Browsing by Author "Rakesh, Vineet"
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- ItemA 3-D mathematical model to identify organ-specific risks in rats during thermal stress.(2013-12-17) Rakesh, Vineet; Stallings, Jonathan D; Helwig, Bryan G; Leon, Lisa R; Jackson, David A; Reifman, JaquesEarly prediction of the adverse outcomes associated with heat stress is critical for effective management and mitigation of injury which may sometimes lead to extreme undesirable clinical conditions such as multiorgan dysfunction syndrome and death Here we developed a computational model to predict the spatiotemporal temperature distribution in a rat exposed to heat stress in an attempt to understand the correlation between heat load and differential organ dysfunction The model includes a three dimensional representation of the rat anatomy obtained from medical imaging and incorporates the key mechanisms of heat transfer during thermoregulation We formulated a novel approach to estimate blood temperature by accounting for blood mixing from the different organs and to estimate the effects of the circadian rhythm in body temperature by considering day night variations in metabolic heat generation and blood perfusion We validated the model using in vivo core temperature measurements in control and heat stressed rats and other published experimental data The model predictions were within 1 SD of the measured data The liver demonstrated the greatest susceptibility to heat stress with the maximum temperature reaching 2 C higher than the measured core temperature and 95 of its volume exceeding the targeted experimental core temperature Other organs also attained temperatures greater than the core temperature illustrating the need to monitor multiple organs during heat stress The model facilitates the identification of organ specific risks during heat stress and has the potential to aid in the development of improved clinical strategies for thermal injury prevention and management
- ItemA computational study of the respiratory airflow characteristics in normal and obstructed human airways.(2014-08-18) Sul, Bora; Wallqvist, Anders; Morris, Michael J; Reifman, Jaques; Rakesh, VineetObstructive lung diseases in the lower airways are a leading health concern worldwide To improve our understanding of the pathophysiology of lower airways we studied airflow characteristics in the lung between the 8th and the 14th generations using a three dimensional computational fluid dynamics model where we compared normal and obstructed airways for a range of breathing conditions We employed a novel technique based on computing the Pearson s correlation coefficient to quantitatively characterize the differences in airflow patterns between the normal and obstructed airways We found that the airflow patterns demonstrated clear differences between normal and diseased conditions for high expiratory flow rates 2300ml s but not for inspiratory flow rates Moreover airflow patterns subjected to filtering demonstrated higher sensitivity than airway resistance for differentiating normal and diseased conditions Further we showed that wall shear stresses were not only dependent on breathing rates but also on the distribution of the obstructed sites in the lung for the same degree of obstruction and breathing rate we observed as much as two fold differences in shear stresses In contrast to previous studies that suggest increased wall shear stress due to obstructions as a possible damage mechanism for small airways our model demonstrated that for flow rates corresponding to heavy activities the wall shear stress in both normal and obstructed airways was Under0 3Pa which is within the physiological limit needed to promote respiratory defense mechanisms In summary our model enables the study of airflow characteristics that may be impractical to assess experimentally
- ItemA virtual rat for simulating environmental and exertional heat stress.(2014-12-02) Rakesh, Vineet; Stallings, Jonathan D; Reifman, JaquesSevere cases of environmental or exertional heat stress can lead to varying degrees of organ dysfunction To understand heat injury progression and develop efficient management and mitigation strategies it is critical to determine the thermal response in susceptible organs under different heat stress conditions To this end we used our previously published virtual rat which is capable of computing the spatiotemporal temperature distribution in the animal and extended it to simulate various heat stress scenarios including 1 different environmental conditions 2 exertional heat stress 3 circadian rhythm effect on the thermal response and 4 whole body cooling Our predictions were consistent with published in vivo temperature measurements for all cases validating our simulations We observed a differential thermal response in the organs with the liver experiencing the highest temperatures for all environmental and exertional heat stress cases For every 3 C rise in the external temperature from 40 to 46 C core and organ temperatures increased by 0 8 C Core temperatures increased by 2 6 and 4 1 C for increases in exercise intensity from rest to 75 and 100 of maximal O2 consumption respectively We also found differences as large as 0 8 C in organ temperatures for the same heat stress induced at different times during the day Even after whole body cooling at a relatively low external temperature 1 C for 20 min average organ temperatures were still elevated by 2 3 to 2 5 C compared with normothermia These results can be used to optimize experimental protocol designs reduce the amount of animal experimentation and design and test improved heat stress prevention and management strategies