A theoretical model is developed to predict the fluid shear stress and streaming potential at the surface of osteocytic processes in the lacunar-canalicular porosity of an osteon when the osteon is subject to mechanical loads that are parallel or perpendicular to its axis. The theory developed in Weinbaum et al. (31) for the flow through a proteoglycan matrix in a canaliculus is employed in a poroelastic model for the osteon. Our formulation is a generalization of that of Petrov et al. (17). Our model predicts that, in order to satisfy the measured frequency dependence of the phase and magnitude of the SGP in macroscopic bone samples, the fiber spacing in the fluid annulus must lie in the narrow range 6-7 nm typical of the spacing of GAG sidechains along a protein monomer. The model predictions for the local SGP profiles in the osteon agree with the experimental observations of Starkebaum et al. (24). The theory predicts that the pore pressure relaxation time, tau d, for a 150-300 microns diameter osteon with the foregoing matrix structure is approximately 0.03-0.13 sec, and that the amplitude of the mean fluid shear stress on the membrane of the osteocytic process at the mean areal radius of the osteon has a maximum at 28 Hz if tau d = 0.06 sec. This maximum, which is independent of the magnitude of the loading, could be important in vivo since the recent experiments of Turner et al. (28) and McLeod et al. (15) have a peak in the strain frequency spectrum between 20 and 30 Hz that also appears to be independent of the type (magnitude) of loading. Numerical predictions for the amplitude of the average fluid shear stress on the osteocytic membrane at the mean areal radius of the osteon show that the fluid shear stress associated with the low amplitude 20-30 Hz spectral strain component is at least as large as the average fluid shear stress associated with the high amplitude 1 Hz stride component, although the latter loading is an order of magnitude larger, and has a magnitude that lies within the middle of the range, 6-30 dynes/cm2, where fluid shear stresses in tissue culture studies with osteoblast monolayers have elicited an intracellular Ca++ response (31). The implications of these results for intracellular electrical communication are discussed.

Biomechanical Phenomena↗

PubMedDate not supplied

Biorheological features of some soft tissues under a surgical tissue expansion procedure.

The aim of this study was to investigate the effects of a surgical tissue expansion procedure on the biomechanical features of the expanded soft tissues. In this procedure a silicone balloon "expander" is surgically inserted into a tissue and inflated. The tissue mass increases under the stretch of the expander. The increased tissue can then be used as an autologous source for the surgical reconstruction of organs. In this article, dog saphenous neurovascular bundle was used. Expanded saphenous nerves, arteries and veins were harvested and their biomechanical features and ultrastructural, histological changes were studied. The stress relaxation features, the continuous spectrum of relaxation time, and the stress-strain relationship of expanded and control specimens were measured. Results show that within two or three weeks after placement of the expanders, the biomechanical properties of expanded saphenous nerves, arteries and veins began to deviate from those of their controls, and the differences between them were proportional to the volume of inflation; but when the expanding period was 15 weeks or longer, the properties of expanded specimens and their controls became close again. Histological study showed that the content of collagenous fibers in blood vessel walls decreased after expansion. The content of elastic fibers in blood vessel walls first increased, then returned to normal, and finally decreased. Ultrastructural studies showed that when elongated by 25-40%, the expanded nerves had well preserved axons and showed fewer smooth myelin sheaths only in the middle and distal part of the expansion.

Animals↗

PubMedDate not supplied

Alterations in the biorheological features of some soft tissues after limb lengthening.

The aim of this study was to investigate the effects of a surgical limb lengthening procedure on the biorheological features of some lengthened soft tissues. In this procedure external fixators were applied to goats' right radius to stretch the tissues. The right forelegs of goats were lengthened by 2, 4 cm, respectively. After lengthening ceased, the goats were examined after different periods of time. The lengthened median nerves, arteries and veins were harvested and used to study their biorheological features. Tensile strength of lengthened and control specimens were measured and their stress relaxation features and stress-strain relationships were studied. Results showed that at the beginning of recovery, the stress-strain curves, relaxation curves and tensile strengths of the lengthened specimens began to deviate from those of their controls. However, with increasing recovery time, the curves and tensile strength of the lengthened specimens reverted to those of their controls. All the tissues studied exhibited the same behavior.

Animals↗

PubMedDate not supplied

Biomechanics in augmentation rhinoplasty.

During the past 6 years, we have treated 406 patients with classical silicone augmentation rhinoplasty. The types and incidence of complications after subcutaneous or subfascial implantation were examined. We have proposed that most complications are related to the depth of the implant and the character of the tissues. In order to improve our operation and prove our hypothesis, we performed subperiosteal augmentation rhinoplasty in 22 cases with satisfactory results. In order to determine scientifically which layer the silicone implant should be inserted into, we investigated the biomechanics of human nasal periosteum and fascia, including tensile strength, stress-strain relationship and stress relaxation characters under uniaxial tension. Although having less failure strain, the periosteum has more tensile strength than the fascia. So, in the view of biomechanics, the periosteum is thicker, tougher and stiffer than the fascia, thus is more suitable for covering silicone implants.

Adult↗

PubMedDate not supplied

A new approach to detect QRS complexes based on a histogram and genetic algorithm.

A new approach, based on a histogram and genetic algorithm (GA), has been developed to rapidly and reliably detect QRS complexes of the ECG curve. Here, the new approach is described and the principle of the histogram and GA is explained. The results of detection of QRS complexes using the new method are given. Additionally, as an example of its novel application, the P-wave and f-wave (when atrial fibrillation is absent and present, respectively) are extracted easily and efficiently from the ECG curve using the method.

Algorithms↗

PubMedDate not supplied

Age validation of Han Chinese centenarians.

Explore the source record for details and available documents.

Adult↗

PubMedDate not supplied

Marriage and fertility in China: 1950-1989.

"This article presents a graphical and a life table analysis that summarizes some 14,000 values of data by single year of age and time on marriage and fertility in China up to 1989. In the 1970s, age at first marriage shifted upward by about four years, and fertility dramatically declined. The age at marriage and childbearing decreased in [the] 1980s, which are associated with some socio-economic factors. Fertility rates slightly increased in the second half of the 1980s, from their low level in 1984. The analysis also reveals that Chinese marriage and childbearing remain virtually universal and occurred at rather young ages." Data are from the 1988 2-in-1,000 fertility and contraceptive survey. (SUMMARY IN FRE AND ITA)

Age Factors↗

PubMedDate not supplied

Epidemiology of dental emergency visits to an urban children's hospital.

All 1482 emergency room dental visits to Seattle's Children's Hospital and Medical Center from 1982 to 1991 were studied to evaluate trends in patients seeking care: 60% of visits were for trauma, the remainder for infection or other reasons. The number of visits was 2.1 times greater in 1991 than in 1982. Comparing the periods of 1982-1987 and 1988-1991, there was an increase in the proportion of infection-related visits from 30.5 to 43.5% of all visits. Spring/summer and weekends had the highest volume. More males (61.2%) than females received care. The largest number of visits (47.9%) occurred between 6:00 PM and midnight. Nearly two-thirds (62%) of children did not have a usual source of medical care; 30.2% of children had no medical insurance, and 21.5% received Medicaid benefits. Medicaid patients were twice as likely to be seen for infection as for trauma. Among the uninsured, there was no difference in the rates of trauma or infection. Non-Caucasian patients were twice as likely to be seen for infection as Caucasians. Infection visits were for pulpitis (32.1%), and periapical and gingival abscess (53.5%). Trauma patients were younger (66 months) than infection patients (89 months). Trauma was primarily to the maxillary anterior teeth (70.1%) and upper lip and gingiva (12.1%). Common agents for trauma were furniture, bicycles, and sports.

Age Factors↗

PubMedDate not supplied

Urinary excretion of nitrosamino acids and nitrate by inhabitants of high- and low-risk areas for nasopharyngeal carcinoma in southern China.

The hypothesis that endogenous synthesis of nitrosamines from dietary precursors is a risk factor for nasopharyngeal carcinoma (NPC) in China was tested by applying the nitrosoproline (NPRO) test to subjects living in high- and low-risk districts for NPC in Zangwu county, Guangxi region, in southern China. Samples of 12-h urine were collected from 77 subjects: (a) before any treatment; (b) after ingestion of proline; and (c) after ingestion of proline together with vitamin C. NPRO, other nitrosamino acids, and nitrate were measured as indices of exposure to preformed and endogenously formed nitrosamines or their precursors. The NPRO level after proline intake was significantly increased in subjects from the high-risk area (P = 0.012) and markedly reduced after ingestion of ascorbic acid (P = 0.007), but such an effect was not seen in subjects from the low-risk area. Levels of N-nitrosothiazolidine-4-carboxylic acid and the sum of nitrosamino acids in subjects in the high-risk area were significantly reduced by ascorbic acid (P < 0.01) but were not reduced in subjects from the low-risk area. The urinary nitrate level was about twice as high in subjects from the high-risk area. In subjects from high- and low-risk areas combined, NPRO levels in any of the three dose groups were highly correlated with nitrate levels (P = 0.0001). These results demonstrate a higher potential for endogenous nitrosation in subjects living in the high-risk area of NPC and suggest the occurrence of nitrosation inhibitors in the diet consumed in the low-risk area.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗