The mechanical behavior of gels of various water content, normal and edematous tissues have been studied. Static deformations and vibrations at low frequencies were applied to an area of each of these structures. Softer structures, e.g., gel containing a high percentage of water and pitting edema, have lower mechanical impedance ...

Mathematical modeling has shown that it should be possible to determine the electrotonic location of membrane conductance changes in single neurons by analysis of the associated changes in the magnitude of the alternating-current (AC) input impedance. The form of the plot of change in the magnitude of the input impedance ...

When studying respiratory impedance by forced oscillations, part of the flow measured at the mouth is lost in upper airway wall motion and does not enter the trachea. The corresponding error was studied in 10 normal subjects and 8 patients with chronic obstructive pulmonary disease (COPD) by measuring respiratory impedance ...

Total respiratory input (Zrs,in) and transfer (Zrs,tr) impedances were obtained from 4 to 30 Hz in 10 healthy males by simultaneously measuring mouth and chest flow while applying pseudo-random pressure variations at the mouth. Compared with Zrs,in, the real part of Zrs,tr was larger up to 10 Hz but exhibited ...

Auditory brainstem responses (ABR) recorded in two groups of 10 normal volunteers were compared under conditions of impeded and unimpeded breathing. Impedance to breathing was accomplished by adding inspiratory flow-resistive loads of varying magnitude. Loaded breathing selectively augmented the amplitude of ABR components generated in the vicinity of the pontomidbrain ...

The frequency response, at various points along the length and circumference, of two isolated human ulnas has been recorded during white noise excitation under 'free-free' conditions. Both bones showed a similar pattern of multiple frequencies of resonance; two fundamental mode resonances occurring in directions mutually at right angles. Further resonances ...

We investigated the effect of changing arterial input impedance over three selected frequency ranges on stroke volume (SV) in nine isolated canine left ventricles. The input impedance was simulated with a three-element Windkessel model (i.e., resistance, characteristic impedance, and compliance) and was imposed on the ventricles with a servo-controlled loading ...

Five electrical characteristics--impedance, broadband noise generation, line interference sensitivity, signal distortion, and common-mode conversion--were measured in five electromyographic (EMG) concentric needle electrodes (CNEs) from each of six commercial manufacturers. Untreated CNEs showed considerable variation in impedance and broadband noise characteristics, both within and among manufacturers. Electrolytic treatment reduced impedances by ...

Stimulated acoustic emissions in the cochlea are explained in terms of its hydraulic properties. The mathematical model predicts that these 'echoes' are caused by reflections which result from a discontinuity in the resistive and reactive components of the impedance which occurs at resonance. This discontinuity is a direct result of ...

A new accurate method to determine the myocardial deformation during the cardiac cycle in vivo is described. The system is based upon the mutual inductance principle, yet with transducers which consist of three perpendicular coils, yielding a spherical radiation and sensing characteristic. Thus the system is invariant with regard to ...

With airways obstruction, panting frequency affects plethysmographically determined thoracic gas volume (Vtg) because the extrathoracic airway acts as a shunt capacitor. Stanescu et al. (19) suggested that in the calculation of Vtg, use of esophageal (delta Pes) rather than mouth pressure (delta Pm) swings might eliminate the problem. We measured ...

The cyclotron frequency of an electron localized in the center of a cylindrical microwave cavity differs slightly from that in free space. To see this, the system is modeled by a series resonant lc circuit for the cyclotron motion connected across the center of a section of two-wire transmission line ...

Lung function responses to inhaled cotton dust were evaluated in a group of 58 healthy subjects by spirometry (MEFV curves) and forced random noise impedance parameters. Twenty-one of these subjects were also examined by body plethysmography to assess changes in airway resistance (Raw). For the study group as a whole, ...

The resonance of the relaxed wrist for flexion-extension movements in the horizontal plane has been investigated by using rhythmic torques generated by a printed motor. In the normal subject the resonant frequency of the wrist is ca. 2 Hz unless the torque is reduced below a certain critical value when ...

In normal human subjects, elbow resonance was measured by driving the forearm over a range of frequencies. The relaxed forearm, in a manipulandum with a low inertial moment, had a resonance of 0.068 +/- 0.06 Hz which was remarkably consistent for either sex and over a wide variety of arm ...

The ear's complex acoustic impedance locus for frequencies from 200 Hz to 2 kHz was obtained for 20 subjects screened for normal hearing. The purpose of the experiment was to observe "kinks" in the total driving point impedance locus of the ear, as measured by acoustic impedance in the ear ...

The mechanical point impedance has been studied in ten different areas of the glabrous skin of the human hand on three male and three female subjects within the frequency range of 20-10 000 Hz. For all tested areas the impedance decreased with increasing frequency down to a minimum value, corresponding ...

Inhaled insoluble particles that deposit along normal healthy tracheobronchial airways of humans and other mammals are transported on the proximally moving mucous lining to the larynx, where they are swallowed. The transit time from the most distal ciliated airways varies from 0.1 to 1 d, with each individual having a ...

Computation of impedances from forced oscillation data during breathing can yield results which reflect not only changes in respiratory mechanics, but artifacts related to the signal analysis. A method has been developed, employing sinusoidal forcing, to determine intra-breath variations of respiratory impedance. The measured pressure and flow waveforms are each ...

The series and shunt components of the impedance of the upper airway (Zuaw) were evaluated from measurements obtained during a Valsalva maneuver by means of a modified forced oscillation technique. When the cheeks are supported, the upper airway can be represented by a single distributed transmission line. The homogeneity of ...

Dielectric spectra representing the frequency dependence of the complex permitivity at a range of depolarizations were obtained from voltage-clamped frog skeletal muscle membranes. This employed an analysis that derived the Fourier coefficients defining the capacitative transients to 10 mV steps as continuous functions of frequency, and so could examine closely ...

Recent data on mechanical movements of the basilar membrane (BM) suggest that the part played in cochlear physiology by a sharpening mechanism is much less important than hitherto has been thought. In an extreme view, one could dispense with a sharpening mechanism completely and assume that (near the threshold) hair-cell ...

At frequencies greater than 2 kHz the acoustic impedance at the human eardrum is an unreliable indicator of the behavior of the middle ear system because of the complicated configuration of the ear canal and tympanic membrane. The energy reflectance at the eardrum, however, when obtained from measurement of the ...

The previous report on the dynamics of spontaneous and evoked activities of the substructures within the cat inferior colliculus (IC) has been extended in order further to demonstrate the high frequency resonance phenomena in the IC. Steady-state evoked potentials, which were recorded by repetitive acoustical stimulation, proved the fact that ...

This article present considerations which pertain to the limits of safe exposure of man to radio frequency and microwave frequency electromagnetic irradiation. Early considerations for the rationale of a 10 mW/cm2 standard and more recent results are summarized. The total frequency range can be conveniently subdivided into four parts: the ...

Some principles underlying acoustic impedance measurements in the ear canal and their evaluation are reviewed. The following topics are included: some methods of measurement, useful frequency range, the middle-ear system, impedance characteristics of normal and some pathological ears, and the relation between the impedance and tympanometric results. Advantages and disadvantages ...

The electrical impedance of isolated chick and toad retinas were measured in the absence of, and during, spreading depression, using sinusoidal measuring currents ranging from 10 to 50,000 Hz. Data obtained in the absence of the reaction indicate an electric heterogeneity of the tissue and suggest that at least two ...

A method is presented for measuring acoustic immittance (admittance or impedance) in the human ear canal and its validity is demonstrated for frequencies from 62 Hz to 4 kHz. Special attention is given to estimating the residual ear-canal space between the eardrum and the tip of the measuring device; estimates ...

When an impulse arrives at an area of impaired conductivity, a slowly rising electrotonic potential may bring the distal tissue to threshold after a delay imposed by the passive electrical properties of the system and by the time-dependent changes of these properties during diastole. This phenomenon can be demonstrated in ...

Phase-matched four-wave mixing in sodium vapor with a helium buffer gas is carried out in a noncoplanar geometry. The directions of the four light beams remain nondegenerate even if all frequencies are equal. A sharp zerodifference frequency resonance in the intensity of the parametrically generated fourth beam by three incident ...

Two methods for measuring respiratory mechanics by forced oscillations were compared, one using a frequency spectrum of 2-32 Hz produced by a pseudorandom noise generator (PRN), the other (Siregnost FD 5) a constant frequency of 10 Hz. In normals and patients with various lung diseases real part of impedance, Re, ...

Using a forced oscillation technique, we measured the resistance (Rrs) and reactance (Xrs) of the respiratory system between 2 and 32 Hz at three different lung volumes in 15 healthy subjects and 7 patients with chronic obstructive pulmonary disease. Rrs and Xrs were partitioned, by means of a pressure recording ...

We considered that phonocardiographic recording could be improved 1) by minimizing the acoustic impedance mismatch between the precordial tissue and transducer, 2) by optimizing the configuration of the impedance-matching medium and transducer design, and 3) by storing signals in digital form through analog-to-digital conversion of analog recordings made at the ...

Ipsilateral acoustic reflex eliciting stimuli were presented via the probes of six impedance meters to cadaver ears to determine the minimum stimulus levels at which apparent impedance changes occurred. These artefactual indications of impedance change were detected in all but one instrument within the range of intensities available for all ...

An important factor in trying to capture the complexity of many manipulation problems is the notion of Output Motor Impedance, i.e., the relationship between a set of disturbing forces and the resulting variation in arm configuration. The functional significance of such force/displacement characteristics is investigated, showing how several aspects of ...

The basic principles of deriving static acoustic-immittance measurements in human ears are presented. Problems caused by differences in instrumentation, computations, and measurement technique are discussed in terms of the utility and comparisons of static acoustic-immittance measurements. Data are provided regarding the short- and long-term variabilities inherent to static measurements. Although ...

A technique for measuring the resonance frequencies of an aluminum bar (used as a gravitational antenna) with high accuracy is presented. This method is based on the positive feedback of the bar, and is much faster than the others commonly in use.

Respiratory mechanical parameters were computed from forced random noise impedance data in normal adults (group 1), asymptomatic smokers (group 2), and patients with obstructive pulmonary disease (group 3). Mean values for all derived parameters were significantly different (p less than 0.025) for group 3. Mean values of resonant frequency, the ...

The magnitude and phase of disposable electrode-skin impedance were studied as functions of time, 0-48 hours, and frequency, 1 Hz-1 kHz. For both unabraded and mildly abraded skin, the impedance decreased as a function of time steadily or exponentially with time constants of several hours. Impedance decreased as a function ...

Measurements were made of the frequency response characteristics of the microphone-separator components of TONAR II instrumentation. The results of our calibration studies revealed 1) appreciable non-uniformity in frequency response of the two microphones, 2) a considerable degree of mismatch in frequency response between the microphones and, 3) dynamic interactions among ...

The sensing of intrathoracic electrical impedance from an esophageal probe may allow relatively noninvasive monitoring of cardiac and respiratory functions of particular interest in anesthesia and intensive care. We have obtained a partial solution of the intrathoracic current-field problem for impedance measurements made from a four-terminal linear array of electrodes ...

In each of 24 randomly selected outpatient the size of the impedance changes elicited by touching the skin in the ipsilateral cavum conchae with cotton wool were compared with those elicited by electrical stimulation of the same skin area. Pulse trains of 0.5 s duration, consisting of individual squarewave constant ...

An automatic recording system for measurements of biological impedances at different frequencies is described. The system comprises a signal synthesizer and a network analyser controlled by a desk calculator. The impedance and phase angle are recorded at one hundred and sixty logarithmically-spaced frequencies between 100 Hz and 1 MHz. A ...

The authors describe an operational amplifier with an adjustable frequency response and its use in membrane physiology, using the voltage clamp and current clamp method. The amplifier eliminates feedback poles causing oscillation. It consists of a follower with a high input resistance in the form of a tube and of ...

Serial distribution of airway properties determines in part the response of the lung to high frequency oscillations. We measured the response of excised dog lungs and lobes between 156 and 10,000 Hz and determined the area-distance function of the acoustically equivalent structure having rigid walls, regular branching, and negligible internal ...

Electrical stimulation of the skin in the cavum conchae is followed by bilateral changes in the acoustic impedance of the ear due to reflex contraction of the stapedius muscle. A stimulator and a special surface electrode for electrical stimulation of the skin have been developed. The apparatus produces square-wave constant-current ...

1. Low-frequency (3-30 Hz) oscillatory rotation of the ankle joint in plantarflexion-dorsiflexion was generated with a torque motor. Torque, rotation about the ankle and electromyograms (e.m.g.s) for the gastrocnemius-soleus and the anterior tibial muscles were recorded.2. Fourier coefficients at each drive frequency were used to calculate the effective compliance (ratio ...

This study was designed to analyse recordings of vocal fold vibrations using the laryngograph, a machine which measures the change in electrical impedance across the larynx. Recordings were made of each patient reading a standard text. The output was analysed in two ways: by study of waveform, and by production ...

A source of error in ipsilateral reflex measurements with impedance methods is explained. It is shown that the inherent non-linearity of the cavity represented by the ear canal and tympanic membrane gives rise to an artifact in the measurement of acoustic impedance which is synchronous with the stimulus. The magnitude ...

The total respiratory resistance determined by means of the forced oscillation technique during spontaneous breathing demonstrates a variability which may be due (1) to variations of the resistance itself, (2) to the superposition of rapid oscillatory and slow respiratory signals, (3) to the presence in the breathing signals of harmonics ...