Effects of assistive devices on cardiorespiratory demands in older adults.

[Foley MP. Prax B, Crowell R, Boone T. Effects of assistive devices on cardiorespiratory demands in older adults. Phys Ther. 1996;76:1313-1319.]

Key Words: Ambulation aids, general; Cardiovascular system; Gait analysis; Geriatrics; Oxygen cost; Respiratory system.

In facilitating the process of gait training, assistive devices are often used and prescribed by physical therapists. These devices are used either as transitional aids, working toward the goal of independent ambulation, or as permanent functional aids that can be used to varying degrees for home or community ambulation.

Ambulating while using an assistive device is known to create a metabolic demand different from that for unassisted ambulation.[1-8] A variety of variables play a role in this alteration, including changes in speed of ambulation; prevention of normal arm swing, which may disrupt normal gait biomechanics; and an increased metabolic demand imposed on the upper extremities. In particular, changing the speed of unassisted ambulation has been shown to affect metabolic demand.[9] Because people tend to ambulate more slowly while using an assistive device[3-7] and because walking slower than typical, self-selected speeds increases metabolic demand,[9-10] the increased metabolic demand with the use of assistive devices is at least in part due to the slower speed. Individuals with either normal or pathologic gait appear to self-select the most efficient ambulation speed.[10]

The increase in metabolic demand imposed on an adult without impaired cardiorespiratory function when using assistive devices for ambulation at a self-selected speed is probably inconsequential because the person's cardiorespiratory reserve should be more than adequate to compensate for the increase. In this context, cardiorespiratory reserve capacity is that portion of an individual's total cardiorespiratory capacity that is not being used at the time (de, "leftover" or "extra" capacity that is available if greater metabolic demand is needed). When a person using an assistive device has compromised cardiorespiratory function, the increased demand may not be within the limits of his or her reserve capacity. When this is the case, close attention to the appropriate selection of an assistive device should be considered relative to the patient's cardiorespiratory capacity (not only for the patient's balance needs). Patients with balance deficits may not have partial weight-bearing or non-weight-bearing status needs, yet the clinician must consider the cardiorespiratory demands of the prescribed assistive device.

Holder et al[5] compared oxygen cost, heart rate (HR), blood pressure, rate-pressure product (RPP), and rating of perceived exertion (RPE) of unassisted, nonweight-bearing ambulation using axillary crutches, a standard walker, and a wheeled walker in nine female physical therapists (mean age=29.11 years, SD=2.62). The authors reported that use of the assistive devices resulted in an increase in metabolic and cardiovascular responses compared with unassisted ambulation. They also stated,

It is possible that the differences in the metabolic and

cardiovascular parameters may be more pronounced in an

older population. Cardiovascular responses of normal,

young females may not be the same as those of an older

population secondary to changes in the cardiovascular

system due to the aging process as well as cardiovascular

disease.[5(p541)]

Because older adults comprise a large sector of the population using assistive devices and because this population tends to have a large percentage of cardiorespiratory complications, there is a need for further investigation of the cardiovascular and metabolic demands of ambulating with assistive devices. Currently, no data exist on the quantification and comparison of metabolic and cardiorespiratory responses during unassisted ambulation and during ambulation with a standard walker, a wheeled walker, or a single-point cane in the aged population.

The purpose of our study, therefore, was to quantify and compare the metabolic and cardiorespiratory demands imposed during unassisted ambulation and during ambulation with a standard walker, a wheeled walker, and a cane in older adults.

Method

Subjects

Ten subjects (3 male and 7 female) participated in this investigation. Their ages ranged from 50 to 74 years (X=60.3, SD=8.34). All subjects filled out a medical history form and signed an informed consent statement in compliance with the guidelines of The College of St Scholastica (Duluth, Minn). None of the subjects were currently using assistive devices or reported any functional limitations secondary to medical problems.

Familiarization 

Each subject attended a familiarization session during which the procedures (collection of expired gases, randomized trials, and rest intervals) were thoroughly explained. Each subject was then instructed on the correct use of the assistive devices and practiced until his or her use of each device was determined to be correct.

Instrumentation

Metabolic variables were measured and recorded using a MedGraphics metabolic measurement cart and a HansRudolph mouth-face mask (#7922).([dagger]) Prior to data collection for each subject, the metabolic measurement cart was calibrated with known (medical grade) gas concentrations and volumes. Heart rate was measured via a Polar Electro HR monitor (model 45930).([doubledagger]) Blood pressure was determined using a standard stethoscope, blood pressure cuff, and aneroid sphygmomanometer. Prior to initiation of this study, the aneroid sphygmomanometer was calibrated with a mercury sphygmomanometer, and the HR monitor was calibrated with a Physiocontrol LifePak 9 monitor.([sub-sections]) The walkers were a standard walker (2.6 kg) and a wheeled walker (2.7 kg) with the same frame unit (Safe-T-Lok Folding Walker([parallel])). Guardian standard walker tips([parallel]) were used on the front of the walker to create a standard walker. Guardian wheels (7.6-cm [3-in]) were used on the front of the walker, and Guardian glider brakes([parallel]) were placed on the back of the walker to create a wheeled walker. The cane was an adjustable aluminum cane with a foam handle. The top of the cane was aligned with the subjects' ulna styloid process.

In a separate study, test-retest-retest reliability was determined for the measurement of oxygen consumption ([Vo.sub.2]). Oxygen consumption was assessed in 10 subjects during unassisted ambulation in one session with three separate test periods (test periods were separated by a resting period). The intraclass correlation coefficient (ICC [3,1]) for [VO.sub.2] was 91.

Experimental Procedures

The HR monitor and the Hans-Rudolph mouth-face mask were placed on the subject, and then the subject ambulated at a self-selected speed under the appropriate condition for approximately 5 minutes until steady-state was achieved.

The ambulation area consisted of a flat, smooth concrete indoor surface that was 45.7 m (150 ft) long and approximately 7.6 m (25 ft) wide. Each subject was instructed to ambulate with full weight bearing with all devices. When the subject reached the end of the ambulation area, he or she turned around and proceeded in the opposite direction. On completion of the 5-minute steady-state period, the subject was connected to the metabolic measurement cart by a breath-by-breath tube and continued ambulation at the self-selected speed for 2 minutes, during which physiologic variables were measured. During this time, one of the testers (MPF) pushed the metabolic measurement cart slightly behind the subject to ensure that the subject was ambulating at his or her self-selected speed. Heart rate was recorded at the end of the first and second minutes without interruption of the subject's forward progression.

Upon completion of the trial, the subject stopped ambulating and standing blood pressure was measured. Next, the subject was asked to rate the perceived effort of exertion (0-10 scale) for the ambulatory session. The subject then rested for at least 10 minutes in a seated position until HR returned to a value approximately equal to the pretesting HR before initiating the other trial sessions in the previously described fashion. The order of the trials was randomized. Two stride lengths per walker advance (each stride being placed beyond the previous stride) were used with the standard walker, whereas continuous ambulation with concurrent continuous walker advance was used with the wheeled walker. Continuous ambulation was used with the cane in the subject's dominant hand, while having the cane advance synchronously with the leg of the opposite side.

Calculation of the Data

Metabolic and ventilatory data were averaged over four 30-second periods for each trial. Rate-pressure product for a particular trial was calculated by multiplying the subject's systolic blood pressure (SBP) by the average HR and then multiplying the product by .01.

Ambulation at speeds other than a self-selected speed increases the metabolic cost of ambulation.[9,10] Nielsen et al[8] recommend that measurement of energy cost per meter should be used as an indicator of gait efficiency. Therefore, we believe that the most clinically acceptable way to quantify and compare the cardiorespiratory and metabolic demands of unassisted ambulation and of ambulation with a standard walker, a wheeled walker, and a cane was to examine the data in relative terms per meter.

Data Analysis

Analysis of variance for repeated measures was used to determine whether differences (P<.05) existed in the mean values for each of the following dependent variables between the four ambulation trials: [VO.sub.2] (in milliliters per kilogram per meter), metabolic equivalent of resting metabolism (MET) (in METs per meter), RPE (in meters per minute), ambulation speed (in meters per second), HR (in beats per meter), SBP (in millimeters of mercury per meter per minute), diastolic blood pressure (DBP) in millimeters of mercury per meter per minute), RPP (in meters per minute), minute ventilation (VE) (in liters per meter), tidal volume (VT) (in milliliters per meter), and frequency of breaths ([f.sub.b]) (in breaths per meter). When a difference was found, a Newman-Keuls post hoc analysis was used to determine where the difference occurred. All data were considered different when the probability of a Type I error was less than 5%.

Results

Tables 1 through 3 present the means, standard deviations, ranges, and probabilities of differences (P<.05) for all dependent variables evaluated in this study. Standard walker ambulation resulted in a higher [VO.sub.2] and lower ambulation speeds as compared with unassisted ambulation and ambulation with a wheeled walker and with a cane (Tab. 1). Additionally, ambulation with a standard walker resulted in higher RPEs as compared with unassisted ambulation and ambulation with a wheeled walker and with a cane (Tab. 1). Ambulation with a standard walker resulted in higher HRs and RPPs as compared with unassisted ambulation and ambulation with a wheeled walker and with a cane (Tab. 2). Systolic blood pressures and DBPs were higher during ambulation with a standard walker as compared with unassisted ambulation and ambulation with a wheeled walker and with a cane (Tab. 2). Minute ventilation was increased during ambulation with a standard walker as compared with unassisted ambulation and ambulation with a wheeled walker and with a cane (Tab. 3). The physiologic adjustments for the increased VE during ambulation with a standard walker when compared with unassisted ambulation were accommodated by increases in both the rate and depth of breaths (Tab. 3). Notably, there was also a 103% increase in VT and a 95% increase in [f.sub.b] during ambulation with a standard walker versus ambulation with a wheeled walker (Tab. 3).

[TABULAR DATA 1-3 OMITTED] Figure 1 presents the percentages of increase (P<.05) in [VO.sub.2] between ambulation with a standard walker and unassisted ambulation, ambulation with a wheeled walker, and ambulation with a cane. Figure 2 displays the percentages of increase (P<.05) in HR between ambulation with a standard walker and unassisted ambulation, ambulation with a wheeled walker, and ambulation with a cane.

Discussion

Gonzalez and Corcoran stated, "An effective rehabilitation program must attempt to increase the patient's ability to perform work and concurrently decrease the amount of work required."[4(P413)] That is, the lower the cardiorespiratory and metabolic costs of ambulation per distance traveled, the greater the efficiency.

Specific comparisons made between this study and previous research should be interpreted carefully because previous studies investigated non-weight-bearing ambulation with assistive devices[2,3,5-7] and different assistive devices[1,3,6,8] and subjects of different ages and health status. In addition, there were differences in experimental design with respect to the dependent variables, method of testing variables, and subject groups.

The results of our study demonstrate that ambulation with a standard walker in older adults required 212% more [VO.sub.2] than did unassisted ambulation (X= 0.53 mL/kg/m versus 0.17 mL/kg/m, respectively) (Tab. 1, Fig. 1). This finding is similar to the results of the study by Holder et al,[5] where ambulation with a standard walker resulted in a 200% increase in [VO.sub.2] compared with unassisted ambulation (X=0.6 mL/kg/m versus 0.2 mL/kg/m, respectively). Our results, however, indicate that there was no difference between unassisted ambulation and ambulation with a wheeled walker (Tab. 1). Holder et a 15 reported that ambulation with a wheeled walker resulted in more oxygen cost compared with unassisted ambulation (X=0.6 mL/kg/m versus 0.2 mL/kg/m, respectively). In contrast, they reported that the oxygen cost of non-weight-bearing ambulation with a wheeled walker and with a standard walker resulted in the same oxygen demand.

In our study, we found that ambulation with a standard walker resulted in greater oxygen cost than did ambulation with a wheeled walker (X=0.53 mL/kg/m versus 0.26 mL/kg/m, respectively, or a 104% increase) (Tab. 1, Fig. 1). The conflicting [VO.sub.2] data for ambulating with a wheeled walker between our study and that of Holder et al[5] may be due to differences in ambulation speeds with a wheeled walker. In our study, ambulation speed with a standard walker (0.29 m/s) was 53% slower than ambulation speed with a wheeled walker (0.62 m/s). Holder et al[5] reported ambulation speeds of 0.30 m/s with a standard walker and 0.40 m/s with a wheeled walker. In addition, there is questionable clinical relevance in measuring the physiologic demands of nonweight-bearing ambulation with a wheeled walker. We believe that non-weight-bearing gait patterns are typically not performed with a wheeled walker. Studies on the physiologic demands of assistive devices during weight-bearing and non-weight-bearing ambulation may not be comparable. Our results indicate that if a wheeled walker can be prescribed versus a standard walker, the patient could still attain the benefits of an assistive device without an increase in metabolic demand.

One characteristic that is quite common among older adults is the possible history of myocardial infarction (MI), which makes minimizing myocardial oxygen demand important. Rate-pressure product is correlated (r=.90) 11 with myocardial [VO.sub.2] and is thus a measure of myocardial oxygen demand. In our study, RPP was 766% greater during ambulation with a standard walker as compared with unassisted ambulation. Comparison of the walkers showed that ambulation with a standard walker resulted in 271% greater RPP as compared with ambulation with a wheeled walker. Therefore, the use of any assistive device with an elderly patient who has a history of MI or who has been identified as having an increased risk for MI (or any condition resulting in a increase in myocardial oxygen demand) should be undertaken with caution and appropriate monitoring. Use of a standard walker with these patients requires a greater degree of caution.

Comparison of the ventilatory mechanics revealed that ambulation with a standard walker resulted in a 207% increase in VE as compared with unassisted ambulation and in a 188% difference between ambulation with a standard walker and ambulation with a wheeled walker. This information is important because clinicians should be cognizant of ventilatory effort in a patient with cardiopulmonary disease. It is conceivable that use of a wheeled walker may improve gait function (de, increase ambulation speed and decrease cardiorespiratory demand) in patients with impaired cardiorespiratory systems.

Recommendations for Additional Study

Further study of how these variables are affected by an altered weight-bearing status within this patient population would be of value, as this study considered only the full bilateral weight-bearing situation. Examination of the use of 12.7-cm (5-in) wheels versus 7.6 cm (3-in) wheels on a wheeled walker is recommended. Investigation of the physiologic demands of ambulation with various assistive devices on varying surfaces found inside homes is warranted.

Conclusions

Ambulation with a standard walker required a 212% increase in relative [VO.sub.2] compared with unassisted ambulation and a 104% increase in greater relative [VO.sub.2] compared with ambulation with a wheeled walker in older adults. People usually ambulate for given distances rather than for specified periods of time; therefore, the wheeled walker may allow greater functional mobility than the standard walker and should be prescribed if the patient does not require the additional stability of the standard walker. When working with a person who has decreased or compromised cardiorespiratory function, use of a standard walker may produce exercise (gait) intolerance due to excessive physiologic demands and in severe cases may be dangerous. We believe that the degree to which this holds true depends on the specific cardiorespiratory dysfunction of the patient.

Differences between other assistive devices considered in this study are highly dependent on the specific condition of the individual. If the patient is considered to have no cardiorespiratory limitations, any of the assistive devices tested should be well within the range of the patient's cardiorespiratory reserve. If an assistive device is to be considered for someone with a compromised cardiorespiratory system, however, choosing the device that will afford the user the most distance and duration for the effort without compromising other factors to be considered in terms of proper assistive device selection (eg, balance) is an important clinical practice. If the assistive device requires too great a physiologic demand for ambulation, the patient may ambulate less with less activity, resulting in a lower cardiorespiratory reserve capacity and more dysfunction or disease.

Acknowledgments

We are grateful to Barb Crowell, PT, for her editorial assistance and clinical insight. We also thank Isernhagen Physical Therapy Inc, Duluth, Minn, for the use of their facility and equipment.

[Figures 1 & 2 ILLUSTRATION OMITTED]

(*) MedGraphics Cardiorespiratory Diagnostic Systems (.PX/D, MedGraphics, St Paul, MN 55101. ([dagger]) Hans-Rudolph Inc, Wyandotte, Kansas City, MO 64114. ([doubledagger]) Polar Electro, Oy, Finland. ([sections]) Physio-control Corp, 11811 Williams Rd NE, Redmond, WA 98052. ([parallel]) Guardian Products Inc, 4175 Guardian St, Simi Valley, CN 93063.

References

[1] Annesley AL, Almada-Norfleet M, Arnall DA, Cornwall MW. Energy expenditure of ambulation using the Sure-Gait[r] crutch and the standard axillary crutch. Phys Ther. 1990;70:18-23. [2] Cordrey LJ, Ford AB, Ferrer MT. Energy expenditure in assisted ambulation. J Chronic Dis. 1958;7:228-233. [3] Ghosh AK, Tibarewala DN, Dasgupta SR, etal. Metabolic cost of walking at different speeds with axillary crutches. Ergonomics. 1980;23:571-577. [4] Gonzalez KG, Corcoran PJ. Energy expenditure during ambulation. In: Downey JA, Myers SJ, Gonzalez KG, Lieberman JS, eds. The PhysioLogical Basis of Rehabilitation Medicine. Boston, Mass: Butterworth Heinemann; 1994:413-446. [5] Holder CG, Haskvitz EM, Weltman A. The effects of assistive devices on the oxygen cost, cardiovascular stress, and perception of nonweight bearing ambulation. J Orthop Sports Phys Ther. 1993;18:537-542. [6] Imms FJ, MacDonald IC, Prestidge SP. Energy expenditure during walking in patients recovering from fractures of the leg. Scand J Rehabil Med. 1976;8:1-9. [7] McBeath AA, Bahrke M, Balke B. Efficiency of assisted ambulation determined by oxygen consumption measurement. J Bone Joint Surg [Am]. 1974;56:994-1000. [8] Nielsen DH, Harris JM, Minton YM, et al. Energy cost, exercise intensity, and gait efficiency of standard versus rocker-bottom axillary crutch walking. Phys Ther. 1990;70:487-493. [9] Blessey RL, Hislop HJ, Waters RL, Antonelli D. Metabolic energy cost of unrestrained walking. Phys Ther. 1976;56:1019-1024. [10] Nielsen DH, Shurr DG, Golden JC, et al. Comparison of energy cost and gait efficiency during ambulation in below-knee amputees using different prosthetic feet: a preliminary report. J Prosthet Orthot. 1988;1:23-30. [11] Kitamura K, Jorgensen CR, Gobel FL, et al. Hemodynamic correlates of myocardial oxygen consumption during upright exercise. J Appl Physiol 1972;32:516-522.

MP Foley, PhD, PT, is Assistant Professor, Department of Physical Therapy, T he College of St Scholastica, 1200 Kenwood Ave, Duluth, MN 55811 (USA). Address all correspondence to Dr Foley.

B Prax, PT, is a traveling therapist. At the time of the study, he was a physical therapist student at The College of St Scholastica.

R Crowell, PT, is Assistant Professor, Department of Physical Therapy, The College of St Scholastica.

T Boone, PhD, is Professor and Chair, Department of Exercise Physiology, The College of St Scholastica.

This study was approved by the Human Subjects Review Committee at The College of St Scholastica.

This article was submitted July 6, 1995, and was accepted August 8, 1996.