Assessment of fitness in patients with cystic fibrosis and mild lung disease

Abstract

Abstracttests, leading to the suggestion that regular Background -Maximal exercise testing is aerobic training may increase life expectancy. 8 used in patients with cystic fibrosis to as-To investigate this important issue, improved sess functional status and prognosis. The methods of quantifying aerobic fitness are relactate threshold is an index of aerobic quired which are not excessively stressful and fitness with significant advantages over are readily acceptable to patients. maximal exercise tests. This study wasVarious techniques have been used to assess undertaken to determine if the lactate fitness in subjects with cystic fibrosis including threshold might be identified, non-in-maximal oxygen consumption, maximum vasively, in adult patients with cystic power output, time to exhaustion during infibrosis and mild lung disease by measure-cremental exercise tests, time to exhaustion at ment of ventilatory and gas exchange para-a fixed work load, or time taken to complete a meters.fixed distance. 5 6 8 9 However, there are many Methods -Ten subjects with mild cystic difficulties associated with their use in this fibrosis (forced vital capacity (FVC) >70% context. 10 In particular, all require the subject predicted) and 10 healthy controls under-to make maximal efforts, rendering such tests took an incremental exercise test on a highly dependent on motivation. bicycle ergometer. Ventilation and gasThe lactate threshold is an alternative index exchange parameters were measured con-of aerobic fitness which has been widely used tinually and arterialised venous blood pH, in athletes. As the workload progressively incarbon dioxide tension (PCO 2 ), and lactate creases during an incremental exercise test, a concentrations were measured at intervals critical exercise intensity is reached above throughout the tests.which blood lactate levels increase proResults -In subjects with cystic fibrosis gressively, reflecting an abrupt rise in lactate there was no significant difference between concentration in the exercising muscles. 10 The the mean gas exchange and lactate thresh-oxygen uptake of the subject at this critical olds (mean difference 1.0 (95% confidence work load is called the lactate threshold (LT), interval (CI) of the mean -1.5 to 3.44) ml/ which is a better indicator of aerobic fitness kg/min). In contrast, there was a sig-than other indices commonly used. It permits nificant difference between the mean identification of the optimum training intensity ventilatory and lactate thresholds (3.8 for an individual and does not require exercise (95% CI 0.9 to 6.7) ml/kg/min). Arterialised to exhaustion for its determination. 10-14 venous PCO 2 increased significantly duringIn healthy subjects the LT may be dethe exercise tests. In healthy subjects the termined non-invasively by identification of the mean differences between these thresholds ventilatory threshold (VenT) which is defined were not significantly different from zero as the point during an incremental exercise test and PCO 2 fell significantly during the...

Symptoms, lactate and exercise limitation at peak cycle ergometry in adults with cystic fibrosis

“…Several smaller studies have included lactate measurement in the assessment of peak exercise, and have shown that CF subjects do generate a rise in blood lactate on progressive exercise [16][17][18][19]. The present authors found raised lactate levels at peak exercise in CF patients across the full range of pulmonary disease severity, with those in the middle/ moderate group achieving very similar peak concentrations to controls.…”

“…This is the case in normal subjects at peak exercise, but in the CF subjects this was occurring at lower work rates. The early occurrence of the ''lactate threshold'' during incremental exercise has been reported in patients with mild CF [18], and also in subjects with COPD [24]. The implication of the present lactate data is that CF patients with mild or moderate pulmonary disease are not limited by ventilation, but rather by nonpulmonary factors leading to muscle fatigue.…”

“…However, there is little data concerning lactate accumulation during exercise in CF, although several small studies in subjects with milder disease have shown that lactate accumulation occurs [16][17][18][19]. There is very little information concerning symptom limitation during exercise in CF.…”

Cardiopulmonary Exercise Testing in the Functional and Prognostic Evaluation of Patients with Pulmonary Diseases

“…In particular, airway dead space is independent from V T , thus in cases of reduction in V T the patient has a greater proportion of dead space for each breath. However, several studies in CF patients with mild or moderate pulmonary disease reported increases in lactate levels [125,126,127,128] and early occurrence of the lactate threshold [127] during incremental exercise, indicating an increase in muscle anaerobic metabolism and suggesting that peak exercise is not limited by ventilation, but rather by nonpulmonary factors that lead to leg fatigue. A relatively low V′ E /MVV at peak exercise and high HR reserve supported this interpretation.…”

Exercise Performance and Breathing Patterns in Cystic Fibrosis

“…Several studies with mild or moderate pulmonary disease reported increases in lactate levels and early occurrence of the lactate threshold during incremental exercise, indicating an increase in muscle metabolism and suggesting that peak exercise is not limited by ventilation, but rather by non pulmonary factors that lead to leg fatigue (Moorcroft et al, 2005, Mc Loughlin et al, 1997, Nikolaizik et al, 1998 In a study included 104 CF who performed progressive cycle ergometry to a symptom limited maximum, the conclusion was that the main factor limiting exercise in mild to moderate disease is peripheral muscle effort (Moorcroft et al, 2005). Reduced muscle performance may be due to poor nutritional status or reduced habitual activity.…”