Effect of changing airway mechanics on maximum expiratory flow

Jones, J. G.; Fraser, R; Nadel, Jay A.

doi:10.1152/jappl.1975.38.6.1012

Cited by 41 publications

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“…Several mathematical models have also been developed that predict MEF as a function of FLS compliance (3 1-33). These models have been supported by subsequent experimental observations (1,32,33).…”

Section: Justijication Of Experimental Preparation Experiments Used supporting

confidence: 67%

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Effect of Ventilation on Mechanical Properties and Pressure-Flow Relationships of Immature Airways

1988

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ABSTRACT. Ventilation of immature airways has been shown to result in pressure-induced deformation and alteration of mechanical properties. These changes in mechanical properties may alter the effect of compressive pressures on pressure-flow relationships. To test this hypothesis, unventilated (Group I, n = 8) and ventilated (group 11, n = 8; mean pressures of 8-12 cm H 2 0 for 2 h duration) tracheal segments were excised from preterm lambs approximately 118 days gestation and mounted in a Krebsfilled chamber for determination of compliances and pressure-flow relationships. Compliance data were obtained for both the inflation loop (inflation compliance) and the collapsing loop (collapsing compliance) of the pressure-volume curve for each segment. Supported by NIH Grant NHLBI HL 3203 1. 1compliance, airway compression, and resistance to airflow has been studied extensively in adult airways (l-3), to a lesser degree in newborn airways (4), and there is no research with respect to the premature airway. Prolonged mechanical ventilation has little effect on adult airways but has been shown to effect the dimensions (5-8) and mechanical properties (5, 9) of preterm and newborn airways. However, analysis of these mechanical properties in preterm and newborn airways extended only to the compliance as determined by the inflation loop of the P-V curve. This provided no insight into airway rigidity under compression. It is therefore unclear how mechanical ventilation affects the immature airway's ability to withstand compressive collapse and thereby influences pressure-flow relationships.This study was designed to evaluate the effects of ventilation on the mechanical properties and pressure-flow relationships of preterm lamb tracheae. Differences in compliances defined by both the inflation and collapsing loops of the P-V curve of ventilated and unventilated tracheal segments were examined. Resistance to airflow over a physiological range of flows and compressive pressures was also determined in both groups, and intergroup differences were associated with observed differences in compliances. This study may help to explain how ventilation influences the ability of the premature airway to withstand compressive collapse, and further aid in the understanding of flow limitation and gas-trapping observed in infants who have been mechanically ventilated. METHODSThe apparatus used in these experiments (Fig.

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Section: Justijication Of Experimental Preparation Experiments Used supporting

confidence: 67%

“…Airway compression results in increased resistance to airflow. This relationship between airway 5 1 compliance, airway compression, and resistance to airflow has been studied extensively in adult airways (l-3), to a lesser degree in newborn airways (4), and there is no research with respect to the premature airway.…”

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confidence: 99%

Effect of Ventilation on Mechanical Properties and Pressure-Flow Relationships of Immature Airways

1988

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“…We wondlered whether our studies of one lung changed AVm,1, by eliminating a length of trachea ancd reducing the airway compliance as described by Jones et al (19). To the extent that the tule in the mainstem bronchus prevented flow limitation in that airway at reduced Vmax, flow increased until transmural pressures of upstream intraparenchymal airways reached their critical transmuiral airway pressure.…”

Section: Discussionmentioning

confidence: 98%

How does HeO2 increase maximum expiratory flow in human lungs?

Mink¹,

Wood²

1980

J. Clin. Invest.

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A B S T R A C T We used the retrograde catheter techni(que to investigate the effect of HeO2 on resistance to maximum expiratory flow (Vmax) in airways stubsegments between alveoli and the equtal pressuire point (EPP), and between EPP and the flow-limiting segment (FLS). FLS were found at the same airway site in sublobar bronchi (i.d., 0.54+0.13 cm) on both air and HeO2 in the six human excised lungs studied. Static elastic recoil pressure (5±1 cm H20) and the lateral pressuire at FLS (critical transmural airway pressuire -6+3 cm H20) were not different on the two gases. AVmax averaged 37±8.9% and was similar to the valuie fouind in healthy subjects of similar age (66+10 yr). EPP were located on HeO2 in peripheral airways (i.d., 0.33±0.03 cm), and EPP on air were located more downstream. Resistance between EPP and FLS was highly density dependent. Resistance between alveoli and EPP behaved as if it were density independent, due in part to Poisecuille flow in the peripheral airways and in part to the consequent narrowing of peripheral airways on HeO2. This density-independent behavior in peripheral airways reduced AVmax on HeO2 from its predicted maximal amount of 62%. Asstuming that FLS is the "choke point" these findings are consistent with wavespeed theory of flow limitationi modified to include futnctionially density-independent pressure losses in peripheral airways. These restults and concltusions are similar to those fouind in living dogs. They question previous interpretation of /Vmax as an index of peripheral airway obstruction, and demonstrate the utility of the wave-speed theory in explaining complicated mechanisms of expiratory flow limitation.

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“…Both adult dogs (16) and rabbits (7) treated with proteolytic enzymes to soften tracheal cartilage have demonstrated significant reductions in Vmax. Inasmuch as neither lung elastic recoil nor upstream resistance was altered in these models, the reductions in Vmax can be attributed solely to alterations in central airway mechanics (7).…”

Section: Developmental Comparisonmentioning

confidence: 99%

Developmental Differences in Tracheal Cartilage Mechanics

1989

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ABSTRACT. Length-tension characteristics were exam- MATERIALS AND METHODSined in tracheal ri& excised from preterm lambs (n = 8) and adult sheep (n = 7) to determine developmental differences in the mechanical properties of tracheal cartilage. Tension was measured in both the complex (comprised of the pars membranacea and its cartilagenous insertion) and the cartilage alone (by severing the pars membranacea) as the ring was lengthened so as to increase the distance between the points of insertion. Analysis of regression lines show significantly greater slopes for both the complex and the cartilage in the adult group compared to the preterm group. These data reveal that age-related differences in tracheal cartilage mechanics parallel and may contribute to age-related differences previously determined in tracheal compliance. Tracheal segments containing one cartilaginous ring were excised from premature lambs (n = 8; 1 18-120 d gestation) from a position approximately 20 mm above the canna. Three rings from each trachea were cut from this area and the experimental values from these three segments were averaged to represent one experiment. Each segment was cut and trimmed so that the width of the PM was equal to the width of the cartilaginous ring. The external fascia was removed from the ring. The segment was then mounted into a tissue bath using two ties so that the axial smooth muscle fibers within the PM were vertically oriented ( Fig. 1). The lower tie attached at one point of insertion of the PM into the cartilage was attached rigidly to the bottom of the bath. The upper tie attached to the other point of insertion was attached via a gold chain to an isometric force transducer, and the ring remained in a fixed plane throughout the course of the Abbreviations length-tension measurements. The length of the PM was deter-PM, pars membranacea mined by measuring the distance between the points of PM ACh, acetylcholine insertion into the cartilage. The resting length was defined as CT, cartilage tension that PM length when no external forces were applied to the TPT, total passive tension tracheal ring. A 1.5-g wt was suspended from the upper tie and served to pull the cartilaginous tips more closely together and therefore reduce the length of the PM to below the resting length. The transducer was mounted to a micrometer so that the length of the PM could be varied. The mounted ring was bathed in In previous studies we have shown tracheae of preterm lambs Krebs-Ringer solution. Temperature was maintained at 37°C to be extremely compliant structures (1, 2). We have also estab-and a gaseous mixture of 95% 02/5% C 0 2 was continuously lished the stiffness of tracheal smooth muscle (contained in the bubbled through the bath to maintain a pH of 7.40 _+ 0.03. posterior wall) as an important determinant of tracheal compliAll transducers were connected to a Grass model 7 polygraph ance (3), and have noted developmental differences in tracheal (Braintree, MA), and tensions were continuously recorded smooth muscle passive tens...

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Effect of changing airway mechanics on maximum expiratory flow

Cited by 41 publications

References 0 publications

Effect of Ventilation on Mechanical Properties and Pressure-Flow Relationships of Immature Airways

Effect of Ventilation on Mechanical Properties and Pressure-Flow Relationships of Immature Airways

How does HeO2 increase maximum expiratory flow in human lungs?

Developmental Differences in Tracheal Cartilage Mechanics

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