DYSANAPSIS

Abstract

Dear Editor-in-Chief: We read with interest the article by Dominelli et al. (1). They present data on dysanapsis and its potential contribution to obtaining expiratory flow limitation during exercise. We agree that dysanapsis may be an important concept regarding the presence of expiratory flow limitation and suggest that it integrates many of the basic principles related to the determination of maximal expiratory flow. These are well stated by Mead (4): “Persons with large lungs do not necessarily have larger airways than do persons with small lungs” and “…maximal expiratory flow is sensitive to lung recoil as well as airway size…” and “For example, a person with a high lung recoil at 50% of forced vital capacity would have a higher flow than would someone with airways of the same size but a lower lung recoil at 50% forced vital capacity (FVC).” Thus, a calculation of dysanapsis (FEF50/[FVC × Pst(l)50]) takes into account the basic interrelationships of flow, volume, and lung recoil pressure, which are so important in the determination of maximal expiratory flow and expiratory flow limitation (2–5). We are concerned that the calculation of dysanapsis using predicted lung recoil will not accurately reflect true dysanapsis in all individuals. As seen in Figure 1 in the original article by Mead (4), plotting flow at 50% of vital capacity against vital capacity has a wide scatter. It is only when the relationship of flow and lung volume is adjusted by individual measurements of lung recoil that the scatter is removed (Fig. 2C in Mead [4]). Likewise, we believe that Figure 4 presented by Dominelli et al. (1) could be quite different if individual measurements of lung recoil were used in the calculation of dysanapsis. The decisive question is whether the reduced flow in the one group of women is accompanied by a decrease in lung recoil pressure or by a normal pressure. In the article, each subject is assumed to have a predicted normal pressure. Adjusting the individual predicted pressures by just the SE of the measure (±1.39 cm H2O) could have a large effect on the individual estimate of dysanapsis. Thus, we believe the dysanapsis values presented by the authors could be grossly misleading. Applying a truly random error to all subjects (means equal zero), as the authors suggested, will not reduce the difference between the two groups. A simpler explanation for their findings is that the expiratory flow limitation (EFL) group had a higher degree of “scooping” on their expiratory flow–volume curves compared with the nonexpiratory flow limitation (NEFL) group (Table 1, where expiratory flows are lower in the EFL group). It would be worthwhile to probe further into the early history of either lung infections or childhood asthma in these groups. Plus, it would have been informative to know if total lung capacity was also reduced in the EFL group, which might help explain why the authors found the subjects with expiratory flow limitation to breathe at a lower end-expiratory lung volume contrary to findings in normal and patient populations studied. Tony G. Babb, PhD Presbyterian Hospital of Dallas Dallas, TX Kenneth C. Beck, PhD KCBeck Physiological Consulting, LLC Liberty, UT Bruce D. Johnson, PhD Mayo Clinic Rochester, MN The authors declare no conflicts of interest.