Oxygen Uptake To Work Rate Relationship During Exercise In Children With Lung, Heart Or Muscle Disease.

Abstract

PURPOSE: The purpose of this study was to investigate the oxygen uptake to work rate relationship (DVO2/DWR) in children with a chronic condition that limits O2 delivery (lung disease or cardiac disease) or utilization (myositis).We hypothesized that lower values of the DVO2/DWR during exercise would be a good indicator for limited O2 delivery or utilization in the above group of patients. METHODS: Four groups of subjects were included in this study; muscle disease (Juvenile dermatomyositis; JDM; N=13), lung disease (cystic fibrosis; CF; N=13), congenital heart disease (CHD; Fontan type circulation (N=4) or repair of tetralogy of Fallot (N=9)), and healthy children (N=44). All children performed a cardiopulmonary exercise test to exhaustion on a cycle ergometer with respiratory gas analysis. Ventilatory threshold (VT) was assessed using the equivalent method (Caiozzo et al JAP 1982). The linear regression was calculated for the relationship between oxygen uptake and work rate using all DVO2/DWR data or using the data from unloaded cycling to the VT (DVO2/DWR-VT). RESULTS: The values of DVO2/DWR-VT slope were significantly lower in children with JDM (7.7±3.0 ml O2/Watt) compared to healthy controls (9.6±1.3 ml O2/Watt; p<0.05). The DVO2/DWR slopes differed when calculated using two different ways in healthy children and in children with congenital heart disease (p<0.05). Compared to the healthy controls (9.2 ±1.0 ml O2/Watt), values for the DVO2/DWR slope were lower in children with CHD (8.4±1.9 ml O2/Watt) and in children with JDM (8.0±2.8 ml O2/Watt). On the other hand, the DVO2/DWR slope values were higher in children with CF (10.1±1.3) than in the controls (9.2 ±1.0 ml O2/Watt; p=0.025). CONCLUSIONS: Lower values of DVO2/DWR-VT and the DVO2/DWR slopes seem to be a good and sensitive indicators of limited O2 delivery or utilization during exercise in children.