Breathing Pattern Adopted by Children with Cystic Fibrosis with Mild to Moderate Pulmonary Impairment during Exercise

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.

Clinical recommendations for cardiopulmonary exercise testing in children with respiratory diseases

INTRODUCTION

Cardiopulmonary exercise testing (CPET) quantitates and qualitates the integrated physiological response of a person to incremental exercise and provides additional information compared to static lung function tests alone.

AREAS COVERED

This review covers rationale for the use of CPET parameters beyond the usual parameters like peak oxygen uptake and peak minute ventilation in children with respiratory disease.

EXPERT OPINION

CPET provides a wealth of data from rest, submaximal and maximal exercise and data during recovery from exercise. In this review, an interpretative approach is described for analyzing CPET data in children with respiratory disease.

Ventilation efficiency to exercise in patients with cystic fibrosis

INTRODUCTION

Exercise ventilation efficiency index in cardiopulmonary exercise testing (CPET) is elevated in patients with heart failure providing useful information on disease progression and prognosis. Few data, however, exist for ventilation efficiency index among cystic fibrosis (CF) patients.

AIMS

To assess ventilation efficiency index (ΔVE/ΔVCO₂ or V'E/V'CO₂ slope) and intercept of ventilation (VE-intercept) in CF patients with mild, moderate, and severe cystic fibrosis (CF) lung disease. To assess possible correlations with ventilation inhomogeneity and structural damages as seen on high resolution computed tomography (HRCT).

METHODS

CF patients with mild (FEV₁  > 80%, n = 47), moderate (60% < FEV₁  < 80%, n = 21), and severe (FEV₁  < 60%, n = 9) lung disease, mean age 14.9 years participated. Peak oxygen uptake (VO₂ peak), pulmonary ventilation at peak exercise (VE), respiratory equivalent ratios for oxygen and carbon dioxide at peak exercise (VE/VO₂ , VE/VCO₂ ), end-tidal CO₂ (PetCO₂ ), and ΔVE/ΔVCO₂ , ΔVE/ΔVO₂ in a maximal CPET along with spirometry and multiple breath washout indices were examined. HRCT scans were performed and scored using Bhalla score.

RESULTS

Mean ΔVE/ΔVCO₂ showed no significant differences among the three groups (P = .503). Mean VE_int discriminated significantly among the different groups (p ² < 0.001). Ventilation efficiency index did not correlate either with LCI or Bhalla score. However, VE together with ΔVE/ΔVCO₂ slope could predict Bhalla score (r ²  = 0.869, P = .006).

CONCLUSION

No significant differences were found regarding ΔVE/ΔVCO₂ slope levels between the three groups. Ventilation intercept (VE_int ) was elevated significantly as disease progresses reflecting increased dead space ventilation. CF patients retain their ventilation efficiency to exercise even as lung function deteriorates by adopting a higher respiratory rate along with increased dead space ventilation.

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.

Ventilatory response to exercise in adolescents with cystic fibrosis and mild-to-moderate airway obstruction

Data regarding the ventilatory response to exercise in adolescents with mild-to-moderate cystic fibrosis (CF) are equivocal. This study aimed to describe the ventilatory response during a progressive cardiopulmonary exercise test (CPET) up to maximal exertion, as well as to assess the adequacy of the ventilatory response for carbon dioxide (CO₂) exhalation. Twenty-two adolescents with CF (12 boys and 10 girls; mean ± SD age: 14.3 ± 1.3 years; FEV₁: 78.6 ± 17.3% of predicted) performed a maximal CPET. For each patient, data of a sex- and age matched healthy control was included (12 boys and 10 girls; mean ± SD age: 14.3 ± 1.4 years). At different relative exercise intensities of 25%, 50%, 75%, and 100% of peak oxygen uptake (VO_2peak), breathing pattern, estimated ventilatory dead space ventilation (VD/VT ratio), minute ventilation (VE) to CO₂ production relationship (VE/VCO₂-slope), partial end-tidal CO₂ tension (P_ETCO₂), and the VE to the work rate (VE/WR) ratio were examined. VO_2peak was significantly reduced in CF patients (P = 0.01). We found no differences in breathing pattern between both groups, except for a significantly higher VE at rest and a trend towards a lower VE at peak exercise in patients with CF. Significantly higher values were found for the estimated VD/VT ratio throughout the CPET in CF patients (P < 0.01). VE/VCO₂-slope and P_ETCO₂ values differed not between the two groups throughout the CPET. VE/WR ratio values were significantly higher in CF during the entire range of the CPET (P < 0.01). This study found an exaggerated ventilatory response (high VE/WR ratio values), which was adequate for CO₂ exhalation (normal VE/VCO₂-slope and P_ETCO₂ values) during progressive exercise up to maximal exhaustion in CF patients with mild-to-moderate airway obstruction.

Mechanical ventilatory constraints during incremental exercise in healthy and cystic fibrosis children

AIM

To analyze breathing pattern and mechanical ventilatory constraints during incremental exercise in healthy and cystic fibrosis (CF) children.

METHODS

Thirteen healthy children and 6 children with cystic fibrosis volunteered to perform an incremental test on a treadmill. Exercise tidal flow/volume loops were plotted every minute within a maximal flow/volume loop (MFVL). Expiratory flow limitation (expFL expressed in %Vt) was evaluated and end-expiratory and end-inspiratory lung volumes (EELV and EILV) were estimated from expiratory reserve volume relative to vital capacity (ERV/FVC) and from inspiratory reserve volume relative to vital capacity (IRV/FVC).

RESULTS

During the incremental exercise, expFL was first observed at 40% of maximal aerobic speed in both groups. At maximal exercise, 46% of healthy children and 83% of CF children presented expFL, without significant effect of cystic fibrosis on the severity of expFL. According to the two-way ANOVA results, both groups adopted similar breathing pattern and breathing strategies as no significant effect of CF has been revealed. But, according to one-way ANOVA results, a significant increase of ERV/FVC associated with a significant decrease of IRV/FVC from resting value shave been observed in healthy children at maximal exercise, but not in CF children.

DISCUSSION

The hypothesis of this study was based on the assumption that mild cystic fibrosis could induce more frequent and more severe mechanical ventilatory constraints due to pulmonary impairment and breathing pattern disturbances. But, this study did not succeed to highlight an effect of mild cystic fibrosis on the mechanical ventilatory constraints (expFL and dynamic hyperinflation) that occur during an incremental exercise. This absence of effect could be due to the absence of an impact of the disease on spirometric data, breathing pattern regulation during exercise and breathing strategy.

Ventilatory pattern and energy expenditure are altered in cystic fibrosis mice

BACKGROUND

Altered ventilatory pattern and increased energy expenditure are facets of the complex cystic fibrosis (CF) phenotype. It is not known whether these are inherent attributes of CF, secondary consequences of lung infection or other disease complications.

METHODS

Studies were performed in congenic C57BL/6J, F508del (Cftr((tm1kth))) and CF gut-corrected (F508del) mice. Ventilatory patterns were measured using whole-body plethysmography. Indirect calorimetry was used to determine oxygen consumption, carbon dioxide production and resting energy expenditure.

RESULTS

CF mice (F508del and F508del gut-corrected) have a significantly faster respiratory rate and increased ventilatory pattern variability as compared to non-CF mice. F508del but not CF gut-corrected mice had significantly increased energy expenditure per gram body weight.

CONCLUSIONS

CF mice exhibit a faster, more variable ventilatory pattern. These changes were present in the absence of detectable infection or illness due to gastrointestinal obstruction. Increased resting energy expenditure does not completely account for these differences.

Is static hyperinflation a limiting factor during exercise in adolescents with cystic fibrosis?

Increased work of breathing is considered to be a limiting factor in patients with cystic fibrosis (CF) performing aerobic exercise. We hypothesized that adolescents with CF and with static hyperinflation are more prone to a ventilatorily limited exercise capacity than non-static hyperinflated adolescents with CF. Exercise data of 119 adolescents with CF [range 12-18 years], stratified for static hyperinflation, defined as ratio of residual volume to total lung capacity (RV/TLC) > 30%, were obtained during a progressive bicycle ergometer test with gas analysis and analyzed for ventilatory limitation. Static hyperinflation showed a significant, though weak association (Φ 0.38; P < 0.001) with a ventilatorily limited exercise capacity (breathing reserve index at maximal effort >0.70; FEV(1)  < 80% predicted and reduced exercise capacity, defined as VO(2peak)  < 85% predicted). Analysis of association for increasing degrees of hyperinflation showed an increase to Φ 0.49 (P < 0.001) for RV/TLC > 50%. In adolescents with static hyperinflation, peak work rate (W(peak) ; 3.1 ± 0.7 W/kg (75.1 ± 17.3% of predicted), peak oxygen uptake (VO(2peak) /kg (ml/min/kg); 39.2 ± 9.2 ml/min/kg (91.0 ± 20.3% of predicted), peak heart rate (HR(peak) ; 176 ± 19 beats/min) were significantly (P < 0.05) decreased when compared with non-static hyperinflated adolescents (W(peak) 3.5 ± 0.5 W/kg (81.4 ± 10.0% of predicted)); VO(2peak) /kg (ml/min/kg); 43.1 ± 7.5 ml/min/kg (98.0 ± 15.1% of predicted); and HR(peak) 185 ± 14 beats/min). Additionally, no difference was found in the degree of association of FEV(1) (%) and RV/TLC (%) with VO(2peak) /kg(pred) and W(peak) /kg(Pred) , but we found the RV/TLC (%) to be a slightly stronger predictor of VO(2peak) /kg(pred) and W(peak) /kg(Pred) than FEV(1) (%). These results indicate that the presence of static hyperinflation in adolescents with CF by itself does not strongly influence ventilatory constraints during exercise and that static hyperinflation is only a slightly stronger predictor of W(peak) /kg(Pred) and VO(2peak) /kg(Pred) than airflow obstruction (FEV(1) (%)).

Supramaximal verification of peak oxygen uptake in adolescents with cystic fibrosis

PURPOSE

To study whether peak oxygen uptake ((Equation is included in full-text article VO₂ peak), attained in traditional cardiopulmonary exercise testing (CPET) in adolescents with cystic fibrosis (CF), could be verified by a supramaximal exercise test.

METHODS

Sixteen adolescents with CF (forced expiratory volume in 1 second as % of predicted [range, 45%-117%]) volunteered and successively performed CPET and a supramaximal test (Steep Ramp Test [SRT] protocol).

RESULTS

Cardiopulmonary exercise testing and the SRT resulted in comparable cardiorespiratory peak values. We found no significant difference in oxygen uptake ((Equation is included in full-text article VO₂ peak/kg) between CPET and the SRT (38.9 ± 7.4 and 38.8 ± 8.5 mL min kg, respectively; P = .81). We found no systemic bias for CPET and SRT measurements of (Equation is included in full-text article VO₂  peak/kg and no differences between CPET and SRT (Equation is included in full-text article VO₂  peak values within and between the maximal and non-maximal effort groups (P > .4).

CONCLUSION

The (Equation is included in full-text article VO₂  peak measured in CPET seems to reflect the true (Equation is included in full-text article.)O2 peak in adolescents with CF.