Category - Part 9
Discriminating Measures and Normal Values for Expiratory Obstruction: Physiologic Defects in Current Smokers
Figure 2 shows marked differences in the variability of FEV1/FVC, FEV3/FVC, and FEF25-75 in never-smokers and current smokers for each fifth percentile of the respective populations when plotted against the percentage of the mean predicted values. The legend emphasizes misclassifications that would result if 80% of mean values was used as the threshold.
Figure 3 shows, for each gender of never-smokers and current smokers, the mean first spirometric fractions of forced expiratory maneuvers (ie, FEV1/ FVC) and last spirometric fractions (ie, 1 — FEV3/ FVC). Over this 60-year span for never-smokers, the average FEV1/FVC percentage decreases from 85.8 to 74.2%, while the average 1 — FEV3/FVC percentage increases from 2.2 to 12.6%. The absolute changes in FEV1/FVC and 1 — FEV3/FVC are nearly similar, whereas the relative changes are much larger for 1 — FEV3/FVC (Fig 3). There are minimal gender differences and even fewer ethnic differences. Thus, the proportion of flow occurring after the third second, while relatively small at age 20 years, increases markedly in association with older age.
Discriminating Measures and Normal Values for Expiratory Obstruction: Pattern Analysis of Current Smokers
We placed each of the currently smoking subjects into 1 of 16 (24) potential categories, depending on whether or not their FEVi, FVC, FEV/FVC, and FEV3/FVC values were below the LLN. This allowed us to decide whether each subject had normal spirometry findins, or had a pattern of obstruction, had probable restriction, or a combination, and whether or not the FEF25_75 values confirmed the diagnosis or were probably false-positive or false-negative findings.
Except where noted, values are reported as the mean ± SD and the 95th percentile as the LLN.
Several key spirometric values, with respect to ethnicity, gender, age, and height, are provided for the NHANES III never-smokers and current smokers in Table 1. The number of never-smokers (5,938) differs from that of Hankinson et al because of differences in age ranges and screening procedures. Table 2 gives the factors needed to derive the linear regression equations for FEV1/FVC and FEV3/FVC for never-smokers (eg, FEV1/FVC or FEV3/ FVC = mean constant — age constant X age). The mean absolute difference in FEV1/FVC between the formulas of Hankinson et al and our formula was only 0.28% for the 5,938 adults that we selected. This reflects the similarity between these two never-smoking series extracted from the same NHANES III database. buy-asthma-inhalers-online
Discriminating Measures and Normal Values for Expiratory Obstruction: Subjects
Utilizing data from the same NHANES III source, we did the following: (1) calculated the mean and LLN values for FEV3/FVC in these never-smoking and currently smoking groups; (2) compared the variability of FEV1/FVC, FEV3/FVC, and FEF25-75 values in never-smokers and current smokers; and (3) assessed changes associated with aging and smoking. We hypothesized that the fraction of the FVC that had not been expired during the first 3 s of the FVC (1 — FEV3/FVC) measures the increase in long-time-constant lung units that is associated with aging and smoking, and thus adding value to the spirometric assessment of airflow limitation. We further hypothesized that FEV3/FVC complements FEV1/FVC and that both are superior to FEF25-75 in identifying and characterizing expiratory airway obstruction, add comment
Discriminating Measures and Normal Values for Expiratory Obstruction
Since Hutchinson introduced spirometry in 1846, a multitude of measurements, including volumes, flows, time constants, and ratios, have evolved to assess normalcy and disease. Five decades ago Lueallan and Fowler2 added maximal midexpiratory flow, later labeled as forced expiratory flow, midexpiratory phase (FEF25-75), to assess expiratory airway obstruction. In 1967, Macklem and Mead divided airway resistance between central and peripheral components. Following the morphologic characterization of small airways disease, many publications reported reference values not only for FVC, FEV1, and FEV1/VC, but also for FEF25-75.
In 1972, a publication entitled, “A Reduction in Maximum Mid-Expiratory Flow Rate: A Spirometric Manifestation of Small-Airways Disease,” without giving FEV1/FVC data, described the conditions of 53 symptomatic smokers as abnormal because their FEF25 75 values were < 80% of the mean predicted values. The common practice of reporting spiromet-ric values as a percent of predicted values with highlighting of values < 80% of predicted added confusion. Despite evidence of high variability of FEF25 75 values and expert opinion recommending the use of statistically derived 95% confidence limits for the lower limit of normal (LLN)” small airways disease continued to be diagnosed if FEF25 75 values were < 75 to 80% of mean percentage of predicted values, and FEV1 or FEV1/FVC were > 75 to 80% of the mean percentage of predicted values. natural asthma inhaler
The Bronchial Response, but not the Pulmonary Response to Inhaled Methacholine Is Dependent on the Aerosol Deposition Pattern: Conclusion
Theoretically, differences in regional deposition of a vasoactive drug might then elicit different responses or time courses of effects, dependent on the deposition pattern. Experimental studies have suggested that a compound may be rapidly redistributed throughout the lung by bronchial blood flow This ability may have a role in airway homeostasis by enhancing the clearance of inhaled agents. In accordance, impairment of the bronchial perfusion prolonged the recovery of airway responses in sheep as well as in an isolated canine lung preparation in contrast to an intact preparation, with unaltered airway blood supply. The time to eliminate high local concentrations of a compound to the level when the receptors—which are situated mainly in the central airways—do not respond, would theoretically be longer than the time to eliminate a low concentration of the same compound. Our findings contrasted to this assumption, and although the intervals between the physiologic measurements in our experiments were not evenly distributed throughout the trial, we judged that the duration of bronchoconstriction was not longer, but rather tended to be shorter after the central airway deposition than after the peripheral airway deposition. The results are, therefore, compatible with a selective enhancement of the bronchial perfusion in the central airways by higher local doses of methacholine, potentially giving a faster clearance of the inhaled drug from the target area. natural inhalers for asthma
The Bronchial Response, but not the Pulmonary Response to Inhaled Methacholine Is Dependent on the Aerosol Deposition Pattern: Conclusion
Similarly, collateral ventilation may also be more effective at a segmental level than when a whole lobe is obstructed, at least in the dog Our findings further support the previously reported discrepancy in time courses of Va/Q mismatch and bronchial constriction, and the discrepancy occurred independently of whether the aerosol was deposited in the central or in the distal airways. Taking these data together, different mechanisms of the methacholine-induced bronchoconstriction and responses of the gas exchanging elements may be suggested. buy ventolin inhaler
The Bronchial Response, but not the Pulmonary Response to Inhaled Methacholine Is Dependent on the Aerosol Deposition Pattern: Comment
Similar to the conditions reported there, we postulated that mixing of the two water-soluble compounds, methacholine and DTPA, was homogeneous, both in the nebulizing chamber and in the separate aerosol particles. We, therefore, assumed that the differences in amounts of methacholine deposited within the various sections of the airways were proportional to the differences in counts per pixel recorded by the gamma camera over the corresponding regions. The surface area facing the air is much larger in the peripheral than in the central parts of the airways, and, consequently, the local drug concentration per unit area of the peripheral airway mucosa would be much lower. Furthermore, only the surface area of trachea and central airways may be similar in the two experiments, while the recipient surface area of the peripheral parts of the airways may vary largely dependent on a number of factors, such as transient airway constriction and mucous plugging. Comparisons of local drug concentrations on mucous membranes via estimations by means of the method we used, therefore, may be hazardous, at least when performed in the peripheral airways. Buy Flovent Inhaler