Mechanical impedance of human parotid area tissues (mastoid)]

Frequency relationship of mechanical impedance of human mastoid has been recorded within the frequency range of 125-15 000 Hz. The technique of measuring mechanical impedance has been described and its error evaluated. From the results obtained equivalent parameters of the mechanical system imitating acoustic properties of human mastoid are calculated. These parameters can serve as the basis for developing the device artificial mastoid.     

Impedance characterization of a piezoelectric immunosensor. Part I: antibody coating and buffer solution

This study investigated the impedance characteristics of a 5 MHz quartz crystal resonator oscillating in a thickness-shear mode for utilization as a biosensor. An impedance analyzer measured the impedance of the quartz crystal, which determined all mechanical properties of the oscillating quartz and its immediate environment. In this study, the impedance behavior of the oscillating crystal was characterized in air, in potassium phosphate buffer solution, and with immobilization of antibodies using protein-A. The potassium phosphate buffer behaved like a Newtonian liquid. The series resonance frequency shifted down about 900 Hz on contact with the buffer. An immobilized-antibody layer on the quartz surface behaved like a rigid mass when immersed in the buffer solution. The impedance curve following immobilization of antibodies was shifted down in frequency by about 200 Hz compared with its value when the bare crystal was immersed in the buffer solution.     

Changes in the Frequency Structure of a Mating Call Decrease Its Attractiveness to Females in the Cricket Frog Acris crepitans blanchardi

In many species, females often prefer male signals that are more complex than in nature or beyond the range of calls naturally produced by conspecific males in spectral, temporal and amplitude features. In this study we examined both the ability of females to recognize signals outside the normal range of spectral frequency variation seen in male advertisement calls, and the influence of increasing call complexity by adding spectral components to enhance the attractiveness of a male advertisement call in the cricket frog Acris crepitans blanchardi, while keeping its amplitude constant. We used two different natural male call groups and created the following synthetic call groups: with a dominant frequency at 3500 Hz, i.e. at the normal dominant frequency with a frequency band within the sensitivity range of the inner ear basilar papilla; with a dominant frequency at 700 Hz, i.e. outside the normal range of variation and with a frequency band outside the sensitivity range of the basilar papilla but within the range of the amphibian papilla; with two dominant frequencies, one at 700 Hz and another at 3500 Hz, stimulating the basilar and amphibian papilla simultaneously. In double choice experiments we tested all combinations of the three call groups, and we tested the 3500 Hz call groups against the same natural call groups. Additionally, we tested the 700 Hz call groups against white noise to see whether these signals are meaningful in mate choice. Females preferred 3500 Hz call groups over all other call groups. The synthetic call group was as attractive to females as the same natural call group. The 700 Hz call group was not meaningful in mate choice. The combined (700 Hz + 3500 Hz) call group was significantly less attractive to females than the 3500 Hz call group. Thus, making a call more spectrally complex without increasing its overall amplitude decreases its attractiveness to cricket frog females.     

Mechanical behavior of the fingertip in the range of frequencies and displacements relevant to touch

It was previously suggested that the mechanical properties of the fingertip could be characterized by elasticity from dc to about 100Hz and by viscosity above this frequency. Using a specifically designed high mobility probe, we accurately measured the impedance of the fingertips of seven participants under a variety of conditions relevant to purposeful touch. Direct measurements vindicated previous indirect observations. We also characterized the dependency of the fingertip impedance upon normal load, orientation, and time.     

Peripheral and central processing of lateral line information

The lateral line is a hydrodynamic sensory system that allows fishes and aquatic amphibians to detect the water motions caused, for instance, by conspecifics, predators or prey. Typically the peripheral lateral line of fishes consists of several hundred neuromasts spread over the head, trunk, and tail fin. Lateral line neuromasts are mechanical low-pass filters that have an operating range from <1 Hz up to about 150 Hz. Within this frequency range, neuromasts encode the duration, local direction, amplitude, frequency, and phase of a hydrodynamic stimulus. This paper reviews the peripheral and central processing of lateral line information in fishes. Special attention is given to the coding of simple and complex hydrodynamic stimuli, to parallel processing, the roles of the various brain areas that process hydrodynamic information and the centrifugal (efferent) control of lateral line information. The review argues that in order to fully comprehend peripheral and central lateral line information processing, it is imperative to do comparative studies that take into account the ecology of fishes, meaning that natural stimulus and noise conditions have to be considered.     

Frequency Specificity of Regional Homogeneity in the Resting-State Human Brain

Resting state-fMRI studies have found that the inter-areal correlations in cortical networks concentrate within ultra-low frequencies (0.01–0.04 Hz) while long-distance connections within subcortical networks distribute over a wider frequency range (0.01–0.14 Hz). However, the frequency characteristics of regional homogeneity (ReHo) in different areas are still unclear. To examine the ReHo properties in different frequency bands, a data-driven method, Empirical Mode Decomposition (EMD), was adopted to decompose the time series of each voxel into several components with distinct frequency bands. ReHo values in each of the components were then calculated. Our results showed that ReHo in cortical areas were higher and more frequency-dependent than those in the subcortical regions. BOLD oscillations of 0.02–0.04 Hz mainly contributed to the cortical ReHo, whereas the ReHo in limbic areas involved a wider frequency range and were dominated by higher-frequency BOLD oscillations (>0.08 Hz). The frequency characteristics of ReHo are distinct between different parts of the striatum, with the frequency band of 0.04–0.1 Hz contributing the most to ReHo in caudate nucleus, and oscillations lower than 0.02 Hz contributing more to ReHo in putamen. The distinct frequency-specific ReHo properties of different brain areas may arise from the assorted cytoarchitecture or synaptic types in these areas. Our work may advance the understanding of the neural-physiological basis of local BOLD activities and the functional specificity of different brain regions.     

Dynamic mechanical characteristics of intact and structurally modified bovine pericardial tissues

Bovine pericardium (BP) is a source of natural biomaterials with a wide range of clinical applications. In the present work we studied the dynamic mechanical behavior of BP in native form and under specific enzymatic degradation with chondroitinase ABC extracted a 17% of the total glycosaminoglycans (GAGs). The GAGs content of native BP was composed mainly from hyaluronan, chondroitine sulfate and dermatan sulfate. Dynamic tensile mechanical testing of BP in the frequency range 0.1-20 Hz demonstrated its viscoelastic nature. The storage modulus was equal to 6.5 (native) and 5.5 (degraded) MPa initially, increased in the region nearby 1 Hz by about 15%. This was related with physical resonance mechanisms activated in this frequency region. The high modulus (modulus of the high linear phase of stress-strain) was equal to 14 (native) and 10 (degraded) MPa, dropped at high frequencies to 7 and 5 Mpa, respectively. The damping, expressed by the hysteresis, was equal to 20% of the loading energy, changed exponentially with the frequency to 30% at 20 Hz. It seemed that of the elastic mechanical parameters, the storage modulus and the high modulus were even slightly dropped as a result of degradation. As a final conclusion, there was evident that GAGs may play a non-negligible role in the dynamic mechanical behavior of BP and, probably in other soft tissue biomechanics. It is suggested that the GAGs content may be considered during the design and chemical modification of biomaterials based on BP and other soft tissues.     

Lung and chest wall mechanics in rabbits during high-frequency body-surface oscillation

In eight anesthetized and tracheotomized rabbits, we studied the transfer impedances of the respiratory system during normocapnic ventilation by high-frequency body-surface oscillation from 3 to 15 Hz. The total respiratory impedance was partitioned into pulmonary and chest wall impedances to characterize the oscillatory mechanical properties of each component. The pulmonary and chest wall resistances were not frequency dependent in the 3- to 15-Hz range. The mean pulmonary resistance was 13.8 +/- 3.2 (SD) cmH2O.l-1.s, although the mean chest wall resistance was 8.6 +/- 2.0 cmH2O.l-1.s. The pulmonary elastance and inertance were 0.247 +/- 0.095 cmH2O/ml and 0.103 +/- 0.033 cmH2O.l-1.s2, respectively. The chest wall elastance and inertance were 0.533 +/- 0.136 cmH2O/ml and 0.041 +/- 0.063 cmH2O.l-1.s2, respectively. With a linear mechanical behavior, the transpulmonary pressure oscillations required to ventilate these tracheotomized animals were at their minimal value at 3 Hz. As the ventilatory frequency was increased beyond 6-9 Hz, both the minute ventilation necessary to maintain normocapnia and the pulmonary impedance increased. These data suggest that ventilation by body-surface oscillation is better suited for relatively moderate frequencies in rabbits with normal lungs.     

The AC Impedance of Frog Skin and Its Relation to Active Transport

The AC electrical impedance of frog skin was measured in the range 1 cycle/second to 50 kc/second by injecting current sinusoidally at low current density. The behavior of the skin was found to be linear so the usual concepts of impedance could be validly employed. In the range 1 cycle/second to 5 kc/second, the impedance traces out a circular arc locus with its center off the real axis; thus the skin could be represented by a series resistance and a parallel combination of a conductance and a phase shift element. The phase shift element has an impedance angle of about 80 degrees , current leading voltage, with an equivalent capacitance of about 2 muf/cm(2). The phase shift and the equivalent capacitance were independent of the experimental conditions. The parallel conductance, which was responsible for most of the low frequency impedance, could be subdivided into two approximately equal conductances, one associated with sodium ion current and the other associated with chloride ion current. Both currents were determined mainly by the concentrations of the respective ions bathing the outside of the skin. The response to changes in concentration and the response to CO(2) indicated that the chloride current was passive, but the sodium current appeared to be associated with the active transport mechanism; little sodium could pass through the skin unless associated with active transport.     

Analysis of shear wave propagation in skin; application to an experimental procedure

An analysis of an experimental procedure used to determine age-related changes in the skin was performed. The experiment is based on the propagation of a shear wave through the skin. The analysis of the experiment was used to determine the effects of parameters such as properties of the skin and subcutaneous fat, skin thickness and experimental conditions on the propagation. Computer simulations showed that at lower frequencies (less than 1000 Hz), measured results depended strongly on skin thickness, while at higher frequencies (2000 Hz) the results were relatively insensitive to both skin thickness and the properties of the subcutaneous fat. Results also depended upon the distance between the applied shear disturbance and the measurement point. The analysis suggests that higher frequency (2000 Hz) experimental results are more indicative of mechanical properties of skin than lower frequency (less than 1000 Hz) results.     

Contribution of electrogenic ion transport to impedance of the algae Valonia utricularis and artificial membranes.

The cell membrane of Valonia utricularis contains an electrogenic carrier system for chloride (Wang et al., Biophys J. 59:235-248 (1991)). The electrical impedance of V. utricularis was measured in the frequency range between 1 Hz and 50 kHz. The analysis of the impedance spectra from V. utricularis and its comparison with equivalent circuit models showed that the transport system created a characteristic contribution to the impedance in the frequency range between 10 Hz and 5 kHz. The fit of the impedance spectra with the formalism derived from the theory of carrier-mediated transport allowed the determination of the kinetic parameters of chloride transport through the cell membrane of V. utricularis, and its passive electrical properties. Simultaneous measurements of the kinetic parameters with the charge pulse method demonstrated the equivalence of both experimental approaches with respect to the evaluation of the translocation rate constants of the free and the charged carriers and the total density of carriers within the membrane. Moreover, the impedance spectra of the protonophor-mediated proton transport by FCCP (carbonylcyanide p-trifluoromethoxyphenyl-hydrazone) were measured in model membranes. The carrier system made a substantial contribution to the impedance of the artificial membranes. The analysis of the spectra in terms of a simple carrier system (Benz and McLaughlin, 1983, Biophys. J. 41:381-398) allowed the evaluation of the kinetic and equilibrium parameters of the FCCP-mediated proton transport. The possible application of the measurement of impedance spectra for the study of biological transport systems is discussed.     

Resistance and capacity in the thallus of Marchantia polymorpha

Calculations of the resistance r and capacity c of cell membrances and the resistancer ₁ of cell interiors of a community of cells in Marchantia polymorpha L. thalli are presented. These parameters of a multicellular system were determined by the adaptation of methods employed for the calculation of the resistance and capacity of single cells. The obtained results indicate that such a procedure is justified. A generally accepted resistance-capacity model of the cell was used as a basis for the determination of r, c, and r₁ (representing membrane resistance, membrane capacity, and resistance of cell interior, respectively). The calculations were based on measurements of impedance and phase shift within the frequency range of 5 Hz-1000 Hz. Stainless steel plates were employed as the measuring electrodes; polarization resistance and capacity were determined by separate measurements. The calculations confirmed the assumption that the parameters r, c, and r₁ were constant within the investigated frequency range.
The calculations of resistance and capacity for 25 plants were constant within the investigated frequency range. The calculations of resistance and capacity for 25 plants were carried out by four different methods and they yielded results of the order of : r = 0.45 kΩ± 0.15 kΩ, r₁= 1.0 kΩ± 0.45 kΩ, c = 11 μF ± 3.5 μF. Circular diagrams of impedance also confirmed the validity of the accepted model within the frequency range of 25–300 Hz.     

Forced oscillatory impedance of the respiratory system at low frequencies

Respiratory mechanical impedances were determined during voluntary apnea in five healthy subjects, by means of 0.25- to 5-Hz pseudo/random oscillations applied at the mouth. The total respiratory impedance was partitioned into pulmonary (ZL) and chest wall components with the esophageal balloon technique; corrections were made for the upper airway shunt impedance and the compressibility of alveolar gas. Neglect of these shunt effects did not qualitatively alter the frequency dependence of impedances but led to underestimations in impedance, especially in the chest wall resistance (Rw), which decreased by 20-30% at higher frequencies. The total resistance (Rrs) was markedly frequency dependent, falling from 0.47 +/- 0.06 (SD) at 0.25 Hz to 0.17 +/- 0.01 at 1 Hz and 0.15 +/- 0.01 kPa X l-1 X s at 5 Hz. The changes in Rrs were caused by the frequency dependence of Rw almost exclusively between 0.25 and 2 Hz and in most part between 2 and 5 Hz. The effective total respiratory (Crs,e) and pulmonary compliance were computed with corrections for pulmonary inertance derived from three- and five-parameter model fittings of ZL. Crs,e decreased from the static value (1.03 +/- 0.18 l X kPa-1) to a level of approximately 0.35 l X kPa-1 at 2-3 Hz; this change was primarily caused by the frequency-dependent behavior of chest wall compliance.     

Reliability of parameter estimates from models applied to respiratory impedance data

Many previous studies have fit lumped parameter models to respiratory input (Zin) and transfer (Ztr) impedance data. For frequency ranges higher than 4-32 Hz, a six-element model may be required in which an airway branch (with a resistance and inertance) is separated from a tissue branch (with a resistance, inertance, and compliance) by a shunt compliance. A sensitivity analysis is applied to predict the effects of frequency range on the accuracy of parameter estimates in this model obtained from Zin or Ztr data. Using a parameter set estimated from experimental data between 4 and 64 Hz in dogs, both Zin and Ztr were simulated from 4 to 200 Hz. Impedance sensitivity to each parameter was also calculated over this frequency range. The simulation predicted that for Zin a second resonance occurs near 80 Hz and that the impedance is considerably more sensitive to several of the parameters at frequencies surrounding this resonance than at any other frequencies. Also, unless data is obtained at very high frequencies (where the model is suspect), Zin data provides more accurate estimates than Ztr data. After adding random noise to the simulated Zin data, we attempted to extract the original parameters by using a nonlinear regression applied to three frequency ranges: 4-32, 4-64, and 4-110 Hz. Estimated parameters were substantially incorrect when using only 4- to 32-Hz or 4- to 64-Hz data, but nearly correct when fitting 4- to 110-Hz data. These results indicate that respiratory system parameters can be more accurately extracted from Zin than Ztr, and to make physiological inferences from parameter estimates based on Zin impedance data in dogs, the data must include frequencies surrounding the second resonance.     

Lung pressures and gas transport during high-frequency airway and chest wall oscillation

The major goal of this study was to compare gas exchange, tidal volume (VT), and dynamic lung pressures resulting from high-frequency airway oscillation (HFAO) with the corresponding effects in high-frequency chest wall oscillation (HFCWO). Eight anesthetized paralyzed dogs were maintained eucapnic with HFAO and HFCWO at frequencies ranging from 1 to 16 Hz in the former and 0.5 to 8 Hz in the latter. Tracheal (delta Ptr) and esophageal (delta Pes) pressure swings, VT, and arterial blood gases were measured in addition to respiratory impedance and static pressure-volume curves. Mean positive pressure (25-30 cmH2O) in the chest cuff associated with HFCWO generation decreased lung volume by approximately 200 ml and increased pulmonary impedance significantly. Aside from this decrease in functional residual capacity (FRC), no change in lung volume occurred as a result of dynamic factors during the course of HFCWO application. With HFAO, a small degree of hyperinflation occurred only at 16 Hz. Arterial PO2 decreased by 5 Torr on average during HFCWO. VT decreased with increasing frequency in both cases, but VT during HFCWO was smaller over the range of frequencies compared with HFAO. delta Pes and delta Ptr between 1 and 8 Hz were lower than the corresponding pressure swings obtained with conventional mechanical ventilation (CMV) applied at 0.25 Hz. delta Pes was minimized at 1 Hz during HFCWO; however, delta Ptr decreased continuously with decreasing frequency and, below 2 Hz, became progressively smaller than the corresponding values obtained with HFAO and CMV.     

Frequency-intensity characteristics of cricket cercal interneurons: units with high-pass functions

Interneurons in the cercal sensory system of crickets respond in a cell-specific manner if the cercal hair sensilla are stimulated by air-particle oscillations at frequencies below about 2000 Hz. We investigated the filter properties of several of these interneurons, and tested the effect of stimulus intensity (typically 0.3–50 mm s⁻¹ peak-to-peak air-particle velocity) on the frequency response in the range 5–600 Hz. We focus on three interneurons (the lateral and medial giant interneurons and interneuron 9-3a) of Acheta domesticus which are characterized by a relatively high sensitivity above ca. 50–200 Hz. The responses of the medial giant interneuron usually increase monotonically with frequency and intensity. Interneuron 9-3a and the lateral giant interneuron exhibit saturation or response decrement at high frequencies and intensities. The lateral giant interneuron has an additional peak of sensitivity below about 40 Hz. Small individual variations in the relative locations of the two response areas of this interneuron within the frequency-intensity field are responsible for a large variability obtained if frequency-response curves are determined for particular intensities. Stimulus frequency does not affect the principal directional preferences of the three interneurons. Nevertheless, if tested individually, the lateral giant interneuron and interneuron 9-3a exhibit small changes of directional tuning. Accepted: 12 November 1997     

Total and local impedances of the chest wall up to 10 Hz

To understand how bical mechanical chest wall (CW) properties are related to those of the CW as a whole, we measured esophageal and gastric pressures, CW volume changes (measured with a head-out body plethysmograph), and anteroposterior and transverse CW diameter changes (measured with magnetometers attached to the surface) during sinusoidal forcing at the mouth (2.5% vital capacity, 0.5-10 Hz) in four healthy subjects. Total CW resistance decreased sharply as frequency rose to 3-4 Hz and remained relatively constant at higher frequencies. Total CW reactance became less negative with increasing frequency but showed no tendency to change sign. Above 2 Hz, diameters measured at different locations changed asynchronously between and within the rib cage and abdomen. "Local pathway impedances" (ratios of esophageal or gastric pressure to a rate of diameter change) showed frequency dependence similar to that of the total CW less than 3 Hz. Local pathway impedances increased during contraction of respiratory muscles acting on the pathway. We conclude that 1) total CW behavior is mainly a reflection of its individual local properties at less than or equal to 3 Hz, 2) local impedances within the rib cage or within the abdomen can change independently in some situations, and 3) asynchronies that develop within the CW during forcing greater than 3 Hz suggest that two compartments may be insufficient to describe CW properties from impedance measurements.     

Respiratory input impedance in anesthetized paralyzed patients

Respiratory impedance (Zrs) was measured between 0.25 and 32 Hz in seven anesthetized and paralyzed patients by applying forced oscillation of low amplitude at the inlet of the endotracheal tube. Effective respiratory resistance (Rrs; in cmH2O.l-1.s) fell sharply from 6.2 +/- 2.1 (SD) at 0.25 Hz to 2.3 +/- 0.6 at 2 Hz. From then on, Rrs decreased slightly with frequency down to 1.5 +/- 0.5 at 32 Hz. Respiratory reactance (Xrs; in cmH2O.l-1.s) was -22.2 +/- 5.9 at 0.25 Hz and reached zero at approximately 14 Hz and 2.3 +/- 0.8 at 32 Hz. Effective respiratory elastance (Ers = -2pi x frequency x Xrs; in cmH2O/1) was 34.8 +/- 9.2 at 0.25 Hz and increased markedly with frequency up to 44.2 +/- 8.6 at 2 Hz. We interpreted Zrs data in terms of a T network mechanical model. We represented the proximal branch by central airway resistance and inertance. The shunt pathway accounted for bronchial distensibility and alveolar gas compressibility. The distal branch included a Newtonian resistance component for tissues and peripheral airways and a viscoelastic component for tissues. When the viscoelastic component was represented by a Kelvin body as in the model of Bates et al. (J. Appl. Physiol. 61: 873-880, 1986), a good fit was obtained over the entire frequency range, and reasonable values of parameters were estimated. The strong frequency dependence of Rrs and Ers observed below 2 Hz in our anesthetized paralyzed patients could be mainly interpreted in terms of tissue viscoelasticity. Nevertheless, the high Ers we found with low volume excursions suggests that tissues also exhibit plasticlike properties.     

Response of <Emphasis Type="Italic">Camptotheca acuminata</Emphasis> calli stimulated by mechanical vibration

Plants in their natural environment are usually affected by mechanical stress because of their sessile growth habit. This work was aimed at determining the effects of mechanical vibration on the growth rate, physiological indexes, and secondary metabolite biosynthesis of Camptotheca acuminata calli. In this study, mechanical vibrations of 1–4 Hz in frequency were applied to stimulate the C. acuminata calli; we found that a mechanical vibration of moderate frequency (2 Hz) can clearly promote the growth rate and increase the soluble protein content and superoxide dismutase (SOD) activity. Under a mechanical vibration of a 2 Hz frequency, camptothecin (CPT), the main secondary metabolite produced by C. acuminata, was increased by about fourfold compared to the control group, In contrast, the increased accumulation disappears at higher frequencies. The optimal vibration time for obtaining the highest levels of biomass and CPT was 60 min. This study showed that there are neutral frequencies and optimal periods of mechanical vibration on C. acuminata calli.     

Mechanical stretching modulates growth direction and MMP-9 release in human keratinocyte monolayer

Cells within human skin are exposed to mechanical stretching that is considered a trigger stimulus for keratinocyte proliferation, while its effect on keratinocyte migration has been poorly investigate. In order to explore the effect of stretching on keratinocyte migration spontaneously immortalized human keratinocyte (HaCaT) monolayers seeded onto collagen I-coated silicon sheets were stimulated three times for 1 hour every 24 hours (total time = 72 hours) by mechanical stretching increasing substrate deformations (10%) applied both as static (0 Hz) and cyclic (0.17 Hz) uniaxial stretching. At the end of stimulations monolayer areas measured in both static and cyclic samples appeared reduced and strongly oriented in a direction perpendicular to the stress direction compared to unstimulated ones. Moreover during the mechanical stimulation period HaCaT monolayers strongly increased the release in the medium of matrix metalloproteinase 9 (MMP-9), a proteolytic enzyme necessary for keratinocyte migration.Key words: keratinocyte, mechanical stretching, migration, MMP-9, MMP-2