Positive effort dependence of maximal expiratory flow

1987 ◽  
Vol 62 (2) ◽  
pp. 718-724 ◽  
Author(s):  
J. L. Allen ◽  
R. G. Castile ◽  
J. Mead
Keyword(s):  
Chest Wall ◽  
Conformational Changes ◽  
Vital Capacity ◽  
Transpulmonary Pressure ◽  
Normal Subjects ◽  
Forced Expiration ◽  
Respiratory Inductive Plethysmography ◽  
Maximal Expiratory Flow ◽  
Expiratory Flow ◽  
Normal Males

The maximal expiratory-flow volume (MEFV) curve in normal subjects is thought to be relatively effort independent over most of the vital capacity (VC). We studied seven normal males and found positive effort dependence of maximal expiratory flow between 50 and 80% VC in five of them, as demonstrated by standard isovolume pressure-flow (IVPF) curves. We then attempted to distinguish the effects of chest wall conformational changes from possible mechanisms intrinsic to the lungs as an explanation for positive effort dependence. IVPF curves were repeated in four of the subjects who had demonstrated positive effort dependence. Transpulmonary pressure was varied by introducing varied resistances at the mouth but effort, as defined by pleural pressure, was maintained constant. By this method, chest wall conformation at a given volume would be expected to remain the same despite changing transpulmonary pressures. When these four subjects were retested in this way, no increases in flow with increasing transpulmonary pressure were found. In further studies, voluntarily altering the chest wall pattern of emptying (as defined by respiratory inductive plethysmography) did however alter maximal expiratory flows, with transpulmonary pressure maintained constant. We conclude that maximal expiratory flow can increase with effort over a larger portion of the vital capacity than is commonly recognized, and this effort dependence may be the result of changes in central airway mechanical properties that occur in relation to changes in chest wall shape during forced expiration.

Pattern and mechanism of airway response to hypocapnia in normal subjects

1979 ◽  
Vol 47 (1) ◽  
pp. 8-12 ◽  
Author(s):  
C. F. O'Cain ◽  
M. J. Hensley ◽  
E. R. McFadden ◽  
R. H. Ingram
Keyword(s):  
Vital Capacity ◽  
Normal Subjects ◽  
Oxygen Mixture ◽  
Flow Volume ◽  
Mixture Density ◽  
Lung Capacity ◽  
Airway Constriction ◽  
Maximal Expiratory Flow ◽  
Airway Response ◽  
Expiratory Flow

We examined the bronchoconstriction produced by airway hypocapnia in normal subjects. Maximal expiratory flow at 25% vital capacity on partial expiratory flow-volume (PEFV) curves fell during hypocapnia both on air and on an 80% helium- 20% oxygen mixture. Density dependence also fell, suggesting predominantly small airway constriction. The changes seen on PEFV curves were not found on maximal expiratory flow-volume curves, indicating the inhalation to total lung capacity substantially reversed the constriction. Pretreatment with a beta-sympathomimetic agent blocked the response, whereas atropine pretreatment did not, suggesting that hypocapnia affects airway smooth muscle directly, not via cholinergic efferents.

Sensitivity of forced expiration indices to induced changes in peripheral airway resistance

1981 ◽  
Vol 50 (1) ◽  
pp. 15-20 ◽  
Author(s):  
J. L. Racineux ◽  
R. Peslin ◽  
B. Hannhart
Keyword(s):  
Vital Capacity ◽  
Normal Subjects ◽  
Forced Expiration ◽  
Peripheral Airways ◽  
Maximal Expiratory Flow ◽  
Transit Times ◽  
Subject Variability ◽  
Peripheral Airway ◽  
Induced Changes ◽  
Within Subject Variability

To assess the actual sensitivity of forced expiration indices to changes in the resistance of peripheral airways, maximal expiratory flow-volume curves were obtained in 30 normal subjects breathing air and breathing an O2-Ne-SF6 gas mixture having the same density as air but a 45% larger viscosity. The measurements were made using a bag-in-box system to circumvent calibration problems, and the data were processed digitally. Besides the usual forced expiration indices, slope ratios, as described by Mead (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 44: 156-165, 1978), and transit time indices were also computed. Breathing the viscous mixture, the largest changes were seen with the slope ratio measured at 60% forced vital capacity, followed by other slope ratios, the standard deviation of transit times, and maximal flows at low lung volumes. However, when the data were compared using the t test for paired measurements, the most significant changes were found with the forced expiratory volumes at 1 and 2 s, due to their low within-subject variability. These indices may therefore by considered as the most suitable for detecting changes in individuals.

OBSTRUCTIVE DISEASE OF THE AIRWAYS IN CYSTIC FIBROSIS

PEDIATRICS ◽  
1968 ◽  
Vol 41 (3) ◽  
pp. 560-573
Author(s):  
Robert B. Mellins ◽  
O. Robert Levine ◽  
Roland H. Ingram ◽  
Alfred P. Fishman
Keyword(s):  
Cystic Fibrosis ◽  
Vital Capacity ◽  
Maximum Flow ◽  
Transpulmonary Pressure ◽  
Forced Expiration ◽  
Lung Volumes ◽  
Flow Rates ◽  
Maximum Expiratory Flow ◽  
Expiratory Flow ◽  
Expiratory Flow Rates

A study of the interrelationships of instantaneous air flow, lung volume, and transpulmonary pressure over the range of the vital capacity has demonstrated striking differences in the determinants of maximum expiratory flow in cystic fibrosis and asthma. At high lung volumes, maximum expiratory flow rates in asthma are limited by the mechanical characteristics of the lungs and airways, whereas in cystic fibrosis and in the normal they are dependent on effort. At lower lung volumes, maximum expiratory flow rates are relatively more reduced in cystic fibrosis than in asthma and pressures in excess of those required to produce maximum flow actually depress flow. Also, forced expiration is associated with a transient reversal in the slope of the single breath nitrogen curve in cystic fibrosis and not in asthma. From these studies it is concluded that: (1) airway obstruction is less uniform and involves larger airways in cystic fibrosis than in asthma, and (2) increased expiratory pressure is associated with collapse of some of the larger airways over most of the range of the vital capacity in cystic fibrosis. A major clinical implication of these studies is that the effectiveness of cough is impaired by large airway collapse in cystic fibrosis.

Determinants of maximal expiratory flow and density dependence in normal humans

1980 ◽  
Vol 49 (5) ◽  
pp. 897-904 ◽  
Author(s):  
R. G. Castile ◽  
R. E. Hyatt ◽  
J. R. Rodarte
Keyword(s):  
Density Dependence ◽  
Vital Capacity ◽  
Peripheral Resistance ◽  
Lung Mechanics ◽  
Large Variability ◽  
Maximal Expiratory Flow ◽  
Normal Humans ◽  
Expiratory Flow ◽  
Normal Males ◽  
Relationship Of

There is a large variability in maximal expiratory flow (V) and density dependence (DD) in normal humans. Lung mechanics and flow-volume curves were obtained in 40 normal males while they breathed air or helium-oxygen (80%-20%). Static lung recoil (Pst) at 50% vital capacity, total lung capacity, and pulmonary resistance each correlated (P < 0.05) with airflow at 50% vital capacity. The relationship of V and Pst was described by Pst = 1/2 p V2/A2 + RV, where p is gas density, A is the critical area at the flow-limiting site, and R is peripheral resistance. At constant Pst and R, this simplified equation predicts an inverse relation between DD and airflow, which was found at recoil pressures of 8 and 7 cmH2O (P < 0.05). If peripheral losses are small, subjects with smaller flow-limiting airways would have lower airflows but higher DD than subjects with larger airways. Our findings are consistent with concept of dysanaptic growth and suggest that the central airways play a significant role in determining V and DD in normal humans.

Volume history and effect on airway reactivity in infants and adults

2002 ◽  
Vol 93 (3) ◽  
pp. 1069-1074 ◽  
Author(s):  
A. Weist ◽  
T. Williams ◽  
J. Kisling ◽  
C. Clem ◽  
R. S. Tepper
Keyword(s):  
Vital Capacity ◽  
Healthy Adults ◽  
Airway Hyperreactivity ◽  
Airway Reactivity ◽  
Maximal Expiratory Flow ◽  
Healthy Infants ◽  
Forced Expiratory Flow ◽  
Residual Capacity ◽  
Expiratory Flow ◽  
Volume History

Volume history is an important determinant of airway responsiveness. In healthy adults undergoing airway challenge, deep inspiration (DI) provides bronchodilating and bronchoprotective effects; however, the effectiveness of DI is limited in asthmatic adults. We hypothesized that, when assessed under similar conditions, healthy infants have heightened airway reactivity compared with healthy adults and that the effectiveness of DI is limited in infants. We compared the effect of DI on reactivity by using full (DI) vs. partial (no DI) forced-expiratory maneuvers on 2 days in supine, healthy nonasthmatic infants (21) and adults (10). Reactivity was assessed by methacholine doses that decreased forced expiratory flow after exhalation of 75% forced vital capacity during a full maneuver and maximal expiratory flow at functional residual capacity during a partial maneuver by 30% from baseline. Reactivity in adults increased when DI was absent, whereas infants' reactivity was unchanged. Infants were more reactive than adults in the presence of DI; however, adult and infant reactivity was similar in its absence. Our findings indicate that healthy infants are more reactive than adults and, like asthmatic adults, do not benefit from DI; this difference may be an important characteristic of airway hyperreactivity.

Correction for nonlinearity of body flow plethysmograph

1981 ◽  
Vol 50 (3) ◽  
pp. 658-662 ◽  
Author(s):  
A. Harf ◽  
G. Atlan ◽  
H. Lorino ◽  
S. Deshayes ◽  
C. Morin ◽  
...  
Keyword(s):  
Vital Capacity ◽  
Normal Subjects ◽  
Forced Expiration ◽  
Wire Screen ◽  
Inertial Component ◽  
High Flows ◽  
Degree Equation ◽  
Drop Flow ◽  
Conventional Signal ◽  
Flow Element

A modification of conventional signal processing for the pressure-compensated flow plethysmograph is proposed to correct the nonlinearity of the flow element that appears for high flows as encountered during forced expiration. Woven screens behave as porous media with a viscous and an inertial component in the resistance; this explains the nonlinearity (23% at 15.1.s-1 with a 400-mesh wire screen area = 50 cm2). It was shown that the pressure drop-flow relationship can be described by a second-degree equation, which can be included in the computation of the thoracic signal from the box pressure. The need for such a correction is evidenced by testing the plethysmograph with a flow step input (0-15 l.s-1) equivalent both in amplitude and in frequency to the thoracic flow during a forced expiration. Such correction for nonlinearity avoids an overestimation of the thoracic forced vital capacity of up to 0.5 liter in normal subjects.

Comparison of measures of forced expiration

1977 ◽  
Vol 42 (4) ◽  
pp. 607-613 ◽  
Author(s):  
J. R. Ligas ◽  
F. P. Primiano ◽  
G. M. Saidel ◽  
C. F. Doershuk
Keyword(s):  
Obstructive Lung Disease ◽  
Vital Capacity ◽  
Mean Transit Time ◽  
Forced Expiration ◽  
Flow Volume ◽  
Minimal Set ◽  
Average Flow ◽  
Maximal Expiratory Flow ◽  
The Mean ◽  
Independent Parameters

Theoretical relationships among a number of parameters were derived for idealized timed vital capacity (TVC) and maximal expiratory flow-volume (MEFV) curves to determine a minimal set of independent parameters. Normal pediatric subjects and those with cystic fibrosis were studied to verify these relationships experimentally. The average flow over the middle half (FEF25–75%) of the forced vital capacity (FVC) and flows at various exhaled percentages of the FVC (FEF50%, FEF75%), as well as moments of the TVC and MEFV curves were computed. From the TVC moments, a mean transit time (MTT) and an index of dispersion (ID) were also calculated. The minimum information needed to detect pulmonary mechanical changes associated with obstructive lung disease requires at least two reproducible measures: one related to the mean slope (e.g., FEF25–75%/FVC or MTT) and the other to the shape (e.g;, ID) of the effort-independent portion of the MEFV curve.

Parenteral vs. inhaled atropine: density dependence of maximal expiratory flow

1982 ◽  
Vol 53 (2) ◽  
pp. 392-396 ◽  
Author(s):  
J. W. Weiss ◽  
E. R. McFadden ◽  
R. H. Ingram
Keyword(s):  
Density Dependence ◽  
Vital Capacity ◽  
Human Subjects ◽  
Atropine Sulfate ◽  
Parenteral Administration ◽  
Elastic Recoil ◽  
Maximal Expiratory Flow ◽  
Parenteral Dose ◽  
Before And After ◽  
Expiratory Flow

Using forced vital capacity maneuvers, we measured maximal expiratory flow rates (Vmax) and static elastic recoil pressures of the lung [Pst(L)] using quasi-static maneuvers in normal nonsmoking human subjects who were breathing air and after a washing of 80% helium-20% oxygen before and after both inhaled and intravenously administered atropine sulfate. By both routes there were equivalent increases in Vmaxair but different effects on density dependence (DD) of Vmax (DD = ratio of VmaxHeO2 to Vmaxair) and on Pst(L). At 30% of vital capacity, DD decreased from an average of 1.47 to 1.32 (P less than 0.01, paired t test) after inhaled drug and did not change after parenteral administration [1.44 vs. 1.48 (P greater than 0.2)]. After inhalation Pst(L) did not change, but after parenteral administration Pst(L) significantly decreased. We interpret these findings to indicate a predominantly large-airway effect with the inhalation route and a more uniform dilatation after the parenteral dose. These results contrast with beta-adrenergic dilatation following which small-airway effects predominate regardless of route of administration.

Airway area distribution from the forced expiration maneuver

2004 ◽  
Vol 97 (2) ◽  
pp. 570-578 ◽  
Author(s):  
Rodney K. Lambert ◽  
Kenneth C. Beck
Keyword(s):  
Normal Subjects ◽  
Relative Distribution ◽  
Forced Expiration ◽  
Flow Volume ◽  
Flow Data ◽  
Initial Model ◽  
Methacholine Challenge ◽  
Maximal Expiratory Flow ◽  
Area Distribution ◽  
Detailed Interpretation

The maximal expiratory flow-volume (MEFV) maneuver is a commonly used test of lung function. More detailed interpretation than is currently available might be useful to understand disease better. We propose that a previously published computational model (Lambert RK, Wilson TA, Hyatt RE, and Rodarte JR. J Appl Physiol 52: 44–56, 1982) can be used to deduce, from the MEFV curve, the serial distribution of airway areas in the larger airways. An automated procedure based on the simulated annealing technique was developed. It was tested with model-generated flow data in which airway areas were reduced one generation at a time. The procedure accurately located the constriction and predicted its size within narrow bounds when the constriction was in the six most central generations of airways. More peripheral constrictions were detected but were not precisely located, nor were their sizes accurately evaluated. Airway areas of generations upstream of the constriction were usually overestimated. The procedure was applied to spirometric data obtained from eight volunteers (4 asthmatic and 4 normal subjects) at baseline and after methacholine challenge. The predicted areas show individual differences both in absolute values, and in relative distribution of areas. This result shows that detailed information can be obtained from the MEFV curve through the use of a model. However, this initial model, which lacks airway smooth muscle, needs further refinement.

Bronchodilatation, lung recoil, and density dependence of maximal expiratory flow

1982 ◽  
Vol 52 (4) ◽  
pp. 874-878 ◽  
Author(s):  
J. W. Weiss ◽  
E. R. McFadden ◽  
R. H. Ingram
Keyword(s):  
Density Dependence ◽  
Vital Capacity ◽  
Human Subjects ◽  
Beta Agonist ◽  
Elastic Recoil ◽  
Maximal Expiratory Flow ◽  
Before And After ◽  
Normal Human ◽  
Expiratory Flow ◽  
Expiratory Flow Rates

Using normal human subjects we have measured maximal expiratory flow rates with air (Vmaxair) and after a washin of 80% He-20% O2 (VmaxHeO2) and static elastic recoil pressures of the lung [Pst(L)] both before and after administration of a beta-agonist, terbutaline. The effects of inhaled drug were compared with those of the subcutaneously administered agent, each given in doses to produce maximal bronchodilatation as assessed by increases in Vmaxair in the mid-vital capacity. Although there was a significant yet modest decrease in Pst(L) only after injection of the agent, density dependence (DD), assessed as the ratio of VmaxHeO2 to Vmaxair, increased significantly and comparably after either route of administration. A modest decrease in Pst(L), therefore, did not affect the changes in DD.

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