AN ANALYSIS OF WHITE AND ABORIGINAL CHILDREN UNDER FIVE YEARS OF AGE ADMITTED TO THE BOURKE DISTRICT HOSPITAL FROM SEPTEMBER 1971 TO AUGUST 1972 1

This study includes all white and Aboriginal children under the age of 5 years admitted to the Bourke District Hospital over a 12 month period. 15% of all white children and 72% of all Aboriginal children in the Bourke shire were admitted to hospital on at least one occasion; Aboriginal children had proportionately 10 times the number of hospital admissions on a population basis.     

Stress/Strain Characteristics of Porcine Mitral Valve Tissue: Parallel Versus Perpendicular Collagen Orientation

Mitral valve tissue was analyzed in uniaxial tension testing. Rectangular strips were excised from fresh, whole, porcine mitral valve leaflets, with the long axis in the following orientation: perpendicular to the annulus (posterior [PPERP] and anterior [APERP]), parallel to the annulus (posterior [PPAR] and anterior [CAPAR]), and parallel to the annulus and involving chordal insertions (anterior [MAPAR]). Basal and marginal chordae were also tested. These samples were tested in uniaxial tension (INSTRON Model 1000) at deformation rates of 5 and 10 mm/min, the load applied along the long axis of the strip. The specimens were preconditioned by cyclically loading from 0 to 4.0 g for five cycles, and then applying a final 50-g load. Whole excised porcine mitral valves were previously examined by small angle light scattering, polarized light microscopy, and routine histologic examination in order to ascertain the collagen fiber orientation throughout the valve. Groups tested in uniaxial tension with collagen fibers parallel to the applied stress are significantly stiffer than those with perpendicular fibers (p less than 0.001). Collagen fiber density is greater in the chordae than in the leaflets, and a corresponding increase in stiffness is demonstrated. This indicates that the mitral valve tissue behaves as a classic fiber reinforced composite, i.e., increasing mechanical stiffness (modulus) is related to density and direction of fibers. This information can be applied to the design of biosynthetic valve substitutes with a similar fiber reinforced composite structure.     

Safety and cardiovascular behavior during pulmonary function in patients with Marfan syndrome

Cipriano GFB, Peres PAT, Cipriano G Jr, Arena R, Carvalho AC. Safety and cardiovascular behavior during pulmonary function in patients with Marfan syndrome. Marfan syndrome (MS) is a dominant autosomal connective tissue disease that impacts multiple systems, such as the cardiovascular system, tissue viscoelastic properties, bone calcification matrix and, most specific to the present investigation, pulmonary parenchyma. The aim of the present study was to evaluate pulmonary function (PF) in patients with MS and relate it to thoracic cage abnormalities (TCA) and the occurrence of cardiac arrhythmias during the spirometric exam (SE). A sample of 75 subjects (46 with MS) underwent clinical, anthropometric, echocardiographic, radiographic and PF evaluation; 51 subjects (33 with MS) had their electrocardiogram (ECG) information evaluated during PF. These individuals were matched and compared with a healthy control group (CG). Forced vital capacity (FVC) and forced expiratory volume (FEV) in the first second (FEV₁) in the patients with MS were significantly lower in comparison with the CG (p = 0.012 and 0.0006) and predicted values (p = 0.04 and 0.003). Subgroup analysis based on TCA revealed differences between patients with MS with two combined abnormalities (scoliosis + pectus) in comparison with both the CG (p = 0.012 and 0.002) and patients without abnormalities (p = 0.05 and 0.006). There were no differences regarding the occurrence of arrhythmia during exertion on the SE. There was a correlation between clinical history, cardiovascular behavior and PF. PF is reduced in patients with MS, and deformities in the thoracic cage appear to contribute to this reduction. Despite the apparent structural alterations in the cardiovascular system in this population, exertion during the SE appears to be safe.     

Comparison of Viscoelastic Properties of Suture Versus Porcine Mitral Valve Chordae Tendineae

Recent reports have advocated the use of polytetrafluoroethylene (PTFE) suture for replacement or reinforcement of ruptured or elongated mitral valve chordae tendineae. The mechanical properties of PTFE (Gore-Tex) and other sutures were determined and compared to those of porcine mitral valve chordae. The results were analyzed to assess how closely chordal mechanical function may be simulated by synthetic suture materials. Chordae tendineae and suture samples were tested in uniaxial tension using an INSTRON Model 1000 at strain rates of 5 and 10 mm/min. The stress (g/mm2) was plotted versus strain, and the elastic modulus determined as the slope of the curve. Chordae tendineae exhibited a nonlinear viscoelastic stress/strain behavior. The elastic modulus of both suture types tested was significantly higher than that of the chordae. However, the PTFE suture did exhibit some viscoelastic characteristics (hysteresis and creep) that begin to approach the chordal behavior. Chordal viscoelastic behavior results from the inherent composite structure (collagen, elastin, endothelium, water, and ground substance). As yet, no synthetic materials are able to imitate this behavior with the appropriate tensile strength and fatigue resistant characteristics. At present, PTFE appears to be the best synthetic alternative for chordal replacement, due to its limited viscoelastic capabilities. Nevertheless, the need to more nearly approximate the mechanical behavior of mitral valve chordae tendineae with synthetic material warrants further investigation.