Oxygen uptake kinetics and exercise capacity in children with cystic fibrosis

Abstract

Exercise capacity, an objective measure of exercise intolerance, is known to predict quality of life and mortality in cystic fibrosis (CF). The mechanisms for exercise intolerance in patients with cystic fibrosis (CF), however, have yet to be fully elucidated. Accordingly, this study sought to investigate oxygen uptake kinetics and the impact of fat-free mass (FFM) on exercise capacity in young patients with CF. 16 young patients with CF (age 13 ± 4 years; 10 female) and 15 matched controls (age 14 ± 3 years; nine female) participated. Pulmonary function and a maximal exercise test on a cycle ergometer using the Godfrey protocol were performed. Exercise capacity (VO2 peak), VO2 response time (VO2 RT), and functional VO2 gain (ΔVO2 /ΔWR) were all determined. Lung function was the only demographic parameter significantly lower (P < 0.05) in CF compared to controls. Exercise capacity was lower in CF (P < 0.014) only when VO2 peak was normalized for FFM (43.5 ± 7.7 vs. 50.6 ± 7.4 ml/kg-FFM/min) or expressed as % predicted (70.1 ± 14.3 vs. 85.4 ± 16.0%). The VO2 RT was slower (36.1 ± 15.1 vs. 25.0 ± 12.4 sec; P = 0.03) and the ΔVO2 /ΔWR slope was lower (8.4 ± 3 ml/min/watt vs. 10.1 ± 1.4 ml/min/watt; P = 0.02) in patients compared to controls, respectively. In conclusion, a delayed VO2 response time coupled with the lower functional VO2 gain (ΔVO2 /ΔWR) suggest that young patients with CF have impairment in oxygen transport and oxygen utilization by the muscles. These data in addition to differences in VO2 peak normalized for FFM provide some insight that muscle mass and muscle metabolism contribute to exercise intolerance in CF.

Evidence of microvascular dysfunction in patients with cystic fibrosis

“…Expired gases were analyzed breath-by-breath by a metabolic cart (True One 2400, ParvoMedics, Sandy, UT). O 2 consumption (V O2) was obtained and normalized for total body weight (V O2/kg) as previously described (13). Maximal exercise capacity (V O2 max) was verified using the American College of Sports Medicine exercise testing criteria (1a).…”

Respiratory muscle training improves respiratory muscle endurance but not exercise tolerance in children with cystic fibrosis

“…Nevertheless, subclinical right heart impairment as contributing factor to exercise limitation cannot be ruled out as CF associated myocardial changes may develop already in childhood . Nutritional status has also been associated with exercise performance in CF with poor nutrition leading to a reduced muscle mass . However, body mass index was in the normal range (median z‐score −0.1) in our population making malnutrition as an exercise limiting factor unlikely.…”

Exercise testing in patients with cystic fibrosis—importance of ventilatory parameters

“…Briefly, expired gases were analyzed in a mixing chamber by a TruOne® 2400 metabolic cart (ParvoMedics, Sandy, UT) and analyzed as 30 second averages to obtain VO 2 peak and peak minute ventilation (V E peak). Ventilatory threshold (VT) was determined using the v-slope method (Beaver et al 1986) for calculation of percent VO 2 peak at VT. Additional ventilatory parameters including the ratio of V E to both VO 2 and carbon dioxide output (VCO 2 ) at peak exercise (V E /VO 2 peak and V E /VCO 2 peak, respectively), end-tidal CO 2 (P ET CO 2 ), and the V E /VCO 2 slope, were determined according to previously published methodology (Schwaiblmair et al 2012; Fielding et al 2015). Maximum voluntary ventilation (MVV) was calculated as 27.7(FEV 1 ) + 8.8(predicted FEV 1 ) for patients aged ≤18 years (Stein et al 2003) or FEV 1 × 40 for patients aged >18 years (Wasserman et al 2005) and expressed relative to peak V E (V E /MVV).…”

“…Several factors contribute to exercise intolerance in CF including skeletal muscle dysfunction, dysfunctional oxygen uptake kinetics, and abnormal pulmonary mechanics (Fielding et al 2015; Gruet et al 2017; Troosters et al 2009; McKone et al 2005). However, while the accelerated long-term decline in lung function and exercise capacity in patients with CF has been well-documented (Corey et al 1976; Penketh et al 1987; Cantin 1995; Pianosi et al 2005), long-term changes in ventilatory responses to exercise in CF remain unclear.…”