Multiple-breath washin of helium and sulfur hexafluoride in sustained microgravity

1998 ◽  
Vol 84 (1) ◽  
pp. 244-252 ◽  
Author(s):  
G. Kim Prisk ◽  
Ann R. Elliott ◽  
Harold J. B. Guy ◽  
Sylvia Verbanck ◽  
Manuel Paiva ◽  
...  
Keyword(s):  
Sulfur Hexafluoride ◽  
Normal Gravity ◽  
Normal Subjects ◽  
Standing Position ◽  
Primary Objective ◽  
Phase Iii ◽  
Gas Concentration ◽  
Residual Capacity ◽  
Diffusive Processes ◽  
Phase Iii Slope

Prisk, G. Kim, Ann R. Elliott, Harold J. B. Guy, Sylvia Verbanck, Manuel Paiva, and John B. West. Multiple-breath washin of helium and sulfur hexafluoride in sustained microgravity. J. Appl. Physiol. 84(1): 244–252, 1998.—We performed multiple-breath washouts of N2 and simultaneous washins of He and SF6 with fixed tidal volume (∼1,250 ml) and preinspiratory lung volume (approximately the subject’s functional residual capacity in the standing position) in four normal subjects (mean age 40 yr) standing and supine in normal gravity (1 G) and during exposure to sustained microgravity (μG). The primary objective was to examine the influence of diffusive processes on the residual, nongravitational ventilatory inhomogeneity in the lung in μG. We calculated several indexes of convective ventilatory inhomogeneity from each gas species. A normal degree of ventilatory inhomogeneity was seen in the standing position at 1 G that was largely unaltered in the supine position. When we compared the standing position in 1 G with μG, there were reductions in phase III slope in all gases, consistent with a reduction in convection-dependent inhomogeneity in the lung in μG, although considerable convective inhomogeneity persisted in μG. The reductions in the indexes of convection-dependent inhomogeneity were greater for He than for SF6, suggesting that the distances between remaining nonuniformly ventilated compartments in μG were short enough for diffusion of He to be an effective mechanism to reduce gas concentration differences between them.

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

2002 ◽  
Vol 92 (3) ◽  
pp. 1232-1238 ◽  
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.

Effect of 60° head-down tilt on peripheral gas mixing in the human lung

2004 ◽  
Vol 97 (3) ◽  
pp. 827-834 ◽  
Author(s):  
I. Mark Olfert ◽  
G. Kim Prisk
Keyword(s):  
Sulfur Hexafluoride ◽  
Normal Gravity ◽  
Fluid Volume ◽  
Phase Iii ◽  
Single Breath ◽  
Multiple Breath Washout ◽  
Conductive Component ◽  
Slope Difference ◽  
Lung Periphery ◽  
Phase Iii Slope

The phase III slope of sulfur hexafluoride (SF6) in a single-breath washout (SBW) is greater than that of helium (He) under normal gravity (i.e., 1G), thus resulting in a positive SF6-He slope difference. In microgravity (μG), SF6-He slope difference is smaller because of a greater fall in the phase III slope of SF6 than He. We sought to determine whether increasing thoracic fluid volume using 60° head-down tilt (HDT) in 1G would produce a similar effect to μG on phase III slopes of SF6 and He. Single-breath vital capacity (SBW) and multiple-breath washout (MBW) tests were performed before, during, and 60 min after 1 h of HDT. Compared with baseline (SF6 1.050 ± 0.182%/l, He 0.670 ± 0.172%/l), the SBW phase III slopes for both SF6 and He tended to decrease during HDT, reaching nadir at 30 min (SF6 0.609 ± 0.211%/l, He 0.248 ± 0.138%/l; P = 0.08 and P = 0.06, respectively). In contrast to μG, the magnitude of the phase III slope decrease was similar for both SF6 and He; therefore, no change in SF6-He slope difference was observed. MBW analysis revealed a decrease in normalized phase III slopes at all time points during HDT, for both SF6 ( P < 0.01) and He ( P < 0.01). This decrease was due to changes in the acinar, and not the conductive, component of the normalized phase III slope. These findings support the notion that changes in thoracic fluid volume alter ventilation distribution in the lung periphery but also demonstrate that the effect during HDT does not wholly mimic that observed in μG.

Similar ventilation distribution in normal subjects prone and supine during tidal breathing

2002 ◽  
Vol 92 (2) ◽  
pp. 622-626 ◽  
Author(s):  
M. J. Rodríguez-Nieto ◽  
G. Peces-Barba ◽  
N. González Mangado ◽  
M. Paiva ◽  
S. Verbanck
Keyword(s):  
Normal Subjects ◽  
Phase Iii ◽  
Ventilation Distribution ◽  
Tidal Breathing ◽  
Ventilation Heterogeneity ◽  
Multiple Breath Washout ◽  
Residual Capacity ◽  
Slope Difference ◽  
The Difference ◽  
Phase Iii Slope

Multiple-breath washout (MBW) tests, with end-expiratory lung volume at functional residual capacity (FRC) and 90% O2, 5% He, and 5% SF6as an inspired gas mixture, were performed in healthy volunteers in supine and prone postures. The semilog plot of MBW N2concentrations was evaluated in terms of its curvilinearity. The MBW N2normalized slope analysis yielded indexes of acinar and conductive ventilation heterogeneity (Verbanck S, Schuermans D, Van Muylem A, Paiva M, Noppen M, and Vincken W. J App Physiol 83: 1907–1916, 1997). Also, the difference between SF6and He normalized phase III slopes was computed in the first MBW expiration. Only MBW tests with similar FRC in the prone and supine postures ( P > 0.1; n= 8) were considered. Prone and supine postures did not reveal any significant differences in curvilinearity, N2normalized slope-derived indexes of conductive or acinar ventilation heterogeneity, nor SF6-He normalized phase III slope difference in the first MBW expiration ( P > 0.1 for all). The absence of significant changes in any of the MBW indexes suggests that ventilation heterogeneity is similar in the supine and prone postures of normal subjects breathing near FRC.

scholarly journals Paradoxical helium and sulfur hexafluoride single-breath washouts in short-term vs. sustained microgravity

1997 ◽  
Vol 82 (3) ◽  
pp. 859-865 ◽  
Author(s):  
Anne-Marie Lauzon ◽  
G. Kim Prisk ◽  
Ann R. Elliott ◽  
Sylvia Verbanck ◽  
Manuel Paiva ◽  
...  
Keyword(s):  
Sulfur Hexafluoride ◽  
Normal Gravity ◽  
Phase Iii ◽  
Homogeneous Distribution ◽  
Volume Distribution ◽  
Short Term ◽  
Single Breath ◽  
Slope Difference ◽  
Phase Iii Slope ◽  
Blood Volume Distribution

Lauzon, Anne-Marie, G. Kim Prisk, Ann R. Elliott, Sylvia Verbanck, Manuel Paiva, and John B. West. Paradoxical helium and sulfur hexafluoride single-breath washouts in short-term vs. sustained microgravity. J. Appl. Physiol. 82(3): 859–865, 1997.—During single-breath washouts in normal gravity (1 G), the phase III slope of sulfur hexafluoride (SF6) is steeper than that of helium (He). Two mechanisms can account for this: 1) the higher diffusivity of He enhances its homogeneous distribution; and 2) the lower diffusivity of SF6 results in a more peripheral location of the diffusion front, where airway asymmetry is larger. These mechanisms were thought to be gravity independent. However, we showed during the Spacelab Life Sciences-2 spaceflight that in sustained microgravity (μG) the SF6-to-He slope difference is abolished. We repeated the protocol during short periods (27 s) of μG (parabolic flights). The subjects performed a vital-capacity inspiration and expiration of a gas containing 5% He-1.25% SF6-balance O2. As in sustained μG, the phase III slopes of He and SF6decreased. However, during short-term μG, the SF6-to-He slope difference increased from 0.17 ± 0.03%/l in 1 G to 0.29 ± 0.06%/l in μG, respectively. This is contrary to sustained μG, in which the SF6-to-He slope difference decreased from 0.25 ± 0.03%/l in 1 G to −0.01 ± 0.06%/l in μG. The increase in phase III slope difference in short-term μG was caused by a larger decrease of He phase III slope compared with that in sustained μG. This suggests that changes in peripheral gas mixing seen in sustained μG are mainly due to alterations in the diffusive-convective inhomogeneity of He that require >27 s of μG to occur. Changes in pulmonary blood volume distribution or cardiogenic mixing may explain the differences between the results found in short-term and sustained μG.

Effect of airway closure on ventilation distribution

1989 ◽  
Vol 66 (6) ◽  
pp. 2511-2515 ◽  
Author(s):  
A. B. Crawford ◽  
D. J. Cotton ◽  
M. Paiva ◽  
L. A. Engel
Keyword(s):  
Normal Subjects ◽  
Phase Iii ◽  
Mixing Efficiency ◽  
Breath Holding ◽  
Airway Closure ◽  
Ventilation Distribution ◽  
Residual Capacity ◽  
Lung Periphery ◽  
Phase Iii Slope ◽  
Volume Range

We examined the effect of airway closure on ventilation distribution during tidal breathing in six normal subjects. Each subject performed multiple-breath N2 washouts (MBNW) at tidal volumes of 1 liter over a range of preinspiratory lung volumes (PILV) from functional residual capacity (FRC) to just above residual volume. All subjects performed washouts at PILV below their measured closing capacity. In addition five of the subjects performed MBNW at PILV below closing capacity with end-inspiratory breath holds of 2 or 5 s. We measured the following two independent indexes of ventilation maldistribution: 1) the normalized phase III slope of the final breaths of the washout (Snf) and 2) the alveolar mixing efficiency of those breaths of the washout where 80–90% of the initial N2 had been cleared. Between a mean PILV of 0.28 liter above closing capacity and that 0.31 liter below closing capacity, mean Snf increased by 132% (P less than 0.005). Over the same volume range, mean alveolar mixing efficiency decreased by 3.3% (P less than 0.05). Breath holding at PILV below closing capacity resulted in marked and consistent decreases in Snf and increases in alveolar mixing efficiency. Whereas inhomogeneity of ventilation decreases with lung volume when all airways are patent (J. Appl. Physiol. 66: 2502–2510, 1989), airway closure increases ventilation inequality, and this is substantially reduced by short end-inspiratory breath holds. These findings suggest that the predominant determinant of ventilation distribution below closing capacity is the inhomogeneous closure of airways subtending regions in the lung periphery that are close together.

Effect of lung volume on ventilation distribution

1989 ◽  
Vol 66 (6) ◽  
pp. 2502-2510 ◽  
Author(s):  
A. B. Crawford ◽  
D. J. Cotton ◽  
M. Paiva ◽  
L. A. Engel
Keyword(s):  
Lung Volume ◽  
Normal Subjects ◽  
Phase Iii ◽  
Mixing Efficiency ◽  
Ventilation Distribution ◽  
Single Breath ◽  
Wide Range ◽  
Residual Capacity ◽  
Phase Iii Slope ◽  
Volume Range

To examine the effect of preinspiratory lung volume (PILV) on ventilation distribution, we performed multiple-breath N2 washouts (MBNW) in seven normal subjects breathing 1-liter tidal volumes over a wide range of PILV above closing capacity. We measured the following two independent indexes of ventilation distribution from the MBNW: 1) the normalized phase III slope of the final breaths of the washout (Snf) and 2) the alveolar mixing efficiency during that portion of the washout where 80–90% of the lung N2 had been cleared. Three of the subjects also performed single-breath N2 washouts (SBNW) by inspiring 1-liter breaths and expiring to residual volume at PILV = functional residual capacity (FRC), FRC + 1.0, and FRC - 0.5, respectively. From the SBNW we measured the phase III slope over the expired volume ranges of 0.75–1.0, 1.0–1.6, and 1.6–2.2 liters (S0.75, S1.0, and S1.6, respectively). Between a PILV of 0.92 +/- 0.09 (SE) liter above FRC and a PILV of 1.17 +/- 0.43 liter below FRC, Snf decreased by 61% (P less than 0.001) and alveolar mixing efficiency increased from 80 to 85% (P = 0.05). In addition, Snf and alveolar mixing efficiency were negatively correlated (r = 0.74). In contrast, over a similar volume range, S1.0 and S1.6 were greater at lower PILV. We conclude that, during tidal breathing in normal subjects, ventilation distribution becomes progressively more inhomogeneous at higher lung volumes over a range of volumes above closing capacity.(ABSTRACT TRUNCATED AT 250 WORDS)

Fast vs. slow exhalation before O2 inhalation alters subsequent phase III slope

1984 ◽  
Vol 56 (1) ◽  
pp. 52-56 ◽  
Author(s):  
T. S. Hurst ◽  
B. L. Graham ◽  
D. J. Cotton
Keyword(s):  
Total Lung Capacity ◽  
Normal Subjects ◽  
Phase Iii ◽  
Breath Holding ◽  
Small Airways ◽  
Residual Volume ◽  
Lung Capacity ◽  
Single Breath ◽  
Subsequent Phase ◽  
Phase Iii Slope

We studied 10 symptom-free lifetime non-smokers and 17 smokers all with normal pulmonary function studies. All subjects performed single-breath N2 washout tests by either exhaling slowly (“slow maneuver”) from end inspiration (EI) to residual volume (RV) or exhaling maximally (“fast maneuver”) from EI to RV. After either maneuver, subjects then slowly inhaled 100% O2 to total lung capacity (TLC) and without breath holding, exhaled slowly back to RV. In the nonsmokers seated upright phase III slope of single-breath N2 test (delta N2/l) was lower (P less than 0.01) for the fast vs. the slow maneuver, but this difference disappeared when the subjects repeated the maneuvers in the supine position. In contrast, delta N2/l was higher for the fast vs. the slow maneuver (P less than 0.01) in smokers seated upright. For the slow maneuver, delta N2/l was similar between smokers and nonsmokers but for the fast maneuvers delta N2/l was higher in smokers than nonsmokers (P less than 0.01). We suggest that the fast exhalation to RV decreases delta N2/l in normal subjects by decreasing apex-to-base differences in regional ratio of RV to TLC (RV/TLC) but increases delta N2/l in smokers, because regional RV/TLC increases distal to sites of small airways obstruction when the expiratory flow rate is increased.

Modification of pulmonary gas mixing by postural changes

1986 ◽  
Vol 61 (1) ◽  
pp. 75-80 ◽  
Author(s):  
H. A. Jones ◽  
E. E. Davies ◽  
J. M. Hughes
Keyword(s):  
Lung Volume ◽  
Sulfur Hexafluoride ◽  
Normal Subjects ◽  
Gas Mixing ◽  
Supine Posture ◽  
Dependent Change ◽  
Postural Changes ◽  
Residual Capacity ◽  
Lateral Decubitus ◽  
The Mean

Mixing for two gases of markedly different gaseous diffusivity, helium (He) (mol wt = 4) and sulfur hexafluoride (SF6) (mol wt = 146) has been studied by a rebreathing method in different postures. In nine normal subjects duplicate measurements were made in the erect (seated), supine, and lateral decubitus posture, at a constant tidal volume (700 ml) and frequency (1 Hz) starting from functional residual capacity (FRC). Additional measurements were made on four of the subjects, rebreathing seated erect at a volume similar to the relaxed FRC supine and supine at a volume similar to the relaxed FRC seated. In the supine posture the mean breath number to reach 99% equilibrium (n99), was not significantly different for the two gases, 8.9 for He and 9.8 for SF6. There was a difference (P less than 0.01) when erect; n99 (He) = 8.2 and n99 (SF6) = 10.9. The greatest He-SF6 difference (P less than 0.001) was in the lateral decubitus position n99 (He) = 10.1 and n99 (SF6) = 15.9. The mean relaxed FRC as percent of seated was 71% supine and 75% in lateral decubitus posture. Rebreathing seated at a lower volume did not abolish the He-SF6 mixing difference nor did rebreathing at a higher volume when supine induce a He-SF6 mixing difference. Thus the effect of posture on gas mixing cannot be due solely to lung volume and must represent a convective and diffusive dependent change in the distribution of ventilation per unit lung volume.

Anomalous behavior of helium and sulfur hexafluoride during single-breath tests in sustained microgravity

1996 ◽  
Vol 80 (4) ◽  
pp. 1126-1132 ◽  
Author(s):  
G. K. Prisk ◽  
A. M. Lauzon ◽  
S. Verbanck ◽  
A. R. Elliot ◽  
H. J. Guy ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Sulfur Hexafluoride ◽  
Anomalous Behavior ◽  
Phase Iii ◽  
Breath Holding ◽  
Breath Hold ◽  
Breath Tests ◽  
Single Breath ◽  
Lung Periphery ◽  
Phase Iii Slope

We performed single-breath wash-in tests for He and SF6 in four subjects exposed to 14 days of microgravity (microG) during the Spacelab flight Spacelab Life Sciences-2. Subjects inspired a vital capacity breath of 5% He-1.25% SF6-balance O2 and then exhaled to residual volume at 0.5l/s. The tests were also performed with a 10-s breath hold at the end of inspiration. Measurements were also made with the subjects standing and supine in 1 G. Phase III slope was measured after the dead-space washout and before the onset of airway closure. In all subjects in 1 G, whether standing or supine, phase III slope for SF6 was significantly steeper than that for He. However, in microG, the slopes became the same. Furthermore, after breath holding in microG, the SF6 slopes were significantly flatter than those for He. On return to 1 G, the changes were reversed, and there was no difference between preflight and postflight values. Because most of the phase III slope reflects events occurring in the acinar regions of the lung, the results suggest that microG causes conformational changes in the acini or changes in cardiogenic mixing in the lung periphery, but in either case the mechanism is unclear.

Effect of posture on the single-breath oxygen test in normal subjects

1976 ◽  
Vol 41 (4) ◽  
pp. 474-479 ◽  
Author(s):  
D. A. Cortese ◽  
J. R. Rodarte ◽  
K. Rehder ◽  
R. E. Hyatt
Keyword(s):  
Prone Position ◽  
Normal Subjects ◽  
Standing Position ◽  
Phase Iii ◽  
Linear Gradient ◽  
Considerable Similarity ◽  
Single Breath ◽  
Normal People ◽  
Lateral Decubitus ◽  
Phase Iv

The effect of posture on phase III (alveolar nitrogen plateau) and phase IV (closing capacity) of the single-breath oxygen test was examined in 10 normal people. In part 1 of the study, subjects inspired and expired in the standing, supine, prone, and right lateral decubitus positions; there was no effect of posture on phase IV but slopes of phase III were higher when subjects were in the supine and lateral positions. In part 2, subjects inspired in the standing position and expired in one of the recumbent positions. Phase IV occurred infrequently except in the prone position (6 of 10 subj); slopes of phase III in part 2 were not consistently altered by changing posture. It is difficult to explain the failure of posture to alter phase IV solely on a model requiring a linear gradient of pleural pressure. The slope of phase III appears to depend more on the emptying patterns of small regions with widely varying volume-to-ventilation ratios than on gravity-dependent sequences of emptying. Finally, the data suggest a considerable similarity between the upright and prone positions in terms of lung filling and emptying.

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