Investigating the Transient Regenerative Potential of Cardiac Muscle Using a Neonatal Pig Partial Apical Resection Model.

Researchers have shown that adult zebrafish have the potential to regenerate 20% of the ventricular muscle within two months of apex resection, and neonatal mice have the capacity to regenerate their heart after apex resection up until day 7 after birth. The goal of this study was to determine if large mammals (porcine heart model) have the capability to fully regenerate a resected portion of the left ventricular apex during the neonatal stage, and if so, how long the regenerative potential persists. A total of 36 piglets were divided into the following groups: 0-day control and surgical groups and seven-day control and surgical groups. For the apex removal groups, each piglet was subjected to a partial wall thickness resection (~30% of the ventricular wall thickness). Heart muscle function was assessed via transthoracic echocardiograms; the seven-day surgery group experienced a decrease in ejection fraction and fractional shortening. Upon gross necropsy, for piglets euthanized four weeks post-surgery, all 0-day-old hearts showed no signs of scarring or any indication of the induced injury. Histological analysis confirmed that piglets in the 0-day surgery group exhibited various degrees of regeneration, with half of the piglets showing full regeneration and the other half showing partial regeneration. However, each piglet in the seven-day surgery group demonstrated epicardial fibrosis along with moderate to severe dissecting interstitial fibrosis, which was accompanied by an abundant collagenous extracellular matrix as the result of a scar formation in the resection site. Histology of one 0-day apex resection piglet (briefly lain on and accidentally killed by the mother sow three days post-surgery) revealed dense, proliferative mesenchymal cells bordering the fibrin and hemorrhage zone and differentiating toward immature cardiomyocytes. We further examined the heart explants at 5-days post-surgery (5D PO) and 1-week post-surgery (1W PO) to assess the repair progression. For the 0-day surgery piglets euthanized at 5D PO and 1W PO, half had abundant proliferating mesenchymal cells, suggesting active regeneration, while the other half showed increased extracellular collagen. The seven-day surgery piglets euthanized at 5D PO, and 1W PO showed evidence of greatly increased extracellular collagen, while some piglets had proliferating mesenchymal cells, suggesting a regenerative effort is ongoing while scar formation seems to predominate. In short, our qualitative findings suggest that the piglets lose the full myocardial regenerative potential by 7 days after birth, but greatly preserve the regenerative potential within 1 day post-partum.

On the bending properties of porcine mitral, tricuspid, aortic, and pulmonary valve leaflets.

The atrioventricular valve leaflets (mitral and tricuspid) are different from the semilunar valve leaflets (aortic and pulmonary) in layered structure, ultrastructural constitution and organization, and leaflet thickness. These differences warrant a comparative look at the bending properties of the four types of leaflets. We found that the moment-curvature relationships in atrioventricular valves were stiffer than in semilunar valves, and the moment-curvature relationships of the left-side valve leaflets were stiffer than their morphological analog of the right side. These trends were supported by the moment-curvature curves and the flexural rigidity analysis (EI value decreased from mitral, tricuspid, aortic, to pulmonary leaflets). However, after taking away the geometric effect (moment of inertia I), the instantaneous effective bending modulus E showed a reversed trend. The overall trend of flexural rigidity (EI: mitral > tricuspid > aortic > pulmonary) might be correlated with the thickness variations among the four types of leaflets (thickness: mitral > tricuspid > aortic > pulmonary). The overall trend of the instantaneous effective bending modulus (E: mitral < tricuspid < aortic < pulmonary) might be correlated to the layered fibrous ultrastructures of the four types of leaflets, of which the fibers in mitral and tricuspid leaflets were less aligned, and the fibers in aortic and pulmonary leaflets were highly aligned. We also found that, for all types of leaflets, moment-curvature relationships are stiffer in against-curvature (AC) bending than in with-curvature bending (WC), which implies that leaflets tend to flex toward their natural curvature and comply with blood flow. Lastly, we observed that the leaflets were stiffer in circumferential bending compared with radial bending, likely reflecting the physiological motion of the leaflets, i.e., more bending moment and movement were experienced in radial direction than circumferential direction.

Computed Tomographic Assessment of Body Fat in Dachshunds: A Pilot Study.

Obesity has not been linked to causing intervertebral disc degeneration, but has been shown to influence time to ambulation, a strong long-term prognostic indicator in dogs with intervertebral disc disease. However, monitoring obesity to date is imprecise and subjective in the clinical setting. Having an objective formula based on morphometric measurements would potentially be more precise to track our patients' weights. Dogs have been shown to gain weight along their lumbar spine more rapidly than other areas. Varying body conformations make extrapolation from nonchondrodystrophic dogs to Dachshunds difficult. This study aimed to establish the region of fat accumulation along the thoracolumbar spine in Dachshunds. Retrospective computed tomographic (CT) analysis was performed on healthy Dachshunds that presented for intervertebral disc disease (IVDD). Fat area measured at L3 and L5 using attenuation ranges -135/-105 Hounsfield units (HU) was the most dependent on body weight (p = 0.05). There appeared to be no difference between subcutaneous, visceral or total percent body fat with weight agreement. T13, L3 and L5 all had linear relationships with patient weight and will likely be helpful for body mass index (BMI) formula creation (p < 0.01). This study indicates that any consistent location between L3 and L5 will give an accurate representation of the abdominal circumference and most obese area of the Dachshund with the umbilicus used as a landmark.

Ultrasound of the right lateral intercostal space.

When performing an abdominal ultrasound examination in dogs, a right lateral intercostal approach often is indicated. This approach allows for a complete examination of the abdomen, especially in large deep-chested dogs, dogs with microhepatica, or dogs with a large volume of intestinal gas or peritoneal effusion. The right lateral intercostal approach provides an acoustic window for the evaluation of the right side of the liver, porta hepatis, right limb and body of the pancreas, duodenum, right kidney, right adrenal gland, and hepatic lymph nodes.