ABSTRACT
Skeletal muscle quadriceps low-frequency fatigue (LFF) during exercise promotes improvements in exercise capacity with exercise training. In healthy subjects, eccentric muscle work induced by downhill walking (DW) generates higher muscular stress, whilst metabolic cost is lower compared to level walking (LW). We investigated quadriceps LFF and metabolic cost of DW in patients with chronic obstructive pulmonary disease. Ten participants (67 ± 7 years, FEV1 51 ± 15% predicted) performed DW, DW carrying a load (DWL) of 10% body weight via vest and LW, in random order. Quadriceps potentiated twitch force (TWqpot) was assessed before and after each walk, and muscle damage was assessed before and 24 hours after each walk via serum creatine kinase (CK) levels. Ventilation (VE) and oxygen consumption (VO2) were measured via breath-by-breath analysis during each walk. DW and DWL resulted in a greater decrease in TWqpot (-30 ± 14 N in DW, p < 0.05; and -22 ± 16 N in DWL, p < 0.05) compared to LW (-3 ± 21 N, p > 0.05). CK levels only increased 24 hours following DW and DWL (p < 0.05). DW and DWL showed lower VE and VO2 than LW (p < 0.05). DW is associated with enhanced quadriceps LFF and lower cardiorespiratory costs than LW. The addition of a chest load to DW does not seem to enhance these effects.
Subject(s)
Exercise Therapy/methods , Pulmonary Disease, Chronic Obstructive/rehabilitation , Walking/physiology , Aged , Dyspnea/etiology , Female , Humans , Male , Middle Aged , Muscle Fatigue , Oxygen Consumption , Pulmonary Disease, Chronic Obstructive/physiopathology , Quadriceps Muscle/physiology , Treatment Outcome , Weight-BearingABSTRACT
BACKGROUND: Fractional exhaled NO (Fe,NO) has yielded inconsistent results in COPD. Measuring exhaled NO at multiple flow rates however, allows to dissect exhaled NO in an alveolar (CAlv,NO) and bronchial (J'aw,NO) fraction, which are claimed to better reflect the bronchial and alveolar inflammation in COPD. We examined whether the use of Fe,NO, CAlv,NO and J'aw,NO may contribute to the clinical diagnosis of COPD. METHODS: One hundred and fifty one patients were included in this case-control design: 28 healthy nonsmokers, 39 healthy smokers, 55 COPD nonsmokers and 29 COPD smokers. Prior to spirometry, exhaled NO was measured at three different flow rates (50, 100 and 200 ml/s; NIOX-FLEX) from which Fe,NO, CAlv,NO and J'aw,NO were calculated. RESULTS: Mean Fe,NO, mean CAlv,NO and mean J'aw,NO of healthy individuals were not significantly different from COPD patients and none of these variables correlated with FEV(1). In both healthy and COPD patients, current smoking significantly reduced Fe,NO, J'aw,NO and CAlv,NO. Multivariate analysis demonstrated that in contrast to gender, age, BMI, GOLD stage and the use of inhaled corticosteroids, current smoking was the only variable affecting CAlv,NO. (p=0.0115) CONCLUSION: We conclude that similar to single breath exhaled NO, exhaled NO at different flow rates does not contribute to the diagnosis of COPD in standard respiratory practice.
