Change In Admittance Research Articles

Differential Effect of Frusemide on Renal Medullary and Cortical Blood Flow in the Anaesthetised Rat

In addition to its known effect on renal tubular transport, frusemide (furosemide) has been shown to affect renal circulation. This study in the anaesthetised rat examined the influence of frusemide (bolus 0.25 or 0.5 mg kg(-1) I.V., then infusion delivering the same dose over 1 h) on renal cortical and medullary circulation measured as laser-Doppler blood (cell) flux. The responses were compared with simultaneously measured changes in renal excretion and in the tissue admittance, an index of medullary ionic hypertonicity of the interstitium. Renal vascular responses to frusemide were significant but not dose dependent. During low-dose frusemide infusion cortical flux decreased 11.5 +/- 0.9% and medullary flux decreased 32.3 +/- 3.5% (difference significant at P < 0.001). During high-dose infusion the decreases were by 13.5 +/- 1.4 and 29.3 +/- 3.8%, respectively (difference significant at P < 0.001). Sodium excretion increased 15-fold (by 3.7 +/- 0.4 micromol x min(-1)) and 30-fold (by 5.9 +/- 1.1 micromol x min(-1)) during low- and high-rate infusion of frusemide, respectively. By contrast, medullary tissue admittance decreased similarly with the two doses: maximally by 13.4 +/- 1.4 and 10.9 +/- 0.9%, respectively. The observations that an exaggerated post-frusemide decrease in blood flow within the medulla coincided with decreasing tissue admittance in this zone and that neither medullary blood flow nor admittance changes were related to the dose suggest a causal relationship between interstitial ionic hypertonicity and vascular resistance. We propose that the post-frusemide decrease in medullary tissue NaCl depressed medullary circulation by inhibiting local generation of vasodilator prostaglandins.

Effects of Wall Admittance Changes on Aeroelastic Stability of Turbomachines

In the present investigation a kind of new lifting surface model has been suggested based on the application of generalized Green’ sfunction theory anddoubleFouriertransformation technique, which issuitableforsupersonic cascadewithsubsonicleading-edgelocus.Thetheoreticalanalysisshowsthatthechangeofwallboundarycondition not only affects the eigenvalues of the system but also the eigenfunction normalizing factor in comparison with a rigid boundary condition, and it is these variations that affect the e ow and acoustic e eld. On the other hand, through the present numerical simulation the change of wall admittance leads to very remarkable effects on both the lift and moment coefe cients, which will determine whether a nonrigid wall has a positive effect on suppressing blade e utter or not. This means that if one aims at suppressing cascade e utter by use of a nonrigid wall one of the best ways is to e nd soft wall with a controllable acoustic admittance. Nomenclature Aab = periphery of a blade Ab = upper or lower surface of a blade b = blade semichord CFqi, CFa i = imaginary part of blade lift coefe cient CFqr, CFa i = real part of blade lift coefe cient CMqi, CMa i = imaginary part of blade moment coefe cient CMqr, CMa r = real part of blade moment coefe cient H = height from the hub to the tip side h = height from the hub to the tip side in the transformed space h1 = stagger distance, measured parallel to chord h2 = gap distance, measured normal to chord i = p i 1 kb

A New Approach for the Determination of Fish Freshness by Electrochemical Impedance Spectroscopy

ABSTRACT Changes in several dielectric parameters of carp, herring and sea bass during their storage after death at 4 °C, 15 °C and 25 °C were examined by electrochemical impedance spectroscopy (EIS) in the frequency range of 0.1 Hz to 100 kHz. This method offers a simple, rapid and in situ measurement of the onset of spoilage. The phase angle and admittance changes are the best freshness indicators, from which four classifications of freshness may be defined for all of the tested fish species. Warburg‐type impedance and CE (chemical reaction preceding an electrochemical reaction) processes were observed in the relaxation process during storage and a proposed equivalent circuit satisfactorily described the overall electrochemical behavior.

Mechanics of the Middle Ear System: Age-Related Changes in Viscoelastic Properties

Morphological studies of age-related changes in the tympanic membrane have suggested a decreased elasticity for increasing age, whereas age-related changes in admittance measured by tympanometry have revealed inconsistent results. In this study we report on the viscoelastic properties of the middle ear system by means of a new method in two different age groups. This method measures hysteresis (μJ), which describes the viscous properties of the system, and compliance (mm³/kPa) reflecting its elasticity. Moreover, P_ec0 (kPa) was recorded, which corresponds to middle ear pressure measured by tympanometry. Recordings were made in a group of 30 older normal subjects (mean age 77 years) and results were compared to previous findings in a group of 39 younger normal subjects (mean age 29). Hysteresis was markedly decreased in the older normal group compared to the younger one (p = 0.057). This may reflect morphological changes previously reported in the tympanic membrane and can be related to theoretical considerations on tympanic membrane rupture pressures. Compliance and P_ec0 were not influenced by variation in age (p = 0.645 and 0.966).

Effects of wall admittance changes on aeroelastic stability of turbomachines

Effects of wall admittance changes on aeroelastic stability of turbomachines

Acoustic reflex detection using wide-band acoustic reflectance, admittance, and power measurements.

The measurement of the acoustic reflex threshold is a basic component of the diagnostic audiological test battery that may subject patients to potentially harmful sound pressures. A wide-band acoustic impedance and reflectance system (D. H. Keefe, R. Ling, & J. C. Bulen, 1992) was investigated as a means of obtaining reflex thresholds at a reduced level and as a means of providing a more complete characterization of the reflex than current clinical methods provide. Reflex thresholds obtained by measuring changes in wide-band admittance, reflectance, and power were at least 8 dB lower than those obtained with the standard clinical technique. These reflex-induced changes were accounted for by a simple oscillator model of the middle ear, assuming that the acoustic reflex results in an increase in stiffness. The results support further investigation of reflectance-based measures of the acoustic reflex as a clinical tool and as a means of studying the reflex mechanism.

Assessment of bronchial reactivity by forced oscillation admittance avoids the upper airway artefact.

The forced oscillation technique (FOT) allows easy assessment of bronchial reactivity. The use of a standard FOT generator (SG) results in changes in respiratory system resistance (delta Rrs,SG) which are affected by an artefact caused by the extrathoracic upper airway (EUA). The aim was to improve the FOT assessment of bronchial reactivity with the SG by computing the change in FOT admittance (delta Ars,SG), which is theoretically unaffected by this artefact. Delta Rrs,SG and delta Ars,SG after bronchial challenge in 17 children were compared with the values measured with a head generator (HG) FOT setup (delta Rrs,HG and delta Ars,HG, respectively), which were taken as a reference, since HG provides data virtually freed from the EUA artefact. At 10 Hz, the SG significantly underestimated the resistance change: delta Rrs,SG=1.77+/-0.62 versus delta Rrs,HG=6.09+/-1.23 hPa x L(-1) x s. Delta Rrs,SG and delta Rrs,HG did not show a significant correlation. By contrast, the amplitude of the change in admittance measured by SG was close to the one obtained with the reference HG: /delta Ars,SG/=29.5+/-4.6 versus /delta Ars,HG/=32.7+/-3.9 mL x hPa(-1) x s(-1). /Delta Ars,SG/ and /delta Ars,HG/ showed a significant correlation (r=0.65, p>0.01). Similar results were found up to 20 Hz. The extrathoracic upper airway artefact was minimized when computing the change in admittance with the standard generator. This forced oscillation technique index may improve the sensitivity in assessing bronchial reactivity with the standard generator setup, which is the most common and easiest to use method for routine lung function testing.

Changes of Equivalent Admittance on Palms between Before and After Exercises or Magnetic Stimulus

Changes of Equivalent Admittance on Palms between Before and After Exercises or Magnetic Stimulus

Fusion Pore Conductance: Experimental Approaches and Theoretical Algorithms

Time-resolved admittance measurements provide the basis for studies showing that membrane fusion occurs through the formation and widening of an initially small pore, linking two previously separated aqueous compartments. Here we introduce modifications to this method that correct the cell-pipette (source) admittance for attenuation and phase shifts produced by electrophysiological equipment. Two new approaches for setting the right phase angle are discussed. The first uses the displacement of a patch-clamp amplifier C-slow potentiometer for the calculation of phase. This calculation is based on amplitudes of observed and expected (theoretical) changes in the source admittance. The second approach automates the original phase adjustment, the validity of which we prove analytically for certain conditions. The multiple sine wave approach is modified to allow the calculation of target cell membrane parameters and the conductance of the fusion pore. We also show how this technique can be extended for measurements of the resting potential of the first (voltage-clamped) membrane. We introduce an algorithm for calculation of fusion pore conductance despite a concurrent change in the resistance of the clamped membrane. The sensitivity of the capacitance restoration algorithm to phase shift errors is analyzed, and experimental data are used to demonstrate the results of this analysis. Finally, we show how the phase offset can be corrected “off-line” by restoring the shape of the capacitance increment.

Changes in Viscoelasticity of Polyaniline during Electrochemical Growth in Aqueous Solutions Probed by In Situ Electrochemical Quartz Crystal Oscillator Method

In situ electrochemical quartz crystal oscillator method was applied to aqueous acid electrolyte solutions of aniline to investigate changes in viscoelasticity of polyaniline during electrochemical growth. Changes in both resonant frequency and resonant admittance were in the order H2SO4 > HNO3 > HBr > HCl > HClO4 ≥ H3PO4 ≥CF3COOH Thus decreases in resonant frequency during electrochemical deposition of polyaniline included contribution from not only mass but also viscosity and the polyaniline film deposited on electrode surface should be considered to be viscoelastic.

An Investigation of Faradaic Admittance for Electrode Processes Involving n State Variables Besides Electrode Potential

Both the general Faradaic admittance equation and the stability condition of steady state for Faradaic electrode processes involving n state variables besides electrode potential are derived from the linear approximation around a steady state when the diffusion effect is ignored. Moreover, the Faradaic admittance equations that n ⩽ 3 are examined by Kramers‐Kronig transforms. Only under the stability conditions can the transform of their real and imaginary parts obey the Kramers‐Kronig relations, indicating that the conditions required by stability for these equations must also be satisfied in Kramers‐Kronig transforms, and testifying that these equations are true mathematic models describing changes of the Faradaic admittance with frequency. These results can be extended to the electrode processes containing more than three state variables in addition to the electrode potential. In addition, a general equivalent circuit to analyze common electrochemical impedance spectroscopy has been established in this paper. The use of the equivalent circuit, together with the mathematic model of Faradaic admittance, exhibits the advantage in analysis of impedance parameters of complicated alternating current impedance spectra.

Correction for the effects of viscoelastic changes in a piezoelectric quartz crystal by the multiple linear regression method

Resonant frequency and resonant admittance are recorded in situ for a piezoelectric quartz crystal. The effects of viscoelastic changes on the frequency can be corrected by the proposed multiple linear regression (MLR) method, which is applied to relate frequency shifts with the resonant admittance (or resistance) and mass changes. The regression equation can be used to correct for the effects caused by the viscoelastic changes. It has been found that the MLR method using resonant resistance as a variable is more effective for less viscoelastic films while the MLR method using resonant admittance as a variable is more effective for more viscoelastic films. Electrochemical synthesis of polyaniline in perchloric acid solutions was used successfully as a model to test the validity of the method.

Analysis of the phase transition of polymer blends using quartz crystal analyser

In this communication we show that an AT-cut quartz crystal analyser (QCA) can be applied to the investigation of the phase transition of polymer blend thin films. The phase transition phenomena of blend films of poly(methyl methacrylate) (PMMA) and poly(vinyl acetate) (PVAc) have been elucidated by simultaneous measurement of the resonant frequency and resonant admittance of the QCA. The PMMA/PVAc blend cast from ethyl acetate exhibited critical changes of resonant frequency and resonant admittance at the glass transition point.

The influence of alternating current frequency on flow related admittance changes of blood: a concept for improvement of impedance cardiography

Impedance cardiography is based on admittance changes induced by volume changes of the intrathoracic blood vessels, but also by the longitudinal orientation of red blood cells induced by flow. An experiment was set up to separate these two phenomena and to study their frequency dependence. Admittance changes of flowing blood with variable haematocrit, of a saline solution and of plasma were measured in an in vitro set-up. Four different alternating current frequencies were used: 100 kHz, 5 MHz, 15 MHz and 20 MHz. The measured admittance appeared to be dependent on blood flow: when blood flow increased, admittance in the longitudinal direction increased. This increase was stronger for higher haematocrits, probably due to the longitudinal orientation of the blood cells. At higher frequencies, the orientation effect of the red cells became negligibly small. No frequency or flow dependent admittance change was detected when saline or plasma was used as the perfusate. It is concluded that the orientation effect can be neglected at high frequencies. Impedance cardiography in this range will give more reliable information about volume changes.

The Relationship Between Electrical Acoustic Reflex Thresholds and Behavioral Comfort Levels in Children and Adult Cochlear Implant Patients

The accuracy with which behavioral comfort levels could be predicted by the electrically elicited acoustic reflex threshold (EART) was examined in 35 Nucleus Cochlear Implant patients (16 adults and 19 children). EARTs were obtained by stimulating bipolar pairs of electrodes through the Nucleus Diagnostic Programming System and monitoring the change in middle ear admittance in the ear contralateral to the implanted ear. EARTs were successfully elicited in 24 patients. EARTs differed from behavioral comfort levels by a mean of 19.4 stimulus level units for adults and 9.6 stimulus level units for children. While EARTs were found to be acceptably close to behavioral comfort levels in four adults and eight children, EARTs significantly overestimated or underestimated comfort levels in the rest. The results of this study suggested that while the EART does not accurately predict comfort levels in all cases, it may provide valuable information regarding levels which should not be exceeded when programming the cochlear implant. Cautious use of information available from the EART may prove useful for programming the cochlear implant in children or adults who are unable to make reliable psychophysical judgments.

Influenza hemagglutinin-mediated fusion pores connecting cells to planar membranes: flickering to final expansion.

We have studied the fusion between voltage-clamped planar lipid bilayers and influenza virus infected MDCK cells, adhered to one side of the bilayer, using measurements of electrical admittance and fluorescence. The changes in currents in-phase and 90 degrees out-of-phase with respect to the applied sinusoidal voltage were used to monitor the addition of the cell membrane capacitance to that of the lipid bilayer through a fusion pore connecting the two membranes. When ethidium bromide was included in the solution of the cell-free side of the bilayer, increases in cell fluorescence accompanied tee admittance changes, independently confirming that these changes were due to formation of a fusion pore. Fusion required acidic pH on the cell-containing side and depended on temperature. For fusion to occur, the influenza hemagglutinin (HA) had to be cleaved into HA1 and HA2 subunits. The incorporation of gangliosides into the planar bilayers greatly augmented fusion. Fusion pores developed in four distinct stages after acidification: (a) a pre-pore, electrically quiescent stage; (b) a flickering stage, with 1-2 nS pores opening and closing repetitively; (c) an irreversibly opened stage, in which pore conductances varied between 2 and 100 nS and exhibited diverse kinetics; (d) a fully opened stage, initiated by an instantaneous, time-resolution limited, increase in conductance leveling at approximately 500 nS. The expansion of pores by stages has also been shown to occur during exocytosis in mast cells and fusion of HA-expressing cells and erythrocytes. We conclude that essential features of fusion pores are produced with proteins in just one of the two fusing membranes.

Rate integration in click‐evoked acoustic reflex thresholds

Effects of click repetition rates on acoustic reflex thresholds were investigated in 11 female subjects (total 22 ears) within the age‐range of 20 to 26 years. Acoustic reflexes were elicited in response to ipsilateral condensation clicks of 100‐μs duration at repetition rates of 50, 100, 150, 200, 250, and 300/s. The probe tone frequency was 226 Hz and the intensity was 85 dB SPL. Acoustic reflex thresholds were defined at the lowest intensity at which a minimum of 0.02‐ml change in admittance was evident on at least two of three trials. The thresholds became significantly better with increase in the repetition rates. The average threshold advantage for the 300/s‐click rate over the 50/s rate was 22.5 dB and that of the 100/s rate over the 50/s rate was 12.5 dB. Although such advantage with increase in stimulus repetition rates has been most commonly referred to as temporal integration, a more appropriate term for this phenomenon may be rate integration. Since the firing rates of auditory neurons are known to increase with increase in stimulus intensity, it is conceivable that stimuli presented at higher repetition rates are perceived as being louder. [Work supported by Bloomsburg University Grants for Research and Creative Projects and State System of Higher Education Minority Faculty Development Fund, Pennsylvania.]

Broadband measurement method using the admittance change between two standards: interpretations of measurements and applications

A new approach to the open-circuit method in broadband measurement is described. The special case of a transition from coaxial to circular waveguide, applied in heterogeneous dielectric solid material characterization by time domain spectroscopy (TDS), is discussed. This method is absolute in the sense that it does not require a relative reference in solid material measurements for system calibration. Some applications are given to verify the validation and the limits of the approach to this problem.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ca 2+-sensitive monolayer electrodes

A Ca 2+ sensor based on the admittance change of synthetic membranes supported on derivatized silicon electrodes is reported. The ion-sensitive membranes consist of mixed monolayers of phospholipid and the Ca 2+-ligand ETH 1001. The electrodes are characterized electrochemically and their sensor performances are described. Through ion complexation by the neutral ligand, electrical charges are incorporated in the low-dielectric-constant environment of the sensitive layer. The number of charged complexes and thus the membrane admittance depend on the ion content of the electrolyte. The membrane response to Ca 2+ and the competitive binding of other cations are studied. A non-competitive process is observed if several ionophores, each one specific for a different ion, are incorporated in the membrane. Mixed layers with tetradecyl-18-crown-6 and ETH 1001 show both K + and Ca 2+ sensitivity. These electrodes allow direct comparison with a previously reported K + sensor based on tetradecyl-18-crown-6.

Voltage modulation of a gated ion channel admittance in platinum-supported lipid bilayers

Platinum-supported phospholipid bilayers containing voltage-dependent anion channels (VDAC) were used to model physically a chemically sensitive amperometric biosensor which would use gated transmembrane channel proteins. An a.c. electrical technique was used to measure admittance changes caused by channel gating. The magnitude of the responses differed from those observed in bilayer lipid membranes (BLM). However, the bilayers were mechanically stable, and permitted reproducible gating of the VDAC conductance in response to d.c. bias voltages in the range of 0 to −60 mV. The technique may be generally suitable for fabrication of durable biosensors using chemically sensitive protein channels.