Relationship between chronic dyspnea and expiratory flow limitation in patients with chronic obstructive pulmonary disease.

Abstract

The purpose of this study was to assess whether expiratory flow limitation (FL), as measured by applying negative pressure at the mouth during tidal expiration, is a better predictor of dyspnea than routine spirometry measurements. The study population consisted of 117 ambulatory patients with COPD. Dyspnea was assessed according to the ATS-DLD respiratory Questionnaire. Expiratory flow limitation was measured in supine and sitting positions, and expressed as a percentage of the expired control tidal volume affected by flow limitation (FL, % VT). Using Spearman's rank correlation (rs), we found that the correlation of dyspnea scale with FL was stronger (rs > 0.5) than with FVC (rs < -0.3) or FEV1 (rs < -0.4) in both positions. In a multiple regression analysis FL remained the best predictor of dyspnea scale even after adjustment for FEV1 (% pred). Finally, FL was almost as sensitive as FEV1 (% pred) but much more specific in assessing the severity of dyspnea scale. These findings suggest that expiratory flow limitation as measured by the negative expiratory pressure technique may be more useful in the evaluation of dyspnea in patients with COPD than spirometry measurements.

Role of inspiratory capacity on exercise tolerance in COPD patients with and without tidal expiratory flow limitation at rest

“…In addition, it was found that 1) in all non-FL patients IC was within normal limits and in the majority of FL subjects the IC was below normal limits; and 2) in all FL subjects V'O 2 ,max was decreased, whereas in 35% of the non-FL patients V'O 2 ,max was within normal limits. In line with ELTAYARA et al [7], a high incidence of FL was found (56% versus 59%, respectively), indicating that FL is a frequent but unrecognized abnormality in these patients. The presented data also confirmed the findings of KOLOURIS et al [8] that a reduced IC is a good marker of FL, as it reflects dynamic hyperinflation (DH).…”

“…1). The FL portion of the tidal expiration was expressed as a percentage of the control VT (FL, %VT) [7]. The latter is presented as average of the five NEP tests.…”

“…In most previous studies, it was found that forced expiratory volume in one second (FEV1) was a poor predictor of exercise capacity [1±3]. Recently, however, it has been shown that indices related to dynamic hyperinflation, such as the inspiratory capacity (IC), are more closely related to exercise tolerance than FEV1 [4,5].Even at rest, patients with COPD often exhibit tidal expiratory flow limitation (FL) [6,7], promoting an increase in end-expiratory lung volume (EELV) due to dynamic hyperinflation with a concomitant decrease in inspiratory capacity and inspiratory reserve volume (IRV) [8,9]. During exercise, normal subjects increase the tidal volume (VT) at the expense of both the IRV and the expiratory reserve volume [8,9].…”

“…Assessment of FL was made using a simple noninvasive method that consists of applying a negative expiratory pressure (NEP) at the mouth during a tidal expiration and comparing the ensuing expiratory flow-volume curve with that of the previous control expiration [6]. The NEP technique has been extensively applied and validated, and has been used in stable COPD patients both at rest and during exercise [7,8,10]. …”

“…Even at rest, patients with COPD often exhibit tidal expiratory flow limitation (FL) [6,7], promoting an increase in end-expiratory lung volume (EELV) due to dynamic hyperinflation with a concomitant decrease in inspiratory capacity and inspiratory reserve volume (IRV) [8,9]. During exercise, normal subjects increase the tidal volume (VT) at the expense of both the IRV and the expiratory reserve volume [8,9].…”