Relationship between Chronic Dyspnea and Expiratory Flow Limitation in Patients with Chronic Obstructive Pulmonary Disease LOUBNA ELTAYARA, MARGARET RIGSBY BECKLAKE, CARLO ALBERTO VOLTA, and JOSEPH MILle-EMILI Meakins-Christie Laboratories, Montreal Chest Institute Research Center; and Respiratory Epidemiology Unit, Department of Epidemiology and Biostatistics, McGill University, Montreal, Quebec, Canada The purpose of this study was to assess whether expiratory flow limitation (FL),as measured byapply- ing negative pressure at the mouth during tidal expiration, isa better predictor of dyspnea than rou- tine 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. Ina multiple regression analysis FL remained the best predictor of dys- pnea 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 expira- tory 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. Eltayara L,Beck- lake MR, Volta CA, Milic-Emili J. Relationship between chronic dyspnea and expiratory flow limi- tation in patients with chronic obstructive pulmonary disease. AM I RESPIR CRIT CARE MED 1996;154:1726-17'14. Dyspnea, especiallyon physical exertion, is the predominant com- plaint of patients with chronic obstructive pulmonary disease (COPD), and it is often the reason for seeking medical atten- tion. The sensation of difficult or uncomfortable breathing is probably the single most important factor that limits the ability of patients with severe COPD to function on a day-to-day basis. Despite its frequency, the mechanisms contributing to dyspnea are not well understood and are likely to be multifactorial (1, 2). Recently, there has been increasing interest in the use of sub- jective measures of dyspnea in the assessment of exercise toler- ance and treatment efficacy in patients with COPD (3), as well as in their clinical management (4, 5). Intuitively, one would expect patients with the most severe airway obstruction, as assessed with routine lung function mea- surements, to be the most dyspneic. However, some patients with severe airway obstruction are minimally symptomatic, whereas others with little objective dysfunction appear to be very dys- pneic (6). Several studies have investigated the correlation be- tween dyspnea and routine lung function. An early study by Bur- rows and coworkers (7) has shown a statistically significant (Received in original form October 23, 7995 and in revised form AprilS, 7996) Supported by the J. T. Costello Memorial Research Fund, Royal Victoria Hospi- tal Foundation, and the Montreal Chest Institute Research Center. Correspondence and requests for reprints should be addressed to Joseph Milic- Emili, M.D., Meakins-Christie Laboratories, McGill University, 3626 St. Urbain Street, Montreal, Quebec, H2X 2P2 Canada. Am J Respir Crit Care Med Vol 154. pp 1726-1734, 1996 correlation between the level of chronic dyspnea and the degree of airway obstruction as expressed by FEV.; however, this corre- lation was weak. Subsequent studies employing newer scaling techniques to quantify breathlessness found either no statisti- cally significant correlation with routine lung function measure- ments (3, 6) or weak correlations (7-9). These findings are not surprising given the common clinical observation that the severity of dyspnea varies considerably among patients with similar values of FEV. (6). Recent studies (10, 11) have provided evidence that the inten- sity of dyspnea during exercisein patients with COPD is closely linked to dynamic pulmonary hyperinflation. The latter condi- tion, which is said to occur when breathing takes place from lung volumes higher than the relaxation volume of the respiratory sys- tem (Vr), is commonly a direct consequence of expiratory flow limitation (12, 13).The fact that patients with severe COPD may be flow-limited even during resting tidal breathing has been long recognized (13). Accordingly, there may be a closer association of dyspnea with expiratory flow-limitation than with FEV. or other routine lung function indices. Originally, direct assessment of expiratory flow limitation was based on determination of isovolume relationships between flow and transpulmonary pressure, which is time-consuming and in- vasive (12, 14). This has led to the proposal by Hyatt in 1961 (14) that expiratory flowlimitation should be assessed by comparing tidal with maximal flow-volume (V-V) curves. However, this ap- proach may lead to erroneous conclusions (15). Recently, a sim- ple and noninvasive approach, namely, the negative expiratory pressure (NEP) technique, has been developed to detect expira- tory flow limitation (15, 16). This technique, which does not re-