The viscoelastic nature of chorioamniotic membranes

This study establishes the viscoelastic nature of the human chorioamniotic membrane. Membrane tissue taken from term pregnancies was placed in a state of biaxial stress consistent with the condition in which membranes rupture in normal healthy patients. The phenomena of creep, stress relaxation, elastic recovery, and time-dependent load deformation relations were demonstrated. The experiments needed to produce these phenomena are described. The results are graphically reported. The experiments were performed using samples of fetal membranes and compared to gum rubber which is a known elastic material. From the results, one can conclude that fetal membranes are viscoelastic. The flow freely under applied stress, and they have elastic and viscous properties which are time dependent.     

THE HYSTERESIS LOOP 3. STRESS-DIP EXPERIMENTS

Abstract— A stress-dip technique for the determination of an effective stress in cyclic straining has been improved. The critical stress drop, Δσ_C, for which zero strain relaxation rate is observed can be obtained from experiments. The significance of this quantity is discussed in terms of the statistical theory of the hysteresis loop. The measurements of the effective stress at different temperatures and along the hysteresis loop are reported. The observed asymmetry of stress in cyclic straining is ascribed to asymmetry of effective stress.     

Purification and characterization of a troponin C-like phosphodiesterase activator from bovine thyroid

A troponin C-like phosphodiesterase activator from bovine thyroid has been purified to homogeneity. The overall purification was about 9,800-fold with a yield of 8%. Bovine thyroid activator protein is identical in biologic properties to that isolated from bovine brain. They have the same specific activity regarding stimulation of bovine brain cyclic nucleotide phosphodiesterase. Both proteins form a Ca2+-dependent complex with heart muscle troponin I which is stable in 6M urea-polyacrylamide gel and which is similar, but not identical, to the troponin C-troponin I complex. The physiochemical properties of bovine thyroid activator protein are identical with those of bovine brain and other phosphodiesterase activator proteins and are similar to heart muscle and skeletal muscle troponin C as follows: (A) they bind 3-4 exchangeable calcium ions/mol with dissociation constants between 10(-5) and 10(-6) M, (B) they are highly acidic with a high content of aspartic and glutamic acids and isoelectric points of approximately 4.1, (C) these proteins have an unusual ultraviolet absorption spectrum with six discrete maxima between 250 and 284 nm which are characteristic of phenylalanine and tyrosine, and (D) these proteins have a low content of cysteine, histidine, tyrosine and proline. The tryptic peptide maps of bovine thyroid and brain activator protein are very similar. However, despite a very similar amino acid composition, the peptide map of bovine heart muscle troponin C is significantly different from that of the other two proteins. The molecular weight of thyroid and brain activator protein is 16,500, while that of heart troponin C is 18,500. Thyroid and brain activator protein, as well as heart troponin C, appear to undergo significant Ca2+-dependent conformational changes, as measured by the difference in the circular dichroism spectrum and electrophoretic mobility observed in the presence and absence of calcium ion.     

Is tubal sterilization associated with an increased risk of subsequent hysterectomy but a decreased risk of ovarian cancer? A review of recent literature

Recent epidemiologic studies have suggested that tubal sterilization (TS) may lead to an increased incidence of subsequent hysterectomy but a decreased risk of ovarian cancer. This review evaluates the nature and magnitude of these two relationships, which should be of great concern and interest to women, clinicians and the administrators of family planning programs. The positive relationship between TS and subsequent hysterectomy is more likely to be of a motivational rather than biological nature, and a considerable number of unnecessary hysterectomies after TS could be avoided by changing the attitudes of physicians and women. The inverse relationship between TS and ovarian cancer appears causal, although the exact biological mechanisms remain to be clarified. Theoretically, this non-contraceptive beneficial effect of TS could be used as a primary preventive measure to curb the incidence of the highly fatal ovarian cancer. However, a number of medical, ethical, and economic questions attending use of a generally irreversible contraceptive procedure as a preventive measure must first be answered. The issue of whether TS is associated with any long-term sequelae, and, if so, whether the association is of a cause-and-effect nature or a by-product of time passage and aging of the woman, should be addressed by well-designed studies.     

Relative strength of scleral tunnel incisions with internal corneal lips constructed in cadaver eyes

We constructed scleral tunnel wounds with internal corneal lips and sutureless closures in ten cadaver eyes without previous intraocular surgery. Each wound differed in width, total incision length, and internal corneal lip size. At a low and high range of initial intraocular pressure (IOP, 10 to 15 mm Hg or 20 to 25 mm Hg), we compared the wounds' resistance to leakage during application of external pressure. A square wound with a 4.0 mm width and 4.0 mm overall length, including a 1.5 mm corneal lip, had the optimum wound dimensions. These produced a stable incision that resisted leakage at external pressures up to 525 pounds per square inch equally well at both IOP ranges. Leakage occurred at lower external pressures for wounds with greater width, smaller corneal lips, or wound widths that were greater than wound lengths; such wounds were also more prone to leakage at the low IOP range. When constructed properly and adequately, the 4.0 mm wide scleral tunnel incision with 1.5 mm internal corneal lip is a strong and safe wound for sutureless cataract surgery.     

The effect of increased weight on peak pressures: implications for obesity and diabetic foot pathology

The purpose of this study was to determine if increased weight contributes to increased mean peak plantar foot pressures when foot function, deformity, and structure are controlled. Ten male and nine female volunteers without sensory neuropathy or other systemic disease were evaluated in the study. Using a repeated measures design, peak plantar foot pressures were compared using the Novel Pedar in-shoe pressure measurement system under three conditions. Baseline measurements were made while volunteers wore the standard test footwear, a thin-soled rubber oxford sneaker. The second and third test conditions involved pressure measurements with an additional 9.1 kg (20 lb) and 18.2 kg (40 lb), respectively, of weight evenly distributed in pockets on the front and back of a workout vest. There was a significant increase in mean peak plantar foot pressures under the metatarsal heads, heel, and midfoot for each incremental increase of weight (baseline vs. 9.1 kg, p < .05; 9.1 kg vs. 18.2 kg, p < .05). The authors conclude that increases in weight increased plantar foot pressures for the first metatarsal, lesser metatarsal, midfoot, and heel regions in both men and women.