Characteristics of victims of trauma requiring invasive mechanical ventilation with a short stay in critical care.

BACKGROUND: Many patients who are admitted to the intensive care unit (ICU) have needs which rapidly resolve and are discharged alive within 24 h. We sought to characterize the outcomes of critically ill trauma victims at our institution with a short stay in the ICU. METHODS: We conducted a retrospective cohort study of all critically ill adult trauma victims presenting to our ED between January 1st, 2011 and December 31st, 2019. We included patients who were endotracheally intubated in either the prehospital setting or the ED and were admitted either to the operating room (OR), angiography suite, or ICU. Our primary outcome was the proportion of patients who were discharged alive from the ICU within 24 h. RESULTS: We included 3869 patients meeting the criteria above who were alive at 24 h. This population was 78% male with a median age of 40 and 76% of patients suffered from blunt trauma. The median injury severity score (ISS) of the group was 21 [inter-quartile range (IQR) 11-30]. In-hospital mortality amongst the group was 12%. 17% of the group were discharged alive from the ICU within 24 h. Thirty-four percent of the group had an ISS ≤ 15. Of the group which left the ICU alive within 24 h, six patients (0.9%) died in the hospital, 2 % of patients were re-admitted to an ICU, and 0.6% of patients required re-intubation. CONCLUSIONS: We found that 17% of patients who were intubated in the prehospital setting or emergency department and subsequently hospitalized were discharged alive from the ICU within 24 h.

A Description of Mechanically Ventilated Patients Admitted From the Emergency Department With a Short Critical Care Stay.

BACKGROUND: Patients admitted to an intensive care unit (ICU) requiring invasive mechanical ventilation who are discharged alive from the ICU within 24 h are poorly characterized in the literature. OBJECTIVE: Our aim was to characterize a cohort of intubated emergency department (ED) patients who are extubated and discharged from the ICU within 24 h. METHODS: We conducted a retrospective, observational cohort study at a single level I trauma center from January 2017 to December 2019. We included adults who were admitted to an ICU from the ED requiring invasive mechanical ventilation. Our primary outcome was the proportion of patients who were discharged from the ICU alive within 24 h. RESULTS: Of 13,374 ED patients admitted to an ICU during the study period, 2871 patients were intubated and ventilated in the prehospital or ED settings. Of these, 14% were discharged alive from the ICU within 24 h of admission. Only 21% of these patients were intubated in the ED. We identified the following two distinct subpopulations comprising 62% of this short-stay group: patients with a primary discharge diagnosis of intoxication (47%) and minimally injured trauma patients (53%), with 4% of patients in both subgroups. CONCLUSIONS: A total of 14% of patients receiving intubation with mechanical ventilation in the prehospital environment or in the ED were discharged alive from the ICU within 24 h. We identified two distinct subgroups of patients with a short stay in intensive care who may be candidates for ED extubation, including patients with intoxication and minimally injured trauma patients.

Microstructure and Mechanical Property of Glutaraldehyde-Treated Porcine Pulmonary Ligament.

There is a significant need for fixed biological tissues with desired structural and material constituents for tissue engineering applications. Here, we introduce the lung ligament as a fixed biological material that may have clinical utility for tissue engineering. To characterize the lung tissue for potential clinical applications, we studied glutaraldehyde-treated porcine pulmonary ligament (n = 11) with multiphoton microscopy (MPM) and conducted biaxial planar experiments to characterize the mechanical property of the tissue. The MPM imaging revealed that there are generally two families of collagen fibers distributed in two distinct layers: The first family largely aligns along the longitudinal direction with a mean angle of θ = 10.7 ± 9.3 deg, while the second one exhibits a random distribution with a mean θ = 36.6 ± 27.4. Elastin fibers appear in some intermediate sublayers with a random orientation distribution with a mean θ = 39.6 ± 23 deg. Based on the microstructural observation, a microstructure-based constitutive law was proposed to model the elastic property of the tissue. The material parameters were identified by fitting the model to the biaxial stress-strain data of specimens, and good fitting quality was achieved. The parameter e0 (which denotes the strain beyond which the collagen can withstand tension) of glutaraldehyde-treated tissues demonstrated low variability implying a relatively consistent collagen undulation in different samples, while the stiffness parameters for elastin and collagen fibers showed relatively greater variability. The fixed tissues presented a smaller e0 than that of fresh specimen, confirming that glutaraldehyde crosslinking increases the mechanical strength of collagen-based biomaterials. The present study sheds light on the biomechanics of glutaraldehyde-treated porcine pulmonary ligament that may be a candidate for tissue engineering.

Dissection flap fenestration can reduce re-apposition force of the false lumen in type-B aortic dissection: a computational and bench study.

Thoracic endovascular aortic repair (TEVAR) has been widely adopted as a standard for treating complicated acute and high-risk uncomplicated Stanford Type-B aortic dissections. The treatment redirects the blood flow towards the true lumen by covering the proximal dissection tear which promotes sealing of the false lumen. Despite advances in TEVAR, over 30% of Type-B dissection patients require additional interventions. This is primarily due to the presence of a persistent patent false lumen post-TEVAR that could potentially enlarge over time. We propose a novel technique, called slit fenestration pattern creation, which reduces the forces for re-apposition of the dissection flap (i.e., increase the compliance of the flap). We compute the optimal slit fenestration design using a virtual design of experiment (DOE) and demonstrate its effectiveness in reducing the re-apposition forces through computational simulations and benchtop experiments using porcine aortas. The findings suggest this potential therapy can drastically reduce the radial loading required to re-appose a dissected flap against the aortic wall to ensure reconstitution of the aortic wall (remodeling).

Can Military Role 1 Practitioners Maintain Their Skills Working at Civilian Level 1 Trauma Centers: A Retrospective, Cross-Sectional Study.

BACKGROUND: Introduction: Military Role 1 practitioners have difficulty maintaining skill competency by working solely in military medical treatment facilities. Recognizing this, the Army Medical Department has renewed focus on physician specialty-specific Individual Critical Task Lists (ICTL) and is increasing the number of military-civilian partnerships, wherein small military treatment teams work full-time in civilian trauma centers. Yet, data to validate this approach is lacking. We hypothesize military Role 1 practitioners working full-time at a civilian Level 1 trauma center would attain similar resuscitation-specific procedural frequency to providers deployed to an active combat zone, and use the emergency medicine (EM) ICTL to compare select procedural frequency between a cohort of trauma patients from a civilian Level 1 trauma center and a cohort of combat casualties from the Department of Defense Trauma Registry (DODTR). METHODS: We compared a selected subset of critically-injured, military-aged (18-35 years) trauma patients who were seen in a Level I Trauma Center emergency department (ED) between January 1, 2016 and December 31, 2017 and dispositioned directly either to the operating room, intensive care unit, or morgue to a selected cohort from the Department of Defense Trauma Registry (DODTR) who were seen in EDs in Iraq and Afghanistan between January 2007 and August 2016 using descriptive statistics. The primary outcome was the frequency of ICTL procedures performed, and the secondary outcome was injury severity. RESULTS: We identified 843 civilian patients meeting inclusion criteria, of 1,719 military-aged patients captured by the trauma registry during the study. The selected cohort from the DODTR included 27,359 patients. Demographics were similar between the 2 groups, except the DODTR cohort included significantly more patients with blast trauma (55% versus 0.4%). We found similar ICTL procedural frequency (1 procedure for every 1.84 patients in the civilian cohort compared to one procedure/1.52 patients in the military cohort). CONCLUSION: Role-1 ICTL trauma procedures were performed at similar frequencies between civilian patients seen at a Level 1 trauma center and combat casualties. With proper practice implementation, the opportunity exists for Role 1 practitioners to maintain their trauma resuscitation skills at civilian trauma centers.

Changes of thoracic duct flow and morphology in an animal model of elevated central venous pressure.

Objective: Investigation of lymph fluid dynamics in thoracic duct during central venous pressure elevation. Background: Lymphatic flow is affected by elevated central venous pressure (CVP) in congestive heart failure. The changes of thoracic duct (TD) lymph flow have not been studied chronically in the setting of elevated CVP. This study is to investigate fluid dynamics and remodeling of the TD in the elevated CVP animal model. Methods: A flow probe was implanted on the swine TD (n = 6) and tricuspid regurgitation (TR) was created by cutting tricuspid chordae percutaneously. Six swine were used as control group animals. The TD flow was measured for 2 weeks (baseline) before TR and 4 weeks postop-TR surgery. Arterial pressure and CVP were measured. The pressure and flow in the TD were measured percutaneously. Histological and morphological analyses were performed. Results: TR resulted in an increase in CVP from 4.2 ± 2.6 to 10.1 ± 4.3 mmHg (p < 0.05). The lymph flow in the TD increased from 0.78 ± 1.06 before TR to 8.8 ± 4.8 ml/min (p < 0.05) 2 days post-TR and remained plateau for 4 weeks, i.e., the TD flow remained approximately 8-11 fold its baseline. Compared to the 8.1 ± 3.2 mmHg control group, the TD average pressures at the lymphovenous junction increased to 14.6 ± 5.7 mmHg in the TR group (p < 0.05). The TD diameter and wall thickness increased from 3.35 ± 0.37 mm and 0.06 ± 0.01 mm in control to 4.32 ± 0.57 mm and 0.26 ± 0.02 mm (p < 0.05) in the TR group, respectively. Conclusion: The elevated CVP results in a significant increase in TD flow and pressure which causes the TD's outward remodeling and thickening. Our study implicates that the outward remodeling may result in the TD valve incompetence due to failure coaptation of leaflets.

A 57-Year-Old Man With COVID-19 Pneumonia Who Required Venovenous Extracorporeal Life Support With a Rapidly Escalating WBC Count.

CASE PRESENTATION: A 57-year-old man who had been intubated and placed on venovenous extracorporeal membrane oxygenation for hypoxemic respiratory failure due to COVID-19 pneumonia was transferred to our facility. He underwent anticoagulation with IV heparin titrated to an anti-Factor Xa goal of 0.1 to 0.3 international unit/mL. Over extracorporeal membrane oxygenation days 13 to 17, his WBC count rose from 17,500 to 47,000 cells/µL. He simultaneously experienced the development of fluid-refractory shock that required multiple vasopressors and received stress-dose hydrocortisone when his WBC was 30,000 cells/µL. He remained afebrile and was started on broad-spectrum antimicrobials that included antifungal and anthelminthic therapy.

Respiratory Mechanics in a Cohort of Critically Ill Subjects With COVID-19 Infection.

BACKGROUND: Patients with coronavirus disease 2019 (COVID-19) often develop acute hypoxemic respiratory failure and receive invasive mechanical ventilation. Much remains unknown about their respiratory mechanics, including the trajectories of pulmonary compliance and [Formula: see text]/[Formula: see text], the prognostic value of these parameters, and the effects of prone positioning. We described respiratory mechanics among subjects with COVID-19 who were intubated during the first month of hospitalization. METHODS: We included patients with COVID-19 who were mechanically ventilated between February and May 2020. Daily values of pulmonary compliance, [Formula: see text], [Formula: see text], and the use of prone positioning were abstracted from electronic medical records. The trends were analyzed separately over days 1-10 and days 1-35 of intubation, stratified by prone positioning use, survival, and initial [Formula: see text]/[Formula: see text]. RESULTS: Among 49 subjects on mechanical ventilation day 1, the mean compliance was 41 mL/cm H2O, decreasing to 25 mL/cm H2O by day 14, the median duration of mechanical ventilation. In contrast, the [Formula: see text]/[Formula: see text] on day 1 was similar to day 14. The overall mean compliance was greater among the non-survivors versus the survivors (27 mL/cm H2O vs 24 mL/cm H2O; P = .005), whereas [Formula: see text]/[Formula: see text] was higher among the survivors versus the non-survivors over days 1-10 (159 mm Hg vs 138 mm Hg; P = .002) and days 1-35 (175 mm Hg vs 153 mm Hg; P < .001). The subjects who underwent early prone positioning had lower compliance during days 1-10 (27 mL/cm H2O vs 33 mL/cm H2O; P < .001) and lower [Formula: see text]/[Formula: see text] values over days 1-10 (139.9 mm Hg vs 167.4 mm Hg; P < .001) versus those who did not undergo prone positioning. After day 21 of hospitalization, the average compliance of the subjects who had early prone positioning surpassed that of the subjects who did not have prone positioning. CONCLUSIONS: Respiratory mechanics of the subjects with COVID-19 who were on mechanical ventilation were characterized by persistently low respiratory system compliance and [Formula: see text]/[Formula: see text], similar to ARDS due to other etiologies. The [Formula: see text]/[Formula: see text] was more tightly associated with mortality than with compliance.

Emergency department characteristics and associations with intensive care admission among patients with coronavirus disease 2019.

OBJECTIVE: There have been few descriptions in the literature to date specifically examining initial coronavirus disease 2019 (COVID-19) patient presentation to the emergency department (ED) and the trajectory of patients who develop critical illness. Here we describe the ED presentation and outcomes of patients with COVID-19 presenting during our initial local surge. METHODS: This is a multicenter, retrospective cohort study using data extracted from the electronic health records at 3 hospitals within a single health system from March 1, 2020 to June 1, 2020. Patients were included in the study if they presented to an ED and had laboratory-confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection during the study period. Data elements were extracted from the electronic health record electronically and by trained data abstractors and entered into a secure database. We used multivariable regression analysis to examine ED factors associated with the development of critical illness and mortality, with a primary outcome of ICU admission. RESULTS: A total of 330 patients with laboratory-confirmed SARS-CoV-2 infection were admitted during the study period. Of these, 112 (34%) were admitted to the ICU. Among these patients, 20% were female, 50% were White, the median age was 61 (interquartile range [IQR], 52-72), and the median body mass index (BMI) was 28.1 (IQR, 24.3-35.1). On univariable analysis, a doubling of lactate dehydrogenase (LDH) (odds ratio [OR], 3.87; 95% confidence interval [CI], 2.40-6.27) or high-sensitivity C-reactive protein (hsCRP; OR, 1.32; 95% CI, 1.11-1.57) above the reference range or elevated troponin (OR, 12.1; 95% CI, 1.20-121.8) were associated with ICU admission. After adjusting for age, sex, and BMI, LDH was the best predictor of ICU admission (OR, 3.54; 95% CI, 2.12-5.90). Of the patients, 15% required invasive mechanical ventilation during their hospital course, and in-hospital mortality was 19%. CONCLUSIONS: Nearly one-third of ED patients who required hospitalization for COVID-19 were admitted to the ICU, 15% received invasive mechanical ventilation, and 19% died. Most patients who were admitted from the ED were tachypneic with elevated inflammatory markers, and the following factors were associated with ICU admission: elevated hsCRP, LDH, and troponin as well as lower oxygen saturation and increased respiratory rate.

Morphometry and Lymph Dynamics of Swine Thoracic Duct.

Background: The goal of this study was to characterize the thoracic duct (TD) both morphologically and hemodynamically. Methods and Results: The lymphatic flow and pressure gradient from the cisterna chyli (CC) to the lymphovenous junction were measured in anesthetized swine (n = 9). After the animals were euthanized, the TD were harvested for histomorphometric analyses in which three samples were perfused with 9% gelatin to obtain the morphometry of the TD valve in both the open and closed configuration. Spectral analyses were performed. An afferent lymphatic vessel of the CC was accessed and cannulated after the animal was euthanized for casting (n = 3) to obtain morphometric data. The in vivo flow rate was 0.7 ± 0.49 mL/minute. Spectral analysis (Fast Fourier Transformation) showed correlation coefficients of 0.858 ± 0.063 and 0.586 ± 0.112 (p < 0.05) for the TD and JVPs, respectively. The average pressure gradient was 8.1 mmHg along the TD. The length of the TD was 35.6 ± 2.2 cm. The maximal width of the CC ranged from 11.4 to 15 mm. The diameter of the TD varied irregularly from 2 to 4.3 mm. The geometry of the TD leaflets was determined to have an area of 1.99 ± 0.53 mm2, a leaflet length of 3.26 ± 0.86 mm, a packet depth of 0.66 ± 0.19 mm, and a wall length of 5.46 ± 2.16 mm. The TD media thickness was ∼7 ± 3 µm. The number of valves ranged from 9 to 13 in the full length of the TD. Conclusions: A relatively constant pressure gradient in the swine TD drives lymph flow from the CC to the jugular vein. The TD is a thin-walled vessel with valves that prevent reflux of lymph flow. This study of morphometric and lymphatic dynamics is important for interventionalists to understand the anatomy and physiology of the TD to design new diagnostic, interventional procedures, and devices.

A Novel Arterial Line Simulation Model.

With damage control surgery and resuscitation teams, the military is bringing surgical as well as intensive care far forward to areas where mass casualty events are an ever-present threat. One procedure that the team is required to be proficient in is arterial line insertion and transducing. To our knowledge, there are no previously described field arterial line simulation models. We present an arterial line insertion and transducer simulator created using medium resistance Thera-band tubing, saline, Coban, and a SAM splint. Ten deployed members of a damage control surgical team received 30 minutes of instruction on how to properly insert an arterial line and how to set up the transducer equipment. All participants were able to show proficiency in radial artery line insertion and transducer setup despite 8 of the 10 participants having never inserted or setup an arterial line. We describe, to our knowledge, the first arterial line insertion and transducing model utilizing only items found in the deployed environment. This model can be easily made and utilized to train medical personnel of all skill levels to augment the capabilities of medical units in areas where mass casualty events are likely.

A Case of Rhabdomyolysis Caused by Blood Flow-Restricted Resistance Training.

Blood flow-restricted resistance (BFRR) training is effective as a means to improve muscle strength and size while enduring less mechanical stress. It is generally safe but can have adverse effects. We present a case of an active duty Soldier who developed rhabdomyolysis as a result of a single course of BFRR training. He was presented to the emergency department with bilateral lower extremity pain, was admitted for electrolyte monitoring and rehydration, and had an uncomplicated hospital course and full recovery. This is an increasingly common mode of rehabilitation in the military, and practitioners and providers should be aware of it and its possible adverse effects.

Constitutive modeling of the passive inflation-extension behavior of the swine colon.

In the present work, we propose the first structural constitutive model of the passive mechanical behavior of the swine colon that is validated against physiological inflation-extension tests, and accounts for residual strains. Sections from the spiral colon and the descending colon were considered to investigate potential regional variability. We found that the proposed constitutive model accurately captures the passive inflation-extension behavior of both regions of the swine colon (coefficient of determination R2=0.94±0.02). The model revealed that the circumferential muscle layer does not provide significant mechanical support under passive conditions and the circumferential load is actually carried by the submucosa layer. The stress analysis permitted by the model showed that the colon tissue can distend up to 30% radially without significant increase in the wall stresses suggesting a highly compliant behavior of the tissue. This is in-line with the requirement for the tissue to easily accommodate variable quantities of fecal matter. The analysis also showed that the descending colon is significantly more compliant than the spiral colon, which is relevant to the storage function of the descending colon. Histological analysis showed that the swine colon possesses a four-layer structure similar to the human colon, where the longitudinal muscle layer is organized into bands called taeniae, a typical feature of the human colon. The model and the estimated parameters can be used in a Finite Element framework to conduct simulations with realistic geometry of the swine colon. The resulting computational model will provide a foundation for virtual assessment of safe and effective devices for the treatment of colonic diseases.

Validated Computational Model to Compute Re-apposition Pressures for Treating Type-B Aortic Dissections.

The use of endovascular treatment in the thoracic aorta has revolutionized the clinical approach for treating Stanford type B aortic dissection. The endograft procedure is a minimally invasive alternative to traditional surgery for the management of complicated type-B patients. The endograft is first deployed to exclude the proximal entry tear to redirect blood flow toward the true lumen and then a stent graft is used to push the intimal flap against the false lumen (FL) wall such that the aorta is reconstituted by sealing the FL. Although endovascular treatment has reduced the mortality rate in patients compared to those undergoing surgical repair, more than 30% of patients who were initially successfully treated require a new endovascular or surgical intervention in the aortic segments distal to the endograft. One reason for failure of the repair is persistent FL perfusion from distal entry tears. This creates a patent FL channel which can be associated with FL growth. Thus, it is necessary to develop stents that can promote full re-apposition of the flap leading to complete closure of the FL. In the current study, we determine the radial pressures required to re-appose the mid and distal ends of a dissected porcine thoracic aorta using a balloon catheter under static inflation pressure. The same analysis is simulated using finite element analysis (FEA) models by incorporating the hyperelastic properties of porcine aortic tissues. It is shown that the FEA models capture the change in the radial pressures required to re-appose the intimal flap as a function of pressure. The predictions from the simulation models match closely the results from the bench experiments. The use of validated computational models can support development of better stents by calculating the proper radial pressures required for complete re-apposition of the intimal flap.

Biomechanical Material Characterization of Stanford Type-B Dissected Porcine Aortas.

Aortic dissection (AD) involves tearing of the medial layer, creating a blood-filled channel called false lumen (FL). To treat dissections, clinicians are using endovascular therapy using stent grafts to seal the FL. This procedure has been successful in reducing mortality but has failed in completely re-attaching the torn intimal layer. The use of computational analysis can predict the radial forces needed to devise stents that can treat ADs. To quantify the hyperelastic material behavior for therapy development, we harvested FL wall, true lumen (TL) wall, and intimal flap from the middle and distal part of five dissected aortas. Planar biaxial testing using multiple stretch protocols were conducted on tissue samples to quantify their deformation behavior. A novel non-linear regression model was used to fit data against Holzapfel-Gasser-Ogden hyperelastic strain energy function. The fitting analysis correlated the behavior of the FL and TL walls and the intimal flap to the stiffness observed during tensile loading. It was hypothesized that there is a variability in the stresses generated during loading among tissue specimens derived from different regions of the dissected aorta and hence, one should use region-specific material models when simulating type-B AD. From the data on material behavior analysis, the variability in the tissue specimens harvested from pigs was tabulated using stress and coefficient of variation (CV). The material response curves also compared the changes in compliance observed in the FL wall, TL wall, and intimal flap for middle and distal regions of the dissection. It was observed that for small stretch ratios, all the tissue specimens behaved isotropically with overlapping stress-stretch curves in both circumferential and axial directions. As the stretch ratios increased, we observed that most tissue specimens displayed different structural behaviors in axial and circumferential directions. This observation was very apparent in tissue specimens from mid FL region, less apparent in mid TL, distal FL, and distal flap tissues and least noticeable in tissue specimens harvested from mid flap. Lastly, using mixed model ANOVAS, it was concluded that there were significant differences between mid and distal regions along axial direction which were absent in the circumferential direction.

Role of Re-entry Tears on the Dynamics of Type B Dissection Flap.

Mortality during follow-up after acute Type B aortic dissection is substantial with aortic expansion observed in over 59% of the patients. Lumen pressure differential is considered a prime contributing factor for aortic dilation after propagation. The objective of the study was to evaluate the relationship between changes in vessel geometry with and without lumen pressure differential post propagation in an ex vivo porcine model with comparison with patient clinical data. A pulse duplicator system was utilized to propagate the dissection within descending thoracic porcine aortic vessels for set proximal (%circumference of the entry tear: 40%, axial length: 2 cm) and re-entry (50% of distal vessel circumference) tear geometry. Measurements of lumen pressure differential were made along with quantification of vessel geometry (n = 16). The magnitude of mean lumen pressure difference measured after propagation was low (~ 5 mmHg) with higher pressures measured in false lumen and as anticipated the pressure difference approached zero after the creation of distal re-entry tear. False lumen Dissection Ratio (FDR) defined as arc length of dissected wall divided by arc length of dissection flap, had mean value of 1.59 ± 0.01 at pressure of 120/80 mmHg post propagation with increasing values with increase in pulse pressure that was not rescued with the creation of distal re-entry tear (p < 0.01). An average FDR of 1.87 ± 0.27 was measured in patients with acute Type B dissection. Higher FDR value (FDR = 1 implies zero dissection) in the presence of distal re-entry tear demonstrates an acute change in vessel morphology in response to the dissection independent of local pressure changes challenges the re-apposition of the aortic wall.

Role of Pulse Pressure and Geometry of Primary Entry Tear in Acute Type B Dissection Propagation.

The hemodynamic and geometric factors leading to propagation of acute Type B dissections are poorly understood. The objective is to elucidate whether geometric and hemodynamic parameters increase the predilection for aortic dissection propagation. A pulse duplicator set-up was used on porcine aorta with a single entry tear. Mean pressures of 100 and 180 mmHg were used, with pulse pressures ranging from 40 to 200 mmHg. The propagation for varying geometric conditions (%circumference of the entry tear: 15-65%, axial length: 0.5-3.2 cm) were tested for two flap thicknesses (1/3rd and 2/3rd of the thickness of vessel wall, respectively). To assess the effect of pulse and mean pressure on flap dynamics, the %true lumen (TL) cross-sectional area of the entry tear were compared. The % circumference for propagation of thin flap (47 ± 1%) was not significantly different (p = 0.14) from thick flap (44 ± 2%). On the contrary, the axial length of propagation for thin flap (2.57 ± 0.15 cm) was significantly different (p < 0.05) from the thick flap (1.56 ± 0.10 cm). TL compression was observed during systolic phase. For a fixed geometry of entry tear (%circumference = 39 ± 2%; axial length = 1.43 ± 0.13 cm), mean pressure did not have significant (p = 0.84) effect on flap movement. Increase in pulse pressure resulted in a significant change (p = 0.02) in %TL area (52 ± 4%). The energy acting on the false lumen immediately before propagation was calculated as 75 ± 9 J/m2 and was fairly uniform across different specimens. Pulse pressure had a significant effect on the flap movement in contrast to mean pressure. Hence, mitigation of pulse pressure and restriction of flap movement may be beneficial in patients with type B acute dissections.

Role of vessel-to-prosthesis size mismatch in venous valve performance.

BACKGROUND: Efforts to treat chronic venous insufficiency have focused on the development of prosthetic venous valves. The role of prosthetic valve-to-vessel size matching has not been determined. The purpose of this investigation was to assess the effect of size mismatching on venous valve function and to establish a mismatch limit that affects valve hemodynamic performance and venous wall stress to improve future valve designs and implants. METHODS: Flow dynamics of prosthetic venous valves were studied in vitro using a pulse duplicator flow loop. Valve performance based on flow rate and pressure measurements was determined at oversizing ratios ranging from 4.2% to 25%. Valve open area ratios at different size mismatching ratios were investigated by image analysis. Finally, a wall stress analysis was used to determine the magnitude of circumferential (hoop) stress in the venous wall at various degrees of oversizing. RESULTS: Our findings indicate that valve regurgitate volume, closing time, and pressure difference across the valve are significantly elevated at mismatch ratios greater than ∼15%. This is supported by increases in regurgitate velocity and open area relative to valves tested at near-nominal diameters. At this degree of size mismatch, the wall stress is increased by a factor of two to three times relative to physiologic pressures. CONCLUSIONS: These findings establish a relationship between valve size matching and valve hemodynamic performance, including vessel wall stress, which should be considered in future valve implants. The size of the prosthetic valve should be within 15% of maximum vein size to optimize venous valve hemodynamic performance and to minimize the hoop wall stress.

Growth and remodeling of canine common iliac vein in response to venous reflux and hypertension.

OBJECTIVE: The passive properties of the venous wall are important for the compliance function of the venous system. The objective of this study was to quantify the passive biomechanical response and structural growth and remodeling of veins subjected to chronic venous reflux and hypertension. METHODS: To investigate the effects of venous reflux on venous mechanics, the tricuspid valve was injured in a canine model by disrupting the chordae tendineae. The conventional inflation-extension protocol in conjunction with intravascular ultrasound was used to investigate the passive biomechanical response of both control common iliac veins (n = 9 dogs) and common iliac veins subjected to 8 weeks of venous reflux and hypertension (n = 9 dogs). The changes in vein wall thickness and constituent composition were quantified by multiphoton microscopy and histologic evaluation. RESULTS: Biomechanical results indicate that the veins became less compliant when exposed to 8 weeks of chronic venous reflux and hypertension. The mechanical stiffening was found to be associated with a significant increase in wall thickness (P < .05) and collagen-to-elastin ratio (P < .05). After 8 weeks of chronic reflux and hypertension, the circumferential vein wall stress was significantly reduced (P < .05) because of wall thickening, although it was not restored to control levels. CONCLUSIONS: The growth and remodeling of the venous wall reduces the wall stress, but the stress remains higher than at baseline at 8 weeks. The compliance of the veins also decreases because of the increase in wall thickness and remodeling of the microstructure of the venous wall. These findings provide insight into potential adaptations of the venous system in reflux and hypertension.