Heat Generation In Tissue Research Articles

Facemask vapor trapping, condensation, and thermoregulation

The widespread adoption of facemasks in various contexts has highlighted challenges associated with prolonged mask-wearing. Despite their effectiveness in preventing the spread of pathogens, issues such as discomfort, stuffiness, and fogging of eyeglasses can deter individuals from wearing masks consistently. Understanding the mechanisms of thermal and humidity regulation during facemask use is crucial for addressing these challenges. This study investigates the impact of face mask-wearing on facial thermoregulation and moisture accumulation, comparing conditions with and without masks. An integrated computational model was developed to consider respiratory flows, tissue heat generation, skin convective heat dissipation, the influence of inhaled cool air and exhaled warm air, and their interactions with the mask media. Model validation was conducted using complementary Schlieren imaging and transient temperature measurements. Results reveal significant increases in facial temperature with well-fitted masks and highlight the role of trapped moisture inside the mask. Thermo-humidity variations beneath the mask and condensations in the mask were quantified, providing insights into facemask-wearing thermoregulation. The effects of moist vs. dry air, steady vs. tidal breathing, and with vs. without buoyancy were quantitatively compared. These findings have implications for improving mask design and promoting adherence in diverse environmental settings. Addressing these discomfort-related challenges is crucial for enhancing mask adherence and ensuring adequate protection.

Impacts of Mask Wearing and Leakages on Cyclic Respiratory Flows and Facial Thermoregulation

Elevated face temperature due to mask wearing can cause discomfort and skin irritation, making mask mandates challenging. When thermal discomfort becomes intolerable, individuals instinctively or unknowingly loosen or remove their facemasks, compromising the mask’s protective efficacy. The objective of this study was to numerically quantify the microclimate under the mask and facial thermoregulation when wearing a surgical mask with different levels of misfit. An integrated ambient–mask–face–airway computational model was developed with gaps of varying sizes and locations and was validated against complementary experiments. The low Reynolds number (LRN) k-ω turbulence model with porous media was used to simulate transient respiratory flows. Both skin convective heat transfer and tissue heat generation were considered in thermoregulation under the facemask, besides the warm air exhaled from the body and the cool air inhaled from the ambient. The results of this study showed that when wearing a surgical mask with a perfect fit under normal breathing, the temperature at the philtrum increased by 4.3 °C compared to not wearing a mask. A small gap measuring 0.51 cm2 (gap A) at the nose top resulted in 5.6% leakage but reduced the warming effect by 28% compared to zero gap. Meanwhile, a gap of 4.3 cm2 (R1L1) caused 42% leakage and a 62% reduction in the warming effect. Unique temporospatial temperature profiles were observed at various sampling points and for different gap sizes, which correlated reasonably with the corresponding flow dynamics, particularly close to the gaps. The temperature change rate also exhibited patterns unique to the gap site and sampling point, with distinctive peaks occurring during the inspiratory–expiratory flow transitions. These results have the significant implications that by using the temporospatial temperature profiles at several landmark points, the gap location can potentially be pinpointed, and the gap size and leakage fractions can be quantified.

Why we should care about soft tissue interfaces when applying ultrasonic diathermy: an experimental and computer simulation study

BackgroundOne goal of therapeutic ultrasound is enabling heat generation in tissue. Ultrasound application protocols typically neglect these processes of absorption and backscatter/reflection at the skin/fat, fat/muscle, and muscle/bone interfaces. The aim of this study was to investigate the heating process at interfaces close to the transducer and the bone with the aid of computer simulation and tissue-mimicking materials (phantoms).MethodsThe experimental setup consists of physiotherapeutic ultrasound equipment for irradiation, two layers of soft tissue-mimicking material, and one with and one without an additional layer of bone-mimicking material. Thermocouple monitoring is used in both cases. A computational model is used with the experimental parameters in a COMSOL® software platform.ResultsThe experimental results show significant temperature rise (42 °C) at 10 mm depth, regardless of bone layer presence, diverging 3 °C from the simulated values. The probable causes are thermocouple and transducer heating and interface reverberations. There was no statistical difference in the experimental results with and without the cortical bone for the central thermocouple of the first interface [t(38) = −1.52; 95% CI = −0.85, 0.12; p = 14]. Temperature rise (>6 °C) close to the bone layer was lower than predicted (>21 °C), possibly because without the bone layer, thermocouples at 30 mm make contact with the water bath and convection intensifies heat loss; this factor was omitted in the simulation model.ConclusionsThis work suggests that more attention should be given to soft tissue layer interfaces in ultrasound therapeutic procedures even in the absence of a close bone layer.

Experimental Modelling of Heat Generation in Porcine Tissue to Investigate the Etiology of Diabetic Foot Ulceration

Diabetic foot ulceration is a major complication of diabetes. A recent systematic review has concluded that an increase in skin temperature is associated with a higher risk of diabetic foot ulceration. However, the mechanism of the rise of foot temperatures is not understood. In this paper, we examine the effect of viscoelastic heating on the foot temperature by experimentally measuring temperature of porcine tissue during cyclic loading. We show that the heat generated in the tissue increases with amplitude and frequency of loading. This viscoelastic heating may contribute to changes in foot tissue temperature.

Biodegradable Photonic Melanoidin for Theranostic Applications.

Light-absorbing nanoparticles for localized heat generation in tissues have various biomedical applications in diagnostic imaging, surgery, and therapies. Although numerous plasmonic and carbon-based nanoparticles with strong optical absorption have been developed, their clearance, potential cytotoxicity, and long-term safety issues remain unresolved. Here, we show that "generally regarded as safe (GRAS)" melanoidins prepared from glucose and amino acid offer a high light-to-heat conversion efficiency, biocompatibility, biodegradability, nonmutagenicity, and efficient renal clearance, as well as a low cost for synthesis. We exhibit a wide range of biomedical photonic applications of melanoidins, including in vivo photoacoustic mapping of sentinel lymph nodes, photoacoustic tracking of gastrointestinal tracts, photothermal cancer therapy, and photothermal lipolysis. The biodegradation rate and renal clearance of melanoidins are controllable by design. Our results confirm the feasibility of biodegradable melanoidins for various photonic applications to theranostic nanomedicines.

Handheld-Level Electromechanical Cartilage Reshaping Device.

We have developed a handheld-level multichannel electromechanical reshaping (EMR) cartilage device and evaluated the feasibility of providing a means of cartilage reshaping in a clinical outpatient setting. The effect of EMR on pig costal cartilage was evaluated in terms of shape change, tissue heat generation, and cell viability. The pig costal cartilage specimens (23 mm × 6.0 mm × 0.7 mm) were mechanically deformed to 90 degrees and fixed to a plastic jig and applied 5, 6, 7, and 8 V up to 8 minutes to find the optimal dosimetry for the our developed EMR device. The results reveal that bend angle increased with increasing voltage and application time. The maximum bend angle obtained was 70.5 ± 7.3 at 8 V, 5 minutes. The temperature of flat pig costal cartilage specimens were measured, while a constant electric voltage was applied to three pairs of electrodes that were inserted into the cartilages. The nonthermal feature of EMR was validated by a thermal infrared camera; that is, the maximum temperate of the flat cartilages is 20.3°C at 8 V. Cell viability assay showed no significant difference in cell damaged area from 3 to 7 minutes exposure with 7 V. In conclusion, the multichannel EMR device that was developed showed a good feasibility of cartilage shaping with minimal temperature change.

Numerical simulation of the enhanced heat production in tissue due to the nonlinear character of high-intensity focused ultrasound (HIFU)

HIFU is used in thermotherapy to destroy tumors located deep in human tissue by heat. It is well known that HIFU is connected with the generation of higher-frequency components due to nonlinear steepening during propagation. An over-proportional heat generation in tissue occurs with enhanced power input. To obtain fundamental information about an optimal dosage of the applied ultrasound, simulations are necessary. A hot spot in healthy tissue must be avoided and a sufficient heat delivery in the tumor region must be guaranteed. Until now most numerical investigations of thermotherapy with HIFU have been carried out under the assumption of linearity. This means an essential underestimation of heat production. Here an improved model is introduced which enables accurate simulations, including nonlinearities. It consists of a set of nonlinear acoustic equations which ensure an accurate full-wave propagation modeling. A broadband absorption model of typical soft-tissue frequency-power-law character is included to obtain a nonlinear modeled heat source. The thermal behavior is described by a bio-heat-transfers-equation. The complete model is solved by means of a high-order FDTD scheme. Exemplary simulations illustrate the efficiency of this method.

Effects of phase aberration on tissue heat generation and temperature elevation using therapeutic ultrasound

The effects of inhomogeneous propagation media on tissue heating patterns and steady-state temperature distributions are investigated analytically for continuous-wave therapeutic ultrasound using a random-phase screen model. Formulas for the statistical moments of the on-axis heat distribution, total heat deposited in a target volume, and axial temperature elevation are derived. Based on the statistical moments, we propose figures of merit to quantitatively assess therapeutic performance for a range of experimental parameters. The analysis relates statistical properties of the aberrator to those of heat generation in tissue. The mean on-axis heat distribution is substantially reduced in the focal zone, while its variance is increased at other axial positions. The amount of heat delivered to a target volume depends on the location of the target and the size of the volume. Compared to the results for homogeneous media, the greatest reduction in temperature increase occurs in the focal zone. Distortions in the temperature elevation patterns are greatest when the perfusion in tissue is large.

Blood flow, substrate utilization and heat generation in tissues drained by the azygos vein in man.

The present study was undertaken to examine the blood flow, heat generation and substrate utilization in tissues drained by the azygos vein in healthy subjects. Catheters were inserted percutaneously into the azygos vein and the pulmonary artery in 10 healthy male subjects in the basal, post-absorptive state. Blood flow in the azygos vein was measured by thermodilution technique, blood temperature was recorded in both the azygos vein and the pulmonary artery and blood samples for the determination of oxygen content and substrate concentrations were collected from both vessels repeatedly at timed intervals. Free fatty acid (FFA) exchange was evaluated following the intravenous infusion of 14-C labelled oleic acid. The average azygos vein blood flow was 94 +/- 10 ml/min. The coefficient of variation for the flow determination was 3.6%. The blood temperature in the azygos vein was consistently higher than that in the pulmonary artery, indicating an average calculated net heat production in the tissues of 0.5 W. The oxygen uptake to the tissues drained by the azygos vein amounted to 6 +/- 1 ml/min. Significant amounts of glucose, FFA and ketone bodies were taken up in the azygos area, while both glycerol and FFA were released. The FFA uptake could, if oxidized, account for about half of the oxygen uptake. In conclusion, the findings indicate that, in the basal state, the tissues drained by the azygos vein utilize both glucose and FFA. Heat is generated within the area but the rate of generation is low and can largely be explained by the oxidative metabolism. The findings do not support an important role for brown adipose tissue metabolism in the interscapular region in man.