Plethysmographic Loops: A Window on the Lung Pathophysiology of COPD Patients

Abstract

Plethysmographic alveolar pressure-flow (Palv–F) loops contain potentially relevant information about the pathophysiology of chronic obstructive pulmonary disease (COPD), but no quantitative analysis of these loops during spontaneous breathing has ever been performed. The area of the loop’s inspiratory (Ains) and expiratory portion (Aexp), and the difference between the end-expiratory and end-inspiratory alveolar pressure (ΔPalv) were measured in 20 young, 20 elderly healthy subjects, and 130 stable COPD patients. Ains and ΔPalv increased by 55 and 78% from young to elderly subjects, and by 107 and 122% from elderly subjects to COPD patients, reflecting changes in mechanical heterogeneity, lung-units recruitment/derecruitment, and possibly air trapping occurring with aging and/or obstructive disease. Aexp increased by 38% from young to elderly subjects, and by 198% from elderly subjects to COPD patients, consistent with the additional contribution of tidal expiratory flow-limitation, which occurs only in COPD patients and affects Aexp only. In COPD patients, Aexp and ΔPalv showed a significant negative correlation with VC, FEV1, IC, and a significant positive correlation with RV/TLC. The results suggest that the analysis of plethysmographic Palv–F loops provides an insight of the pathophysiological factors, especially tidal expiratory flow-limitation, that affect lung function in COPD patients.

Diagnostic Insights from Plethysmographic Alveolar Pressure Assessed during Spontaneous Breathing in COPD Patients

“…Interestingly, induction of bronchoconstriction in asthmatic patients resulted in small changes in the shape and extension of the expiratory loops. These data are compatible with the notion that tEFL is the major determinant of the expansion of the expiratory P alv - loop as previously suggested [ 21 , 31 ], and it is tempting to speculate that the “openers” and “non-openers” of Topalovic et al were patients with or without tEFL. In addition, the limited changes of the expiratory loops in asthmatics after methacholine are in line with this concept: indeed, most of stable asthmatic patients are not flow-limited, and only in a minority of them tEFL appears when methacholine is administered [ 35 ].…”

“…Plethysmographic P alv has been systematically investigated in terms of P alv - plots in healthy young and elderly subjects and in COPD patients spontaneously breathing at rest [ 21 ]. A particular attention was paid to looping of the P alv - relation, which was characterized by sense of rotation of the loops and area of the inspiratory (A ins ) or expiratory loop (A exp ).…”

“…Finally, a marked increase of A exp was noted in COPD patients relative to healthy subjects, as it could be expected considering the characteristics of their disease, which includes mechanical heterogeneity, recruitment/derecruitment, gas trapping, and tEFL [ 23 , 24 ]. In the observational study of Radovanovic et al [ 21 ], the relative weight of the different loop-generating factors could only be hypothesized. However, several lines of evidence suggested that tEFL played a prominent role in the appearance of the large expiratory loop shown by many COPD patients.…”

Nasal high-flow bronchodilator nebulization: a randomized cross-over study

“…Plethysmography loops were evaluated, and patients were classified as presenting expiratory flow limitation or not [20, 21]. Volumetric capnography was performed before and after each procedure (5 duplicate measurements, patients breathing out at slow and steady flow from maximal inspiration to maximal expiration) and the slope of the third phase of the capnogram measured.…”

Expiratory flow-limitation in mechanically ventilated patients: A risk for ventilator-induced lung injury?

“…Both these findings are suggestive but not demonstrative of the presence of EFL[9]. A plethysmographic method for EFL detection not requiring the introduction of an esophageal balloon is under development[10].…”