Closing volume detection by single breath gas washout and forced oscillation technique

Closing volume (CV) is commonly measured by single-breath nitrogen washout (CVSBW). A method based on the forced oscillation technique was recently introduced to detect a surrogate CV (CVFOT). As the two approaches are based on different physiological mechanisms, we aim to investigate CVFOT and CVSBW relationship at different degrees and patterns of airway obstruction. A mathematical model was developed to evaluate the CVSBW and CVFOT sensitivity to different patterns of airway obstruction, either located in a specific lung region or equally distributed throughout the lung. The two CVs were also assessed during slow vital capacity (VC) maneuvers in triplicate in 13 healthy subjects and pre and post-methacholine challenge (Mch) in 12 mild-moderate asthmatics. Model simulations suggest that CVSBW is more sensitive than CVFOT to the presence of few flow-limited or closed airways that modify the contribution of tracer-poor and tracer-rich lung regions to the overall exhaled gas. Conversely, CVFOT occurs only when at least ~65% of lung units are flow-limited or closed, regardless of their regional distribution. CVSBW did not differ between healthy subjects and asthmatics (17±9%VC vs 22±10%VC) while CVFOT did (16±5%VC vs 23±6%VC, p<0.01). In asthmatics, both CVSBW and CVFOT increased post-Mch (33±7%VC p<0.001 and 43±12%VC p<0.001, respectively). CVSBW weakly correlated with CVFOT (r=0.45, p<0.01). The closing capacities (CV+residual volume) were correlated (r=0.74, p<0.001) but the changes with Mch in both CVs and closing capacities did not correlate. CVFOT is easy to measure and provides a reproducible parameter useful for describing airway impairment in obstructive respiratory diseases.

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Inflection point on transpulmonary pressure-volume curves and closing volume

Journal of Applied Physiology ◽

10.1152/jappl.1975.38.2.228 ◽

1975 ◽

Vol 38 (2) ◽

pp. 228-235 ◽

Cited By ~ 23

Author(s):

M. Demedts ◽

J. Clement ◽

D. C. Stanescu ◽

K. P. van de Woestijne

Keyword(s):

Inflection Point ◽

Vital Capacity ◽

Transpulmonary Pressure ◽

Bronchial Obstruction ◽

Closing Volume ◽

Lung Volumes ◽

Nitrogen Washout ◽

Single Breath ◽

Space Effect ◽

Washout Curves

In 20 healthy subjects and 18 patients with bronchial obstruction, closing volume (CV) on single-breath nitrogen washout curves and inflection point (IP) on transpulmonary pressure-volume curves were recorded simultaneously during slow expiratory vital capacity maneuvers. IP and CV did not occur at identical lung volumes, IP being systematically larger than CV for small CV values. This discrepancy could not be attributed to an esophageal or mediastinal artifact. It is suggested that, though CV and IP both express “airway closure,” their sensitivity to closure may differ: CV underestimates closure because of a dead space effect; the latter may vary individually. On the other hand, IP may not reflect the true beginning of closure, particularly when it occurs at higher lung volumes.

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Tracheal dead space influences regional ventilation measurement in dogs

Journal of Applied Physiology ◽

10.1152/jappl.1990.68.2.792 ◽

1990 ◽

Vol 68 (2) ◽

pp. 792-795

Author(s):

L. Delaunois ◽

R. Boileau ◽

R. R. Martin

Keyword(s):

Dead Space ◽

Vital Capacity ◽

Bolus Injection ◽

Regional Distribution ◽

Closing Volume ◽

Regional Ventilation ◽

Single Breath ◽

A Value ◽

Simultaneous Measurements ◽

The Difference

The lung volume at which airway closure begins during expiration (closing volume, CV) can be measured 1) with a radioactive bolus inspired at residual volume (RV) and 2) with the single-breath N2 elimination test. In previous studies in dogs, we observed that N2 CV was systematically larger than 133Xe bolus CV (Xe CV) [N2 CV %vital capacity (VC) = 35 +/- 2.3 (SE) vs. Xe CV %VC = 24 +/- 2.2, P less than 0.01]. Because the regional RV in the dog is evenly distributed throughout the lung and all airways closed at RV, N2 CV is related to the regional distribution of the tracheal N2; differences between N2 and Xe CV could then be related to the size of the inhaled dead space. Simultaneous measurements of Xe and N2 CV were performed at various sites of Xe bolus injection while the regional distribution of the bolus was measured. Injections at the level of the carina increased Xe CV to a value (30 +/- 1.4%VC) near simultaneous N2 CV (32 +/- 1.5%VC) and increased the unevenness of regional distribution of the Xe bolus. The difference between N2 and Xe CV is then the result of the size of the inspired tracheal dead space. Moreover, comparisons between different values of Xe CV require injections of the boluses at the same distance from the carina.

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Regional gas distributions and single-breath washout curves in head-down position

Journal of Applied Physiology ◽

10.1152/jappl.1983.54.2.361 ◽

1983 ◽

Vol 54 (2) ◽

pp. 361-365 ◽

Cited By ~ 5

Author(s):

M. Demedts ◽

I. Clarysse ◽

M. Verhamme ◽

M. Marcq ◽

M. De Roo

Keyword(s):

Blood Volume ◽

Healthy Subjects ◽

Vital Capacity ◽

Regional Distribution ◽

Mirror Image ◽

Residual Volume ◽

Air Trapping ◽

Pulmonary Blood Volume ◽

Single Breath ◽

Washout Curves

Regional distributions of inspired 133Xe and single-breath washout curves were compared in six young healthy subjects for the upright and the head-down positions. The regional distributions of volumes (at 0, 25, 50, and 75% vital capacity, VC) and of 133Xe boluses inhaled at residual volume (RV) were inverted in the head-down position, thus behaving as if they were determined by gravity acting via the weight of the lung rather than by thoracicoabdominal shape adaptations. Nevertheless no mirror image was obtained. The vertical differences in regional distribution of the 133Xe RV bolus and of the volumes at 25% VC were increased in the head-down position, whereas the vertical difference in volumes at RV was decreased, indicating enhanced air trapping and sequential ventilation at low volumes. This was attributed to the effect of the increased pulmonary blood volume in the head-down posture. Accordingly the size of phase IV on the washout curves with the SF6-bolus as well as with the N2-resident gas method was increased in the head-down position.

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Mode shift of an inhaled aerosol bolus is correlated with flow sequencing in the human lung

Journal of Applied Physiology ◽

10.1152/japplphysiol.00655.2001 ◽

2002 ◽

Vol 92 (3) ◽

pp. 1232-1238 ◽

Cited By ~ 5

Author(s):

Christopher N. Mills ◽

Chantal Darquenne ◽

G. Kim Prisk

Keyword(s):

Vital Capacity ◽

Normal Subjects ◽

Phase Iii ◽

Mode Shift ◽

Nitrogen Washout ◽

Single Breath ◽

Posture Change ◽

Supine Posture ◽

Residual Capacity ◽

Phase Iii Slope

We studied the effects on aerosol bolus inhalations of small changes in convective inhomogeneity induced by posture change from upright to supine in nine normal subjects. Vital capacity single-breath nitrogen washout tests were used to determine ventilatory inhomogeneity change between postures. Relative to upright, supine phase III slope was increased 33 ± 11% (mean ± SE, P < 0.05) and phase IV height increased 25 ± 11% ( P < 0.05), consistent with an increase in convective inhomogeneity likely due to increases in flow sequencing. Subjects also performed 0.5-μm-particle bolus inhalations to penetration volumes (Vp) between 150 and 1,200 ml during a standardized inhalation from residual volume to 1 liter above upright functional residual capacity. Mode shift (MS) in supine posture was more mouthward than upright at all Vp, changing by 11.6 ml at Vp = 150 ml ( P < 0.05) and 38.4 ml at Vp = 1,200 ml ( P < 0.05). MS and phase III slope changes correlated positively at deeper Vp. Deposition did not change at any Vp, suggesting that deposition did not cause the MS change. We propose that the MS change results from increased sequencing in supine vs. upright posture.

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Gravitational independence of single-breath washout tests in recumbent dogs

Journal of Applied Physiology ◽

10.1152/jappl.1988.64.2.642 ◽

1988 ◽

Vol 64 (2) ◽

pp. 642-648 ◽

Cited By ~ 4

Author(s):

S. Tomioka ◽

S. Kubo ◽

H. J. Guy ◽

G. K. Prisk

Keyword(s):

Prone Position ◽

Regional Distribution ◽

Transpulmonary Pressure ◽

Phase Iii ◽

Closing Volume ◽

Body Rotation ◽

Single Breath ◽

Volume Curve ◽

Pressure Volume Curve ◽

Phase Iv

To examine the mechanisms of lung filling and emptying, Ar-bolus and N2 single-breath washout tests were conducted in 10 anesthetized dogs (prone and supine) and in three of those dogs with body rotation. Transpulmonary pressure was measured simultaneously, allowing identification of the lung volume above residual volume at which there was an inflection point in the pressure-volume curve (VIP). Although phase IV for Ar was upward, phase IV for N2 was small and variable, especially in the prone position. No significant prone to supine differences in closing capacity for Ar were seen, indicating that airway closure was generated at the same lung volumes. The maximum deflections of phase IV for Ar and N2 from extrapolated phase III slopes were smaller in the prone position, suggesting more uniform tracer gas concentrations across the lungs. VIP was smaller than the closing volume for Ar, which is consistent with the effects of well-developed collateral ventilation in dogs. Body rotation tests in three dogs did not generally cause an inversion of phase III or IV. We conclude that in recumbent dogs regional distribution of ventilation is not primarily determined by the effect of gravity, but by lung, thorax, and mediastinum interactions and/or differences in regional mechanical properties of the lungs.

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Xenon and nitrogen single-breath washout curves in patients with airway obstruction

Journal of Applied Physiology ◽

10.1152/jappl.1976.41.2.185 ◽

1976 ◽

Vol 41 (2) ◽

pp. 185-190 ◽

Cited By ~ 8

Author(s):

M. Demedts ◽

M. de Roo ◽

J. Cosemans ◽

L. Billiet ◽

K. P. van de Woestijne

Keyword(s):

Airway Obstruction ◽

Chronic Obstructive Lung Disease ◽

Chronic Obstructive ◽

Closing Volume ◽

Residual Volume ◽

Time Constants ◽

Single Breath ◽

Volume Curve ◽

Washout Curves ◽

Severe Airway Obstruction

In patients with chronic obstructive lung disease, we determined single-breath N2 and 133 Xe washout curves, and regional distributions of volumes (Vr) and of 133Xe boluses inhaled at residual volume (VIRV). Patients suffering from emphysema with minimal airway obstruction demonstrated large closing volumes and apicobasal distribution gradients, apparently because of a steep pulmonary recoil pressure-volume curve. In one subject with basal small airway disease there was no vertical gradient in regional residual volume; closing volume was increased with the 133Xe technique but almost absent with the N2 technique. Patients with moderate-to-severe airway obstruction had upward-sloping alveolar plateaus without distinct phase IV, and small apicobasal differences in Vr and VIRV. The latter resulted probably from increased regional differences in time constants counteracting the influence of gravity. Finally, patients with severe airway obstruction and basal emphysema demonstrated a rising N2 but a descending 133Xe plateau; the gradient for VIRV was normal, and reversed for Vr. This pattern was attributed to nongravitational differences in time constants causing a first in-first out distribution.

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