Physiological Cost Index as a Proxy Measure for the Oxygen Cost of Gait in Stroke Patients

Abstract

Background. Stroke survivors can exhibit abnormally elevated oxygen consumption during walking. Therapeutic interventions can improve gait deficits and oxygen consumption. A practical measure of oxygen cost is not available. This study tested the usefulness of an indirect index of oxygen cost, the Physiological Cost Index, and the ability of this index to discriminate between healthy adults and stroke survivors. Methods. The authors studied 17 subjects with stroke and 10 healthy control participants. Participants walked 10 minutes at their chosen comfortable speed on a treadmill. Oxygen consumption and heart rate data were collected. Primary measures were oxygen cost and the Physiological Cost Index. Secondary measures were age and gait speed. Results. The Physiological Cost Index and oxygen cost had a good to excellent correlation ( r = .83, P < .001) for subjects with stroke. Both oxygen cost and the Physiological Cost Index were comparable in detecting a significantly abnormal elevation for stroke survivors versus healthy adults ( P = .003 and .002, respectively). Age was not correlated with oxygen cost, the Physiological Cost Index, or chosen gait speed. A moderate correlation of gait speed to both the Physiological Cost Index and oxygen cost was found. Conclusions. The Physiological Cost Index can be used as a proxy index for the oxygen cost of walking in subjects after stroke because it is correlated with oxygen cost and is comparable to oxygen cost in its capability to discriminate between healthy controls and subjects with stroke. The Physiological Cost Index can be performed inexpensively on a routine basis in a clinical environment.