Cystic fibrosis and physiological responses to exercise

Abstract

Cardiopulmonary exercise testing is underutilized within the clinical management of patients with cystic fibrosis. But within the last 5 years, there has been considerable interest in its implementation, which has included deliberations by the European Cystic Fibrosis Society about incorporating this method within the clinical assessment of patients. This review examines the current use of cardiopulmonary exercise testing in assessing the extent and cause(s) of exercise limitation from a pediatric perspective. Examples of the measured parameters and their interpretation are provided. Critical synthesis of recent work in the oxygen uptake (VO₂) kinetics response to and following exercise is also discussed, and although identified more as a research tool, its utilization advances researchers understanding of the cardiovascular, respiratory and muscular limitations to exercise tolerance. Finally, exercise and its application in therapeutic interventions are highlighted and a number of recommendations made about the utility of exercise prescription.

Keywords::

• cardiopulmonary exercise testing
• inspiratory muscle training
• Ivacaftor
• oxygen uptake kinetics
• pediatrics
• skeletal muscle

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Despite the acceptance by clinical and exercise physiologists that the cardiopulmonary exercise testing (CPET) is the most objective test to determine the limits and/or mechanisms of exercise (in)tolerance, it remains underutilized in clinical practice.

• However, the CPET is growing in popularity as more normative data are published and its applicability to clinical practice is being established, especially in the context of exercise interventions.

• The CPET has been found to be a valid and reliable method for the assessment of aerobic function in children and adolescents with cystic fibrosis (CF). A ‘verification phase’ can conclusively confirm the attainment of a valid maximal oxygen uptake (VO_2max) test, although this ‘verification phase’ has yet to be fully integrated into the clinical setting.

• Submaximal parameters collected during a CPET allow for a comprehensive evaluation of patients’ cardiorespiratory fitness (i.e., lactate threshold [or its non-invasive equivalent, the gas exchange threshold], the kinetics of VO₂ and work efficiency [ΔVO₂/ΔWR]) and need to be evaluated alongside maximal values.

• Test–re-test reliability in children and adolescents with CF show higher within-subject variation compared to adults, but this data allows for the establishment of clinically meaningful changes in VO_2max.

• Methods to establish the cause of aerobic function limitations in patients with CF, that is, reduced central or peripheral mechanisms, are more relevant to clinical research studies, but the documenting of exercise dysfunction will ultimately enhance our understanding of targeted therapeutic interventions.

• The exciting development of gene-targeted drugs for patients with CF has led to good improvements in traditional outcome measures, that is, FEV₁, sweat chloride and body mass, but there is a lack of objective aerobic exercise function measurements.

• Objectively measured aerobic function tests such as the CPET should be a standard clinical measurement in any assessment and monitoring of health of the CF patient.