Multiple interacting mechanisms control the formation and dissolution of clots to maintain blood in a state of delicate balance. In addition to a myriad of biochemical reactions, rheological factors also play a crucial role in modulating the response of blood to external stimuli. The broad stimuli for clot formation were laid out, more than a century ago, in, what is now referred to as, Virchow’s triad. To date, a comprehensive model for clot formation and dissolution, that takes into account the biochemical, medical and rheological factors, has not been put into place, the existing models emphasizing either one or the other of the factors. In this dissertation, a model is developed for clot formation and dissolution that incorporates many of the relevant crucial factors that have a bearing on the problem. The model, though just a first step towards understanding a complex phenomenon goes further than previous models in integrating the biochemical, medical and rheological factors that come into play. The model is tested in some simple flow situations as part of an attempt to elucidate Virchow’s triad. Extensions to the model, along with detailed numerical studies, will hopefully aid in a clearer understanding of the phenomenon, and in making relevant clinical correlations.

Background: Lung transplant is the fastest growing solid organ transplant procedure and venous thromboembolism has been described to occur in 8-29% of cases. This is much higher than any other solid organ and the exact incidence has yet to be determined. Risk factors for the development of venous thromboembolic disease (VTE) specific to lung transplant are not fully understood. Purpose: The purpose of this research was to describe the incidence and risk factors for VTE disease during the first year following lung transplant at a busy transplant center in the Southwest United States. Methods: A descriptive retrospective study design was used. Virchow's triad was used as a theoretical model to identify selected variables common to lung transplant in an effort to understand possible risk factors for the development of VTE in this patient population. Consecutive lung transplant cases between June 1, 2013 and May 31, 2014 at St. Joseph's Medical Center in Phoenix, Arizona were retrospectively reviewed and followed for exactly one year following the lung transplant date. Demographic variables, Virchow's triad variables, and variables previously identified in the literature as being risk factors for VTE were collected and analyzed using descriptive, frequency, t-test, chi-square, and logistic regression. Results: The incidence of VTE in this patient population was 25.8% and is consistent with findings from previous studies. Using the constructs of Virchow's triad did not yield any statistically significant predictors for VTE in this patient population. However, lung allocation score (LAS) (OR 1.109, CI 1.038-1.185), body mass index (BMI) (OR 1.362, CI 1.034-1.794), and time on the waitlist (OR 1.094, CI 1.023-1.171) did reach statistical significance as possible predictors for VTE following lung transplant in this patient sample. Conclusions: VTE is a common complication of lung transplant that has a high incidence during the first year following lung transplant. This study did identify LAS, BMI, and time on the waitlist as being possible risk factors for the development of VTE following lung transplant. LAS may be a useful surrogate to determine the risk for VTE in this population.