Preliminary Assessment of Intra-Aneurysm Sac Pressure During Endovascular Aneurysm Repair as an Early Prognostic Factor of Aneurysm Enlargement.

Purpose: Numerous cases of abdominal aortic aneurysm (AAA) enlargement, and even rupture, despite endovascular aneurysm repair (EVAR), have been documented. This has been linked to increased aneurysm sac pressure (ASP). We decided to conduct further research with the aim to identify correlations between ASP during EVAR and subsequent aneurysm enlargement. Patients and Methods: This experimental prospective study included 30 patients undergoing EVAR of infrarenal AAAs. Invasive ASP measurements were done using a thin pressure wire. Aortic pressure (AP) was measured using a catheter placed over the wire. Systolic pressure index (SPI), diastolic pressure index (DPI), mean pressure index (MPI), and pulse pressure index (PPI) were calculated both for ASP and AP. The results of follow-up computed tomography angiography (CTA) at 3 months were compared with baseline CTA findings. Results: During EVAR, a significant reduction was observed for SPI (from 98% to 61%), DPI (from 100% to 87%), MPI (from 99% to 74%), and PPI (from 97% to 34%). There were no significant correlations of pressure indices with an aneurysm diameter, cross-sectional area, velocity, thrombus shape and size, number of patent lumbar arteries, length and diameter of aneurysm neck, diameter of the inferior mesenteric artery, as well as diameter and angle of common iliac arteries. On the other hand, aneurysm neck angulation was significantly inversely correlated with reduced PPI. After combining CTA findings with pressure measurements, we identified a positive correlation between PPI and aneurysm enlargement (ratio of the cross-sectional area at the widest spot at baseline and at 3 months after EVAR). Conclusion: The study showed that ASP can be successfully measured during EVAR and can facilitate the assessment of treatment efficacy. In particular, PPI can serve as a prognostic factor of aneurysm enlargement and can help identify high-risk patients who remain prior monitoring.

Biomechanical effect of rapid mucoperiosteal palatal tissue expansion with the use of osmotic expanders.

The comparative study was performed to investigate the biomechanical properties (maximum tangential stiffness, maximum tangential modulus and tensile strength) of expanded mucoperiosteal palatal tissue after rapid expansion regimen correlated with histological findings. Rabbit palatal model was used to correlate the non-operated control group, sham-operated control (subperiosteal tissue dissection) groups and 24- and 48-hour tissue expansion groups. There was no observed damage of tissue collagen network in both tissue expansion groups analyzed immediately after expansion, and biomechanical profile was not significantly different from the profile of control groups. However, rapid tissue expansion activates remodeling of mucoperiosteal tissue structure that revealed significant changes in mechanical properties during the 4-week follow-up. The 24-hour expansion induced transient increase of resilience observed 2 weeks after surgery in comparison to the control groups. As a result of maturation of newly created collagen fibers and mucoperiosteum rebuilding, there were no significant differences between any of the analyzed tensile parameters 4 weeks after the 24-hour expansion. Increased and elongated inflammatory response and connective matrix synthesis observed during healing of 48-hour expanded tissue led to a significant decrease of tensile strength value in comparison to the control groups. Even though 4 weeks after surgery, the resilience of 48-hour expanded tissue was similar to the control groups, tissue healing was not completed and limited scar formation might considerably change the final biomechanical tissue profile. These findings provide new information about tensile properties to rapid mucoperiosteal palatal tissue expansion with the use of osmotic expanders for cleft palate repair by tissue augmentation.

Mechanical response of brain to mechanical stimuli--animal model investigation.

BACKGROUND AND PURPOSE: Conventional neurosurgical procedures give surgeons both tactile and visual feedback. Unlike conventional procedures, minimally invasive surgery is devoid of haptic feedback. Incorporation of tactile feedback into neurosurgical robotic systems can greatly enhance the results of minimally invasive procedures. Hence, the ultimate goal of the research presented here is to define the force response of the brain to different types of mechanical stimuli (short- and long-term). The experimental results describe the force responses of brain during indentation tests. MATERIAL AND METHODS: Seven ovine head specimens with exposed brain were fixed to an MTS Synergie 100 testing machine using a rigid clamp--metallic frame with sharp-end screws. Four regions were loaded by a hemispherically-ended cylindrical indentor. Each of the indentations applied to the brain was divided into two general stages: insertion and hold which was constant for 180 s. Measurements for the following 3 loading velocities were conducted. The force response of brain to mechanical stimulus was acquired for each case. RESULTS: The force response of brain to short-term mechanical stimulus depends on both loading velocities and regions of indentation, whereas the long-term force response depends on the history of loadings. CONCLUSIONS: The development of minimally invasive neurosurgical systems requires estimation of the mechanical response of brain to contact with surgical devices. For this reason, investigation of the force response of brain employing different boundary conditions is necessary.