under the curve (temperature change over time) is greater because the catheter senses changes in temperature over a longer period. The curves vary according to the patient’s clinical condition and according to deviations in technique (Figure 2). Concerns about contamination of prefilled syringes of injectate and proximal port of a pulmonary artery catheter located in the right atrium. In the atrium, the injectate mixes with the blood and passes through the tricuspid valve into the right ventricle. A thermistor within the catheter senses the change in blood temperature as the blood passes the catheter tip located in the pulmonary artery. A curve that shows the change in temperature over time is calculated ProtocolsforPractice

Absence of Selective Brain Cooling in Free‐Ranging Zebras in Their Natural Habitat

We used implanted miniature data loggers to measure brain and arterial blood temperatures in three free-ranging zebras (Equus burchelli) in their natural habitat, every 5 min for 9 days. The animals experienced globe temperatures exceeding 40 C, and radiant heat load of about 1000 W m-2. Arterial blood exhibited a moderate amplitude (1.7 C) nychthemeral rhythm, with an acrophase at 19.00 h and a nadir late in the morning, at 10.00 h. Brain temperature consistently exceeded blood temperature, on average by 0.2-0.4 C, and changes in brain temperature closely tracked changes in blood temperature. There was no evidence of selective brain cooling, even during the hyperthermia which followed surgery or that associated with intense, short-duration exercise. The relationship between brain and arterial blood temperatures in free-ranging zebras was unlike that reported for horses in the laboratory. Our results do not support the view that mammals lacking a carotid rete can achieve selective brain cooling.

Brain, abdominal and arterial blood temperatures of free-ranging eland in their natural habitat.

Using implanted miniature data loggers we measured brain, arterial blood and abdominal temperatures at 5-min intervals in two free-ranging eland (Tragelaphus oryx) in their natural habitat. The animals were subjected to a nychthemeral range of globe temperature which exceeded 40 degrees C. Arterial blood exhibited a moderate amplitude (2.3 degrees C) nychthemeral rhythm, with a temperature peak at 1600-1800 hours, and a trough in the early morning at 0600-0800 hours. Mean abdominal temperature was 0.2-0.3 degrees C lower than the corresponding blood temperature, and had a peak-to-trough amplitude of 2.6 degrees C. Brain temperature closely paralleled changes in blood temperature but usually exceeded blood temperature by about 0.5 degrees C. Sporadic episodes of selective brain cooling occurred in one animal, but the duration and magnitude of such cooling was small (less than 0.4 degrees C), and took place only well above the mode of blood temperature. Our results do not support the concept that eland routinely employ adaptive heterothermy and selective brain cooling to survive in their natural environment.

Geometry and temperature dependence of conductance ventriculography.

The conductance catheter allows continuous monitoring of ventricular volume in vivo, but shape and temperature dependence have not been defined. Accordingly, an in vitro experiment was performed to assess the potential utility of conductance for volume measurement during hypothermia and in asymmetric chambers resembling the right ventricle. A 5 Fr conductance catheter was placed inside an ellipsoidal latex balloon, and known volumes of normal saline were infused, while conductance volumes were measured. The geometry of the right ventricle was then approximated by compressing the balloon in a mandrel constructed of two hemi-cylinders. Measurements were repeated in this geometry. Temperature was varied at volumes of 90 ml and 120 ml in an ellipsoidal balloon, and conductance was measured. Conductance volumes were plotted versus known volumes and regression analysis was applied. Compared with the line of identity, there was no statistical difference between slopes of left ventricular geometry and RV geometry, but conductance was highly dependent upon temperature. This was reflected in rho, the resistivity of saline. Rho varied from 80 to 51 (omega-cm) while temperature varied from 8 to 38 degrees C (p < 0.01). These observations suggest that conductance may be useful for measuring right as well as left ventricular volumes. During changes in blood temperature, multiple measurements of rho, in appropriately drawn blood samples, are necessary to maintain accuracy.

Cardiovascular changes during continuous hyperthermic peritoneal perfusion.

Changes in blood temperature, hemodynamics, and oxygen transport were evaluated in 11 patients during continuous hyperthermic peritoneal perfusion (CHPP), a technique in which the peritoneal cavity is perfused continuously with heated solution to treat intraperitoneal cancer. CHPP was undertaken 46.8 min after the resection of cancer. Blood temperature, measured with a thermistor of a pulmonary artery catheter, reached 39.2 degrees C. Heart rate increased to 100.7 +/- 21.4 bpm (mean +/- SD) and the cardiac index to 4.61 +/- 0.80 L.min-1.m-2. Mean arterial pressure decreased to 75.5 +/- 10.8 mm Hg and systemic vascular resistance index to 1239 +/- 394 dynes.s.cm-5.m2. Oxygen consumption greatly increased to 139.1 +/- 35.2 mL.min-1.m-2, concurrently with a smaller increase in oxygen delivery to 619.7 +/- 83.7 mL.min-1.m-2 and a slight increase in oxygen extraction. Pulmonary oxygenation capacity was also disturbed. Although these cardiovascular changes were mainly due to systemic hyperthermia, other changes may be caused by splanchnic heating, abdominal distention, and pharmacologic action of methoxamine, propranolol, diltiazem, and fentanyl.

Potential errors in pulse oximetry

There is no absolute reference for oxygen saturation, although multiwavelength in vitro oximeters are accepted as the 'gold standard'. Regardless of whether fractional or functional saturation is used by manufacturers to calibrate their oximeters, evaluation against fractional saturation is recommended since this is the clinically relevant variable. The use of standard notation and comparisons based on bias and precision is recommended. The accuracy of pulse oximetry is intrinsically limited by the use of only two wavelengths, and is dependent on the initial calibration population. The empirical algorithms used to convert the signal to its 'readout value' and the quality control of hardware may both be important sources of variability between oximeters. Change in blood temperature may introduce errors in pulse oximeter and in vitro oximeter saturation readings, but these will be clinically insignificant. Changes in blood pH should not decrease pulse oximetry accuracy.

Effects of selective blood and tissue heating on blood flow in the dog hindlimb

This study investigated the effects of independent and combined heating of blood and tissue to 40-44 degrees C on femoral blood flow in the hindlimb of the anaesthetized dog. An increase in arterial blood temperature by means of an extracorporeal circuit increased femoral vascular resistance. An increase in limb tissue temperature, induced by external hot packs, decreased femoral vascular resistance. These responses occurred both before and after sympathetic blockade. Neither blood heating nor tissue heating affected the hyperaemic response to exercise. When blood and tissue heating were combined, femoral vascular resistance remained unaffected. We conclude that changes in blood temperature do not contribute to the hyperaemic effect of limb warming and that exercise combined with limb warming is no more effective as a therapeutic tool for promoting limb flow than exercise alone.

Vascular Stability in Hemofiltration: Respective Roles of Blood Temperature Changes and of Sodium Mass Transfer

The respective roles of blood temperature changes and of sodium mass transfer on vascular stability (VS) in hemofiltration (HF) were studied in 7 uremic patients. Two conditions of Na removal have been studied: (1) ‘Physiological’ Na removal: withdrawal in HF of the previous intersession Na intake, and (2) ‘unphysiological’ Na removal: isotonic Na removal unrelated to oral intake. These two conditions were challenged with blood temperature changes. Results show that ‘warm’ HF impairs VS; nevertheless, this impairment is hindered by Na removal adaptations; the influence of Na balance is not evident in ‘cold’ HF.

Microcomputer-based cardiac pacemaker-control system through blood temperature.

A microcomputer-based temperature-sensitive cardiac pacemaker system and some preliminary experiments are described. The system consists of a microcomputer, a twin 5 in floppy disk unit, expansion and interface units, a visual display unit and a printer. It senses the blood temperature in the right atrium, determines the pacing rate and supplies the heart with stimulating pulses. System-heart interfacing is performed by the separate pacing and sensing units which communicate with the computer via a peripheral interface IC in an expansion unit. The pacing rate is determined by software, rather than a combination of hardware elements. The temperature response time of the system, from 25 degrees C to 40 degrees C is about 26 s, and this would seem to be satisfactory given that smaller and slower changes in blood temperature are normal.

Effects of hemodynamic changes induced by hyper- or hypothermia on intravenous lipid clearance rate and lipoprotein lipase activity in dogs.

Hyper- and hypothermia was induced in dogs by peritoneal perfusion with warm or cold Lactate-Ringer's solution, the objective being to alter cardiac output. Changes in cardiac index, intravenous lipid clearance rate (K-value), and lipoprotein lipase (LPL) activity, concomitantly with changes of the temperature of the mixed venous blood were investigated. The cardiac index increased significantly with the hyperthermia and there was a close correlation between the cardiac index and the K-value. The LPL activity did not change significantly with changes in blood temperature, and the correlation between the LPL activity and the K-value was not significant. The hemodynamics has to be considered when attempting to discuss the intravenous lipid clearance rate.

Biochemical adaptation to rapid temperature changes in scombrid red blood cell enzymes

1. 1. The physiological adaptations of skipjack tuna lead to 10°C changes in blood temperature every few seconds. 2. 2. The change in reaction rate of red blood cell LDH, MDH and GAPD to change in temperature are large under saturating substrate conditions but under intra-cellular substrate conditions reaction rate is almost independent of temperature. 3. 3. It seems likely that the biochemical effects observed are mediated through changes in K m with temperature. 4. 4. Three species related to the skipjack, but lacking its extreme physiological adaptations, had many of the biochemical adaptations seen in the skipjack. 5. 5. The primitive ancestor of the skipjack probably had the biochemical preadaptations needed to allow the physiological evolution seen in this lineage.

A temperature-sensitive cardiac pacemaker

An artificial cardiac pacemaker which is sensitive to the temperature of blood in the right atrium has been fabricated. For a temperature change of 20 degrees C the circuit achieves 90% of its final response within a period of 18 s. In the authors' opinion this is satisfactory since changes in blood temperature are generally small. Cardiac output in dogs rose from 2.37 +/- 0.65 to 4.54 +/- 1.15 l/min when the rate was increased from 202.6 beats/min(b.p.m.) at 37.6 degrees C to 231.6 b.p.m. at 41 degrees C. Cardiac output was found, from statistical observation, to be improved at temperatures over 39.6 degrees C.