Biomedical subjects

Z Hantos

Publications and source records attributed to Z Hantos.

At least 37 records · Page 2Linked to original sources

PubMed1997

Airway and tissue constrictions are greater in closed than in open-chest conditions.

We measured lung impedance (ZL) before and after four doses of methacholine (Mch) infusion in five intact chest (with esophageal balloon) and six open-chest dogs from 0.2 to 8 Hz with an optimal ventilator waveform. From ZL, we estimated airway resistance (R(aw)) and inertance (Iaw) and tissue viscance (GL) and elastance (HL). Two-way analysis of variance revealed that: (1) Mch had a strong influence on all parameters (p < 0.001), but small effect on hysteresivity, nL = GL/HL; (2) closed-chest GL and HL were significantly higher and Iaw lower than their open-chest values (p < 0.002, p < 0.05 and p < 0.0001); and (3) at the highest Mch dose, the relative increase in R(aw) was six times higher in the closed-chest condition. The reduced impact of Mch on open-chest mechanics may be due to constrictions superimposed on grossly different lung configurations and/or some humoral effects initiated by the thoracotomy. We conclude that Mch doses that elicit mild constriction in open-chest condition can cause a severe constriction in intact animals.

Airway Resistance↗

PubMed1997

Methacholine-induced bronchoconstriction in rats: effects of intravenous vs. aerosol delivery.

To determine the predominant site of action of methacholine (MCh) on lung mechanics, two groups of open-chest Sprague-Dawley rats were studied. Five rats were measured during intravenous infusion of MCh (i.v. group), with doubling of concentrations from 1 to 16 micrograms.kg-1.min-1. Seven rats were measured after aerosol administration of MCh with doses doubled from 1 to 16 mg/ml (ae group). Pulmonary input impedance (ZL) between 0.5 and 21 Hz was determined by using a wave-tube technique. A model containing airway resistance (Raw) and inertance (Iaw) and parenchymal damping (G) and elastance (H) was fitted to the ZL spectra. In the iv group, MCh induced dose-dependent increases in Raw [peak response 270 +/- 9 (SE) % of the control level; P < 0.05] and in G (340 +/- 150%; P < 0.05), with no increase in Iaw (30 +/- 59%) or H (111 +/- 9%). In the ae group, the dose-dependent increases in Raw (191 +/- 14%; P < 0.05) and G (385 +/- 35%; P < 0.05) were associated with a significant increase in H (202 +/- 8%; P < 0.05). Measurements with different resident gases [air vs. neon-oxygen mixture, as suggested (K.R. Lutchen, Z. Hantos, F. Peták, A. Adamicza, and B. Suki J. Appl. Physiol. 80: 1841-1849, 1996)] in the control and constricted states in another group of rats suggested that the entire increase seen in G during the i.v. challenge was due to ventilation inhomogeneity, whereas the ae challenge might also have involved real tissue contractions via selective stimulation of the muscarinic receptors.

Administration, Inhalation↗

PubMed1997

Mechanical impedance of the lung periphery.

The mechanics of the regional airways and tissues was studied in isolated dog lobes by means of a modified wave-tube technique. Small-amplitude pseudorandom forced oscillations between 0.1 and 48 Hz were applied through catheters wedged in 2-mm-diameter bronchi in three regions of each lobe at translobar pressures (PL) of 10, 7, 5, 3, 2, and 1 cmH2O. The measured regional input impedances were fitted by a model containing the resistance (R1) and inertance (I) of the regular (segmental) airways, the resistance of the collateral channels (R2), and the damping (G) and elastance (H) of the local tissues. This model gave far better fits to the data on impedance of the lung periphery than when G and H were replaced by a single tissue compliance, which explains why interruption of segmental flow did not lead to monoexponential pressure decay in previous studies. The interlobar and intralobar variances of the parameters were equally significant, and poor correlations were found between the airway parameters R1 and R2 and between any airway and tissue parameter (e.g., R1 and H). R2 was on average approximately 10 times higher than R1, although the R2-to-R1 ratios and their dependencies on PL were regionally highly variable. However, for the total of 33 regions studied, the PL dependence was the same for R1 and R2, which may reflect similar morphological structures for the regular and collateral airways. The dependencies of G and H on PL showed high interregional variations; generally, however, they assumed their minima at medium PL values (approximately 5 cmH2O).

Airway Resistance↗

PubMed1997

Volume dependence of respiratory impedance in infants.

We previously studied low-frequency respiratory impedance (Zrs) data at an elevated lung volume to separate airway and tissue mechanical properties in normal infants (Am. I. Respir. Crit. Care Med. 1996; 154:161-166). The aim of the present study was to determine the volume dependence of the airway and tissue mechanics by extending Zrs measurements to lower lung volumes. Zrs spectra between 0.5 and 21 Hz were measured in supine sleeping infants (n = 8; 7 to 26 mo of age) at mean transrespiratory pressures (Ptr[mean]) of 20, 10, and 0 cm H2O, during periods of apnea induced by inflating the infants' lungs to a pressure of 20 cm H2O through a face mask. At each inflation pressure, a model containing airway resistance (Raw) and inertance (law) and tissue damping (G) and elastance (H) was fitted to Zrs data. At FRC, the values of Raw, law, G, and H were 20.6+/-4.9 (SD) cm H2O x s/L, 0.037+/-0.014 cm H2O x s2/L, 39.6+/-10.3 cm H2O/L, and 147+/-35 cm H2O/L, respectively. Increase of Ptr(mean) caused a monotonous decrease in Raw (42+/-7% of the value at FRC), while law remained constant. The tissue parameters were minimal at a Ptr(mean) of 10 cm H2O (68+/-10% and 78+/-6% in G and H, respectively) and significantly higher at both 0 and 20 cm H2O. Although Zrs measurements can be made in most infants at lung volumes as low as FRC, an inflation pressure of 20 cm H2O provides a higher success rate and is therefore a more suitable condition for general use.

Airway Resistance↗

PubMed1996

Airway inhomogeneities contribute to apparent lung tissue mechanics during constriction.

Recent studies have suggested that part of the measured increase in lung tissue resistance after bronchoconstriction is an artifact due to increased airway inhomogeneities. To resolve this issue, we measured lung impedance (ZL) in seven open-chest rats with the lungs equilibrated on room air and then on a mixture of neon and oxygen (NeOx). The rats were placed in a body box with the tracheal tube leading through the box wall. A broadband flow signal was delivered to the box. The signal contained seven oscillation frequencies in the 0.234- to 12.07-Hz range, which were combined to produce tidal ventilation. The ZL was measured before and after bronchoconstriction caused by infusion of methacholine (MCh). Partitioning of airway and tissue properties was achieved by fitting ZL with a model including airway resistance (Raw), airway inertance, tissue damping (G), and tissue elastance (H). We hypothesized that if the inhomogeneities were not significant, the apparent tissue properties would be independent of the resident gas, whereas Raw would scale as the ratio of viscosities. Indeed, during control conditions, the NeOx-to-air ratios for G and H were both 1.03 +/- 0.04. Also, there was a small increase in lung elastance (EL) between 0.234 and 4 Hz that was similar on air and NeOx. During MCh infusion, Raw and G increased markedly (45-65%), but the increase in H was relatively small ( < 13%). The NeOx-to-air Raw and H ratios remained the same. However, the NeOx-to-air G ratio increased to 1.19 +/- 0.07 (P < 0.01) and the increase in EL with frequency was now marked and dependent on the resident gas. These results provide direct evidence that for a healthy rat lung airway inhomogeneities do not significantly influence the lung resistance or EL vs. frequency data. However, during MCh-induced constriction, a large portion of the increase in tissue resistance and the altered frequency dependence of EL are virtual and a consequence of the augmented airway inhomogeneities.

Airway Resistance↗

PubMed1996

Airway closure and reopening assessed by the alveolar capsule oscillation technique.

An alveolar capsule oscillation technique was used to determine 1) the lobe pressure and volume at which airways close and reopen, 2) the effect of expiration rate on closing volume and pressure, 3) the phase in the breathing cycle at which airway closure occurs, and 4) the site of airway closure. Experiments were conducted in excised dog lobes; closure was detected by an abrupt increase in the input impedance of surfacemounted alveolar capsules. Mean transpulmonary pressure (Ptp) at closure was slightly less than zero (Ptp = -2.3 cmH2O); the corresponding mean reopening pressure was Ptp = 14 cmH2O. The expiration rate varied between 1 and 20% of total lobe capacity per second and had no consistent effect on the closing volume and pressure. When lung volume was cycled up to frequencies of 0.2 Hz, closure generally occurred on expiration rather than inspiration. These observations support the conclusion that mechanical collapse, rather than meniscus formation, is the most likely mechanism producing airway closure in normal excised dog lungs. Analysis of measured acoustic impedances and reopening pressures suggests that closure occurs in the most peripheral airways. Reopening during inspiration was often observed to consist of a series of stepwise decreases in capsule impedance, indicating a sequence of opening events.

Airway Resistance↗

PubMed1996

Measurement of low-frequency respiratory impedance in infants.

Low-frequency respiratory impedance (Zrs) data permit the separate estimation of the mechanical properties of the airways and the tissues, but they are difficult to collect in humans because of the need for apneic conditions. We exploited the apneic phase produced by invoking the Hering-Breuer reflex with end-inspiratory airway occlusion in five sedated infants aged 9 to 16 mo. A computer-controlled pump and solenoid valves were used to inflate the supine infants through a face mask to a transrespiratory pressure of 20 cm H2O and to affect the airway occlusion. A loudspeaker-in-box system was connected to the mask through a side-arm, and small-amplitude pseudorandom oscillations containing 23 frequency components between 0.5 and 20.75 Hz were applied for 6 s. Four consecutive measurements were made in each infant, and the averaged Zrs spectra were evaluated on the basis of a model containing the frequency-independent resistance (Raw) and inertance (law) of the airways, and the viscous damping (G) and elastance (H) parameters of the constant-phase compartment of the chest wall and parenchymal tissues. The measured Zrs values were consistent with the model up to 15 Hz, and the average fitting error was 0.89 +/- 0.11 (SD) cm H2O.s/L. The following parameter values were obtained: Raw = 10.0 +/- 2.1 cm H2O.s/L, law = 0.061 +/- 0.014 cm H2O.s2/L, G = 28.6 +/- 4.9 cm H2O/L, H = 141 +/- 55 cm H2O/L. The tissue hysteresivity (G/H) values were 0.218 +/- 0.061. Our results indicate that, in short apneic periods evoked by the Hering-Breuer reflex, reliable low-frequency Zrs data can be collected to partition the tissue and airway impedances in sedated infants.

Airway Resistance↗

PubMed1995

Partitioning of airway and lung tissue properties: comparison of in situ and open-chest conditions.

The purpose of this study was to investigate under physiological breathing conditions whether airway and lung tissue properties are different in situ and in open-chest conditions. We measured lung input impedance in dogs from 0.2 to 8 Hz with an optimal ventilator waveform at four tidal volumes (VT; from 75 to 450 ml) in intact animals using an esophageal balloon as well as after opening the chest. The lung impedance from both conditions was partitioned into airway and tissue compartments as characterized by airway resistance and inertance (Iaw) and tissue damping (G) and elastance (H) parameters respectively. All parameters except Iaw depended to some extent on VT. The in situ tissue G and H slightly decreased with VT while in the open-chest condition; G decreased and H increased slightly with VT. We found small but significant differences between the mechanical properties of the airway and lung tissues in situ and in open-chest conditions. Over the total population, the G, airway resistance, and Iaw parameters were 13% (not significant), 35% (P < 0.001), and 31% (P < 0.001) smaller, respectively, in situ than in the open-chest condition. However, the H was 15% larger in situ (P < 0.001). Although we cannot completely rule out certain artifacts, these differences most likely reflect real alterations in the lung due to the different configurations and possible differences in the distribution of pleural pressures in the two conditions. The G being smaller and E being larger in situ resulted in hysteresivity (G/H) 36% smaller in situ (P < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗

PubMed1995

Differential responses of global airway, terminal airway, and tissue impedances to histamine.

The forced oscillation and alveolar capsule techniques were applied to determine the input impedance of the lungs and the airway transfer impedances between 0.2 and 20 Hz in six open-chest dogs in the control state, during intravenous infusion of histamine at seven rates between 0.25 and 16 micrograms.kg-1.min-1, and after the infusion. In each condition, the input impedances seen from the alveolar capsules, i.e., terminal airway impedance (Zaw,ter), were measured by imposing 2- to 200-Hz oscillations from the capsules (B. L. K. Davey and J. H. T. Bates. Respir. Physiol. 91:165-182, 1993). Airway resistance (Raw) and inertance and tissue damping and elastance were derived from the lung impedance data. For all dogs, histamine progressively increased Raw and the real part of airway transfer impedance (airway transfer resistance), reaching, at 16 micrograms.kg-1.min-1, 241 +/- 109 (SD) and 370 +/- 186%, respectively, of the control value but caused greater, although locally highly variable, increases (769 +/- 716% of the control value) in the real part of Zaw,ter extrapolated to zero frequency (R0). With increasing doses of histamine, the changes in R0 always preceded those in Raw and airway transfer resistance implying that bronchoconstriction developed first in the lung periphery. It is therefore concluded that the measurement of Zaw,ter offers a sensitive method for the detection of early nonuniform responses to bronchoconstrictor stimuli that are not yet reflected by the values of the overall Raw. In one-half of the cases, significant increases in tissue damping and elastance occurred before any change in R0; this suggests that the mechanisms of airway and parenchymal constrictions may be unrelated.

Airway Resistance↗

PubMed1994

Avalanches and power-law behaviour in lung inflation.

When lungs are emptied during exhalation, peripheral airways close up. For people with lung disease, they may not reopen for a significant portion of inhalation, impairing gas exchange. A knowledge of the mechanisms that govern reinflation of collapsed regions of lungs is therefore central to the development of ventilation strategies for combating respiratory problems. Here we report measurements of the terminal airway resistance, Rt, during the opening of isolated dog lungs. When inflated by a constant flow, Rt decreases in discrete jumps. We find that the probability distribution of the sizes of the jumps and of the time intervals between them exhibit power-law behaviour over two decades. We develop a model of the inflation process in which 'avalanches' of airway openings are seen--with power-law distributions of both the size of avalanches and the time intervals between them--which agree quantitatively with those seen experimentally, and are reminiscent of the power-law behaviour observed for self-organized critical systems. Thus power-law distributions, arising from avalanches associated with threshold phenomena propagating down a branching tree structure, appear to govern the recruitment of terminal airspaces.

Airway Resistance↗

PubMed1994

Airway and tissue mechanics during physiological breathing and bronchoconstriction in dogs.

In five open-chest dogs and with four to five alveolar capsules we used an optimal ventilator waveform (OVW) to follow frequency and tidal volume (VT) dependence of lung, airway, and tissue resistance (R) and elastance (E) before and during constant infusion of histamine (16 micrograms.kg-1.min-1). OVW contains sufficient flow energy between 0.234 and 4.7 Hz, avoids nonlinear harmonic interactions, and simultaneously ventilates with physiological VT. Each OVW breath permits a smooth estimate of frequency dependence of R and E for the whole lung. A constant-phase model analysis provided estimates of purely viscous resistance (Rvis), which represents the sum of airway resistance (Raw) and any purely newtonian component of tissue resistance (Rti), and parameters G and H, which govern frequency dependence of Rti and tissue elastance (Eti), respectively. Tissue structural damping (eta) is calculated as G/H. This model was applied to the whole lung and tissue impedance as estimated from each capsule. We found a small but inconsequential purely newtonian component of Rti, even during constriction. Four dogs showed a peak response at approximately 4 min in lung Rvis coupled (in time) to initial increases in G, H, eta, and airway inhomogeneities. In two of these dogs the response was severe. Tissue properties estimated from whole lung impedance (G, H, and eta) were nearly identical to values estimated from unobstructed capsules throughout infusion. By using a technique independent of alveolar capsules, our results indicate that a major if not dominant response to a constrictive agonist occurs in lung tissues, resulting in a large increase in Rti and Eti. With severe constriction, significant increases occur in Raw and airway inhomogeneities as well. Finally, separation of airway and tissue properties using input impedance estimated from the frequency-rich OVW avoids use of alveolar capsules and may prove an effective tool for partitioning airway and tissue properties in humans.

Airway Resistance↗

PubMed1993

Partitioning of pulmonary impedance: modeling vs. alveolar capsule approach.

Pulmonary input impedance (ZL), transfer tissue impedances (Ztti), and transfer airway impedances (Ztaw) were measured in open-chest dogs and isolated canine lungs by means of small-amplitude pseudorandom oscillations between 0.2 and 21.1 Hz. In the determination of Ztti and Ztaw, local alveolar pressures (PA) sensed in alveolar capsules were used. The global impedances of the airways (Zaw) and tissues (Zti) were estimated by fitting to the ZL data between 0.2 and 4.9 Hz (open-chest dogs) and between 0.2 and 5.9 Hz (isolated lungs) two models based on Hildebrandt's formulations (Bull. Math. Biophys. 31: 651-667, 1969), the parameters of which included airway resistance (Raw) and inertance (Iaw) and tissue damping (GL) and elastance (HL). The tissue parameters of Ztti (Gti and Hti) were also obtained from model fitting, whereas the Ztaw data were evaluated in terms of resistance (Rtaw) and inertance (Itaw). Excellent agreement was found between HL and Hti in both experimental groups and between GL and Gti in the isolated lungs (r > or = 0.999). The damping coefficients were also closely related in the open-chest dogs (r = 0.95), but Gti overestimated GL slightly (by 9%). Raw was underestimated by Rtaw (by 3-33%) and Iaw by Itaw (by 2-16%), depending on the model type and, in the excised lungs, the number of punctures in the capsules. In the case of the airway parameters, the systematic differences were accompanied by lower r values (0.535-0.935), which are explained primarily by the regional variations in PA.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Resistance↗

PubMed1992

Viscoelastic properties of the visceral pleura and its contribution to lung impedance.

The mechanical impedances of 10 dog lung lobes (ZL) and circular pleura samples 1.6 cm in diameter (Zpl) were measured with small-amplitude forced oscillations between 0.2 and 4.2 Hz. Two to four samples were ablated from each lobe after their in situ tension had been fixed at 5 cmH2O transpulmonary pressure with plastic rings. Lobe resistance was inversely proportional to frequency (f) and lobe elastance increased linearly with the logarithm of f by 23%/decade. The real part of Zpl (Rpl) decreased hyperbolically with f. Pleural elastance (Epl) showed only a 5%/decade increase with log f. The regional variability of Epl was large and the data allowed the lumping of Epl into only two groups. The variability of Epl was higher in the group of Epl values from the coastal surfaces than in the group of Epl values from any other surfaces (3105 +/- 2741 (SD) vs 2263 +/- 1152 cm H2O/L). The mean intraindividual variation of Epl corresponding to costal and to other surfaces was 38 +/- 25 and 32 +/- 23%, respectively. The hysteresivity index (Fredberg and Stamenovic, J. Appl. Physiol., 67: 2408-2419, 1989) of the pleura was significantly smaller than that of the lobes (0.025 vs 0.148). Extrapolation of Zpl to the entire lobe surface predicted pleural/lobar resistance and elastance ratios of 2.7 +/- 0.4 and 16.8 +/- 10.6%, respectively, at 0.2 Hz, and 0.4 +/- 0.4 and 15.5 +/- 10.6%, respectively, at 4.2 Hz. This suggests that for small deformations and medium lung volumes the pleural contribution to ZL is almost ideally elastic and only slightly frequency-dependent.

Airway Resistance↗

PubMed1992

Input impedance and peripheral inhomogeneity of dog lungs.

Tracheal pressure, central airflow, and alveolar capsule pressures in cardiac lobes were measured in open-chest dogs during 0.1- to 20-Hz pseudorandom forced oscillations applied at the airway opening. In the interval 0.1-4.15 Hz, the input impedance data were fitted by four-parameter models including frequency-independent airway resistance and inertance and tissue parts featuring a marked negative frequency dependence of resistance and a slight elevation of elastance with frequency. The models gave good fits both in the control state and during histamine infusion. At the same time, the regional transfer impedances (alveolar pressure-to-central airflow ratios) showed intralobar and interlobar variabilities of similar degrees, which increased with frequency and were exaggerated during histamine infusion. Results of simulation studies based on a lung model consisting of a central airway and a number of peripheral units with airway and tissue parameters that were given independent wide distributions were in agreement with the experimental findings and showed that even an extremely inhomogeneous lung structure can produce virtually homogeneous mechanical behavior at the input.

Airway Resistance↗

PubMed1992

A comparison of interrupter and forced oscillation measurements of respiratory resistance in the dog.

We compared the values of resistance produced by the forced oscillation technique (FOT) and the flow interruption technique (IT) when applied to six anesthetized paralyzed tracheostomized dogs. The FOT returned values of respiratory system resistance as a function of frequency [Re(f)] between 0.25 and 20 Hz. The IT returned a single value of resistance (Rinit) calculated by dividing the immediate change in tracheal pressure occurring upon interruption by the preinterruption flow. We found Rinit to coincide closely with Re(f) in the frequency range 5-20 Hz. Rinit has previously been interpreted as the high-frequency resistance of a resistance-elastance model of the respiratory system airways and tissues. It has also been shown previously, by direct measurement of alveolar pressure in dogs, that Rinit from the lungs alone is an accurate measure of airways resistance while Rinit obtained from the total respiratory system equals airways resistance plus a modest contribution from the chest wall. Re(f) at a frequency of approximately 10 Hz thus appears to be a useful quantity to measure as an index of airways resistance in the dog.

Airway Resistance↗

PubMed1992

Mechanical impedances of lungs and chest wall in the cat.

In nine anesthetized and paralyzed cats, the mechanical impedances of the total respiratory system (Zrs) and the lungs (ZL) were measured with small-volume pseudorandom forced oscillations between 0.2 and 20 Hz. ZL was measured after thoracotomy, and chest wall impedance (Zw) was calculated as Zw = Zrs-ZL. All impedances were determined by using input airflow [input impedance (Zi)] and output flow measured with a body box [transfer impedance (Zt)]. The differences between Zi and Zt were small for Zrs and negligible for ZL. At 0.2 Hz, the real and imaginary parts of ZL amounted to 33 +/- 4 and 35 +/- 3% (SD), respectively, of Zrs. Up to 8 Hz, all impedances were consistent with a model containing a frequency-independent resistance and inertance and a constant-phase tissue part (G-jH)/omega alpha, where G and H are coefficients for damping and elastance, respectively, omega is angular frequency, and alpha determines the frequency dependence of the real and imaginary parts. G/H was higher for Zw than for ZL (0.29 +/- 0.05 vs. 0.22 +/- 0.04, P less than 0.01). In four cats, the amplitude dependence of impedances was studied: between oscillation volumes of 0.8 and 3 ml, GL, HL, Gw, and Hw decreased on average by 3, 9, 26, and 29%, respectively, whereas the change in G/H was small for both ZL (7%) and Zw (-4%). The values of H were two to three times higher than the quasistatic elastances estimated with greater volume changes (greater than 20 ml).

Airway Resistance↗

PubMed1991

Nonlinearity and harmonic distortion of dog lungs measured by low-frequency forced oscillations.

The nonlinearity of lung tissues and airways was studied in six anesthetized and paralyzed open-chest dogs by means of 0.1-Hz sinusoidal volume forcing at mean transpulmonary pressures (Ptp) of 5 and 10 cmH2O. Lung resistance (RL) and elastance (EL) were determined in a 32-fold range (15-460 ml) of tidal volume (VT), both by means of spectrum analysis at the fundamental frequency and with conventional time-domain techniques. Alveolar capsules were used to separate the tissue and airway properties. A very small amplitude dependence was found: with increasing VT, the frequency-domain estimates of RL decreased by 5.3 and 14%, whereas EL decreased by 20 and 22% at Ptp = 5 and 10 cmH2O, respectively. The VT dependences of the time-domain estimates of RL were higher: 10.5 and 20% at Ptp = 5 and 10 cmH2O, respectively, whereas EL remained the same. The airway resistance increased moderately with flow amplitude and was smaller at the higher Ptp level. Analysis of the harmonic distortions of airway opening pressure and the alveolar pressures indicated that nonlinear harmonic production is moderate even at the highest VT and that VT dependence is homogeneous throughout the tissues. In three other dogs it was demonstrated that VT dependences of RL and EL were similar in situ and in isolated lungs at both Ptp levels.

Airway Resistance↗

PubMed1990

Mechanical impedance of the canine diaphragm. Part 1. Experimental system and measurements.

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 flow caused by the vibration of the membrane the incremental mechanical impedance spectrum was computed in the 0.25-5 Hz frequency range at three different levels of initial stress. The diaphragm tissue was found to be basically elastic. However, the small viscous component showed a sharp negative frequency dependence between 0.25 and 2 Hz. The quasistatic elastances of the samples were in good agreement with the elastance values derived from the impedance data. The relationship between the elastance and the initial stress was close to linear. It was concluded that the method is applicable to the study of the incremental dynamic properties of planar soft tissue samples.

Animals↗