Gait speed as a measure of functional status in COPD patients

Abstract

Chronic obstructive pulmonary disease (COPD) is a disease associated with dyspnea, fatigue, and exercise intolerance. The degree of functional debility and level of exercise capacity greatly influences quality of life and mortality in patients with COPD, and the measures of exercise capacity are to be an integral part of patient assessment but often not feasible in routine daily practice, resulting in likely suboptimal care. There is a need for simple ways to identify functional decline in the clinical setting in order to guide resources to preventive interventions or proper care, including palliative care. Gait speed, or measuring how long it takes for a patient to walk a short distance, takes very little time and space, and can serve as a candidate measure of physical function in COPD. Gait speed has been shown to be an indicator of disability, health care utilization, and survival in older adults. It is a simple, reliable, and feasible measure to perform in the clinic and has been promoted as the next vital sign, providing insight into patients' functional capacity. Gait speed is mainly determined by exercise capacity but reflects global well-being as it captures many of the multisystemic effects of disease severity in COPD rather than pulmonary impairment alone. It is an excellent screening measure for exercise capacity and frailty; in COPD, the usual gait speed (4-m course with rolling start) has been very accurate in identifying clinically relevant benchmarks of the 6-minute walk test, poor (<350 m) and very poor (<200 m) 6-minute walk test distances. A specific cut-off point of 0.8 m · s(-1) had a positive predictive value of 69% and negative predictive value of 98% in predicting very poor exercise capacity. The increasing evidence on gait speed is promising as a simple test that can inform the clinician about many important functional aspects of the COPD patient. Further work will likely show the strength of gait speed as a predictive marker of hospitalizations, re-admissions, and mortality. Instead of relying on the "eyeball test" regarding the patient's frailty or exercise capacity, a gait speed in its simplicity represents a much more solid assessment. Furthermore, repeat measures over serial clinic visits may show a pattern and further guide a change in therapy, whether it be medications, rehabilitation, or even initiation of palliative care discussions.

Keywords: emphysema; exercise capacity; frailty; palliative care; physical activity; quality of life.

Figure 1

Gait speed construct: correlation (r) between psychological and functional variables. Abbreviations: 6MWT, 6-minute walk test; BMI, body mass index; CRQ, chronic respiratory questionnaire; DLCO, diffusing capacity of the lung for carbon monoxide; FEV₁, forced expiratory volume in one second; FVC, forced vital capacity; METS, metabolic equivalent task; mMRC, modified Medical Research Council; PHQ-2, patient health questionnaire-2; RV, residual volume.

Figure 2

Gait speed measurement track.