Aerobic and anaerobic capacity in juvenile idiopathic arthritis: the cardiorespiratory response during aerobic exercise

Abstract

Juvenile idiopathic arthritis (JIA) is a common chronic disease of childhood. Children with JIA have lower peak oxygen consumption (V0₂ peak) than healthy children. In order to examine the cardiorespiratory response during aerobic exercise and the anaerobic to aerobic ratio (metabolic index), maximal exercise tests were performed in JIA subjects and age- and sex-matched controls (CON). Thirteen children aged 10 to 17 years with JIA and 9 CON participated. Peak powe r(watts, W) and total work (Joules, j) were determined with the Wingate anaerobic cycling test. VO₂ peak was measured by a maximal staged exercise test on a cycle ergometer. Cardiac output (CO, liters/minute) was measured with Doppler echocardiography. Arterial — mixed venous oxygen index (A-V0₂) and systemic vascular resistance (SVR) were calculated. Patient questionnaires included habitual activity, visual analog scale for joint pain and the childhood health assessment questionnaire. Physician completed data included active joint count and articular severity index. Compared to CON and reference age-matched norms, JIA subjects had lower aerobic fitness. VO₂ peak in JIA was 31.3 ml/min/kg (20.2-49.9), Z score -1.4 (-.06 – 2.4) and in CON was 47.9 ml/min/kg (32.7-54.1), Z score of -0.17 (-1.6-.87). [p = 0.013 V0₂ peak, p=0.011 Z score]. There were no significant differences in CO, A-V0₂ or SVR buttrends towards lower CO and higher SVR in JIA subjects were observed. During anaerobic exercise JIA subjects completed less total work (168.5 j/kg (107-252) JIA, 224 j/kg (180-248) CON, p=.036) but had similar peak power (9.7 W/kg (5.6-13.7) JIA, 11.3 W/kg (9.8-14.5) CON, p=.095). The metabolic index did not differ between JIA and CON. There was no significant correlation between disease activity, function and fitness measures in JIA subjects. Children with JIA have moderate impairments in aerobic fitness. CO and A-V0₂ during aerobic exercise did not significantly differ between JIA subjects and CON. Anaerobic fitness was mildly impaired with less total work completed by JIA subjects. Further research with larger numbers is required to determine factors contributing to limited fitness in JIA.