Discrete vessel heat transfer in perfused tissue - model comparison

The aim of this paper is to compare two methods of calculating heat transfer in perfused biological tissue using a discrete vessel description. The methods differ in two important aspects: the representation of the vascular system and the algorithm for calculating the heat flux between tissue and blood vessels. The first method was developed at the University of Utrecht between 1994 and 1998 and has been used in several clinical applications. The second method has been proposed by the first author. The methods are briefly described, their assumptions and limitations are discussed. Finally, the test simulation is introduced and the results produced by both methods are compared. The test indicates that the simpler, and less computationally intensive method proposed by the present author for calculating 2D problems containing countercurrent blood vessel systems can reproduce quite well some features of the solution obtained by the more complex 3D method. The observed discrepancies could be explained on physical grounds

Numerical simulation of scalp cooling to prevent chemotherapy-induced alopecia

One way of treating cancer' is by chemotherapy. Side-effects of chemotherapy include hair loss. Cooling the scalp during trearment can reduce hair loss. For this cooling, a cap containing a cold tluid (cold cap) is used. However, the rate of success of this method varies strongly, because precise mechanisms of preservation are unknown. Temperature and perfusion are thought to play an important role in the hair preservative effect of scalp cooling. To gain more insight into these parameters, a computer model has been developed. With this, the influence of perfusion models is studied. The computer model comprises a head and cold cap, modeled with concentric shells representing brain, skull, fat, skin. hair and cold cap. Metabolism is temperalure dependent and two relations from literature are used to model temperature dependent perfusion. Pennes' bio-heat equaation is used to determine the heat transfer in the head. Steady state temperatures without cold cap are calculated and used as basal temperatures for metabolism and perfusion. Then a cold cap (T = -30'C) is added and the development of temperature in time is calculated. For constant perfusion, a minimum skin temperature of 16.0·C is reached aftel' 476 seconds. When skin blood flow is set to zero, Ihe minimum temperature drops a further 1.5 C to 14.5 C. For the perfusion modeIs, the drop in skin temperature results in a decreased perfusion, down to a value ranging from 19% to 33% of base level. The thickness of the hair layer is of great importance for bath perfusion and temperature. Reducing the thickness resulted in a decrease i.n temperature of 5.7 C, and decreased relative perfusion by a further 0.10, indicating that chances of preserving hair are higher. For optimal protection against hair loss, the cold cap should fit the scalp as tightly as possible

Modelling of temperature and perfusion during scalp cooling

Hair loss is a feared side effect of chemotherapy treatment. It may be prevented by cooling the scalp during administration of cytostatics. The supposed mechanism is that by cooling the scalp, both temperature and perfusion are diminished, affecting drug supply and drug uptake in the hair follicle. However, the effect of scalp cooling varies strongly. To gain more insight into the effect of cooling, a computer model has been developed that describes heat transfer in the human head during scalp cooling. Of main interest in this study are the mutual influences of scalp temperature and perfusion during cooling. Results of the standard head model show that the temperature of the scalp skin is reduced from 34.4 °C to 18.3 °C, reducing tissue blood flow to 25%. Based upon variations in both thermal properties and head anatomies found in the literature, a parameter study was performed. The results of this parameter study show that the most important parameters affecting both temperature and perfusion are the perfusion coefficient Q10 and the thermal resistances of both the fat and the hair layer. The variations in the parameter study led to skin temperature ranging from 10.1 °C to 21.8 °C, which in turn reduced relative perfusion to 13% and 33%, respectively

Heat transfer in patients under hypothermic conditions

Most bio-heat transfer models for patients under hypothermic conditions contain three sub-models: a passive heat transfer model, an active coupling between local blood flow and temperature, and a pharmacological model to incorporate the effects of drugs. In this paper an illustrative example will be given focussed on scalp cooling to prevent chemotherapy induced hair loss. Scalp cooling can reduce hair loss. Unfortunately, the efficacy of scalp cooling varies strongly. A systematic evaluation of the current hypothesis for the hair preservative effect of scalp cooling is necessary for a better understanding of the various important parameters of scalp cooling. To quantify the contribution of the putative mechanisms of scalp cooling, a computational model was developed, partly based on experimental data. With the complete model, we evaluated the effect of several scalp cooling protocol parameters

Modelling heat transfer in humans

Temperature plays an important role in the functioning of biological systems. To predict tissue temperatures, the influence of blood flow must be accounted for. The collective effect of blood vessels in a tissue volume may be reasonably successfully described by a heatsink. This is for instance the case in our study of using scalp cooling to prevent hair loss induced by chemotherapy. In the calculation of overall temperature distributions the thermoregulatory mechanisms of vasoaction, sweating and shivering need to be considered. Models get increasingly sophisticated, but accurate predictions for individuals (rather than average behaviour) remain difficult because of the many influencing factors. A predictive tool for individual patients, including effect of anaesthesia, is being developed for use during hypothermic (cardiac) surgery

Modelling of temperature and perfusion during scalp cooling

Hair loss is a feared side effect of chemotherapy treatment. It may be prevented by cooling the scalp during administration of cytostatics. The supposed mechanism is that by cooling the scalp, both temperature and perfusion are diminished, affecting drug supply and drug uptake in the hair follicle. However, the effect of scalp cooling varies strongly. To gain more insight into the effect of cooling, a computer model has been developed that describes heat transfer in the human head during scalp cooling. Of main interest in this study are the mutual influences of scalp temperature and perfusion during cooling. Results of the standard head model show that the temperature of the scalp skin is reduced from 34.4 °C to 18.3 °C, reducing tissue blood flow to 25%. Based upon variations in both thermal properties and head anatomies found in the literature, a parameter study was performed. The results of this parameter study show that the most important parameters affecting both temperature and perfusion are the perfusion coefficient Q10 and the thermal resistances of both the fat and the hair layer. The variations in the parameter study led to skin temperature ranging from 10.1 °C to 21.8 °C, which in turn reduced relative perfusion to 13% and 33%, respectively

A flexible algorithm for construction of 3-D vessel networks for use in thermal modeling

A new algorithm for the construction of artificial blood vessel networks is presented. The algorithm produces three-dimensional (3-D) geometrical representations of both arterial and venous networks. The key ingredient of the algorithm is a 3-D potential function defined in the tissue volume. This potential function controls the paths by which points are connected to existing vessels, thereby producing new vessel segments. The potential function has no physiological interpretation, but, by adjustment of parameters governing the potential, it is possible to produce networks that have physiologically meaningful geometrical properties. If desired, the veins can be generated counter current to the arteries. Furthermore, the potential function allows fashioning of the networks to the presence of bone or air cavities. The resulting networks can be used for thermal simulations of hyperthermia treatment