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Biomedical subjects

F Robicsek

Publications and source records attributed to F Robicsek.

At least 361 records · Page 20Linked to original sources
PubMedDate not supplied

Influence of sizing and subcoronary implantation technique on the function of porcine aortic homografts.

The function and longevity of the homograft aortic valve may be influenced by valve size and subcoronary implantation technique. Dynamic function and leaflet configuration of the porcine aortic valve were analysed first in its natural root in a left heart simulator using glycerol at 120/80 mm Hg pressure and 4 l min-1 Cardiac Output (C.O.). Then the valve was implanted in the porcine root and studied: Group I (n = 4) 1-2 mm smaller, Group II (n = 8) 3-4 mm smaller and Group III (n = 4) 5-7 mm smaller donor valve than the recipient. A silicone rubber mould of the implanted valve was made and analysed. In the donor aortic root the commissural expansion for 0 to 80 mm Hg pressure was 42% which was reduced significantly in all assemblies. Group I showed the largest decrease in the orifice area (OA). In Group III decrease in the OA was less, however, two of the four valves had aortic insufficiency (AI). In Group II decrease in the OA was only 13% and there was no AI. During opening the leaflet surface was smooth and free of wrinkles in the intact valve, but had creases and folds in all three groups. All implanted valves had an indentation along the suture line disrupting the leaflet-sinus continuity. Hence, to enhance valve longevity, donor valve 3-4 mm smaller than the recipient should be chosen and the implantation technique modified to preserve the leaflet-sinus continuity.

Animals↗
PubMedDate not supplied

Mechanical properties of abdominal aortic aneurysm wall.

There is a need to understand why and where the abdominal aortic aneurysm may rupture. Our goal therefore is to investigate whether the mechanical properties are different in different regions of the aneurysm. Aorta samples from five freshly excised whole aneurysms, > or = 5 cm in diameter, from five patients, average age 71 +/- 10 years, were subjected to uniaxial testing. We report the wall thickness, yield stress and strain, and parameters that describe nonlinear stress-strain curves for the anterior, lateral and posterior regions of the aneurysm. The posterior region was thicker than the anterior region (2.73 +/- 0.46 mm versus 2.09 +/- 0.51 mm). The stress-strain curves were described by sigma = a epsilon(b), where sigma is true stress and epsilon is engineering strain. In the circumferential direction, the wall stiffness increased from posterior to anterior to lateral. In the longitudinal direction, the lateral and anterior regions showed greater wall stiffness than the posterior region. The wall stiffness was greater in the circumferential than longitudinal direction. The anterior region was the weakest, especially in the longitudinal direction (yield stress sigmaY = 0.38 +/- 0.18 N mm(-2)). For a less complex model the aneurysmal wall could be considered orthotropic with sigma = 12.89epsilon(2.92) and 4.95epsilon(2.84) in the circumferential and longitudinal directions. For the isotropic model, sigma =7.89epsilon(2.88). In conclusion, different regions of the aneurysm have different yield stress, yield strains, and other mechanical properties, and this must be considered in understanding where the rupture might occur.

Aged↗
PubMedDate not supplied

Wall stress as a possible mechanism for the development of transverse intimal tears in aortic dissections.

In aortic dissection intimal tear develops in a transverse direction. Since dissection is associated with the aneurysm of the aorta, its mechanism was investigated by analysing the pressure induced wall stress as a function of 'growth' of the aneurysm. The stresses were determined using a finite element analysis where the aorta was modelled as an isotropic, nonlinear, hyperelastic material. Growth of the aneurysm was simulated by dilating an aortic segment in increments of 10% of the initial diameter. At each dilation luminal pressure of 120 mm Hg was applied and stress determined. In the aneurysm bulb, longitudinal stress increased significantly as the bulb became larger, while circumferential stress changed only a little. In the undilated segment both the longitudinal and circumferential stresses remained relatively unchanged. The increase in the longitudinal stress in the bulb occurred primarily due to change in shape of the aorta from cylindrical to ellipsoidal to spherical. Hence, as the aneurysm 'grows', the longitudinal stress in the bulb increases rapidly and could be responsible for the transverse tear in the aortic dissection.

Aortic Dissection↗
PubMedDate not supplied

Extending myocardial viability during heart preservation with cyclosporine A.

BACKGROUND AND AIM OF STUDY: Hypothermic preservation (PRES) of donor hearts is limited to 12-14 hours for complete functional recovery after reperfusion. In a canine heterotopic heart transplant model, 50% to 60% functional recovery returned after 18 hours of PRES with University of Wisconsin (UW) solution. Concomitant with functional changes were marked increases in apoptotic cells at 2 (2.69%) and 6 (5.98%) hours of reperfusion with a concomitant decrease in lamin B1 (2% and 7.6%, respectively) with no evidence of necrotic cells. These results suggested that blockade of apoptosis may prolong myocardial viability during PRES and reperfusion. METHODS: Donor hearts were subjected to 18 and 24 hours of PRES (2 degrees C to 4 degrees C) with and without cyclosporine A (CyS) treatment (apoptosis blocker). CyS was given to the donor animal (10 mg/kg), in the PRES solution (10(-5) mol/L), slowly infused during the PRES period (1 mL/min), and also to the recipient animal (2.5 mg/kg). RESULTS: After 18 hours of PRES with CyS, function returned to 100% within 1 hour and stayed at this level throughout a 6-hour recovery period. Apoptotic myocytes were reduced (55%) after 18 hours PRES with CyS treatment, and 6-hour reperfusion lamin B1 was reduced to only 3.7%. Twenty-four hour PRES in UW resulted in no functional recovery. However, after CyS treatment, functional recovery returned to 100% after 4 hours of reperfusion. Adenosine triphosphate (ATP) and creatine phosphate (CP) concentrations were surprisingly the same with or without CyS treatment at 18 hours and lower with 24 hours. CONCLUSIONS: Use of CyS in the PRES solution prolongs myocardial viability during donor heart PRES. The mechanism of action may be associated with the mitochondrial permeability transition (MPT) pore via cyclophilin D binding.

Adenosine↗
PubMedDate not supplied

Comparison of intermittent warm and cold blood perfusion during hypothermic myocardial preservation on functional and metabolic recovery.

Numerous techniques are used to maintain intraoperative heart viability. The studies presented here evaluated heart function and metabolism after various periods of preservation up to 4 hours with intermittent warm and cold blood perfusion. Using a heterotopic heart model cooled to 10 degrees C and maintained for 1, 2, 3, and 4 hours, various preservation techniques were compared. Changes in myocardial metabolism were determined from substrate uptakes and biopsy samples of the left ventricular muscle for high-energy phosphates. Preservation techniques included: (1) sustained hypothermia, (2) 1 or 2 hours of sustained warm blood perfusion with fibrillation, (3) intermittent cold blood perfusion during 2, 3, and 4 hours of preservation, (4) intermittent warm blood perfusion during 2, 3, and 4 hours of preservation and (5) a control group (no preservation). Normothermic fibrillation had no effect on postpreservation functional or metabolic parameters. Sustained hypothermia reduced functional recovery proportional to the length of ischemia. The cold intermittent procedures maintained function and metabolism better than sustained hypothermia, while warm intermittent preservation maintained function and metabolism at control levels throughout the recovery period for all preservation techniques. Changes in ATP mirrored the functional changes. Creatine phosphate (CP) was markedly reduced during heart isolation and preservation and exceeded the control by 100% during reperfusion. For operative procedures of 2 hours or less, functional and metabolic recovery was not affected by the various preservation methods applied. Warm intermittent perfusion during hypothermic preservation offered the best protection for the myocardium. The warming cycles during hypothermia may provide some degree of preconditioning and protect the myocardium during reperfusion.

Animals↗
PubMedDate not supplied

Long-range observations with external aortic grafts.

The late results of aortic aneurysms treated by external grafting are presented. This procedure consists of completely dissecting the involved aortic segment and suturing it in a well-fitted tubular Dacron prosthesis. The operation was carried out under the following circumstances: (a) Small fusiform aneurysm of the abdominal aorta. (b) Small and medium-sized aneurysms of the thoracic aorta. (c) Aneurysms unfavorably located in the very old and very debilitated. (d) Aneurysms involving the origin of the renal arteries. (e) Aneurysmatic dilatation of the aortic arch. Sixty-two patients were operated upon with this method with the follow-up period ranging from three months to seven years. There were no deaths during this period which could be directly related to either the aneurysm or the procedure itself.

Aorta, Abdominal↗
PubMedDate not supplied

Compression of the true lumen by retrograde perfusion during repair of aortic dissection.

The anatomic situation is described in which during repair of DeBakey Type I dissecting aneurysms blood flow may be directed into the false lumen by a large intimal flap at the distal reentry site in spite of seemingly properly placed femoral arterial perfusion cannula. An illustrative clinical case is presented and measures are recommended by which this serious complication may be recognized in time and be properly corrected before irreversible changes occur.

Adult↗