Prognostic relevance of dynamic hyperinflation during cardiopulmonary exercise testing in adult patients with cystic fibrosis

Change in the 6-min walk test among 71 patients with cystic fibrosis treated with elexacaftor/tezacaftor/ivacaftor

BACKGROUND

Elexacaftor/tezacaftor/ivacaftor (ETI) has led to substantial improvements in the clinical outcome of people with cystic fibrosis (pwCF). However, its effects on exercise capacity remain uncertain.

METHODS

This retrospective cohort study included 71 pwCF who started ETI between March 2020 and September 2022. The best performance on the 6-min walk test (6MWT), defined as the peak walking distance achieved, was compared between the 12 months preceding ETI initiation and the first 14 months of treatment. Pulmonary function tests (PFT) and Cystic Fibrosis Questionnaire-Revised (CFQ-R) were analyzed at treatment initiation and after 12 months.

RESULTS

After starting ETI, the 6MWT was performed at a median interval of 356 [296-380] days. The mean 6-min walk distance (6MWD) was 641 m ± 85.5 at baseline. After treatment, the 6MWD showed a significant absolute increase of 15.8 m (P = 0.007). Improvement was greater in pwCF with a percent predicted FEV1 (ppFEV1) ≤40, showing a mean increase of 37.8 m (P = 0.009), and in those without prior CFTR modulator therapy with an increase of 21.6 m (P = 0.016). After 12 months, the absolute increase in ppFEV1 was 15.8 (P < 0.001). The absolute changes from baseline in CFQ-R physical and respiratory scores were 17.9 (P < 0.001) and 27 points (P < 0.001), respectively. No correlation was found between changes in 6MWT and changes in PFT results.

CONCLUSIONS

ETI improved exercise capacity in pwCF, as evidenced by a significant increase in the 6MWD. ETI was also associated with improvements in physical-related quality of life. Changes in PFT results cannot predict changes in 6MWT results after ETI therapy.

Dynamic Hyperinflation While Exercising-A Potential Predictor of Pulmonary Deterioration in Cystic Fibrosis

BACKGROUND

Lung function deterioration in cystic fibrosis (CF) is typically measured by a decline in the forced expiratory volume in one second (FEV1%), which is thought to be a late marker of lung disease. Dynamic hyperinflation (DH) is seen in obstructive lung diseases while exercising. Our aim was to assess whether DH could predict pulmonary deterioration in CF; a secondary measure was the peak VO2.

METHODS

A retrospective study was conducted of people with CF who performed cardiopulmonary exercise tests (CPETs) during 2012-2018. The tests were classified as those demonstrating DH non-DH. Demographic, genetic, and clinical data until 12.2022 were extracted from patient charts.

RESULTS

A total of 33 patients aged 10-61 years performed 41 valid CPETs with valid DH measurements; sixteen (39%) demonstrated DH. At the time of the CPETs, there was no difference in the FEV1% measurements between the DH and non-DH groups (median 83.5% vs. 87.6%, respectively; p = 0.174). The FEV1% trend over 4 years showed a decline in the DH group compared to the non-DH group (p = 0.009). A correlation was found between DH and the lung clearance index (LCI), as well as the FEV1% (r = 0.36 and p = 0.019 and r = -0.55 and p = 0.004, respectively). Intravenous (IV) antibiotic courses during the 4 years after the CPETs were significantly more frequent in the DH group (p = 0.046). The peak VO2 also correlated with the FEV1% and LCI (r = 0.36 and p = 0.02 and r = -0.46 and p = 0.014, respectively) as well as with the IV antibiotic courses (r = -0.46 and p = 0.014).

CONCLUSIONS

In our cohort, the DH and peak VO2 were both associated with lung function deterioration and more frequent pulmonary exacerbations. DH may serve as a marker to predict pulmonary deterioration in people with CF.

Investigation of dynamic hyperinflation and its relationship with exercise capacity in children with bronchiectasis

BACKGROUND AND AIM

Dynamic hyperinflation (DH) is a major contributor to exercise intolerance in patients with obstructive lung diseases. However, it has not been investigated in children with bronchiectasis (BE). We aimed to investigate dynamic ventilatory responses and their influence on functional exercise capacity in children with BE.

METHODS

Forty children with BE (mean forced expiratory volume in 1 s [FEV₁ ] = 78 ± 19%pred) were included. Six-minute walk test (6MWT) was conducted using Spiropalm 6MWT® for evaluating dynamic ventilatory responses including inspiratory capacity (IC), minute ventilation (VE), breathing reserve (BR) and respiratory rate (RR). A decrease of ≥100 ml in IC during exertion was defined as DH. Also, spirometry was performed, and peripheral muscle strength were measured.

RESULTS

Twenty patients (50%) developed DH, and four patients (10%) were ventilatory limited (BR < %30) during 6MWT. There was a 176 [100-590] ml decrease in IC after exertion in patients with DH. DH did not correlate to clinical or functional indicators of the disease, except for an increase in RR (∆RR) during exertion. High ∆RR was associated with presence of DH (r_pb = 0.390; p < 0.05). Clinical features, peripheral muscle strength, and Spiropalm 6MWT metrics including 6MWT distance did not differ between patients with and without DH. Univariate analysis revealed FVC% (R = 0.340), VE_peak (R = 0.565), quadriceps strength (R = 0.698) and handgrip strength (R = 0.711) were the only predictors of 6MWT distance (p < 0.05).

CONCLUSION

Although DH is common in children with BE, the severity of DH is rather low and may not seem to affect functional exercise capacity. However, peripheral muscle strength was a major contributor to functional exercise capacity.

Ventilatory efficiency and its clinical and prognostic value in adults with cystic fibrosis

Cystic fibrosis, due to the absence or abnormal function of the cystic fibrosis transmembrane conductance regulator, is the most common life-limiting autosomal recessive genetic disorder among the Caucasian population. The lungs are particularly affected due to thick and tenacious mucus causing parenchymal anomalies ranging from bronchiectasis, progressive airflow limitation, respiratory infections, lung destruction and ultimately respiratory failure. Despite the remarkable advances in treatment that have greatly improved survival, most patients experience progressive exercise curtailment, with the consequence that a growing number of patients with cystic fibrosis will be referred for exercise-based evaluations in the forthcoming years. Cardiopulmonary exercise testing, in particular, is a useful tool to assess the mechanisms of exercise intolerance in individual patients that may have treatment and prognostic implications. In this review, we will focus on ventilatory efficiency and its clinical and prognostic value in adults with cystic fibrosis.

The role of inspiratory capacity and tidal flow in diagnosing exercise ventilatory limitation in Cystic Fibrosis

BACKGROUND

Exercise ventilatory limitation conventionally defined by reduced breathing reserve (BR) may underestimate the effect of lung disease on exercise capacity in patients with mild to moderate obstructive lung diseases.

OBJECTIVE

To investigate whether ventilatory limitation may be present despite a normal BR in Cystic Fibrosis (CF).

METHODS

Twenty adult CF patients (age 16-58y) with a wide range of pulmonary obstruction severity completed a symptom-limited incremental exercise test on a cycle ergometer. Operating lung volumes were derived from inspiratory capacity (IC) measurement during exercise and exercise tidal flow volume loop analysis.

RESULTS

six patients had a severe airway obstruction (FEV₁<45% predicted) and conventional evidence of ventilatory limitation (low BR). Fourteen patients had mild to moderate-severe airway obstructive (FEV₁ 46-103% predicted), and a normal BR [12-62 L/min, BR% (17-40)]. However, dynamic respiratory mechanics demonstrated that even CF patients with mild to moderate-severe lung disease had clear evidence of ventilatory limitation during exercise. IC was decreased by (median) 580 ml (range 90-1180 ml) during exercise, indicating dynamic hyperinflation. Inspiratory reserve volume at peak exercise was 445 ml (241-1350 ml) indicating mechanical constraint on the respiratory system. The exercise tidal flow met or exceeded the expiratory boundary of the maximal flow volume loop over 72% of the expiratory volume (range 40-90%), indicating expiratory flow limitation.

CONCLUSION

Reduced BR as a sole criterion underestimates ventilatory limitation during exercise in mild to moderate-severe CF patients. Assessment of dynamic respiratory mechanics during exercise revealed ventilatory limitation, present even in patients with mild obstruction.

Maximal Voluntary Ventilation Should Not Be Estimated From the Forced Expiratory Volume in the First Second in Healthy People and COPD Patients

PURPOSE

To evaluate the concordance between the value of the actual maximum voluntary ventilation (MVV) and the estimated value by multiplying the forced expiratory volume in the first second (FEV1) and a different value established in the literature.

METHODS

A retrospective study was conducted with healthy subjects and patients with stable chronic obstructive pulmonary disease (COPD). Five prediction formulas MVV were used for the comparison with the MVV values. Agreement between MVV measured and MVV obtained from five prediction equations were studied. FEV1 values were used to estimate MVV. Correlation and agreement analysis of the values was performed in two groups using the Pearson test and the Bland-Altman method; these groups were one group with 207 healthy subjects and the second group with 83 patients diagnosed with COPD, respectively.

RESULTS

We recruited 207 healthy subjects (105 women, age 47 ± 17 years) and 83 COPD patients (age 66 ± 6 years; 29 GOLD II, 30 GOLD III, and 24 GOLD IV) for the study. All prediction equations presented a significant correlation with the MVV value (from 0.38 to 0.86, p < 0.05) except for the GOLD II subgroup, which had a poor agreement with measured MVV. In healthy subjects, the mean difference of the value of bias (and limits of agreement) varied between -3.9% (-32.8 to 24.9%), and 27% (-1.4 to 55.3%). In COPD patients, the mean difference of value of bias (and limits of agreement) varied between -4.4% (-49.4 to 40.6%), and 26.3% (-18.3 to 70.9%). The results were similar in the subgroup analysis.

CONCLUSION

The equations to estimate the value of MVV present a good degree of correlation with the real value of MVV, but they also show a poor concordance. For this reason, we should not use the estimated results as a replacement for the real value of MVV.

Reduced exercise ventilatory efficiency in adults with cystic fibrosis and normal to moderately impaired lung function

Despite being a hallmark and an independent prognostic factor in several cardiopulmonary diseases, ventilatory efficiency-i.e., minute ventilation/carbon dioxide output relationship (V̇e/V̇co₂)-has never been systematically explored in cystic fibrosis (CF). To provide a comprehensive frame of reference regarding measures of ventilatory efficiency in CF adults with normal to moderately impaired lung function and to confirm the hypothesis that V̇e/V̇co₂ is a sensitive marker of early lung disease. CF patients were divided into three groups, according to their spirometry: normal (G₁), mild impairment (G₂), and moderate impairment (G₃) in lung function. All participants underwent incremental cardiopulmonary exercise testing on a cycle ergometer. Lowest V̇e/V̇co₂ ratio (nadir) and the slope and the intercept of the linear region of the V̇e/V̇co₂ relationship were contrasted in a two-center retrospective analysis, involving 72 CF patients and 36 healthy controls (HC). Compared with HC, CF patients had significantly higher V̇e/V̇co₂ nadir, slope, and intercept (P < 0.001, P < 0.001, and P = 0.049, respectively). Subgroup analysis revealed significant differences in nadir (P = 0.001) and slope (P = 0.012) values even between HC and G₁. Dynamic hyperinflation related negatively with slope (P = 0.045) and positively with intercept (P = 0.001), while no impact on nadir was observed. Ventilatory inefficiency is a clear feature of adults with CF, even among patients with normal spirometry. V̇e/V̇co₂ nadir seems to be the most reliable metric to describe ventilatory efficiency in CF adults. Further prospective studies are needed to clarify whether V̇e/V̇co₂ could represent a useful marker in the evaluation of early lung disease in CF.NEW & NOTEWORTHY This is the first study to investigate ventilatory efficiency in a cohort of adult cystic fibrosis (CF) patients with nonsevere lung disease. The finding of impaired ventilatory efficiency in patients with normal lung function confirms the higher sensitivity of exercise testing in detecting early lung disease compared with spirometry. Dynamic hyperinflation plays a significant role in determining the behavior of V̇e/V̇co₂ slope and intercept values with increasing lung function impairment. Apparently free from interference from mechanical constraints, V̇e/V̇co₂ nadir seems the most reliable parameter to evaluate ventilatory efficiency in CF adults.

The value of high-resolution computed tomography (HRCT) to determine exercise ventilatory inefficiency and dynamic hyperinflation in adult patients with cystic fibrosis

Introduction

In Cystic Fibrosis (CF), exercise ventilatory inefficiency and dynamic hyperinflation (DH) cause exercise limitation and induce poor exercise tolerance. High-resolution computed tomography (HRCT) of the lung can detect pulmonary abnormalities in CF patients. We aimed to identify the determinants of exercise ventilatory inefficiency and DH using HRCT-derived metrics.

Methods

Fifty-two adult CF patients were prospectively enrolled; all participants underwent cardio-pulmonary exercise test (CPET) and HRCT. Radiological impairment was evaluated by the Brody II scoring system. Slope and intercept of the minute ventilation/CO₂ production (V’_E/V’_CO2) regression line and the ratio of inspiratory capacity/total lung capacity (IC/TLC) at rest and at peak of exercise were measured.

Results

Four groups of patients were identified based on the combination of ventilatory efficiency (Vef) or inefficiency (Vin) and the presence/absence of DH. Compared to other groups, CF adults with Vin and DH had worse functional status and higher total (T), bronchiectasis (B) and air trapping (AT) scores at HRCT. Significant correlations were found between V’_E/V’_{CO2 intercept} and V’_E/V’_{CO2 slope} (ρ − 0.455, p = 0.001) and between V’_E/V’_{CO2 intercept} and Δ inspiratory capacity (IC) (ρ − 0.334, p = 0.015). Regression analysis identified AT score (cut-off 7.9, odds ratio-OR 3.50) as the only independent predictor of Vin and T (cut-off 53.6, OR 4.98), B (cut-off 16.1, OR 4.88), airways wall thickening (AWT) (cut-off 13, OR 3.41), and mucous plugging (MP) scores (cut-off 11.7, OR 4.18) as significant predictors of DH.

Conclusion

In adult CF cohort, values of HRCT metrics are determinants of Vin (AT) and DH (T, B, AWT, MP).

Is daily physical activity affected by dynamic hyperinflation in adults with cystic fibrosis?

Background

The aim of this study was to investigate the relationship between dynamic hyperinflation and daily physical activity (DPA) in adults with cystic fibrosis (CF).

Methods

Thirty-four clinically stable CF were studied. All patients undertook incremental cardiopulmonary exercise testing (CPET). CPET-related measurements included: oxygen uptake (V’O₂), carbon dioxide production (V’CO₂), ventilatory profile, work rate (W), inspiratory capacity (IC), end-expiratory lung volume (EELV). PA was assessed using the accelerometer SenseWear Pro3 Armband.

Results

Exercise tolerance was reduced in most of patients and the mean V’O_2,peak value was 75.2% of predicted (28.5 ± 4.8 ml/min/kg). Seventy % of patients responded to CPET with dynamic hyperinflation. Higher incidence of dynamic hyperinflation was found in CF males compared to CF females (p = 0.026). Patients who developed dynamic hyperinflation during CPET had higher vigorous PA (p = 0.01) and more total energy expenditure (p = 0.006) than patients who did not. EELVΔ was related to activities requiring vigorous intensity and total energy expenditure (R = 0.46, p = 0.001; R = 0.57, p <  0.001).

Conclusions

In adults with CF and mild to moderate lung impairment, DPA might not be limited by dynamic hyperinflation.

Electronic supplementary material

The online version of this article (10.1186/s12890-018-0623-7) contains supplementary material, which is available to authorized users.

Static hyperinflation is associated with ventilatory limitation and exercise tolerance in adult cystic fibrosis

INTRODUCTION

Lung hyperinflation is a potential mechanism limiting exercise tolerance. However, available data on the impact of static hyperinflation on exercise performance in adult cystic fibrosis are lacking. Furthermore, the relative contribution of both static and dynamic hyperinflation to exercise performance is unknown.

OBJECTIVES

The aim of this study was to determine the impact of static hyperinflation on exercise tolerance and lung dynamics in adult cystic fibrosis.

METHODS

Clinical data of 107 adult patients with cystic fibrosis, including pulmonary function, lung volumes and cardiopulmonary exercise from the Toronto Cystic Fibrosis database, were collected and analyzed. Patients were classified as having static hyperinflation with a residual volume to total lung capacity (RV/TLC) ratio of 30% or greater.

RESULTS

Patients with static hyperinflation demonstrated a significant reduction in exercise performance [peak oxygen uptake (% predicted) 70 ± 17 vs 80 ± 17; P = .006] and were more likely to experience ventilatory limitation when exercising (Fisher's exact test P < .001). Correlation analysis showed significant relationships between measures of static hyperinflation [RV/TLC ratio (%)] and exercise performance [peak oxygen uptake (% predicted); r = -.38, P < .001] and dynamic hyperinflation (r = -.35, P < .001). Multiple linear regression showed that the contribution of static hyperinflation to exercise performance [peak oxygen uptake (% predicted)] was greater than that of airway obstruction (forced expiratory volume in 1 second).

CONCLUSION

Clinicians working with this patient group in a pulmonary rehabilitation or health care setting may wish to consider using measures of static hyperinflation as end points to determine program or treatment efficacy.

Ventilatory limitation and dynamic hyperinflation during exercise testing in Cystic Fibrosis

OBJECTIVE

To investigate the presence of dynamic hyperinflation after the Modified Shuttle Test (MST) and its relationship with lung function, exercise tolerance, and clinical symptoms in Cystic Fibrosis (CF).

METHODS

Retrospective observational study. Subjects in clinically stable condition with a CF diagnosis based on a positive sweat test (chloride >60 mEq/L) and/or presence of two disease causing mutations, with available data on MST, spirometry, maximal voluntary ventilation, and inspiratory capacity manoeuvres were considered for the analysis. Breathing reserve was calculated and a threshold value of 0.7 was subsequently chosen as a value of pulmonary mechanical limit. Subjects were then categorized into two groups according to the change in the inspiratory capacity from rest to peak exercise. Unconditional logistic regression was used to estimate unadjusted odds ratios, 95% confidence intervals and P-values.

RESULTS

Twenty-two subjects demonstrated evidence of dynamic hyperinflation during the MST. Thirteen out of 22 subjects were ventilatory limited during exercise including 5 of those without evidence of dynamic hyperinflation (P = 0.24). No combination of variables resulted in a parsimonious regression model.

CONCLUSIONS

Dynamic hyperinflation is common in CF and it is not associated with traditionally defined ventilatory limitation parameters during the MST. Pediatr Pulmonol. 2017;52:29-33. © 2016 Wiley Periodicals, Inc.

Cardiorespiratory and sensory responses to exercise in adults with mild cystic fibrosis

The purpose of this study was to evaluate cardiorespiratory fitness and reasons for exercise curtailment in a contemporary adult cystic fibrosis (CF) cohort with mild lung disease. Adults with mild CF (n = 19, forced expiratory volume in 1 s = 95 ± 17% predicted) were age-, sex-, ethnicity-, and body mass index-matched to healthy controls (n = 19) and underwent a detailed cardiopulmonary cycle exercise test. While CF subjects had a reduced peak oxygen uptake compared with controls, the values were normal when expressed as %predicted in 14/19 (74%) of subjects. Both groups demonstrated a normal cardiovascular limitation to exercise and stopped exercise primarily because of leg fatigue. Despite not being exercise-limited by respiratory factors, there was some evidence of ventilatory abnormalities as patients with mild CF had increased end-inspiratory lung volumes and reached an inflection/plateau in tidal volume relative to minute ventilation at lower exercise intensities compared with controls. Subjects with CF were not more likely to demonstrate expiratory flow limitation compared with controls and did not have evidence of dynamic hyperinflation during exercise. Despite increased end-inspiratory lung volumes and an earlier tidal volume inflection/plateau, CF subjects did not experience higher levels of dyspnea. In an exploratory analysis, a significant inverse correlation was observed between sweat chloride and peak work rate. Adult CF subjects with relatively well preserved spirometry have normal exercise performance relative to reference values and are primarily limited by nonrespiratory factors. However, ventilatory abnormalities were detected even in this mild CF cohort and should be evaluated in future therapeutic trials focused on disease-modifying therapies in mild CF.

Variability of the perception of dyspnea in healthy subjects assessed through inspiratory resistive loading

Objective:

Few studies have evaluated the variability of the perception of dyspnea in healthy subjects. The objective of this study was to evaluate the variability of the perception of dyspnea in healthy subjects during breathing against increasing inspiratory resistive loads, as well as to assess the association between the level of perception of dyspnea and the level of physical activity.

Methods:

This was a cross-sectional study involving healthy individuals 16 years of age or older. Subjects underwent inspiratory resistive loading testing, in which the level of perception of dyspnea was quantified with the modified Borg scale. We also determined body mass indices (BMIs), assessed maximal respiratory pressures, performed pulmonary function tests, applied the international physical activity questionnaire (IPAQ)-long form, and conducted six-minute walk tests (6MWTs). The level of perception of dyspnea was classified as low (Borg score < 2), intermediate (Borg score, 2-5), or high (Borg score > 5).

Results:

We included 48 healthy subjects in the study. Forty-two subjects completed the test up to a load of 46.7 cmH₂O/L/s. The level of perception of dyspnea was classified as low, intermediate, and high in 13, 19, and 10 subjects, respectively. The level of perception of dyspnea was not significantly associated with age, gender, BMI, IPAQ-long form score, maximal respiratory pressures, or pulmonary function test results.

Conclusions:

The scores for perceived dyspnea induced by inspiratory resistive loading in healthy subjects presented wide variability. The perception of dyspnea was classified as low in 31% of the subjects, intermediate in 45%, and high in 24%. There was no association between the level of perception of dyspnea and the level of physical activity (IPAQ or six-minute walk distance).

Airflow limitation following cardiopulmonary exercise testing and heavy-intensity intermittent exercise in children with cystic fibrosis

The clinical importance of exercise testing and training in the healthcare management of young patients with cystic fibrosis (CF) is growing. The aim of the present study was to determine the incidence of airflow limitation following cardiopulmonary exercise testing (CPET) and heavy-intensity intermittent exercise (HIIE) in young patients with CF. Nineteen young patients with CF and respective paired-matched controls performed CPET and HIIE on separate days. Forced expiratory volume in one second (FEV1) was measured pre- and post each exercise modality. A fall in FEV1 of 10 % or greater was used to define airflow limitation. The incidence of airflow limitation was significantly greater in the CF group than in the controls following CPET (32 vs. 5 %; p = 0.03); however, no significant difference in the incidence of airflow limitation was shown following HIIE between the CF group and controls (11 vs. 16 %; p = 0.64).

CONCLUSION

Our data show that the incidence of airflow limitation following CPET in young patients with CF is high. Therefore, clinicians may wish to identify whether young CF patients experience airflow limitation following strenuous exercise, such as CPET, before it is performed. However, HIIE carries a low risk for airflow limitation and may be prescribed as a safe, yet effective exercise modality for young patients with CF.

Putting lung function and physiology into perspective: cystic fibrosis in adults

Adult cystic fibrosis (CF) is notable for the wide heterogeneity in severity of disease expression, both between patients and within the lungs of individuals. Although CF airways disease appears to start in the small airways, in adults there is typically widespread bronchiectasis, increased airway secretions, and extensive obstruction and inflammation of the small airways. The complexity and heterogeneity of airways disease in CF means that although there are many different methods of assessing and describing lung 'function', none of these single-dimensional tests is able to provide a comprehensive assessment of lung physiology across the spectrum seen in adult CF. The most widely described measure, the forced expiratory volume in 1 s, remains a useful and simple clinical tool, but is insensitive to early changes and may be dissociated from other more detailed assessments of disease severity such as computed tomography. In this review, we also discuss the use of more sensitive novel assessments such as multiple breath washout tests and impulse oscillometry, as well as the role of cardiopulmonary exercise testing. In the future, hyperpolarized gas magnetic resonance imaging techniques that combine regional structural and functional information may help us to better understand these measures, their applications and limitations.

Dyspnea perception in cystic fibrosis patients

We evaluated dyspnea perception in cystic fibrosis patients compared with normal subjects, during an inspiratory resistive loading test and 6-min walk test. We also evaluated the correlation between dyspnea scores induced by resistive loads and by the 6-min walk test. In this prospective, cross-sectional study, 31 patients with cystic fibrosis (≥15 years of age) and 31 age-, gender-, and ethnicity-matched healthy volunteers (20 females and 11 males per group) underwent inspiratory resistive loading, spirometry, and the 6-min walk test. As the magnitude of the inspiratory loads increased, dyspnea scores increased (P<0.001), but there was no difference between groups in dyspnea score (P=0.654). Twenty-six (84%) normal subjects completed all the resistive loads, compared with only 12 (39%) cystic fibrosis patients (P<0.001). Dyspnea scores were higher after the 6-min walk test than at rest (P<0.001), but did not differ between groups (P=0.080). Post-6-min walk test dyspnea scores correlated significantly with dyspnea scores induced by resistive loads. We conclude that dyspnea perception induced in cystic fibrosis patients by inspiratory resistive loading and by 6-min walk test did not differ from that induced in normal subjects. However, cystic fibrosis patients discontinued inspiratory resistive loading more frequently. There were significant correlations between dyspnea perception scores induced by inspiratory resistance loading and by the 6-min walk test. This study should alert clinicians to the fact that some cystic fibrosis patients fail to discriminate dyspnea perception and could be at risk for delay in seeking medical care.