scholarly journals Effect of expiratory flow limitation on respiratory mechanical impedance: a model study

1996 ◽  
Vol 81 (6) ◽  
pp. 2399-2406 ◽  
Author(s):  
R. Peslin ◽  
R. Farré ◽  
M. Rotger ◽  
D. Navajas
Keyword(s):  
Respiratory System ◽  
Input Impedance ◽  
Wave Speed ◽  
Mechanical Impedance ◽  
Flow Limitation ◽  
Maximal Flow ◽  
Expiratory Flow Limitation ◽  
Rubber Tubing ◽  
Model Study ◽  
Expiratory Flow

Peslin, R., R. Farré, M. Rotger, and D. Navajas.Effect of expiratory flow limitation on respiratory mechanical impedance: a model study. J. Appl. Physiol. 81(6): 2399–2406, 1996.—Large phasic variations of respiratory mechanical impedance (Zrs) have been observed during induced expiratory flow limitation (EFL) (M. Vassiliou, R. Peslin, C. Saunier, and C. Duvivier. Eur. Respir. J. 9: 779–786, 1996). To clarify the meaning of Zrs during EFL, we have measured from 5 to 30 Hz the input impedance (Zin) of mechanical analogues of the respiratory system, including flow-limiting elements (FLE) made of easily collapsible rubber tubing. The pressures upstream (Pus) and downstream (Pds) from the FLE were controlled and systematically varied. Maximal flow (V˙max) increased linearly with Pus, was close to the value predicted from wave-speed theory, and was obtained for Pus-Pds of 4–6 hPa. The real part of Zin started increasing abruptly with flow (V˙) >85%V˙max and either further increased or suddenly decreased in the vicinity of V˙max. The imaginary part of Zin decreased markedly and suddenly above 95%V˙max. Similar variations of Zin during EFL were seen with an analogue that mimicked the changes of airway transmural pressure during breathing. After pressure andV˙ measurements upstream and downstream from the FLE were combined, the latter was analyzed in terms of a serial (Zs) and a shunt (Zp) compartment. Zs was consistent with a large resistance and inertance, and Zp with a mainly elastic element having an elastance close to that of the tube walls. We conclude that Zrs data during EFL mainly reflect the properties of the FLE.

Effect of negative expiratory pressure on respiratory system flow resistance in awake snorers and nonsnorers

1999 ◽  
Vol 87 (3) ◽  
pp. 969-976 ◽  
Author(s):  
Claudio Tantucci ◽  
Alexandre Duguet ◽  
Anna Ferretti ◽  
Selma Mehiri ◽  
Isabelle Arnulf ◽  
...  
Keyword(s):  
Respiratory System ◽  
Supine Position ◽  
Flow Resistance ◽  
Upper Airway ◽  
Flow Limitation ◽  
Expiratory Flow Limitation ◽  
Upper Airways ◽  
Flow Interruption ◽  
Expiratory Flow ◽  
Spontaneously Breathing

In spontaneously breathing subjects, intrathoracic expiratory flow limitation can be detected by applying a negative expiratory pressure (NEP) at the mouth during tidal expiration. To assess whether NEP might increase upper airway resistance per se, the interrupter resistance of the respiratory system (Rint,rs) was computed with and without NEP by using the flow interruption technique in 12 awake healthy subjects, 6 nonsnorers (NS), and 6 nonapneic snorers (S). Expiratory flow (V˙) and Rint,rs were measured under control conditions with V˙ increased voluntarily and during random application of brief (0.2-s) NEP pulses from −1 to −7 cmH2O, in both the seated and supine position. In NS, Rint,rs with spontaneous increase inV˙ and with NEP was similar [3.10 ± 0.19 and 3.30 ± 0.18 cmH2O ⋅ l−1 ⋅ s at spontaneous V˙ of 1.0 ± 0.01 l/s and atV˙ of 1.1 ± 0.07 l/s with NEP (−5 cmH2O), respectively]. In S, a marked increase in Rint,rs was found at all levels of NEP ( P < 0.05). Rint,rs was 3.50 ± 0.44 and 8.97 ± 3.16 cmH2O ⋅ l−1 ⋅ s at spontaneous V˙ of 0.81 ± 0.02 l/s and atV˙ of 0.80 ± 0.17 l/s with NEP (−5 cmH2O), respectively ( P < 0.05). With NEP, Rint,rs was markedly higher in S than in NS both seated ( F = 8.77; P < 0.01) and supine ( F = 9.43; P < 0.01). In S,V˙ increased much less with NEP than in NS and was sometimes lower than without NEP, especially in the supine position. This study indicates that during wakefulness nonapneic S have more collapsible upper airways than do NS, as reflected by the marked increase in Rint,rs with NEP. The latter leads occasionally to an actual decrease in V˙ such as to invalidate the NEP method for detection of intrathoracic expiratory flow limitation.

Helium–oxygen ventilation in the presence of expiratory flow-limitation: A model study

2007 ◽  
Vol 157 (2-3) ◽  
pp. 326-334 ◽  
Author(s):  
Chiara Brighenti ◽  
Paolo Barbini ◽  
Gianni Gnudi ◽  
Gabriele Cevenini ◽  
Matteo Pecchiari ◽  
...  
Keyword(s):  
Flow Limitation ◽  
Expiratory Flow Limitation ◽  
Model Study ◽  
Expiratory Flow

Mechanisms of increased maximum expiratory flow during HeO2 breathing in dogs

1979 ◽  
Vol 47 (3) ◽  
pp. 490-502 ◽  
Author(s):  
S. Mink ◽  
M. Ziesmann ◽  
L. D. Wood
Keyword(s):  
Density Dependence ◽  
Wave Speed ◽  
Flow Limitation ◽  
Elastic Recoil ◽  
Expiratory Flow Limitation ◽  
Pressure Losses ◽  
Peripheral Airways ◽  
Catheter Technique ◽  
Maximum Expiratory Flow ◽  
Expiratory Flow

We used the retrograde-catheter technique to investigate the effect of a helium-oxygen gas mixture (HeO2) on resistance to maximum expiratory flow (Vmax) in airways subsegments between alveoli and the equal pressure point (EPP), and between EPP and the flow-limiting segment (FLS). FLS were found at the same site in main-stem bronchi on both air and HeO2 in most dogs studied. Static elastic recoil pressure (Pel = 7 +/- 1 cmH2O) and the lateral pressure at FLS (Ptm' = 11 +/- cmH2O) were not different on the two gases, and delta Vmax averaged 33 +/- 12%. EPP were located on HeO2 in segmental bronchi (7 +/- 2 mm ID), and EPP on air were always located more downstream. There was no density dependence of resistance between alveoli and EPP on HeO2, and delta Vmax was due to the marked density dependence of the pressure losses of convective acceleration in the short airway segment between EPP HeO2 and FLS. Assuming that FLS is the “choke point,” these findings are consistent with wave-speed theory of flow limitation modified to account for viscous pressure losses in peripheral airways. These results and conclusions question previous interpretations of delta Vmax as an index of peripheral airways obstruction, and demonstrate the utility of wave-speed theory in explaining complicated mechanisms of expiratory flow limitation.

Expiratory flow limitation

1983 ◽  
Vol 55 (1) ◽  
pp. 1-7 ◽  
Author(s):  
R. E. Hyatt
Keyword(s):  
Wave Speed ◽  
Signal To Noise Ratio ◽  
Major Advance ◽  
Flow Limitation ◽  
Flow Volume ◽  
Expiratory Flow Limitation ◽  
Flow Curves ◽  
Maximal Expiratory Flow ◽  
Airway Mechanics ◽  
Expiratory Flow

The first major advance in understanding expiratory flow limitation of the lungs came with the description of isovolume pressure-flow curves. These curves documented the existence of a volume-dependent limit to maximal expiratory flow and led directly to the description of the maximal expiratory flow-volume (MEFV) curve. Definitive modeling of flow limitation awaited the description of a localized mechanism that dominated the flow-limiting process. The phenomenon of wave speed limitation of flow was shown to apply to the airways and provided the needed localized mechanism. Using this concept and recent data on airway mechanics and the frictional losses in the flow, a computational model of the MEFV curve has been developed. Further progress will require modeling of inhomogeneous emptying in diseased lungs, perfecting noninvasive techniques of estimating pertinent airway characteristics, and improving techniques for increasing the signal-to-noise ratio in MEFV curves.

Modeling expiratory flow from excised tracheal tube laws

1999 ◽  
Vol 87 (5) ◽  
pp. 1973-1980 ◽  
Author(s):  
Nikolai Aljuri ◽  
Lutz Freitag ◽  
José G. Venegas
Keyword(s):  
Static Pressure ◽  
Pressure Recovery ◽  
High Frequency Ventilation ◽  
Flow Limitation ◽  
Flow Conditions ◽  
Expiratory Flow Limitation ◽  
Elastic Tubes ◽  
Viscous Losses ◽  
Forced Expiratory Flow ◽  
Expiratory Flow

Flow limitation during forced exhalation and gas trapping during high-frequency ventilation are affected by upstream viscous losses and by the relationship between transmural pressure (Ptm) and cross-sectional area ( A tr) of the airways, i.e., tube law (TL). Our objective was to test the validity of a simple lumped-parameter model of expiratory flow limitation, including the measured TL, static pressure recovery, and upstream viscous losses. To accomplish this objective, we assessed the TLs of various excised animal tracheae in controlled conditions of quasi-static (no flow) and steady forced expiratory flow. A tr was measured from digitized images of inner tracheal walls delineated by transillumination at an axial location defining the minimal area during forced expiratory flow. Tracheal TLs followed closely the exponential form proposed by Shapiro (A. H. Shapiro. J. Biomech. Eng. 99: 126–147, 1977) for elastic tubes: Ptm = K p[( A tr/ A tr0)− n − 1], where A tr0 is A tr at Ptm = 0 and K p is a parametric factor related to the stiffness of the tube wall. Using these TLs, we found that the simple model of expiratory flow limitation described well the experimental data. Independent of upstream resistance, all tracheae with an exponent n < 2 experienced flow limitation, whereas a trachea with n > 2 did not. Upstream viscous losses, as expected, reduced maximal expiratory flow. The TL measured under steady-flow conditions was stiffer than that measured under expiratory no-flow conditions, only if a significant static pressure recovery from the choke point to atmosphere was assumed in the measurement.

scholarly journals Viscoelasticity of the trachea and its effects on flow limitation

2006 ◽  
Vol 100 (2) ◽  
pp. 384-389 ◽  
Author(s):  
Nikolai Aljuri ◽  
Jose G. Venegas ◽  
Lutz Freitag
Keyword(s):  
Wave Speed ◽  
Mathematical Representation ◽  
Forced Expiration ◽  
Flow Limitation ◽  
Time Dependency ◽  
Cross Sectional ◽  
Elastic Tubes ◽  
Forced Expiratory Flow ◽  
Expiratory Flow ◽  
The Relationship

To test the hypothesis that peak expiratory flow is determined by the wave-speed-limiting mechanism, we studied the time dependency of the trachea and its effects on flow limitation. For this purpose, we assessed the relationship between transmural pressure and cross-sectional area [the tube law (TL)] of six excised human tracheae under controlled conditions of static (no flow) and forced expiratory flow. We found that TLs of isolated human tracheae followed quite well the mathematical representation proposed by Shapiro (Shapiro AH. J Biomech Eng 99: 126–147, 1977) for elastic tubes. Furthermore, we found that the TL measured at the onset of forced expiratory flow was significantly stiffer than the static TL. As a result, the stiffer TL measured at the onset of forced expiratory flow predicted theoretical maximal expiratory flows far greater than those predicted by the more compliant static TL, which in all cases studied failed to explain peak expiratory flows measured at the onset of forced expiration. We conclude that the observed viscoelasticity of the tracheal walls can account for the measured differences between maximal and “supramaximal” expiratory flows seen at the onset of forced expiration.

scholarly journals Clinical characteristics of COPD patients with tidal expiratory flow limitation

2017 ◽  
Vol Volume 12 ◽  
pp. 1503-1506 ◽  
Author(s):  
James Dean ◽  
Umme Kolsum ◽  
Paul Hitchen ◽  
Vanadana Gupta ◽  
Dave Singh
Keyword(s):  
Clinical Characteristics ◽  
Flow Limitation ◽  
Expiratory Flow Limitation ◽  
Copd Patients ◽  
Expiratory Flow

Expiratory flow limitation during exercise in prepubescent boys and girls: prevalence and implications

2010 ◽  
Vol 108 (5) ◽  
pp. 1267-1274 ◽  
Author(s):  
Katherine E. Swain ◽  
Sara K. Rosenkranz ◽  
Bethany Beckman ◽  
Craig A. Harms
Keyword(s):  
Body Composition ◽  
Oxygen Saturation ◽  
Tidal Volume ◽  
Lean Body Mass ◽  
Lung Volume ◽  
Arterial Oxygen Saturation ◽  
Arterial Oxygen ◽  
Flow Limitation ◽  
Expiratory Flow Limitation ◽  
Expiratory Flow

The purpose of this study was to compare the prevalence and implications of expiratory flow limitation (EFL) during exercise in boys and girls. Forty healthy, prepubescent boys (B; n = 20) and girls (G; n = 20) were tested. Subjects completed pulmonary function tests and an incremental cycle maximal oxygen uptake (V̇o2max) test. EFL was recorded at the end of each exercise stage using the % tidal volume overlap method. Ventilatory and metabolic data were recorded throughout exercise. Arterial oxygen saturation (SpO2) was determined via pulse oximetry. Body composition was determined using dual-energy X-ray absorptiometry. There were no differences ( P > 0.05) in height, weight, or body composition between boys and girls. At rest, boys had significantly higher lung volumes (total lung capacity, B = 2.6 ± 0.5 liters, G = 2.1 ± 0.5 liters) and peak expiratory flow rates (B = 3.6 ± 0.6 l/s; G = 1.6 ± 0.3 l/s). Boys also had significantly higher V̇o2max (B = 46.9 ± 5.9 ml·kg lean body mass−1·min−1, G = 41.7 ± 6.6 ml·kg lean body mass−1·min−1) and maximal ventilation (B = 49.8 ± 8.8 l/min, G = 41.2 ± 8.3 l/min) compared with girls. There were no sex differences ( P > 0.05) at V̇o2max in VE /Vco2, end-tidal Pco2, heart rate, respiratory exchange ratio, or SpO2. The prevalence (B = 19/20 vs. G = 18/20) and severity (B = 58 ± 7% vs. G = 43 ± 8% tidal volume) of EFL was not significantly different in boys compared with girls at V̇o2max. A significant relationship existed between % EFL at V̇o2max and the change in end-expiratory lung volume from rest to maximal exercise in boys ( r = 0.77) and girls ( r = 0.75). In summary, our data suggests that EFL is highly and equally prevalent in prepubescent boys and girls during heavy exercise, which led to an increased end-expiratory lung volume but not to decreases in arterial oxygen saturation.

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