ENERGY COST INDEX AS AN ESTIMATE OF ENERGY EXPENDITURE OF

ASSISTED AMBUMTION CEREBRAL-PALSIED CHILDREN DURING

Jessica Rose John M. Medeiros Rochelle Parker

Decisions regarding the use of ambulatory aids are often based on a subjective assessment of the patient’s gait. The purposes of aids range from allowing ambulation in an otherwise non-ambu- latory patient to improving the efficiency or cosmesis of gait. Information on energy expenditure during assisted ambulation provides additional objective data and allows for a more logical and appropriate selection or modification of equipment.

Energy expenditure decreases when appropriate assistive devices are used (Bard and Ralston 1959, Erdman et al. 1960, Inman et al. 1961, Dasco e f al. 1963, Corcoran et al. 1970, Ganguli et a/ . 1974a, b, Hash 1978). Any ambulatory aid that increases the effort required is likely to be abandoned (Long and Lawton 1955, Gordon 1956, Gordon and Vanderwalde 1956, Clinkingbeard e f al. 1964, Rosman and Spira 1974).

Indirect calorimetry estimates energy expenditure accurately by recording oxygen consumption. However, this method is cumbersome and in many clinics the instrumentation may not be available (Shepherd 1975, Ghosh et al. 1980). Although heart rate may be affected by medication and illness, in a controlled environment during the steady state of work, heart rate is a convenient index of energy expenditure. For normal people and those with lower-extremity handicaps

the relationship between heart rate and oxygen consumption is linear from the resting state up to submaximal exercise level, although the slope is different for the two groups (Asmussen et al. 1960, Poulsen and Asmussen 1963, Astrand and Rodahl 1970, Ganguli et al. 1975, Ganguli 1977, Ganguli and Datta 1978, Ghosh e f al. 1980). For normal children and teenagers, heart rate and oxygen consumption data during ambulation appear to be positively correlated (Waters ef al. 1978, Ralston 1983).

An energy cost index based on heart rate per unit distance walked reflects heart rate in relation to speed. In a clinical setting this is a practical way of objectively evaluating ambulation with assistive equipment. Similar energy cost indices have been derived utilizing oxygen consumption in relationship to speed, e.g. milliliters of oxygen consumed per meter (Nakagiri 1976) and average distance walked per liter of oxygen consumed (Dounis et al. 1980).

Objective studies on energy expenditure of assisted ambulation in children are scarce. Most research compares the energy expenditure of ambulation of cerebral- palsied children with that of normal children (Campbell and Ball 1978, Sutherland 1978).

Many children with cerebral palsy are candidates for ambulation with either a wheeled walker or bilateral quad canes.

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TABLE I Sex, age, height, weight and ambulatory aid used daily for each child

~~ ~ ~

Child Sex Age Height Weight Ambulatory (yrs) (em) (kg) aid

1 M 4.5 91.4 13.4 2' M 4.5 101.5 14.7 3' M 12.0 135.6 30.8 4' F 6.5 90.3 13.2 5 M 7.0 106.3 17.7 6 M 7.0 106.7 18.2 7 M 7 . 0 116.8 20.8 8' M 5 . 5 96.4 16.3 9 F 4.0 96.5 16.3

10' M 12.0 136.8 31.6 11' F 5.5 92.3 16.2 12' F 5 . 0 91.2 16.0

canes canes walker walker canes canes canes

walker canes canes

walker walker

'Group 11.

When making a decision as to which device should be used on a daily basis the clinician must weigh up the benefits of the walker (i. e. better support and increased stability) against those of the quad canes (i.e. better postural alignment and a more normal gait pattern). The purpose of this study was to derive an energy cost index for cerebral- palsied children using both devices, allowing an objective decision to be made.

Material and method Twelve children (eight males, four females) participated in the study. All had either quadriplegic or diplegic spastic cerebral palsy. Table I lists the sex, age, height, weight and type of ambulatory aid used on a daily basis for each child. The mean age of the children was 6.7 years (range 4 to 12 years), mean height was 105.2cm (range 90.3 to 135.6cm) and mean weight was 18.8kg (range 12.2 to 31.6kg). Selection criteria for inclusion in this study were as follows: (1) Capable of ambulating independently with bilateral quad canes and wheeled walkers for at least six months. (2) Able to walk continuously with both a wheeled walker and bilateral quad cane for at least five minutes. (3) Currently living at home and attending a special education school.

A rectangular tract 10 meters long and 6

meters wide was marked off with tape in a quiet, uncarpeted area. For each child the order that ambulatory aids were used in the walking trials was determined randomly.

Each child attended one session during which heart-rate recordings and distance walked were obtained. Surface electrodes were applied to the skin on the right and left midclavicular lines, directly over the clavicles and near the seventh intercostal space on the left midclavicular line. The electrodes were attached to a Hewlett- Packard ECG telemetry transmitter. The heart rate was recieved by an antenna and fed into the Hewlett-Packard recorder (Hewlett-Packard Medical Electronics Division, 175 Wyman Street, Waltham, MA 02154). Resting heart rate was monitored for the last two minutes of a period of five minutes of quiet sitting. Each child was then instructed to walk at a comfortable speed and subsequently walked around the rectangular track at a self-selected speed using either a wheeled walker or bilateral quad canes for five minutes. Heart rate was monitored for the last two minutes of the trial and the distance walked was measured. The child then sat quietly until heart rate had returned to a resting state f5 per cent of baseline and remained there for at least two minutes. The second walking trial then began with the child using the other ambulatory aid.

Data analysis For each trial the child's average heart rate, walking speed and number of heart beats per unit distance walked were calculated. Mean heart rate in beats per minute was determined by averaging the heart rate values obtained over the two- minute measuring interval. The average speed in meters per minute was determined by dividing the distance walked in the five- minute walking trial by five minutes.

In order to take into account the varying speed of each child, an energy cost index was derived based upon the average number of heart beats per unit distance walked i. e. heart beats per minute divided by meters per minute. Significant changes in heart rate were defined as changes in excess of 10 beats per minute (Stallard er al. 1978b).

190 180 170 160 150

Average heart rate in 140

130 120 110 100 90 80 7 0

beats per minute

I- 'i 187 0 RESTING OUADCANES WALKERS

2 3 4 8 10 11 12 1 5 6 7 9 - - GROUP 1 GROUP 2

Fig. I . Average heart rate for each child at rest and ambulating with wheeled walkers and bilateral quad canes.

50

4 0

Average speed in meters per minute 30

20

1 0

0

I 50 6 QUADCANES

2 3 4 0 to 11 12 1 5 6 7 9 L.---y-%- ,J -

GROUP 1 GROUP 2

Fig. 2. Average speedfor each child ambulating with a wheeled walker and bilateral quad canes.

Results Figure 1 shows the average heart rate for each child at rest and while walking with a walker and canes. The mean resting heart rate for all children was 101 beats per minute (bpm). Heart rate was significantly higher during walking. The mean value recorded while ambulating with a walker was 164bpm and with canes was 157bpm.

Figure 2 shows average walking speed in meters per minute (m/min) for each child during ambulation with a walker and canes. Average walking speed was 20m/min with a walker and 27m/min with canes.

Figure 3 shows the energy cost index o r average number of heart beats per meter for each child during ambulation with a walker and canes. Two functional groups appeared according to the energy cost index, Group I consisted of children 2, 3 ,4 , 8, 10, 11 and 12 whose energy cost indices were from 1 . 7 to 39.8 beats per meter lower when ambulating with walkers than when ambulating with quad canes. Five of these children (3, 4, 8, 11 and 12) used walkers on a daily basis and the other two (2 and 10) used quad canes on a daily basis. Group 11 consisted of children 1,5,6,7 and 9 whose energy cost indices 48 7

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488

QUADCANES 50 1 WALKERS

40

Average number of heart beats per meter 30

2 0

10

0 2 3 4 8 1 0 1 1 1 2 0 1 5 6 7 9 --- -

GROUP 1 GROUP 2

Fig. 3. Energy cost index for each child walking with a wheeled walker and bilateral quad canes.

were from 0 to 1 8 beats per meter lower when ambulating with quad canes than when ambulating with walkers (Fig. 3). All children in this group utilized quad canes on a daily basis.

Discussion The mean resting heart rate of children with cerebral palsy was l0lbpm. This does not differ from the mean values published for normal children of the same age (Johnson et al. 1978).

In general, extremely high heart rates and slow walking speeds were recorded for the children during ambulation with assistive devices. The mean heart rate while ambulating with walkers and canes was 164bpm and 157bpm, respectively, as compared to 114bpm for normal children ambulating without assistive devices (Waters et al. 1983). The mean walking speed while ambulating with walkers and canes was 27m/min and 20m/min, respectively, as compared to 70m/min for normal children ambulating without assistive devices (Waters eral. 1983). These high heart rates and slow walking speeds suggest that a high physiological workload was sustained during ambulation. This high workload indicates the impractic- ability of encouraging the children in the study to walk long distances with walkers or canes. Thus, therapeutic equipment that decreases the physiological workload of

mobility needs to be encouraged when the children are required to walk long distances, in order to avoid undue fatigue.

Investigations of energy expenditure of subject’s ambulating with assistive equip- ment is primarily based upon oxygen- consumption data (Waring 1976, Fisher and Gullickson 1976). The energy cost of ambulation of patients with hemiplegia or amputated limbs decreases when appropri- ate assistive devices are used (Bard and Ralston 1959, Erdman et al. 1960, Inman et al. 1961, Dacso et al. 1963, Corcoran ef al. 1970, Ganguli et al. 1974a, b, Hash 1978). Stallard and colleagues reported measurements of energy expenditure of patients with spina bifida requiring assisted ambulation (Stallard ef al. 1978~) . In their study heart rate and speed of ambulation with and without an orthosis were compared. In all five patients, heart rate decreased and speed increased during ambulation with the orthosis. Studies investigating ambulation of paraplegic patients concluded that the energy cost of ambulation with braces and crutches depended upon the lesion level, and that if the energy cost was too great the patients did not ambulate for functional purposes or abandoned the assistive equipment entirely (Long and Lawton 1955, Gordon 1956, Gordon and Vanderwalde 1956, Clinkingbeard et al. 1964, Rosman and Spira 1974). Thus, in terms of energy

expenditure, it would be advisable for all children in group I to use walkers on a daily basis, since they demonstrated a lower energy cost index during ambulation with walkers than with canes (Fig. 3).

Children in group I1 exhibited energy cost indices that were the same or lower during ambulation with canes as compared to walkers. The closer a gait pattern is to normal, the less energy will be expended (Bard and Ralston 1959, Erdman ef a/. 1960, Inman et a/. 1961, Ganguli ef a/. 1974a. b, Stallard ef a/. 1978b). Since walking with canes provides a more normal gait pattern, it is not surprising to find that the children in group I1 with lower energy cost indices when walking with canes used canes on a daily basis. These children did not appear to need the extra stability provided by the walker. The two children in group I1 who had equal

energy cost indices during ambulation with canes and walkers used canes on a daily basis. This may be attributed to the increased mobility provided by the canes or may be the result of parental and medical staff pressure. Acknowledgements This study was aided by donation of equipment from the Hewlett Packard Company. Our sincere thanks to H. J. Ralston, Ph.D., J. G. Gamble, M.D., Ph.D., E. E. Bleck, M.D., C. Block, P. T., M. Maruyama, P.T., J. Bakich, P.T., K. Sletski, P.T., C. Stone, P.T. and V. Coon, P.T., M.A., for their valuable consultative services.

Authors’ Appointments Jessica Rose, P.T., M.A., Staff Physical Therapist; *John M. Medeiros, P.T., Ph.D., Assistant Professor in Physical Therapy; and Director of the Motion Analysis Laboratory; Rochelle Parker, P.T., M.A., Senior Lecturer in Physical Therapy; Stanford University School of Medicine, Stanford, California.

*Correspondence to second author

SUMMARY The energy expenditure of cerebral-palsied children ambulating with bilateral quad canes and wheeled walkers was estimated, using average heart rate and speed of walking. An energy cost index (average number of heart rates per unit distance walked) was derived to allow for varying speeds among patients. Children were then categorized into those who had a lower energy cost index when using quad canes and those who had a lower index when using walkers. This made it possible to offer treatment recommendations based on objective data.

R ~ S U M ~ Index de colit inergitique comme estimation de la dipense inergitique denfanrs IMC duranr une dkambulation assisrie La dtpense d’knergie d’enfants IMC se dtplacant avec cannes quadripodes bilattrales a t te apprCcite en mesurant le rythme cardiaque moyen et la vitesse de dtplacement. Un index de coiit Cnergttique (nombre moyen de battements cardiaques par unitC de distance franchie) a CtC ttabli pour des vitesses varites parmi les sujets ttudits. Les sujets ont alors CtC classts entre ceux qui avaient un index de coiit tnergttique plus bas lorsqu’ils utilisaient des quadripodes et ceux qui avaient un index plus bas en utilisant des fauteuils. Ceci a permis d’ttablir des conseils de traitement basts sur des donntes objectives.

ZUSAMMENFASSUNG Energiebedarfsindex als Schatzwert des Energieverbrauchs bei Kindern mit Cerebralparese wahrend assistierrer Bebvegung Bei Kindern mit Cerebralparese, die sich mit beidseitigen Gehstiitzen und Rollstiihlen fortbewegten, wurde anhand der durchschnittlichen Herzfrequenz und der Bewegungsgeschwindigkeit der Energieverbrauch bestimmt. Der Energiebedarfsindex (durchschnittliche Anzahl der Herzschlage pro zuriickgelegter Gehstrecke) wurde ermittelt, um die unterschiedlichen Geschwindigkeiten der Patienten zu beriichsichtigen. Die Probanden wurden dann eingeteilt in solche, die einen niedrigeren Energieverbrauchsindex beim Gehen mit Gehstiitzen und solche. die einen niedrigeren Energieverbrauchsindex beim Rollstuhlfahren hatten. Dadurch war man in der Lage, anhand objektiver Daten Behandlungsvorschlage zu machen.

RESUMEN Indire de roste de energia como estimacion del gasto de energia en nitio.r con paralisis cerebral durante la deambulacidn asisrida Se evaluo el gasto energttico en niiios con paralisis cerebral andando con muletas bilaterales o con andadores con ruedas, observando el promedio de frecuencia cardiaca y la velocidad de la marcha. Se deduio un indice de gasto de energia (promedio de frecuencia cardiaca por unidad de distancia andada) para ser aplicado a diversas velocidades de marcha segun 10s pacientes. Los pacientes se categorizaron en 10s que tenian un bajo indice de gasto energttico al andar con muletas y 10s que lo tenian al usar andores con ruedas. Esto hizo posible ofrecer tratamientos recomendados en base a datos objetivos.

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