Testing Gait Efficiency of Limb-Deficient Children Using the Physiological Cost Index

DOREEN J. BARTLETT, BSc, PT


Gait efficiency is defined as energy cost per distance travelled.' Traditionally, energy expenditure is assessed by oxygen uptake monitoring and is calculated from the ratio of oxygen uptake to walking velocity and is expressed in millilitres of oxygen per kilogram body weight per meter travelled. Oxygen uptake monitoring equipment is not available to most clinicians, and in addition, is cumbersome in its application to children, particularly those with physical handicaps.

Butler et all have developed a formula for the Physiological Cost Index (PCI) of walking, with the knowledge that oxygen uptake and heart rate are linearly related at submaximal levels. The PCI is a gait efficiency measure and is expressed in heart beats per meter travelled. It is calculated as follows:

PCI = (HR(w) - HR(r) ) / S

Where:

HR(w) = Heart Rate Walking (heart beats/minute)
HR(r) = Heart Rate Resting (heart beats/minute)
S = Speed of Walking (meters/minute)

This group of researchers established norms with 72 children between 3 and 12 years. The mean PCI was 0.4 heart beats/meter with a standard deviation of 0. 13. No appreciable difference existed with age in this prepubertal group; although the speed of walking increases with age, the resting heart rate decreases and the ratio remains relatively constant. Test/retest reliability was within 0. 1 heart beats/meter.

Method

To administer the PCI, the following equipment is required:

a) reliable ambulatory pulse rate meter

b) stopwatch

c) alcohol swabs

d) 25 metre (27.3 yard) walkway

  1. Attach ambulatory pulse rate meter as described by manufacturer, ensuring that the skin surface is first rubbed with isopropyl alcohol to reduce skin resistance, and that all attachments are firm to reduce movement artifact.
  2. Record resting heart rate with the child seated.
  3. Ask the child to walk up and down the walkway at a comfortable walking speed. It is well known that individuals use greater energy when walking at a speed faster or slower than their free cadence3 hence the child must choose the pace. Establish a steady state.
  4. Record heart rate and time at the end of each excursion of 25 meters, repeated eight times.
  5. Calculate average walking heart rate and average speed and PCI.

Application to Limb-Deficient Children

Test/retest reliability of five limb-deficient children at British Columbia's Children's Hospital was within the same limits as described by the group that developed the PCI.

The PCI is a simple, reliable, clinical tool which can be used to compare the gait efficiency of children with lower-limb deficiencies:

  1. with different prosthetic designs,
  2. prior to and following surgical intervention,
  3. before and after a vigorous exercise program,
  4. using different ambulatory aids.

Recommendations for management can then be based on objective data.

Use of the norms established by Butler et al is not recommended for comparison because of the small sample size. PCI is, however, an appropriate means of comparing functional performance of an individual over a period of time.

Acknowledgment

I would like to thank Bonnie Sawatsky, BPE, Research Assistant, Department of Orthopedics, British Columbia's Children's Hospital, for her assistance in this project.

British Columbia's Children's Hospital, 4480 Oak Street, Vancouver, British Columbia V6H 3V4, Canada

References:

  1. Nielsen DH, Shurr DG, Golden JC, Meier K: Comparison of Energy Cost and Gait Efficiency During Ambulation in Below-Knee Amputees Using Different Prosthetic Feet-A Preliminary Report. Journal of Prosthetics and Orthotics 1:24-31, 1989.
  2. Butler P, Engelbrecht M, Major RE, TbLit JH, Stallard J, Patrick JH: Physiological Cost Index of Walking for Normal Children and Its Use as an Indicator of Physical Handicap. Developmental Medicine and Child Neurology 26:607-612, 1984.
  3. Pagliarulo MA, Waters R, Hislop Hk Energy Cost of Walking of Below-Knee Amputees Having No Vascular Disease. Physical Therapy 59:538-542, 1979.