| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Department of Medicine, University of California, San Diego, La Jolla, California 92093-0931
 |
ABSTRACT |
|---|
 TOP
 ABSTRACT
 INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
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.
convective ventilatory inhomogeneity; posture; single-breath washout; supine
| |
INTRODUCTION |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
VENTILATORY INHOMOGENEITY in the human lung is a function of two main factors: convection-dependent inhomogeneity (CDI) and diffusion-convection-dependent inhomogeneity (19, 25). Whereas diffusion-convection-dependent inhomogeneity occurs mainly between intra-acinar lung regions, CDI occurs between regions of the lung too widely separated for significant diffusion to take place between them. Nonuniformity of airflow to these regions results in CDI. Gravity and functional variability of characteristics between lung units contribute to CDI (14, 21).
In single-breath nitrogen washout (SBW) experiments, a postural change from upright to supine has generally been shown to increase phase III slope (7, 8, 14, 21). Because such a postural change is expected to primarily affect large-scale ventilation patterns, the change in phase III slope is likely the result of a change in CDI. Two conditions are required in order for CDI to contribute to phase III slope in SBW experiments. First, there must be inhomogeneity of specific ventilation, resulting in different gas concentrations in different regions of the lung after the nitrogen-free vital capacity inspiration. Second, there must be flow sequencing, a process whereby not all lung units empty simultaneously and the relative contribution of different lung units to the total expirate changes as the expiration proceeds. Thus a change in phase III slope induced by an change in CDI must be the result of a change in the range of specific ventilation, a change in sequencing, or both (3, 6, 13, 21).
Data from multiple-breath nitrogen washout experiments, in which the range of specific ventilation was determined, indicate that this range only changes modestly in response to a change in posture (20). Aside from a change in the range of specific ventilation, a change in flow sequencing is the only other contributor to an increase in phase III slope from CDI effects. Thus an increase in phase III slope is likely to be at least partly the result of an increase in sequencing.
Phase IV results from loss of the contribution of airways affected by airway closure to the expired breath; the airways still communicating with the environment after closing volume is reached tend to be in the nondependent (upper) areas and less well ventilated, resulting in a sudden increase in nitrogen concentration. A widening range of specific ventilation throughout the lung would be reflected in an increase in phase IV height, whereas a change in sequencing would be expected to have a less-pronounced effect (2, 12). Influences of upright-to-supine posture change on phase IV height have produced variable and inconsistent results between studies (7, 8, 14, 21); each of these studies, however, demonstrated a strong effect of upright-to-supine posture change on phase III slope.
Aerosol bolus tests (ABTs) offer an opportunity to examine inhomogeneity in pulmonary ventilation by measuring mode shift, dispersion, and deposition. Experiments with particles of various sizes have indicated that 0.5-µm-diameter particles are appropriate tracers for convective gas transport in the lungs, because they are large enough to be minimally affected by diffusion and small enough to minimize sedimentation (22). Mode shift refers to the change in position of the peak concentration of an expired bolus relative to its inspired penetration volume (Vp) and thus indicates the peripheral or central shift of the bolus. Deposition is the percentage of inspired particles that remain in the lung at the end of expiration; deposition of particles peripherally results in a mouthward (negative) mode shift (5). Dispersion is the degree of spread of the expired vs. inspired bolus and allows a measurement that is specific for convective inhomogeneity, since aerosol particles are too large to demonstrate significant diffusion.
Possible causes of mode shift apart from peripheral deposition include changes in specific ventilation and/or sequencing. Indeed, mode shift has been noted to move mouthward under conditions where an increase in inhomogeneity is expected. Patients with cystic fibrosis (1, 4) and emphysema (16) demonstrated a greater mouthward mode shift of an expired aerosol bolus than did normal subjects. This effect was exaggerated at high Vp. In another ABT experiment, mode shift moved mouthward in a dose-dependent fashion after bronchoconstriction induced by methacholine in normal subjects (15). However, because each of these four studies also found aerosol deposition in the lung to be significantly greater under the more inhomogeneous conditions, it was not possible to determine whether the change in mode shift was due to increased peripheral deposition vs. an increase in specific ventilation range and/or sequencing.
We hypothesized that an increase in flow sequencing, rather than deposition, might have contributed to the mode shift changes observed in previous studies. To test this hypothesis, we performed SBW experiments and ABTs in normal subjects in whom we elicited a modest change in CDI, at least partly because of a change in sequencing, by changing posture from upright to supine.
| |
METHODS |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
Subjects
Nine healthy, nonsmoking, nonasthmatic subjects (Table 1) performed SBW experiments and ABTs after they gave informed consent to a protocol reviewed and approved by the Institutional Review Board of the University of California, San Diego. Subjects were tested in upright and supine postures to elicit small gravitational changes in CDI. Subjects were supine for ~5 min before the start of testing in that posture.
|
Single-Breath Washout Tests
Equipment. The SBW test apparatus has been described previously in detail (14). The relevant features comprised a bag-in-box system containing a bag filled with the nitrogen-free inspired gas mixture connected to a mouthpiece-valve system with a 60-ml dead space. The inspiratory valve allowed selection of air or test gas consisting of 93.75% oxygen-5% helium-1.25% sulfur hexafluoride. For the purposes of these experiments, the helium and sulfur hexafluoride data are not reported.
Flow of ambient air to and from the bag-in-box was measured in a long straight duct with use of a linearized pneumotachograph connected to a pressure transducer. The flow data were integrated during repeated strokes of a 3-liter syringe for calibration, which was performed before each measurement session. Calibrated flows were corrected to BTPS. Gas was sampled at the mouthpiece by a respiratory mass spectrometer. Gas data were corrected by a time shift equal to the delay to the midpoint of the response of the spectrometer, which was measured at each session. Calibration was verified at each session by sampling premixed test gases.Performance of the SBW test. The subject breathed air on the mouthpiece and then exhaled to residual volume (RV) while the inspiratory path was switched to allow inspiration of the test gas. On reaching RV, the subject inhaled the test gas at 0.5 l/s to total lung capacity (TLC). A bar display of flow allowed the subject to comply accurately. The subject then immediately exhaled at 0.5 l/s back to RV. Six tests were performed in the upright posture and six tests were performed in the supine posture for each subject.
Data recording. Data were logged at 100 Hz with the use of a 12-bit analog-to-digital converter. A general-purpose data-handling program was used to perform the scaling and corrections previously described. A dedicated software package was then used to analyze the SBW test as follows.
The inspiratory and expiratory vital capacities were defined by searching for volume maxima and minima, with graphic display of the results for operator validation. Tests in which inspired and expired vital capacities differed by >5% were discarded. Expired nitrogen plots as a function of volume were then displayed. Phase III was defined iteratively by the operator using a cursor (14). Phase III slope (%N2/l) was taken to be the slope of the final line fitted to phase III. This straight line was fitted using an iterative process between a point early in expiration after clearance of the dead space and the point at which nitrogen concentration rose and remained above the fitted line. This was taken as the beginning of phase IV (14). The maximal height of phase IV (%N2) was measured relative to extrapolated phase III slope (Fig. 1).
|
Aerosol Bolus Tests
Equipment. ABT data were collected by using the equipment described in detail in previous studies (9, 10). The system allowed injection of an aerosol bolus of ~70 ml at a given point in the inhaled air by switching computer-controlled pneumatic valves. Measurement of the aerosol concentration and the flow rate were provided by a photometer and a pneumotachograph, respectively. The pneumotachograph was calibrated by integration of the flow from strokes of a 3-liter calibration syringe. Measurement of the flow rate was not affected by the presence of particles in the breathing air. The photometer, pneumotachograph, and valves were heated to body temperature to prevent water condensation. A diffusion dryer was located between the photometer and the mouthpiece.
Aerosol generation. The bolus tube was filled with aerosol containing spherical monodisperse polystyrene latex particles with a specified size of 0.497 ± 0.0094 (SD) µm. For convenience, these are referred to as 0.5-µm-diameter particles. The particles were supplied in suspension (water), and the concentrate was diluted and dispensed via two Acorn II nebulizers. Before entering the bolus tube, the aerosol flowed through a heated hose and a diffusion dryer to remove water droplets.
Performance of the ABT. After a few normal breaths, the subject exhaled to RV to ensure a known lung volume starting point. The test breath consisted of an inspiration from RV to a predetermined lung volume (fixed for each subject) approximately equal to 1 liter above their upright functional residual capacity (FRC), at a flow rate of ~0.45 l/s, immediately followed by an expiration to RV, also at a flow rate of ~0.45 l/s. A bar display of flow allowed the subject to comply accurately. During the inspiration, an aerosol bolus of ~70 ml was introduced at different Vp. The Vp was defined as the volume of air inhaled from the mode of the aerosol bolus to the end of the inhalation. Vp levels of 150, 500, 800, and 1,200 ml were used for testing. The protocol was repeated four times for each Vp in upright and supine postures.
Data recording. A personal computer equipped with a 12-bit analog-to-digital card was used for data acquisition. Signals from the photometer and the pneumotachograph were sampled at 100 Hz. For the data acquisition, we used the custom software described in previous studies (9, 10).
Data analysis. Graphs representing the bolus concentration profile as a function of volume were generated, and the measurements and calculations described below were made using custom software. In all calculations, the volumes at which the bolus concentration was equal to 5% of the peak concentration for that bolus curve were used as the end point of integration to minimize the contribution of background noise to the overall result (24).
Mode shift (Mex
Vp) was measured as the
difference between the amount of volume expired by the subject before
the peak of expired bolus concentration (Mex) and the
inspired Vp (taken to be the amount of volume inspired
after the peak bolus concentration). A negative mode shift denoted that
the mode of the expired bolus shifted mouthward relative to the
location of the bolus in the inspired air. Deposition was measured by
integrating concentration over volume as the percentage of the number
of particles that exited the lung (Nex) relative
to the number that entered the lung (Nin)
measured as follows: 100 × (Nin Nex)/Nin. Dispersion was
measured as the change in half-width of the expired
(Hex) vs. inspired (Hin)
bolus: (H
H
|
Statistics
Statistical analysis of the SBW and ABT data was accomplished using the two-tailed paired Student's t-test (Excel 5.0), with P < 0.05 as the level of significance. Experiments for the same experimental conditions with the same subjects were averaged before statistical analysis.| |
RESULTS |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
Single-Breath Washout Tests
Phase III slope was 1.22 ± 0.11 and 1.62 ± 0.21% N2/l (mean ± SE) in the upright and supine posture, respectively, representing a significant increase of 33 ± 11% (P < 0.05; Fig. 3A). Phase III slope ranged from 0.63 to 1.72% N2/l in the upright posture and from 0.86 to 3.08% N2/l in the supine position. Eight of the nine subjects had a steeper phase III slope in the supine than in the upright position.
|
Phase IV height was 3.24 ± 0.69 and 4.07 ± 0.69% N2 (mean ± SE) in the upright and supine posture, respectively, a significant increase of 25 ± 11% (P < 0.05; Fig. 3B). Phase IV height ranged from 1.57 to 6.93% N2 in the upright posture and from 2.16 to 6.90% N2 in the supine position. Seven of the nine subjects had a greater phase IV height in the supine than in the upright position.
Aerosol Bolus Test
Mode shift moved significantly mouthward (became more negative) in the supine posture at all Vp tested, except 500 ml (P < 0.05 at 150, 800, and 1,200 ml and P = 0.19 at 500 ml). Deeper Vp yielded larger mouthward mode shifts in upright and supine positions. For a Vp of 150 ml, mean mode shift was +8.4 ml upright (range13.1 to +20.7 ml) and 3.2 ml supine (range 30.9 to +18.6 ml; Fig.
4A). For a Vp of
1,200 ml, mean mode shift was 46.2 ml (range 101.2 to +11.6 ml)
upright and 84.7 ml (range 201.6 to +1.0 ml) supine (Fig.
4B). At Vp of 150 and 1,200 ml, all but one
subject had a larger mouthward mode shift when supine than when
upright.
|
Deposition was not different between the two postures. As expected,
deeper Vp corresponded with greater deposition rates. For
Vp of 150 ml, mean deposition was 9.1% upright (range
0.1-16.7%) and 10.7% supine (range 0.1-18.7%). For
Vp of 1,200 ml, mean deposition was 49.8% upright (range
33.5-67.9%) and 49.7% supine (range 32.8-74.5%; Fig.
5A).
|
Dispersion, like deposition, was not significantly affected by posture change. Deeper Vp was associated with greater values of dispersion. For Vp of 150 ml, mean dispersion was 199 ml upright (range 151-255 ml) and 213 ml supine (range 147-246 ml). For Vp of 1,200 ml, mean dispersion was 582 ml upright (range 285-811 ml) and 643 ml supine (range 538-873 ml; Fig. 5B).
Relationship Between Single-Breath Washout and Aerosol Bolus Tests
We analyzed the relationship between our SBW and mode shift results. When the change in phase III slope was plotted against the change in mode shift between postures, a positive correlation was present only with deeper Vp. Vp of 150, 500, 800, and 1,200 ml produced correlation coefficients of 0.02, 0.13, 0.59, and 0.52, respectively. Figure 6 shows the correlation for Vp of 800 and 1,200 ml.
|
Comparison of the change in phase IV height vs. the change in mode shift between postures resulted only in very weakly positive correlation coefficients (r2 < 0.24) at all Vp.
| |
DISCUSSION |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
Single-Breath Washout Tests
Phase III slope was significantly steeper in the supine than in the upright position, which is consistent with previous results (7, 8, 14, 21) (Fig. 3A). This indicates that the lung has more ventilatory inhomogeneity in the supine than in the upright position. Although diffusive inhomogeneity is an important factor in phase III slope generally, it is unlikely to contribute to the phase III slope response to postural change because postural change principally affects interaction between large-scale lung units (14, 25). Studies that used helium and sulfur hexafluoride have shown no change in acinar level inhomogeneity between upright and supine postures (20).The CDI component of phase III slope results in part from relatively empty dependent (lower) alveoli filling with nitrogen-free gas to a greater extent and earlier than nondependent (upper) alveoli. The dependent alveoli also tend to empty their nitrogen-poor contents first, and as expiration progresses the (upper) alveoli containing more nitrogen eventually empty as well (17). The result is a positive contribution to the slope of phase III. Nongravitational contributions to phase III slope also exist, such as differences in mechanical properties between lung regions (18); these are thought to be similar between postures (20). Thus the increase in phase III slope in the supine compared with the upright position results primarily from an increase in specific ventilation range, an increase in sequencing, or both (3, 6, 21).
Phase IV height increased significantly in the supine compared with the upright posture, although this result only just reached the level of significance. Previous studies have shown considerable variability in the effect of postural change on phase IV height: from no effect (7) to an effect opposite to that seen in our experiment (14). Phase IV height represents large lung units reaching closing volume in an inhomogeneous fashion. In contrast to phase III slope, which is affected by changes in sequencing and/or changes in specific ventilation range in response to a change in CDI, phase IV height is not thought to be greatly affected by changes in sequencing but, rather, by changes in specific ventilation range (2, 12). The barely significant increase in phase IV height we observed suggests that a change in specific ventilation range may have occurred between postures; however, a prior study that analyzed the range of specific ventilation carefully using multiple-breath washout experiments indicated that a posture change from upright to supine influences specific ventilation only modestly (20). This previous study provides an indication that the change in specific ventilation distribution is likely not prominent enough to cause phase III slope to increase to the degree we observed, thereby implicating another contributor to phase III slope, namely, flow sequencing. Thus it is likely that the increase in phase III slope with the change from an upright to a supine position is at least partly due to an increase in flow sequencing in the supine posture, which is in agreement with previous studies (20).
Aerosol Bolus Tests
In the ABTs, deposition and dispersion were unaffected by posture change between supine and upright (Fig. 5). In sharp contrast, mode shift became clearly more mouthward (negative) when supine relative to upright (Fig. 4). Possible causes of such a mode shift change include an increase in sequencing, a change in specific ventilation distribution, and peripheral deposition.Flow Sequencing
A change in flow sequencing induced by the change in posture is a likely cause of the increased supine vs. upright phase III slope observed in the SBW tests. In the ABTs, such a change in sequencing could be manifest as a mouthward mode shift without necessarily increasing dispersion of the bolus. This is because sequencing does not necessarily imply a change in the relative filling of different regions of the lung but, rather, a reordering of the emptying sequence of those regions. Furthermore, previous studies have suggested that convective inhomogeneity is not a major mechanism of dispersion in the normal lung at the volume at which these ABTs were performed (4, 11).One factor thought to influence sequencing is the hypothesis that the most dependent parts of the lung are relatively deflated at end expiration because of the overlying weight of the rest of the lung; they have more capacity to inflate than the nondependent alveoli, which are already relatively inflated. Thus the dependent regions tend to inflate earlier in inspiration; the overlying weight also imparts greater intra-alveolar pressures in dependent areas and preferentially deflates them before nondependent alveoli (17). This phenomenon (first in-first out) would cause the most pronounced mouthward mode shift of a bolus inserted early in inspiration (i.e., to deep Vp), whereas a bolus inserted late in inspiration (i.e., to shallow Vp) would be expected to have less mouthward mode shift. This hypothesis is consistent with our observations that deeper Vp yielded more mouthward mode shifts.
Distribution of Specific Ventilation
If the distribution of specific ventilation were substantially affected by the postural change of our experiment, we would expect to see a change in the dispersion of an inhaled bolus, because the lung units receiving particles of the bolus become less uniformly ventilated as inhomogeneity increases. As some units become more ventilated and others less, alterations in the transit time to and from any given lung unit cause an overall increase in spread of the expired bolus. In fact, in the supine posture, no increase in bolus dispersion occurred relative to the upright posture. Furthermore, a previous study has shown that specific ventilation only changes modestly with posture change (20). The lung volumes probed in that experiment were between FRC and FRC + 700 ml, a range comparable to the volumes probed by our ABTs, between FRC 200 ml and FRC + 1 liter.
Peripheral Deposition
Findings of previous studies have also demonstrated a mouthward mode shift in situations of increasing convective inhomogeneity (1, 4, 15, 16). However, each of these studies demonstrated a concomitant increase in deposition that could potentially account for the mode shift change. Our data, however, demonstrate equal deposition fractions between upright and supine postures (49.8 and 49.7%, respectively, at the deepest Vp) in these normal subjects. Thus we cannot account for the observed change in mode shift as a change in deposition between postures.Relationship Between Single-Breath Washout and Aerosol Bolus Tests
To evaluate the extent of correlation between the observed changes in phase III slope and mode shift, we correlated the changes in both in response to the change in posture. There was a positive correlation coefficient at deeper Vp but not at shallow Vp. The positive correlation is an indication that a common process is partially responsible for changing phase III slope and mode shift between postures. We further theorize that this progression to a positive correlation at deeper Vp is a result of sequencing becoming a more prominent factor as the aerosol bolus reaches the more peripheral lung regions.Our finding that the change in phase IV height between postures did not correlate well with the change in mode shift suggests that SBW and ABTs are likely not measuring the same processes. This is probable, since phase IV height is known to be primarily a reflection of change in the distribution of specific ventilation (2, 12).
Potential Sources of Error
An important consideration when the results of the two types of experiment are compared is the fact that they were each performed at their standard lung volumes, which are not equal to each other: vital capacity for SBW and near tidal volume for ABT. The experiment was designed to compare tests done in a standard fashion. Performing the two types of experiments at comparable lung volumes may be a useful extension of these studies.Potential sources of systematic error were sought unsuccessfully to explain the mode shift discrepancy between postures. The fact that other measured parameters such as dispersion and deposition were very similar between postures suggests further that the mode shift change we observed was from a postural change in the lung's ventilation pattern, rather than from error.
In conclusion, the significant change in mode shift with a change in posture from upright to supine indicates that placement in the supine posture does result in a change in distribution of pulmonary ventilation that is detectable at intermediate lung volumes by aerosol probing. It is also likely that mode shift is more sensitive than dispersion as an indicator of convective inhomogeneity resulting from flow sequencing.
| |
ACKNOWLEDGEMENTS |
|---|
This work was supported by National Aeronautics and Space Administration Grant NAGW 4372 and Contract NAS9-98124. C. Darquenne was a Parker B. Francis Fellow in Pulmonary Research during this work.
| |
FOOTNOTES |
|---|
Address for reprint requests and other correspondence: G. K. Prisk, Dept. of Medicine, 0931, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0931 (E-mail: kprisk{at}ucsd.edu).
The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
10.1152/japplphysiol.00655.2001
Received 26 June 2001; accepted in final form 4 November 2001.
| |
REFERENCES |
|---|
|
TOP
ABSTRACT
INTRODUCTION
METHODS
RESULTS
DISCUSSION
REFERENCES
|
|---|
1.
Anderson, PJ,
Blanchard JD,
Brain JD,
Feldman HA,
McNamara JJ,
and
Heyder J.
Effect of cystic fibrosis on inhaled aerosol boluses.
Am Rev Respir Dis
140:
1317-1324,
1989[Web of Science][Medline].
2.
Anthonisen, NR,
Peress LJ,
Siegler DIM,
and
Dhingra S.
Lung volume, volume history, and the distribution of inhaled boluses.
Respir Physiol
33:
279-288,
1978[Web of Science][Medline].
3.
Anthonisen, NR,
Robertson PC,
and
Ross WRD
Gravity-dependent sequential emptying of lung regions.
J Appl Physiol
28:
589-595,
1970
4.
Brown, JS,
Gerrity TR,
and
Bennett WD.
Effect of ventilation distribution on aerosol bolus dispersion and recovery.
J Appl Physiol
85:
2112-2117,
1998
5.
Brown, JS,
Gerrity TR,
Bennett WD,
Kim CS,
and
House DE.
Dispersion of aerosol boluses in the human lung: dependence on lung volume, bolus volume, and gender.
J Appl Physiol
79:
1787-1795,
1995
6.
Buist, AS,
and
Ross BB.
Quantitative analysis of the alveolar plateau in the diagnosis of early airway obstruction.
Am Rev Respir Dis
108:
1078-1087,
1973[Web of Science][Medline].
7.
Clarke, SW,
Jones JG,
and
Glaister DH.
Change in pulmonary ventilation in different postures.
Clin Sci
37:
357-369,
1969[Medline].
8.
Cortese, DA,
Rodarte JR,
Rehder K,
and
Hyatt RE.
Effect of posture on the single-breath oxygen test in normal subjects.
J Appl Physiol
41:
474-479,
1976
9.
Darquenne, C,
West JB,
and
Prisk GK.
Deposition and dispersion of 1-µm aerosol boluses in the human lung: effect of micro- and hypergravity.
J Appl Physiol
85:
1252-1259,
1998
10.
Darquenne, C,
West JB,
and
Prisk GK.
Dispersion of 0.5- to 2-µm aerosol in µG and hypergravity as a probe of convective inhomogeneity in the lung.
J Appl Physiol
86:
1402-1409,
1999
11.
Dutrieue, B,
Lauzon AM,
Verbanck S,
Elliott AR,
West JB,
Paiva M,
and
Prisk GK.
Helium and sulfur hexafluoride bolus washin in short-term microgravity.
J Appl Physiol
86:
1594-1602,
1999
12.
Engel, LA,
Landau L,
Taussig L,
Martin RR,
and
Sybrecht G.
Influence of bronchomotor tone on regional ventilation distribution at residual volume.
J Appl Physiol
40:
411-416,
1976
13.
Engel, LA,
and
Macklem PT.
Gas mixing and distribution in the lung.
In: International Review of Physiology. Respiratory Physiology II, , edited by Widdicombe JG.. Baltimore, MD: University Park, 1977, vol. 14.
14.
Guy, HJB,
Prisk GK,
Elliott AR,
Deutschman RA,
and
West JB.
Inhomogeneity of pulmonary ventilation during sustained microgravity as determined by single-breath washouts.
J Appl Physiol
76:
1719-1729,
1994
15.
Hardy, KG,
Gann LP,
Tennal KB,
Walls R,
Hiller FC,
and
Anderson PJ.
Sensitivity of aerosol bolus behavior to methacholine-induced bronchoconstriction.
Chest
114:
404-410,
1998
16.
Kohlhaufl, M,
Brand P,
Meyer T,
Scheuch G,
Weber N,
Haussinger K,
Schultz H,
and
Heyder J.
Detection of impaired intrapulmonary convective mixing by aerosol bolus dispersion in patients with emphysema.
Eur J Med Res
2:
121-128,
1997[Medline].
17.
Milic-Emili, J,
Henderson JAM,
Dolovich MB,
Trop D,
and
Kaneko K.
Regional distribution of inspired gas in the lung.
J Appl Physiol
21:
749-759,
1966
18.
Olson, LE,
and
Rodarte JR.
Regional differences in expansion in excised dog lung lobes.
J Appl Physiol
57:
1710-1714,
1984
19.
Paiva, M,
and
Engel LE.
Theoretical studies of gas mixing and ventilation distribution in the lung.
Physiol Rev
67:
750-796,
1987
20.
Prisk, GK,
Guy HJB,
Elliott AR,
Paiva M,
and
West JB.
Ventilatory inhomogeneity determined from multiple-breath washouts during sustained microgravity on Spacelab SLS-1.
J Appl Physiol
78:
597-607,
1995
21.
Prisk, GK,
Lauzon AM,
Verbanck S,
Elliott AR,
Guy HJB,
Paiva M,
and
West JB.
Anomalous behavior of helium and sulfur hexafluoride during single-breath tests in sustained microgravity.
J Appl Physiol
80:
1126-1132,
1996
22.
Schultz, H,
Schultz A,
and
Heyder J.
Influence of intrinsic particle properties on the assessment of convective gas transport by aerosol bolus technique.
Exp Lung Res
22:
393-407,
1996[Web of Science][Medline].
23.
Sybrecht, G,
Landau L,
Murphy BG,
Engel LA,
Martin RR,
and
Macklem PT.
Influence of posture on flow dependence of distribution of inhaled 133Xe boli.
J Appl Physiol
41:
489-496,
1976
24.
Verbanck, S,
Darquenne C,
Prisk GK,
Vincken W,
and
Paiva M.
A source of experimental underestimation of aerosol bolus deposition.
J Appl Physiol
86:
1067-1074,
1999
25.
Verbanck, S,
Linnarsson D,
Prisk GK,
and
Paiva M.
Specific ventilation distribution in microgravity.
J Appl Physiol
80:
1458-1465,
1996
This article has been cited by other articles:
|
|
 |
|
  S. Montmerle, P. Sundblad, and D. Linnarsson Residual heterogeneity of intra- and interregional pulmonary perfusion in short-term microgravity J Appl Physiol, June 1, 2005; 98(6): 2268 - 2277. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. M. Olfert and G. K. Prisk Effect of 60{degrees} head-down tilt on peripheral gas mixing in the human lung J Appl Physiol, September 1, 2004; 97(3): 827 - 834. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Visit Other APS Journals Online |
, Average value
upright; 
, average value supine. A: mean
phase III slope increased significantly, by 33%, between upright
(1.22 ± 0.11% N2/l) and supine (1.62 ± 0.21%
N2/l) postures (P < 0.05). B:
mean phase IV height increased by 25% between upright (3.24 ± 0.69% N2) and supine (4.05 ± 0.69% N2)
postures. *P < 0.05.
