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Biomedical subjects

C R Steele

Publications and source records attributed to C R Steele.

At least 19 recordsLinked to original sources
PubMed1995

Orthotropic piezoelectric properties of the cochlear outer hair cell wall.

The mammalian outer hair cell has been shown to possess significant coupling between mechanical and electrical properties. This electromotile property may play a key role in cochlear tuning. In order to characterize quantitatively the electrical and mechanical behavior, the cell wall is modeled as a thin linear elastic piezoelectric material. Experimental findings from several investigators are used to determine the mechanical and electrical generalized stiffness coefficients described by the model. The model analysis indicates that orthotropic mechanical properties in the plane of the cell wall are required to match experimental behavior. The calculated orthotropic coefficients predict that the outer hair cell deforms due to cilia deflection with a force gain of 0.5 for perfectly constrained end conditions and a displacement gain of 3.6 for free end conditions. These values reflect the potential role of the OHC as a feedback mechanism to the basilar membrane. Results are for small deformation and quasi-static conditions with viscosity and inertial effects neglected. It is further assumed that cell permeability is negligible at the time scale of the fast deformation considered here.

Animals↗
PubMed1992

In vivo assessment of forearm bone mass and ulnar bending stiffness in healthy men.

The cross-sectional bending stiffness EI of the ulna was measured in vivo by mechanical resistance tissue analysis (MRTA) in 90 men aged 19-89 years. MRTA measures the impedance response of low-frequency vibrations to determine EI, which is a reflection of elastic modulus E and moment of inertia I for the whole ulna. EI was compared to conventional estimates of bone mineral content (BMC), bone width (BW), and BMC/BW, which were all measured by single-photon absorptiometry. Results obtained from the nondominant ulna indicate that BW increases (r = 0.27, p = 0.01) and ulnar BMC/BW decreases (r = -0.31, p < or = 0.005) with age. Neither BMC nor EI declined with age. The single best predictor of EI was BW (r2 = 0.47, p = 0.0001), and further small but significant contributions were made by BMC (r2 = 0.53, p = 0.0001) and grip strength (r2 = 0.55, p = 0.0001). These results suggest that the resistance of older men to forearm fracture is related to age-associated changes in the moment of inertia achieved by redistributing bone mineral farther from the bending axis. We conclude that the in vivo assessment of bone geometry offers important insights to the comprehensive evaluation of bone strength.

Absorptiometry, Photon↗
PubMed1991

Noninvasive assessment of ulnar bending stiffness in women.

The load-carrying capacity of cortical bone is closely related to its geometry and to its fundamental material properties, including mineral content (BMC). Together these determine the bending stiffness EI, where I is the cross-sectional moment of inertia and E is Young's modulus of elasticity. To assess the relationship of BMC and bone width (BW) to EI in healthy women, we used mechanical response tissue analysis (MRTA), a noninvasive method that involves analysis of tissue responses to ulnar vibration. A total of 48 healthy women were enrolled into an older (64 +/- 1y, n = 25) and a younger (25 +/- 0.6y, n = 23) group. BMC and BW of the dominant ulna were measured by single-photon absorptiometry (SPA). EI was determined by MRTA. BMC (0.75 +/- 0.02 versus 0.63 +/- 0.02 g/cm), BMC/BW (0.75 +/- 0.02 versus 0.63 +/- 0.02 g/cm2), and EI (27.7 +/- 1.3 versus 21.3 +/- 1.1 N.m2) were significantly greater (p less than 0.005) in the young subjects. BW did not change with age (1.00 +/- 0.01 versus 1.01 +/- 0.01 cm). In young women, simple correlations of BMC and BW with EI were both significant. By multiple regression analysis only BW independently predicted EI (EI = -0.35 + 39.1 x BMC, R2 = 0.52). In older women BMC and BW correlated with EI, but in multiple regression only BMC was significant (EI = -34.5 + 62.1 x BW; R2 = 0.45). When this analysis of older women included only those whose BMC values were within 2 SD of the young mean, BMC remained the only significant predictor of EI.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorptiometry, Photon↗
PubMed1988

Influence of physical activity on the regulation of bone density.

Using a mathematical model which relates bone density to daily stress histories, the influence of physical activities on the apparent density of the calcaneal cancellous bone was investigated. Assuming that the mechanical bone maintenance stimulus is constant for all bone tissue, bone apparent density was calculated by a linear superposition of the mechanical stimulus provided by different daily physical activities. An empirical weighting factor, m, accounted for possible differences in the relative importance of load magnitude and number of cycles in each activity. By considering hypothetical variations in body weight and occupational activity levels, the range of probable m values was established. The model was then applied to the results of two previous running studies in which calcaneal density was measured to obtain an estimate of the stress exponent parameter, m. The results indicate that stress magnitudes (or joint forces) have a greater influence on bone mass than the number of loading cycles. We demonstrate that by carefully considering the magnitudes of imposed skeletal forces and the number of loading cycles, it may be possible to design exercise programs to achieve predictable changes in bone mass.

Body Weight↗
PubMed1988

Noninvasive determination of ulnar stiffness from mechanical response--in vivo comparison of stiffness and bone mineral content in humans.

An approach referred to as Mechanical Response Tissue Analysis (MRTA) has been developed for the noninvasive determination of mechanical properties of the constituents of the intact limb. Of specific interest in the present study is the bending stiffness of the ulna. The point mechanical impedance properties in the low frequency regime, between 60 and 1,600 Hz are used. The procedure requires a proper design of the probe for good contact of the skin at midshaft and proper support of the proximal and distal ends of the forearm to obtain an approximation to "simple support" of the ulna. A seven-parameter model for the mechanical response is then valid, which includes the first mode of anterior-posterior beam bending of the ulna, the damping and spring effect of the soft tissue between probe and bone, and the damping of musculature. A dynamic analyzer (HP3562A) provides in seconds the impedance curve and the pole-zero curve fit. The physical parameters are obtained from a closed-form solution in terms of the curve-fit parameters. The procedure is automated and is robust and analytically reliable at about the five percent level. Some 80 human subjects have been evaluated by this mechanical response system and by the Norland single photon absorptiometer, providing for the first time in vivo, a comparison of elastic bending stiffness (ulna) and bone mineral content (radius). Three functional parameters of potential clinical value are the cross-sectional bending stiffness EI, the axial load capability Pcr (Euler buckling load) and the bone "sufficiency" S, defined as the ratio of Pcr to body weight. The correlation between EI and bone mineral (r = 0.81) is only slightly less than previous in vitro results with both measurements on the same bone (r = 0.89). When sufficiency is taken into consideration, the correlation of Pcr and bone mineral content is improved (r = 0.89). An implication is that "quality" of bone is a factor which is not indicated by bone mineral content but which is indicated by stiffness. Bone mineral is necessary for proper stiffness but not sufficient. Therefore mechanical measurement should provide a new dimension to be used toward a better understanding of the factors related to bone health and disease.

Biomechanical Phenomena↗
PubMed1987

Electrokinetic model of cochlear hair cell motility.

Recent experiments have shown that isolated outer hair cells of the cochlea can vibrate under the influence of a transcellular oscillating electric field. Since high voltages have been measured in the cochlea, this result might suggest a basis for electromechanical feedback. A mechanical model of the hair cell has been developed and adapted to test the electrokinetic theory of motility, a postulate of which is that cochlear voltage gradients act on charged proteins embedded in the cell membrane to deform the cell. From the model it was deduced that the amount of charge density required is within the physiologic range. The significant result is that the amplitude of cell elongation for a fixed voltage amplitude is virtually constant for frequency less than a certain cutoff. The value of this frequency depends on the various physical parameters of the system and especially on the spacing between cells. Power transfer to the basilar membrane appears to peak near the cutoff frequency, and the amount is not very dependent on cell length, but is highly dependent on cell spacing.

Animals↗
PubMed1987

Functional capacity of marginated and bone marrow reserve granulocytes.

Marginated and bone marrow reserve granulocytes were obtained from young healthy volunteers after subcutaneous administration of aqueous epinephrine (0.4 ml/m2) or intravenous administration of hydrocortisone sodium succinate (250 mg), respectively. These leukocytes were compared with circulating granulocytes for the ability to adhere to surfaces, migrate in a random fashion, respond to chemoattractants, interact with autologous serum opsonins, and phagocytize and kill five common bacterial pathogens. As contrasted with circulating neutrophils, marginated cells had enhanced phagocytic and killing capacity for some pathogens, whereas adherence, random migration, chemotaxis, and chemiluminescence for the two cell populations were equivalent. Bone marrow reserve cells demonstrated increased activity for three functional mechanisms; chemotaxis for these cells averaged 21% higher than that for circulating cells, and phagocytosis was 32% higher, with 6 to 17% greater killing of the five bacterial species studied. All of these differences were statistically significant (P less than 0.05). Random migration and interaction with serum opsonins were unchanged in bone marrow granulocytes. These enhanced functional properties of neutrophils which are outside of the circulating pool may represent important host defense mechanisms during episodes of bacterial infection.

Bacteria↗
PubMed1986

Leukocyte survival in cerebrospinal fluid.

Delays in the laboratory examination of cerebrospinal fluid are commonly encountered in clinical medicine. The present studies were designed to evaluate changes in cerebrospinal fluid leukocyte counts relative to time elapsed before analysis. Neutrophil counts decreased most rapidly, being 68 +/- 10% (standard error of the mean) and 50 +/- 12% of initial values at 1 and 2 h, respectively. Lymphocyte and monocyte numbers were not significantly altered until 3 h.

Cell Survival↗
PubMed1985

Effect of coiling in a cochlear model.

Transformation of the three-dimensional equations of fluid motion into cylindrical coordinates allowed analysis of a coiled cochlear model by the WKB technique. The model includes a single transverse mode of basilar membrane deflection and inviscid fluid. The results calculated using realistic parameters for the guinea pig show no significant difference in the basilar membrane amplitude and phase between the straight and coiled models. Some differences exist in the fluid pressure found in the scala. The conclusion is that the macromechanical response is not significantly affected by coiling.

Acoustics↗
PubMed1985

Effect of opening and draining the cochlea.

The WKB approximation was used in calculations of the pure-tone response of a two-dimensional inviscid model of the human cochlea and a three-dimensional inviscid model of the guinea pig cochlea. The common experimental procedure of opening the scala tympani was simulated. Basilar membrane displacement was unaffected at and beyond the peak, but was slightly lower pre-peak. The peak location shifted to a significant extent apically only when the fluid level in the scala tympani was lowered to less than 1/10 of normal depth.

Animals↗
PubMed1983

Tibial changes in experimental disuse osteoporosis in the monkey.

We studied the mechanical properties and structural changes in the monkey tibia with disuse osteoporosis and during subsequent recovery. Bone bending stiffness was evaluated in relationship to microscopic changes in cortical bone and Norland bone mineral analysis. Restraint in the semireclined position produced regional losses of bone most obviously in the anterior-proximal tibiae. Following 6 months of restraint, the greatest losses of bone mineral in the proximal tibiae ranged from 23% to 31%; the largest changes in bone stiffness ranged from 36% to 40%. Approximately 8 1/2 months of recovery were required for restoration of normal bending properties. However, even after 15 months of recovery, bone mineral content did not necessarily return to normal levels. Histologically, resorption cavities in cortical bone were seen within 1 month of restraint; by 2 1/2 months of restraint there were large resorption cavities subperiosteally, endosteally, and intracortically. After 15 months of recovery, the cortex consisted mainly of first-generation haversian systems. After 40 months, the cortex appeared normal with numerous secondary and tertiary generations of haversian systems.

Animals↗
PubMed1981

Three-dimensional model calculations for guinea pig cochlea.

The WKB approximation was used for calculations of the pure tone response of a straight box model of the guinea pig cochlea with square scale cross sections and the fluid density and viscosity of water. Only one mode of elastic deformation of the partition was considered, corresponding to a flexible pectinate zone of the basilar membrane (BM) with rigid bony shelf, arches, and spiral ligament. Four distributions of pectinate zone transverse bending stiffness were considered, corresponding to volume compliances: (1) CB, measured by Békésy in the guinea pig post mortem, (2) CB/4, (3) CPL, deduced from Békésy's point load measurements in a human, with BM thickness inversely proportional to the width and rescaled for the guinea pig, and (4) 10CPL. We also considered various values of the relative longitudinal stiffness of the basilar membrane and the condition of drained or filled scala tympani. When compared to in vivo and post-mortem measurements of the guinea pig, the model results lead to the conjecture that the transverse fibers of the basilar membrane decrease in stiffness with time post mortem, while the ground substance increases in stiffness. Calculations using the compliance CB/4, with the ST drained with zero longitudinal BM stiffness give a response similar in location, peak shape, and phase to the in vivo capacitance probe measurements of Wilson and Johnstone [J., Acoust. Soc. Am 57, 705--23 (1975)]. Calculations for the ST filled and closed show a BM amplitude similar in location and shape to the spiral ganglion cell threshold curves obtained by Robertson and Johnstone [J. Acoust. Soc. Am. 57, 466--469 (1979)] from abnormal cochleas without outer hair cells. This indicates that the normal peak neural stimulation occurs about 1 mm apical of the BM peak amplitude. Naturally, the discrepancies between the postulated physical model and the cochlea prevent firm conclusions about cochlear function.

Animals↗
PubMed1981

Cochlear model including three-dimensional fluid and four modes of partition flexibility.

The WKB solution is developed for the analysis of a straight box cochlear model which includes four modes of partition displacement, simulating the motion of the bony shelf and arches of Corti, as well as the pectinate zone of the basilar membrane. The theory is similar to that previously used for the 1-mode model with scalar quantities now replaced by 4-vectors. Calculations are carried out for the guinea pig cochlea with stiffness computed mainly from the anatomy and assumed physiological values for the materials. Results show that the stiffness is such that the amplitude and phase of the basilar membrane response are not significantly altered from those given by the 1-mode model. For primates and some other mammals, the bony shelf is substantially weaker than in the guinea pig and causes a much more rapid accumulation of phase along the basilar membrane. Thus, with anatomically and physiologically consistent parameters, the model yields good correlation in phase and amplitude with the in vivo measurements which have been made in the squirrel monkey by Rhode [J. Acoust. Soc. Am. 64, 158-176 (1978)] as well as in the guinea pig by Wilson and Johnstone [J. Acoust. Soc. Am. 57, 705-723 (1975)] and Rhode [Basic Mechanisms in Hearing (Academic, New York, 1973), pp. 49-63].

Animals↗
PubMed1980

An improved WKB calculation for a two-dimensional cochlear model.

The finite difference calculations of Neely [E.D. thesis, California Institute of Technology, Pasadena, CA (1977)] and the WKB solution of Steele and Taber [J. Acoust. Soc. Am. 65, 1001-1006 (1979)] generally agree, except in the "phase plateau" region, where both are irregular. In the present work, an improvement in the accuracy of the WKB procedure is gained by using a closed-form integral which gives the phase and damping functions in the short wavelength region. The present results agree qualitatively with the preceding but show a smooth variation with frequency and distance along the cochlea.

Cochlea↗
PubMed1979

Noninvasive measures of bone bending rigidity in the monkey (M. nemestrina).

The in vivo bending rigidity and bone mineral content of monkey ulnae and tibiae were measured. Bending rigidity in the anteroposterior plane was measured by an impedance probe technique. Forced vibrations of the bones were induced with an electromechanical shaker, and force and velocity at the driving point were determined. The responses over the range of 100-250 Hz were utilized to compute the bending rigidity. Bone mineral content in the cross section was determined by a photon absorption technique. Seventeen male monkeys (Macaca nemestrina) weighing 6-14 kg were evaluated. Repeatability of the rigidity measures was 4%. Bone mineral content was measured with a precision of 3.5%. Bending rigidity was correlated with the mineral content of the cross section, r = 0.899. Two monkeys were evaluated during prolonged hypodynamic restraint. Restraint produced regional losses of bone most obviously in the proximal tibia. Local bone mineral content declines 17 to 24% and the average bending rigidity declines 12 to 22%. Changes in bones leading to a reduction in mineral content and stiffness are discussed.

Animals↗
PubMed1979

Comparison of WKB and finite difference calculations for a two-dimensional cochlear model.

There are many points of uncertainty in the subject of cochlear models. In this paper only the question of efficient computing methods is addressed. For the cochlear model with a one-dimensional approximation for the fluid motion, Zweig, Lipes, and Pierce [J. Acoust. Soc. Am. 59, 975-982 (1976)] have shown that the WKB method agrees well with a direct numerical integration. For the two-dimensional fluid model, Neely [E.D. thesis, California Institute of Technology, Pasadena, CA (1977)] has shown that a direct finite difference solution is an order of magnitude faster than the integral equation approach used by Allen [J. Acoust. Soc. Am 61, 110-119 (1977)]. In the present work, a formal WKB solution is derived following Whitham [Linear and Nonlinear Waves (Wiley, New York, 1974)]. The advantage of this formulation is simplicity, but the disadvantage is that no error estimate is available. We find that the numerical results from the WKB solution agree well with those of Neely (1977), while the computer time is reduced by another order of magnitude. Thus, the WKB method seems to offer the satisfactory accuracy, efficiency, and flexibility for treating the more realistic cochlear models.

Cochlea↗
PubMed1979

Comparison of WKB calculations and experimental results for three-dimensional cochlear models.

The WKB asymptotic method is applied to the calculation of cochlear models with square scala cross section, for which the fluid motion is fully three dimensional. The analysis begins with the exact solution for wave propagation in a duct with constant properties. This solution is somewhat tedious but straightforward, since it requires a Fourier series expansion across the duct. Then with the formulation of Whitham [Linear and Nonlinear Waves (Wiley, New York, 1974)], the approximate solution is readily generated for the duct with properties which vary slowly along the length. Numerical calculations are carried out for the experimental models of Cannel [Ph.D. thesis, Univ. of Warwick (1969)] and Helle [Dr.-Ing. disser., Technische Univ., Müchen (1974)] who furnish quantitative details of both "basilar membrane" response and model parameters. Without any free parameters for adjusting, the present WKB solution shows quite satisfactory agreement with the experimental model results. Computer time is reasonable; the calculation of displacement envelope and phase at a number of stations along the cochlea for a given frequency requires only one second of CPU time. Thus the credibility and practically of the approach is established for the investigation of yet more realistic and more elaborate cochlear models.

Cochlea↗