Determination of the frequency response of pneumotachographs is needed whenever they are used to measure high-frequency flows, such as in the forced oscillation method. When screen and capillary pneumotachographs are calibrated using an adiabatic compression in a closed box as a reference impedance, they can be adequately described by a ...

Numerous techniques and many materials are available to the surgeon for the reconstruction of defects of the tympano-ossicular system. The author would like modestly to recall certain aspects of middle-ear physiology and physics, and the impact that a knowledge of these ought to have in the mind and in the ...

The material properties of lead zirconate titanate (PZT) ceramics for operation in the thickness mode at frequencies as high as 80 MHz are reported. Each of the ceramics tested showed a reduction in k (t) with increasing frequency. In a fine-grained PZT, values of k(t) as high as 0.44 were ...

The contribution of the bulla to low-frequency hearing capability was studied in the gerbilline rodent Pachyuromys duprasi. In the frequency range of 0.6-3 kHz, the sound pressure behind the tympanic membrane is higher than the pressure in the meatus acusticus externus near the eardrum. Gradual augmentation of frequencies above 0.6 ...

Mustached bats, Pteronotus p. parnellii, use complex, multiharmonic biosonar signals with prominent approx. 60 kHz (CF) components. The sense of hearing is especially acute to sounds near 60 kHz and the cochlea shows a number of specializations in the 60 kHz region. Foremost is a remarkable degree of cochlear resonance. ...

A technique to obtain the spacing distribution of macro- and microstructures of hypercholestrolemic liver, lymphoidlucosed liver, rhinosporidium of man and ethmoidal tumour of bovine is presented. The method uses signal processing of spatially averaged spectra of ultrasonic backscattering from tissues in the frequency range 2-8 MHz. The macrostructure is obtained ...

In the course of conducting second analyses, the analyst has a uniquely advantageous position from which to study the psychoanalytic process. His or her observations of the unfolding of the second analysis can be compared with the analysand's description of the earlier experience. Investigation of the differences throws light on ...

A heterodyne interferometer proved to be a very accurate tool to measure amplitude and phase of the malleus response during acoustical stimulation. It was shown that to obtain equal accuracy in the acoustical pressure measurements, pressure response must be remeasured at short time intervals. At frequencies above 4 kHz various ...

A probe is described for determining the dielectric permittivity and dielectric loss of organ tissues at very high frequencies (VHF) in a non-violating manner. Instead of the usual reflection coefficient measurement, with this probe the electromagnetic wave transmission coefficient is measured between two coplanar electrodes on the organ surface which ...

In order to assess the renal corticomedullary electrolyte gradient, electrical impedance (zeta) and phase angle (phi) were measured in the in-situ kidney of anaesthetized rats. A set of platinum/iridium needle electrodes was used, and the frequency (f) of the measuring current was varied between 0.5 and 50 kHz. zeta and ...

A technique which does not require the measurement of strain has been developed for the investigation of the incremental dynamic properties of soft tissue sheets. Radially prestressed and circularly clamped canine diaphragm samples were exposed to small-amplitude pseudorandom pressure variations. From the measurement of these pressure variations and the volume ...

The frequency dependence of respiratory impedance (Zrs) from 0.125 to 4 Hz (Hantos et al., J. Appl. Physiol. 60: 123-132, 1986) may reflect inhomogeneous parallel time constants or the inherent viscoelastic properties of the respiratory tissues. However, studies on the lung alone or chest wall alone indicate that their impedance ...

The application of forced oscillations has been introduced as a noninvasive method to measure the impedance of the respiratory system. Impedance can be partitioned into a real part or resistance and an imaginary part or reactance. The reactance depends on the elastic and inertial properties of the respiratory system. In ...

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 ...

Spontaneous breathing may impair the reliability of forced oscillatory impedance estimates at low frequencies, especially when the oscillatory power is distributed among many frequency values. Since the amplitude of the external forcing is limited to avoid non-linearities, it is suggested that the total energy of a composite electrical signal driving ...

To measure impedance one measures or estimates flow, which is commonly done by measuring the pressure drop across a pneumotachometer. The frequency response characteristics of standard pneumotachometer/pressure transducers (PPT) limit their use to relatively low frequencies. Also, the frequency response of PPTs has been reported to be "load" dependent. Thus, ...

A four-channel impedance plethysmograph has been designed. Impedance signals are obtained at two frequencies by measuring both real and imaginary parts. Particular attention has been paid to the sine wave generation circuits that provide system versatility. The required phase-sensitive demodulation is achieved by means of analogue multiplexers. Results show that ...

The authors propose a technique that allows them to size bubbles with the same accuracy as with the double-frequency method and to locate them with the same range resolution as with the pulsed Doppler velocimeter. They demonstrate that the signal scattered by the bubble insonified by a high-frequency pulsed ultrasonic ...

The mechanical impedance of the hand and arm was studied on ten healthy subjects during exposure to sinusoidal vibration within the frequency range of 2 to 1000 Hz. A special handle for the measurements was constructed. The influence of vibration direction, handle grip, grip force, vibration level, hand-arm posture and ...

Ring piezoelectric transducers generating ultrasonic energy in air were designed and tested experimentally and numerically. The radiation pattern of the transducer is very narrow (4 degrees ) and its frequency response has a broadband character. Resonant frequencies of the transducers were determined experimentally and verified theoretically. Applications of the proposed ...

1. Resonant frequency of the chest-lung system in six tracheotomized, spontaneously breathing dogs was determined by analyzing the shape of the respiratory flow curve. 2. The resonant frequency was calculated from the periodic deviations from a sinusoidal flow pattern observed in the inspiratory phase of the breathing cycle. 3. Mean ...

Definition of multisegment hemodynamic changes that take place in the body would provide a more complete understanding of the physiologic responses to various orthostatic stress techniques. A self-contained impedance device is described which may be used to measure the electrical transmission characteristics produced by blood flow and volume changes in ...

Lung impedance was measured from 0.01 to 0.1 Hz in six healthy adults by superimposing small-amplitude forced oscillations on spontaneous breathing. Measurements were made with an almost constant-volume input (160-180 ml) or with an almost constant-flow input (20-30 ml.s-1). No significant difference was found between the two conditions. Lung resistance ...

Our studies are concerned with the frequency tuning that is provided by the electrical resonance of tuberous electroreceptors. Frequency selectivity had previously been measured in the electroreceptor's afferent fibers, and resonant conductances in the electroreceptor cell membrane had been implicated in producing the selectivity. With transdermal application of sinusoidal current, ...

Total respiratory impedance was measured rapidly and noninvasively in conscious horses over the frequency range 3 to 40 Hz by the forced random noise method. The shape of curve of impedance versus frequency in horses was markedly different from that of humans. Respiratory resistance was readily found as the real ...

To minimize the flow-dependent effects caused by an endotracheal tube during impedance measurements, we recorded pressure inside the tube at its distal end. We used a commercial endotracheal tube with a lumen built into its wall with the opening located near the outlet of the tube. We characterized the effect ...

Eight normal domestic pigs (Large White breed) of body weights 17 kg to 62 kg were subjected to high frequency jet ventilation (HFJV) at frequencies of 1 to 10 Hz (60-600 breaths/min). Six animals survived the study. The gain response curves and phase shift response curves obtained for these animals ...

In this study the electrical and dielectric properties of wet human cancellous bone from distal tibiae were examined as a function of frequency and direction. The resistance and capacitance of the cancellous bone specimens were measured at near 100% relative humidity. The measurements were made in all three orthogonal directions ...

The mass loading effects of adsorbing and desorbing contaminant molecules on the magnitude and characteristics of frequency fluctuations in a thickness-shear resonator are studied. The study is motivated by the observation that the frequency of a thickness-shear resonator is determined predominantly by such mechanical parameters as the thickness of the ...

In the development and evaluation of mechanical ventilation on the basis of high-frequency oscillation, appropriate surrogates of the lung are important, because they allow the measurement and control of various parameters which are not accessible in animal models. Yet, criteria have to be established according to which results obtained with ...

The wrist has been moved rhythmically in the horizontal plane by sinusoidal torques provided by a printed motor. Measurements have been made on normal subjects and subjects with rheumatoid arthritis. Both groups exhibited a resonance, the oscillations being greatest when the applied torque was of certain frequency. In both groups ...

We measured chest wall "pathway impedances" (ratios of pressure changes to rates of volume displacement at the surface) with esophageal and gastric balloons and inductance plethysmographic belts around the rib cage and abdomen during forced volume oscillations (5% vital capacity, 0.5-4 Hz) at the mouth of five relaxed, seated subjects. ...

By expressing the respiratory system as a two-compartment model and assigning a phasor in the complex plane to each impedance element in the model, the phasor of the respiratory impedance could be constructed graphically, the frequency characteristics determined from the locus of the latter and the effects of variations in ...

A computer study of rectified diffusion was made over the biomedical frequency range (1-10 MHz). Solutions of the Gilmore-Akulichev [E. Cramer, in Cavitation and Inhomogeneities in Underwater Acoustics, edited by W. Lauterborn (Springer, New York, 1980), pp. 54-63] formulation for bubble dynamics were combined with the Eller-Flynn [A. Eller and ...

We have determined the resistance (Rrs) and the reactance (Xrs) of the total respiratory system in unsedated spontaneously breathing calves at various frequencies. A pseudorandom noise pressure wave was produced at the nostrils of the animals by means of a loudspeaker adapted to the nose by a tightly fitting mask. ...

The efficiency of optooptieal light deflection by nondegencrote four-wave mixing can be increased significantly by placing the grating in a resonant cavity. Theory and experiment are presented for linear and ring cavities. Efficiency improvement by an order of magnitude is predicted, and improvements by a factor of 5.6 hove been ...

When electrical resonances were observed in acoustic sensory cells of lower vertebrates, the hearing research community was presented with the exciting possibility that tuning in the ears of those animals might be explained directly in terms of familiar molecular devices. It is reported here that in the frog sacculus, where ...

The real--Re(Z)--and imaginary--Im(Z)--parts of the ventilatory system impedance were measured between 6 and 30 Hz in 18 normal infants and in 19 with airway obstruction. The intercept (R0) and slope (S) of the Re(Z)-frequency function, as well as inertance (I) and compliance (C) estimated from Im(Z), were compared with ventilatory ...

The twinship paradigm describes a pattern of dyadic, quasi-object relationship, the purpose of which is to facilitate differentiation, separation, and integration. Twinships can arise at any point in the life cycle, when the self faces a developmental impasse. The twin functions as an alter-ego. Twin selection is based on two ...

The effects of posture on the mechanics of the respiratory system are not well known, particularly in terms of total respiratory resistance. We have measured respiratory impedance (Zrs) by the forced random noise excitation technique in the sitting and the supine position in 24 healthy subjects. Spirometry and lung volumes ...

The electrical parameter used to define defibrillation strength is energy. Peak current, however, may more accurately reflect the field quantities (i.e., electric field strength and current density) that mediate defibrillation and therefore should be a better clinical descriptor of threshold than energy. Though transthoracic impedance is a major determinant of ...

A modified forced oscillatory technique was used to determine the respiratory mechanical impedances in anesthetized, paralyzed rats between 0.25 and 10 Hz. From the total respiratory (Zrs) and pulmonary impedance (ZL), measured with pseudorandom oscillations applied at the airway opening before and after thoracotomy, respectively, the chest wall impedance (ZW) ...

Total respiratory resistance and reactance from 3 to 30 Hz were determined by the method of forced random noise oscillation in 12 normal male subjects before and after bronchodilatation and bronchoconstriction induced by deep breaths of aerosols of isoproterenol and atropine and of methacholine and histamine. Isoproterenol and atropine induced ...

The biodynamics of the forearm of a number of relaxed human subjects have been investigated using a printed motor as a torque generator. Oscillation in the horizontal plane at the resonant frequency has been maintained by feed-back of a modified velocity signal. By means of negative position feed-back the stiffness ...

The forced oscillation technique is a noninvasive and effort-independent test used to characterize the mechanical impedance of the respiratory system. The aim of this study was to assess the sensitivity of this method in detecting early airway abnormalities caused by smoking or occupational hazards. Respiratory mechanical parameters by the forced ...

A review is given of the dielectric properties of various mammalian tissues and biological fluids for the frequency range from 1 Hz to 10 GHz. The properties considered are the frequency variations of the relative permittivity and electrical conductivity. An attempt has been made to present data which can be ...

Relaxed expirations were obtained from five anesthetized dogs under control conditions and during various rates of intravenous infusion of histamine. All volume vs. time curves obtained from 20 ms to 2 s after the start of expiration were poorly described by a single exponential function but were fitted very well ...

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 ...

Dielectric permittivity and conductivity of bone in different physiological conditions and collagen, a major component of bone are measured in the frequency range 400-1300 MHz using a Network analyzer. The dielectric dispersion observed in each cases are explained in terms of the relaxation of 'bound water' in this frequency range. ...

A new method for measuring total respiratory input impedance (Zrs), which ensures minimal motion of extrathoracic airway walls, was tested over frequencies of 4-30 Hz in 14 normal subjects and 10 patients with airway obstruction. It consists of applying pressure variations around the head, rather than at the mouth, so ...