Inspired volume dependence of the slope of the alveolar plateau

doi:10.1016/0034-5687(84)90067-7

Respiration Physiology

Volume 56, Issue 3, June 1984, Pages 309-325

Respiration Physiolo...

https://doi.org/10.1016/0034-5687(84)90067-7 Get rights and content

Abstract

Two series of experiments were performed in nine healthy subjects. In series I, 96 single breath tests were performed in two subjects. The inspired gas contained 90% O₂, 5% He and 5% SF₆ and the slope of the alveolar plateau for N₂, He and SF₆ was computed. The following experimental conditions were considered variable: inspired volume with preinspiratory lung volume equal to residual volume or functional residual capacity (FRC), both with and without 10 sec breath-holding. In series II, each of the other 7 subjects performed 12 single breath N₂ tests in which the subject inspired both 1 L and an inspiratory capacity (IC) of O₂ from FRC with and without 10 sec breath-holding. The main experimental observation is that without breath-holding the absolute value of the slope of the alveolar plateau is larger for 1 L inspiration than for an IC inspiration, whereas this volume dependence was smaller after 10 sec of breath-holding. Based on Milic-Emili model of the lung and on simulations of a multibranch point model of the acinus we concluded that, in so far as these models adequately describe gas distribution in the lung, intraregional parallel units presenting a sequential convective flow play an important role in the genesis of the alveolar plateau.

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Cited by (32)

Different patterns of exhaled nitric oxide response to β<inf>2</inf>-agonists in asthmatic patients according to the site of bronchodilation
2016, Journal of Allergy and Clinical Immunology
Citation Excerpt :
In the present study the relief of ventilation heterogeneities caused by regional clearance enhancement, as induced by the bronchodilatory action of β2-mimetics, resulted in different patterns of slope decreases. The absence of a significant decrease of both the He and SF6 slopes in the group of patients exhibiting no Feno value change after bronchodilation suggests a central obstruction relief that the FRC+1| single-breath washout test did not detect, with He and SF6 slopes essentially sensitive to peripheral changes.32,33 The decrease of the He slope with no change in the SF6 slope in the group exhibiting a Feno value increase suggests an obstruction relief up to the terminal bronchioles.
In asthmatic patients undergoing airway challenge, fraction of exhaled nitric oxide (Feno) levels decrease after bronchoconstriction. In contrast, model simulations have predicted both decreased and increased Feno levels after bronchodilation, depending on the site of airway obstruction relief.
We sought to investigate whether β₂-agonists might induce divergent effects on Feno values in asthmatic patients as a result of airway obstruction relief occurring at different lung depths.
Feno, FEV₁, and the slope of phase III of the single-breath washout test (S) of He (S_He) and sulfur hexafluoride (S_SF6) were measured in 68 asthmatic patients before and after salbutamol inhalation. S_He and S_SF6 decreases reflected preacinar and intra-acinar obstruction relief, respectively. Changes (Δ) were expressed as a percentage from the baseline.
No Feno change (|ΔFeno| ≤ 10%) was found in 16 patients (mean [SD]: 2.5% [5.2%]; ie, Feno= group); a ΔFeno value of greater than 10% was found in 23 patients (31.7% [20.3%]; ie, the Feno+ group); and a ΔFeno value of less than −10% was found in 29 patients (−31.5% [17.3%]; ie, the Feno− group). All groups had similar ΔFEV₁ values. In the Feno= group neither S_He nor S_SF6 changed, in the Feno+ group only S_He decreased significantly (−21.8% [SD 28.5%], P = .03), and in the Feno− group both S_He (−29.8% [24.0%], P < .001) and S_SF6 (−27.2% [23.3%], P < .001) decreased.
Three Feno behaviors were observed in response to β₂-agonists: a decrease likely caused by relief of an intra-acinar airway obstruction that we propose reflects amplification of nitric oxide back-diffusion, an increase likely associated with a predominant dilation up to the preacinar airways, and Feno stability when obstruction relief involved predominantly the central airways. In combination, these results suggest a new role for Feno in identifying the site of airway obstruction in asthmatic patients.
Lung function measurement with multiple-breath-helium washout system
2013, Medical Engineering and Physics
Citation Excerpt :
The washout results from individuals with lung diseases have steeper phase III slopes compared to normal subjects because of the greater inhomogeneity of their respiratory ventilation [4,7,8,10,11]. Other minor effects such as body posture or inspiration and expiration flow rates can also increase the phase III slopes [8,9]. During washout, for unevenly ventilated lungs, the alveolar gas concentration becomes unequal from unit to unit and the first breath in the washout reflects the gas flow mostly from the better-ventilated units.
Multiple-breath-washout (MBW) measurements are regarded as a sensitive technique which can reflect the ventilation inhomogeneity of respiratory airways. Typically nitrogen is used as the tracer gas and is washed out by pure oxygen in multiple-breath-nitrogen washout (MBNW) tests. In this study, instead of using nitrogen, ⁴He is used as the tracer gas with smaller gas density which may be able to reach deeper into our lungs in a given time and the helium washout results may be more sensitive to the ventilation inhomogeneity in small airways. A multiple-breath-helium-washout (MBHW) system developed for the lung function study is also presented. Quartz tuning forks with a resonance frequency of 32,768 Hz have been used for detecting the change of the respiratory gas density. The resonance frequency of the quartz tuning fork decreases linearly with increasing density of the surrounding gas. Knowing the CO₂ concentration from the infrared carbon dioxide detector, the helium concentration can be determined. Results from 14 volunteers (3 mild asthmatics, 4 tobacco smokers, 1 with asthma history, 1 with COPD history, 5 normal) have shown that mild asthmatics have higher ventilation inhomogeneity in either conducting or acinar airways (or both). A feature has been found in washout curve of single breaths from 4 tobacco smokers with different length of smoking history which may indicate the early stage of respiratory ventilation inhomogeneity in acinar airways.
Axial distribution of nitric oxide airway production in asthma patients
2013, Respiratory Physiology and Neurobiology
Citation Excerpt :
This test based on 1 l inspired from FRC was shown to better reflect distal ventilation than the standard vital capacity test (Paiva et al., 1988). A shorter inspiratory time allows for peripheral diffusion-driven heterogeneities to be preserved, while it is less influenced by larger-scale heterogeneities (Paiva et al., 1984). The gas mixture (containing 90% O2) is also routinely used to assess nitrogen dilution in other contexts.
In healthy subjects, axial distribution of nitric oxide (NO) airway production is likely heterogeneous: notably a distal peak of production in terminal bronchioles and a quasi-nil NO production in the most of the conducting airways. In asthma, few information exists about the contributions of the proximal and distal airways to NO overproduction. In 18 asthma patients, sites of constriction after methacholine and adenosine 5′-monophosphate (AMP) challenges were assessed by ventilation distribution tests with He and SF₆. The resulting decreases in fractional exhaled NO (FENO) were measured. Changes in He and SF₆ slopes indicated a pre-acinar bronchoconstriction due to AMP and a more proximal action for methacholine. FENO decreased by 38.7% and 20.2% (p < 0.001) after AMP and methacholine challenges, respectively. Significant FENO decreases after AMP and methacholine implies substantial pre-acinar but also, contrary to healthy subjects, more proximal airway production. In conclusion, nitric oxide overproduction in asthma patients appears to involve the most part of the conducting airways.
Differences in regional wash-in and wash-out time constants for xenon-CT ventilation studies
2005, Respiratory Physiology and Neurobiology
Xenon-enhanced computed tomography (Xe-CT) has been used to measure regional ventilation by determining the wash-in (WI) and wash-out (WO) rates of stable Xe. We tested the common assumption that WI and WO rates are equal by measuring WO–WI in different anatomic lung regions of six anesthetized, supine sheep scanned using multi-detector-row computed tomography (MDCT). We further investigated the effect of tidal volume, image gating (end-expiratory EE versus end-inspiratory EI), local perfusion, and inspired Xe concentration on this phenomenon. Results: WO time constant was greater than WI in all lung regions, with the greatest differences observed in dependent base regions. WO–WI time constant difference was greater during EE imaging, smaller tidal volumes, and with higher Xe concentrations. Regional perfusion did not correlate with WI–WO. We conclude that Xe-WI rate can be significantly different from the WO rate, and the data suggest that this effect may be due to a combination of anatomic and fluid mechanical factors such as Rayleigh–Taylor instabilities set up at interfaces between two gases of different densities.
Mechanisms of ventilation inhomogeneity during vital capacity breaths standing and supine
2002, Respiration Physiology
Overall inhomogeneity of ventilation distribution, as measured by single-breath vital capacity (VC) washout (SBW) is known to be greater supine vs. standing. To establish the underlying mechanisms 13 healthy males performed VC SBW of 4% SF₆ and He, standing and supine, with or without a 10 sec breathhold (BH). Overall inhomogeneity, as indicated by normalized phase III slopes, was >50% greater supine (SF₆ 13.1×10⁻³; He 10.7×10⁻³ L⁻¹) than standing (SF₆ 8.6×10⁻³; He 6.4×10⁻³ L⁻¹; P<0.001). The (SF₆–He) slope, an index of intraacinar inhomogeneity, did not change with posture. Breathholding, assumed to eliminate convective dependent inhomogeneity within and/or between small lung units, produced twice as great reduction of inhomogeneity when supine vs. standing. After BH inhomogeneity remained significantly greater supine vs. standing. In conclusion, at least two events seem to underlie the increased inhomogeneity when supine: (1) a substantially increased convection dependent non-uniformity between well-separated lung regions; and (2) a somewhat increased convection dependent non-uniformity within and/or between peripherally located lung units.
Airway cross section strongly influences alveolar plateau slope of capnograms for smaller tidal volumes
2000, Respiration Physiology
We compared the predictions of the single path convection-diffusion model (SPM) and the well-mixed single acinus model (SAM) with the normalized slopes (NS) of experimentally measured volumetric capnograms in which Vt was varied in three healthy spontaneously breathing adults. For values of Vt greater than 15 ml/kg, the tidal volume penetrates deep into the acinar airways, mixing by molecular diffusion is rapid and the predictions of the SAM and SPM both agree with the experiment. The SPM however shows much better agreement with the experimental NS data than does the SAM for values of Vt less than 10 ml/kg. The explanation for the departure of the SAM from the observed experimental data, at small Vt, is that it represents the limiting case (of well-mixed alveolar gas) for the SPM, only at large Vt, where the assumption of rapid mixing is most accurate. We conclude that in general, gas phase diffusivity and total acinar airway cross sectional area variation with cumulative volume into the lung are essential to realistically model airway gas exchange between Vt and FRC and to obtain agreement with experimental data under the widest range of breathing conditions.

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^☆: This work was supported partly by a contract with the Ministère de la Politique Scientifique (Actions Concertées), and by contract n° 7248.11.005 with the European Community for Coal and Steel (Luxembourg).

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Inspired volume dependence of the slope of the alveolar plateau☆

Abstract

Respir. Physiol.

Respir. Physiol.

Respir. Physiol.

Respir. Physiol.

Comput. Biomed. Res.

Respir. Physiol.

Comput. Biomed. Res.

Gravity-dependent sequential emptying of lung regions

J. Appl. Physiol.

Corrections for the response time and delay of mass spectrometers

J. Appl. Physiol.

Gas mixing in an asymmetrical model of the pulmonary acinus with asymmetrical alveolar ducts

J. Appl. Physiol.

Quantitative analysis of the alveolar plateau in the diagnosis of early airway obstruction

Am. Rev. Respir. Dis.

Changes in distribution of ventilation with lung growth

J. Appl. Physiol.

Reverse nitrogen gradients in the study of phase III and cardiogenic oscillations of the single-breath nitrogen test

Am. Rev. Respir. Dis.

Ventilation distribution in anatomical lung units

J. Appl. Physiol.

Gas mixing and distribution in the lung