Nancy Lennon, P.T.
Freeman Miller,M.D., Patrick Castagno,M.S.,James Richards,Ph.D.
The Alfred I. duPont Institute
1600 Rockland Road
Wilmington, Delaware 19803
INTRODUCTION: The physiologic measurement of energy expenditure is used in gait analysis to asses walking efficiency. Children with cerebral palsy often have reduced mechanical efficiency resulting in a higher energy cost of walking compared to age-matched peers. Various surgeries, orthotic devices, and physical therapy treatments attempt to improve movement efficiency and reduce this energy consumption. Developing accurate and reliable methods to measure the energy cost of walking can provide a functional outcome assesment of gait interventions in this population. The reliability of these methods and the reproducibility of physiologic measures in children with cerebral palsy needs to be documented. The purpose of this study was to investigate the between day variability of energy consumption measurements for children with CP.
METHODOLGY: Ten children, five with CP, and five non-disabled, age-matched peers volunteered for this study. Age of subjects ranged from six to sixteen years, with a mean age of ten years. Energy consumption was measured for each subject on five seperate days. A portable telemetric testing system was used to collect heart rate and oxygen consumption (VO2). Expired air was continuously sampled, mixed in a dynamic chamber, and analyzed for % O2. The portable unit transmitted data to a receiver, where it was later downloaded to a PC. Velocity was measured in meters/ minute. Heart rate and VO2 were recorded in three phases, resting, self- paced walking, and post-walk resting. Equipment was calibrated prior to each test. At the beginning of each session, HR monitor and Rudolph mask were applied and the child was asked to sit quietly for three minutes. The child then walked through an extended hallway while a minimum of four minutes of steady state walking were recorded. Mean VO2 and HR (at rest and during walk) and mean walking velocity were calculated for each subject.
RESULTS: Figure 1. Displays mean values for energy cost (energy consumption/ velocity) as a factor of either HR or VO2, for all ten subjects. Figure 2. reports the percent variation in the measurements of resting HR and VO2, walking HR, and VO2, walking velocity, and energy cost. These percentages were calculated by converting the mean and standard deviation for each variable, per subject, to a normalized score (SD/mean), and comparing scores within groups. Findings indicate that the variation in energy consumption measures for children with CP is similar to that in normal children. Despite relatively large variations in velocity for all subjects, the variability of VO2 was minimal, and demonstrated less fluctuation than measures of energy cost.
DISCUSSION: The clinical assesment of energy cost of walking has proved difficult in the past due to sophisticated testing equipment needs, and a poverty of pediatric normative data. This study examined a practical clinical method to collect energy consumption measurements. Findings for children with CP are comparable to other reports on the variability of these measures in normal children. This indicates that methods for testing established for the normal population can be applied to children with cerebral palsy as a functional outcome assesment. The relationship of velocity to VO2 needs further investigation. Although the data here do not provide a clear indication of which measures will be most useful in outcome assesment, we are encouraged with its potential for clinical testing.
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