Optimal ventilation waveforms for estimating low-frequency respiratory impedance

1993 ◽  
Vol 75 (1) ◽  
pp. 478-488 ◽  
Author(s):  
K. R. Lutchen ◽  
K. Yang ◽  
D. W. Kaczka ◽  
B. Suki
Keyword(s):  
Broad Band ◽  
Viscoelastic Model ◽  
Harmonic Distortion ◽  
Low Frequency ◽  
Amplitude Dependence ◽  
Asthmatic Subject ◽  
Healthy Humans ◽  
Before And After ◽  
Airway Opening ◽  
Nonlinear Viscoelastic Model

We present a broad-band optimal ventilator waveform (OVW), the concept of which was to create a computer-driven ventilator waveform containing increased energy at specific frequencies (f). Values of f were chosen such that nonlinear harmonic distortion and intermodulation were minimized. The phases at each f were then optimized such that the resulting flow waveform delivered sufficient volume to maintain gas exchange while minimizing peak-to-peak airway opening pressure. Simulations with a linear anatomically consistent branching airway model and a nonlinear viscoelastic model showed that respiratory resistance (Rrs) and elastance (Ers) estimates at 0.1–2 Hz from the OVW are far superior to those from a standard step ventilator waveform (SVW) during healthy and obstructed conditions and that the OVW reduces the influences of harmonic interactions. Using a servo-controlled oscillator, we applied individual sine waves, an OVW containing energy at 0.15625–2.4 Hz, and an SVW to healthy humans and one symptomatic asthmatic subject before and after bronchodilation. The OVW was markedly superior to the SVW and always provided smooth estimates of Rrs and Ers. Before bronchodilation in the asthmatic subject Rrs was highly elevated and Ers was markedly increased with f; after bronchodilation the level of Rrs and the f dependence of Ers decreased. Although based on results from only one asthmatic subject, these data suggest a dominant influence of airway constriction and lung inhomogeneities during asthmatic bronchoconstriction that is alleviated by bronchodilators. These and other results indicate that the OVW approach has high potential for simultaneously probing f and amplitude dependence in the mechanical properties of clinical subjects during physiological breathing conditions and perhaps during dynamic bronchoconstriction.

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

1991 ◽  
Vol 71 (1) ◽  
pp. 69-75 ◽  
Author(s):  
B. Suki ◽  
Z. Hantos ◽  
B. Daroczy ◽  
G. Alkaysi ◽  
S. Nagy
Keyword(s):  
Time Domain ◽  
Harmonic Distortion ◽  
Low Frequency ◽  
Forced Oscillations ◽  
Amplitude Dependence ◽  
Airway Opening ◽  
The Time Domain ◽  
Isolated Lungs ◽  
Level Analysis

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.

Low-frequency respiratory mechanical impedance in the rat

1987 ◽  
Vol 63 (1) ◽  
pp. 36-43 ◽  
Author(s):  
Z. Hantos ◽  
B. Daroczy ◽  
B. Suki ◽  
S. Nagy
Keyword(s):  
Frequency Dependence ◽  
Chest Wall ◽  
Low Frequency ◽  
Mechanical Impedance ◽  
Total Resistance ◽  
Low Frequencies ◽  
Chest Wall Compliance ◽  
Before And After ◽  
Airway Opening ◽  
Wall Compliance

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) was calculated as ZW = Zrs - ZL. The pulmonary (RL) and chest wall resistances were both markedly frequency dependent: between 0.25 and 2 Hz they contributed equally to the total resistance falling from 81.4 +/- 18.3 (SD) at 0.25 Hz to 27.1 +/- 1.7 kPa.l–1 X s at 2 Hz. The pulmonary compliance (CL) decreased mildly, from 2.78 +/- 0.44 at 0.25 Hz to 2.36 +/- 0.39 ml/kPa at 2 Hz, and then increased at higher frequencies, whereas the chest wall compliance declined monotonously from 4.19 +/- 0.88 at 0.25 Hz to 1.93 +/- 0.14 ml/kPa at 10 Hz. Although the frequency dependence of ZW can be interpreted on the basis of parallel inhomogeneities alone, the sharp fall in RL together with the relatively constant CL suggests that at low frequencies significant losses are imposed by the non-Newtonian resistive properties of the lung tissue.

A nonlinear viscoelastic model of lung tissue mechanics

1991 ◽  
Vol 71 (3) ◽  
pp. 826-833 ◽  
Author(s):  
B. Suki ◽  
J. H. Bates
Keyword(s):  
Lung Tissue ◽  
Linear Models ◽  
Viscoelastic Model ◽  
Low Frequency ◽  
Simulated Data ◽  
Tissue Mechanics ◽  
Model Parameters ◽  
Volume Dependence ◽  
Nonlinear Viscoelastic ◽  
Nonlinear Viscoelastic Model

There have been a number of attempts recently to use linear models to describe the low-frequency (0–2 Hz) dependence of lung tissue resistance (Rti) and elastance (Eti). Only a few attempts, however, have been made to account for the volume dependence of these quantities, all of which require the tissues to be plastoelastic. In this paper we specifically avoid invoking plastoelasticity and develop a nonlinear viscoelastic model that is also capable of accounting for the nonlinear and frequency-dependent features of lung tissue mechanics. The model parameters were identified by fitting the model to data obtained in a previous study from dogs during sinusoidal ventilation. The model was then used to simulate pressure and flow data by use of various types of ventilation patterns similar to those that have been employed experimentally. Rti and Eti were estimated from the simulated data by use of four different estimation techniques commonly applied in respiratory mechanics studies. We found that the estimated volume dependence of Rti and Eti is sensitive to both the ventilation pattern and the estimation technique, being in error by as much as 217 and 22%, respectively.

Relationship between frequency and amplitude dependence in the lung: a nonlinear block-structured modeling approach

1995 ◽  
Vol 79 (2) ◽  
pp. 660-671 ◽  
Author(s):  
B. Suki ◽  
Q. Zhang ◽  
K. R. Lutchen
Keyword(s):  
Sine Wave ◽  
Lung Model ◽  
Amplitude Dependence ◽  
Tissue Impedance ◽  
Basic Model ◽  
Time Domain Data ◽  
Tissue Resistance ◽  
Before And After ◽  
Airway Opening ◽  
Block Structured

During lung constriction, there is an increase in both the frequency and tidal volume (VT) dependences of lung tissue resistance (Rti) and elastance (Eti). This suggests that 1) significant alterations take place in the mechanisms contributing to both the linear and nonlinear characteristics of lung tissues; and 2) the frequency and VT dependences of Rti and Eti are coupled. We examined these issues for the case of sine wave and special pseudorandom inputs by utilizing the theory of nonlinear block-structured systems. Two basic model structures were considered: the Hammerstein and the Wiener structures. The Hammerstein structure is a cascade connection of a nonlinear zero-memory (N) system and a linear dynamic process (L). This structure predicts that frequency and VT dependences of Rti and Eti are decoupled. The Wiener structure is an inverse cascade of these two blocks (i.e., L-N) in which the frequency and VT dependences of Rti and Eti are coupled. These two structures were combined with a nonlinear airway compartment and fitted to measured airway opening and alveolar capsule pressure-flow time domain data in dogs before and after histamine-induced constriction. The best lung model was a linear airway compartment combined with a Wiener structure consisting of a constant-phase linear tissue impedance in cascade with a polynomial nonlinearity, suggesting that frequency and VT dependences of Rti and Eti are indeed coupled during control and constricted conditions. Moreover, histamine caused much larger changes in the linear tissue parameters than in the nonlinear coefficients.

Changes in external ear position modify the spatial tuning of auditory units in the cat's superior colliculus

1987 ◽  
Vol 57 (3) ◽  
pp. 672-687 ◽  
Author(s):  
J. C. Middlebrooks ◽  
E. I. Knudsen
Keyword(s):  
Superior Colliculus ◽  
Broad Band ◽  
Low Frequency ◽  
Sound Field ◽  
External Ear ◽  
Recording Site ◽  
Sound Sources ◽  
Spatial Tuning ◽  
Before And After ◽  
Contralateral Ear

This study examines the influence of external ear position on the auditory spatial tuning of single units in the superior colliculus of the anesthetized cat. Unit responses to broad-band stimuli presented in a free sound field were measured with the external ears in a forward symmetrical position or with one or the other ear turned 40 degrees to the side; the ears are referred to as contra- or ipsilateral with respect to the side of the recording site. Changes in the position of either ear modified the spatial tuning of units. The region of space from which a stimulus was most effective in activating a unit is referred to as the unit's “best area”. Whenever the contralateral ear was turned to the side, best areas shifted peripherally and somewhat upward, roughly in proportion to the magnitude of the change in ear position. A turn of the ipsilateral ear to the side had more variable effects, but best areas generally shifted frontally. Best areas located between approximately 10 and 40 degrees contralateral when the ears were forward were least affected by changes in ipsilateral ear position. Changes in ear position also modified the maximum response rates of many units. Units with best areas located within approximately 20 degrees of the frontal midline when the ears were forward exhibited a pronounced decrease in responsiveness when either ear was turned. Units with more peripheral best areas tended to show no change or a slight increase in responsiveness. The influence of ear position on the directionality of the external ears was determined by mapping the cochlear microphonic response to tones or one-third-octave bands of noise before and after turning the ear. When the ears were forward, maximum interaural intensity differences (IIDs) were produced by high-frequency sound sources (greater than or equal to 20 kHz) located 20-40 degrees from the frontal midline and by lower frequency sources located further peripherally. The influence of ear position on the locations from which maximum IIDs were produced was similar to the influence of ear position on unit best areas. Changes in ipsilateral ear position had different effects on high- and low-frequency IIDs that were comparable with the effects of changes in ear position on frontally and peripherally located best areas, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of activation frequency and force on low-frequency fatigue in human skeletal muscle

1999 ◽  
Vol 86 (4) ◽  
pp. 1337-1346 ◽  
Author(s):  
Stuart A. Binder-Macleod ◽  
David W. Russ
Keyword(s):  
Healthy Subjects ◽  
Human Skeletal Muscle ◽  
Low Frequency ◽  
Variable Frequency ◽  
Activation Pattern ◽  
Constant Frequency ◽  
Mean Frequency ◽  
Before And After ◽  
Low Frequency Fatigue ◽  
Force Time

No comparison of the amount of low-frequency fatigue (LFF) produced by different activation frequencies exists, although frequencies ranging from 10 to 100 Hz have been used to induce LFF. The quadriceps femoris of 11 healthy subjects were tested in 5 separate sessions. In each session, the force-generating ability of the muscle was tested before and after fatigue and at 2, ∼13, and ∼38 min of recovery. Brief (6-pulse), constant-frequency trains of 9.1, 14.3, 33.3, and 100 Hz and a 6-pulse, variable-frequency train with a mean frequency of 14.3 Hz were delivered at 1 train/s to induce fatigue. Immediately postfatigue, there was a significant effect of fatiguing protocol frequency. Muscles exhibited greater LFF after stimulation with the 9.1-, 14.3-, and variable-frequency trains. These three trains also produced the greatest mean force-time integrals during the fatigue test. At 2, ∼13, and ∼38 min of recovery, however, the LFF produced was independent of the fatiguing protocol frequency. The findings are consistent with theories suggesting two independent mechanisms behind LFF and may help identify the optimal activation pattern when functional electrical stimulation is used.

Free volume based nonlinear viscoelastic model for polyurea over a wide range of strain rates and temperatures

2021 ◽  
Vol 152 ◽  
pp. 103650
Author(s):  
Chencheng Gong ◽  
Yan Chen ◽  
Ting Li ◽  
Zhanli Liu ◽  
Zhuo Zhuang ◽  
...  
Keyword(s):  
Free Volume ◽  
Viscoelastic Model ◽  
Strain Rates ◽  
Nonlinear Viscoelastic ◽  
Wide Range ◽  
Nonlinear Viscoelastic Model

scholarly journals The Low-Frequency Array (LOFAR): Opening a New Window on the Universe

2002 ◽  
Vol 199 ◽  
pp. 474-483
Author(s):  
Namir E. Kassim ◽  
T. Joseph W. Lazio ◽  
William C. Erickson ◽  
Patrick C. Crane ◽  
R. A. Perley ◽  
...  
Keyword(s):  
Angular Resolution ◽  
Broad Band ◽  
Low Frequency ◽  
Electromagnetic Spectrum ◽  
Interferometric Imaging ◽  
Very Large Array ◽  
Long Wavelength ◽  
Calibration Techniques ◽  
Long Baselines ◽  
The Universe

Decametric wavelength imaging has been largely neglected in the quest for higher angular resolution because ionospheric structure limited interferometric imaging to short (< 5 km) baselines. The long wavelength (LW, 2—20 m or 15—150 MHz) portion of the electromagnetic spectrum thus remains poorly explored. The NRL-NRAO 74 MHz Very Large Array has demonstrated that self-calibration techniques can remove ionospheric distortions over arbitrarily long baselines. This has inspired the Low Frequency Array (LOFAR)—-a fully electronic, broad-band (15—150 MHz)antenna array which will provide an improvement of 2—3 orders of magnitude in resolution and sensitivity over the state of the art.

Identification of Nonlinear Viscoelastic Models of Flexible Polyurethane Foam From Uniaxial Compression Data

2016 ◽  
Vol 138 (2) ◽  
Author(s):  
Yousof Azizi ◽  
Patricia Davies ◽  
Anil K. Bajaj
Keyword(s):  
Uniaxial Compression ◽  
Viscoelastic Model ◽  
Viscoelastic Behavior ◽  
Model Parameters ◽  
Viscoelastic Models ◽  
Nonlinear Viscoelastic ◽  
Compression Data ◽  
Computationally Intensive ◽  
Nonlinear Viscoelastic Model ◽  
Flexible Polyurethane

Flexible polyethylene foam is used in many engineering applications. It exhibits nonlinear and viscoelastic behavior which makes it difficult to model. To date, several models have been developed to characterize the complex behavior of foams. These attempts include the computationally intensive microstructural models to continuum models that capture the macroscale behavior of the foam materials. In this research, a nonlinear viscoelastic model, which is an extension to previously developed models, is proposed and its ability to capture foam response in uniaxial compression is investigated. It is hypothesized that total stress can be decomposed into the sum of a nonlinear elastic component, modeled by a higher-order polynomial, and a nonlinear hereditary type viscoelastic component. System identification procedures were developed to estimate the model parameters using uniaxial cyclic compression data from experiments conducted at six different rates. The estimated model parameters for individual tests were used to develop a model with parameters that are a function of strain rates. The parameter estimation technique was modified to also develop a comprehensive model which captures the uniaxial behavior of all six tests. The performance of this model was compared to that of other nonlinear viscoelastic models.

scholarly journals Correlation between Traits of Emotion-Based Impulsivity and Intrinsic Default-Mode Network Activity

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
Jizheng Zhao ◽  
Dardo Tomasi ◽  
Corinde E. Wiers ◽  
Ehsan Shokri-Kojori ◽  
Şükrü B. Demiral ◽  
...  
Keyword(s):  
Brain Activity ◽  
Low Frequency ◽  
Cingulate Cortex ◽  
Posterior Cingulate Cortex ◽  
Anterior Cingulate ◽  
Network Activity ◽  
High Risk Behaviors ◽  
Posterior Cingulate ◽  
Healthy Humans ◽  
Dorsolateral Prefrontal

Negative urgency (NU) and positive urgency (PU) are implicated in several high-risk behaviors, such as eating disorders, substance use disorders, and nonsuicidal self-injury behavior. The current study aimed to explore the possible link between trait of urgency and brain activity at rest. We assessed the amplitude of low-frequency fluctuations (ALFF) of the resting-state functional magnetic resonance imaging (fMRI) signal in 85 healthy volunteers. Trait urgency measures were related to ALFF in the lateral orbitofrontal cortex, dorsolateral prefrontal cortex, ventral and dorsal medial frontal cortex, anterior cingulate, and posterior cingulate cortex/precuneus. In addition, trait urgency measures showed significant correlations with the functional connectivity of the posterior cingulate cortex/precuneus seed with the thalamus and midbrain region. These findings suggest an association between intrinsic brain activity and impulsive behaviors in healthy humans.

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