Ventilation efficiency to exercise in patients with cystic fibrosis

Abstract

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 (VO2peak), 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 VEint 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 (VEint) 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.

Does partitioning the subcomponents of the ventilatory equivalent for carbon dioxide slope provide evidence that ventilatory efficiency is retained in cystic fibrosis?

“…Clinicians and physiologists interested in cardiopulmonary exercise testing (CPET) and ventilatory efficiency appreciate adolescent physiological responses to exercise are not directly translational to the adult, and vice‐versa . It follows that while Kampouras et al provides plentiful discussion involving comparisons between their CPET data and those of our group (Van Iterson et al) reported in adult CF, they missed a critical opportunity to dissect the body of evidence so as to underscore why they consider it is reasonable to compare studies of adults with those of adolescents, particularly in CF. This is a key omission because contrary to their CPET interpretations and discussion, it is recognized the V̇ E /V̇CO 2 slope and reported thresholds for adults are not translational to adolescent populations and vice‐versa, ventilatory efficiency inversely relates with adult age, and cardiopulmonary disease exacerbates effects of aging on ventilatory inefficiency .…”

“…Basic human factors, such as female sex and again, increasing adult age, can lead to an elevated V̇ E /V̇CO 2 slope without heeding effects caused by disease . The comparison of V̇ E /V̇CO 2 slope responses across stratifications of percent predicted V̇O 2peak in Kampouras et al also does not account for age since the reference equations used take only into account height. Equally concerning, American Thoracic Society reference equations used by Kampouras et al to calculate percent predicted FEV 1 reflect spirometry of preschool aged children (2‐6 years).…”

“…The authors propose a thought‐provoking mechanistic association aimed at explaining why individuals with CF do not demonstrate abnormal ventilatory efficiency when others have suggested otherwise. Compensatory high respiratory frequency (f B ) coupled with increased physiological dead space (V D ) ventilation is a key mechanism which the authors claim help individuals with CF “retain” ventilatory efficiency . In this context, there are two major aspects of the study by Kampouras et al that in our opinion would benefit from further clarification and commentary.…”

“…Compensatory high respiratory frequency (f B ) coupled with increased physiological dead space (V D ) ventilation is a key mechanism which the authors claim help individuals with CF “retain” ventilatory efficiency . In this context, there are two major aspects of the study by Kampouras et al that in our opinion would benefit from further clarification and commentary.…”

“…We have recently read with great interest the manuscript by Kampouras et al who explored the topic of ventilatory efficiency in individuals with cystic fibrosis (CF). These authors should be given credit for an outstanding job of highlighting there is clinical value in understanding the integrative physiological mechanisms and origins from which the slope for the ventilatory equivalent for carbon dioxide (V̇ E /V̇CO 2 ) measurement relates with ventilatory efficiency.…”