Classification of chronic venous diseases based on skin temperature patterns

Objective. Infrared thermography has the potential to complement the classification of chronic venous diseases (CVD), but lacks sophisticated insights on the association between recorded skin temperatures and the severity of CVD. This research aims to identify temperature patterns in the lower legs of patients that are distinct in specific forms of CVD, including florid ulcers.Approach. Infrared images were acquired in a clinical trial with 36 patients and segmented using a region selection algorithm. The regions were analyzed with respect to seven predefined features. The most prominent thermal features were translated into rules to classify CVD.Main results. Patients with mild forms of CVD show local increases in skin temperature by more than 1.5 °C. These regions were 2.0 °C warmer when CVD is more severe. Temperature variations of on average 0.4 °C occurred within venous leg ulcers. Furthermore, these wounds were 1.1 °C-6.3 °C colder than periwound skin.Significance. Temperature patterns characterized by differences in temperature that occur within a few centimeters or millimeters are distinct to specific stages of CVD. These patterns are present in the locations of varicose veins and tissue damages.Significance. The findings increase the body of knowledge on the potential for the early detection of CVD using infrared thermography. Applying the presented algorithms and rules, infrared thermography may become a complementary tool for the objective classification of CVD.

Improved Estimation of Left Ventricular Volume from Electric Field Modeling

Volume measurement is beneficial in left ventricular assist device (LVAD) therapy to quantify patient demand. In principle, an LVAD could provide a platform that allows bioimpedance measurements inside the ventricle without requiring additional implants. Conductance measured by the LVAD can then be used to estimate the ventricular radius, which can be applied to calculate ventricular volume. However, established methods that estimate radius from conductance require elaborate individual calibration or show low accuracy. This study presents two analytical calculation methods to estimate left ventricular radius from conductance using electric field theory. These methods build on the established method of Wei, now considering the dielectric properties of muscle and background tissue, the refraction of the electric field at the blood-muscle boundary, and the changes of the electric field caused by the measurements. The methods are validated in five glass containers of different radius. Additional bioimpedance measurements are performed in in-vitro models that replicate the left ventricle's shape and conductive properties. The proposed analytical calculation methods estimate the radii of the containers and the in-vitro models with higher accuracy and precision than Wei's method. The lead method performs excellently in glass cylinders over a wide range of radii (bias: 1.66%-2.48%, limits of agreement < 16.33%) without calibration to specific geometries.

Object-oriented modeling of thoracic fluid balance to study cardiogenic pulmonary congestion in humans

BACKGROUND AND OBJECTIVE

We hypothesized that a biophysical computational model implemented in an object-oriented modeling language (OOML) would provide physiological information and simulative data to study the development and treatment of cardiogenic pulmonary congestion.

METHODS

This work is based on the object-oriented cardiopulmonary interaction introduced in [1]. This paper describes the novel model components required to study cardiogenic pulmonary congestion: i) interstitial fluid exchange related to the Starling equation, ii) the lymphatic pump, and iii) the interconnection of these elements with the original cardiopulmonary model. The presented model succeeds in i) describing lymphatic flow at the capillary artery and venous end, ii) activation of the lymphatic pump at elevated pulmonary pressures, and iii) the simulation of the different safety factors related to lung tissue, osmotic gradient, and the lymphatic system during the development of lung congestion.

RESULTS

Simulations show a qualitative correlation between model behavior and physiological data from literature. The model also demonstrates the beneficial effect of continuous positive airway pressure therapy on fluid clearance and respiratory mechanics.

CONCLUSION

This study demonstrates the successful use of OOML to describe the development of cardiogenic congestion by introducing a model of the lymphatic system and the thoracic fluid balance system, as well as connecting them to the existing cardiopulmonary model.

An object-oriented computational model to study cardiopulmonary hemodynamic interactions in humans

BACKGROUND AND OBJECTIVE

This work introduces an object-oriented computational model to study cardiopulmonary interactions in humans.

METHODS

Modeling was performed in object-oriented programing language Matlab Simscape, where model components are connected with each other through physical connections. Constitutive and phenomenological equations of model elements are implemented based on their non-linear pressure-volume or pressure-flow relationship. The model includes more than 30 physiological compartments, which belong either to the cardiovascular or respiratory system. The model considers non-linear behaviors of veins, pulmonary capillaries, collapsible airways, alveoli, and the chest wall. Model parameters were derisved based on literature values. Model validation was performed by comparing simulation results with clinical and animal data reported in literature.

RESULTS

The model is able to provide quantitative values of alveolar, pleural, interstitial, aortic and ventricular pressures, as well as heart and lung volumes during spontaneous breathing and mechanical ventilation. Results of baseline simulation demonstrate the consistency of the assigned parameters. Simulation results during mechanical ventilation with PEEP trials can be directly compared with animal and clinical data given in literature.

CONCLUSIONS

Object-oriented programming languages can be used to model interconnected systems including model non-linearities. The model provides a useful tool to investigate cardiopulmonary activity during spontaneous breathing and mechanical ventilation.