{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,5]],"date-time":"2026-10-05T19:24:11Z","timestamp":1791228251932,"version":"4.1.0"},"reference-count":32,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,7,3]],"date-time":"2026-07-03T00:00:00Z","timestamp":1783036800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Physiol."],"abstract":"<jats:sec>\n                    <jats:title>Rationale<\/jats:title>\n                    <jats:p>An excessive decrease in the flow at the late expiratory portion of the flow volume loop (FVL) or \u201cflattening\u201d reflects small airway diseases (SAD). The flattening is subjectively assessed by visual inspection. In this study, we hypothesized that an objective flattening index (FI) would correlate with age and that an abnormal FI is associated with SAD.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Methods<\/jats:title>\n                    <jats:p>PFT reports with FEV1\/FVC \u22650.7, FEV1 \u226580%pred, and FVC \u226580%pred were downloaded from electronic medical records. We digitized and converted FVLs to data points. We calculated the slopes of segment AB (between the peak expiratory flow [point A] and the point corresponding to 75% of the expiratory vital capacity [point B]) and segment BC (between point B and the point where the expiratory portion of the FVL intersects with the x-axis [point C]). Moreover, 75% is chosen because it roughly corresponds to the start of small airways. FI is the angle formed by segment AB and segment BC. We also extracted demographic data from PFT reports.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Results<\/jats:title>\n                    <jats:p>\n                      A total of 490 PFTs (161 men and 329 female) were included. FI was 156\u00b0\u00a0\u00b1\u00a012\u00b0 in men and 160\u00b0\u00a0\u00b1\u00a014\u00b0 in women (\n                      <jats:italic>p<\/jats:italic>\n                      \u00a0=\u00a00.0079). FI correlated negatively with age and BMI in both genders. The threshold value (mean-1.64 \u00d7 SD) was 136\u00b0for men and 137\u00b0for women. A total of 21 PFTs (4.3%) in 15 patients had FI &amp;lt;threshold value. All patients had CT findings consistent with SAD and\/or lung diseases involving primarily small airways.\n                    <\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusions<\/jats:title>\n                    <jats:p>FI decreased with increasing age and BMI. It can be a useful parameter on PFTs to assist clinicians in identifying SAD.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.3389\/fphys.2026.1765817","type":"journal-article","created":{"date-parts":[[2026,7,3]],"date-time":"2026-07-03T04:22:50Z","timestamp":1783052570000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":1,"title":["Clinical significance of a flattening index derived from the flow-volume loop"],"prefix":"10.3389","volume":"17","author":[{"given":"Albert","family":"Liu","sequence":"first","affiliation":[{"name":"Department of Biomedical Engineering, Pratt School of Engineering, Duke University","place":["Durham, NC, United States"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Hengji","family":"Chen","sequence":"additional","affiliation":[{"name":"Department of Biomedical Engineering, Pratt School of Engineering, Duke University","place":["Durham, NC, United States"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Elle","family":"Commerce","sequence":"additional","affiliation":[{"name":"Department of Biomedical Engineering, Pratt School of Engineering, Duke University","place":["Durham, NC, United States"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Yuh-Chin T.","family":"Huang","sequence":"additional","affiliation":[{"name":"Department of Medicine, School of Medicine, Duke University","place":["Durham, NC, United States"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2026,7,3]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","first-page":"1494","DOI":"10.1164\/rccm.201401-0178oc","article-title":"The nonallergic asthma of obesity. 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