Anomalous relationship of heart rate to oxygen consumption in children with hemiplegic cerebral palsy
Background: Co-contraction and spasticity may distort the normal relationship between heart rate and oxygen consumption in cerebral palsy.
Purpose. To compare cardio-respiratory responses to sustained isometric exercise (SET) at 50% of maximal torque between children with hemiplegic cerebral palsy (CP) and healthy controls,
Methods. Participants were 10 children with right-sided CP (nine males, one female; age 13 2 years), and 10 age- and sex-matched controls.
Results. Cybex Norm II testing showed that in CP both affected and unaffected legs had a reduced muscle volume and a low absolute maximal isometric torque. When expressed per litre of muscle volume (anthropometric estimate), torque was reduced in the affected leg, but normal for the unaffected leg. Cosmed K4b2 gas analysis during SET at 50% of maximal torque showed disproportionately high oxygen consumptions relative to heart rate and ventilation in CP, whichever leg was being tested.
Conclusions. Correction of weakness in the unaffected leg of children with CP depends on increasing muscle volume by resistance training and appropriate nutrition. Other factors such as co-contraction and spasticity compound weakness per unit volume of muscle in the affected leg. During SET, the oxygen consumption is disproportionately high relative to heart rate and ventilation. The added oxygen consumption probably reflects co-contraction and spasticity in muscles where blood flow is not restricted by the required action. This issue complicates estimates of oxygen consumption from heart rate during isometric effort, and may also modify the heart rate/oxygen consumption relationship during aerobic activity.
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