Heart rate was reportedly 85% of maximum at the end of a 6MWT, while oxygen consumption was 70% of peak values, after a progressive, standardized exercise test, in patients with stroke. Whether 6MWT is an adequate measure of aerobic fitness has been queried, but there is strong evidence to support the reliability and construct validity of using the 6MWT in people after stroke. In clinical practice, the 6-minute walk test (6MWT) is therefore often used as a sub-maximal test to assess walking capacity and cardiovascular fitness in this group of patients. The mean VO 2peak measured during a 6MWT is similar to cycle graded exercise test value. Stroke-specific impairments such as muscle weakness, fatigue, poor balance, contracture and spasticity often limit the patient reaching their maximum capacity using these standard exercise tests. Assessment of peak oxygen uptake (VO 2peak) by indirect calorimetry during progressive cardiopulmonary exercise testing (CPET) is the gold standard for evaluation of aerobic capacity, however this is invariably impractical in patients with stroke. Appropriate prescription of an effective exercise program requires accurate monitoring and evaluation of aerobic capacity. To counteract the decline in aerobic fitness in this population, rehabilitation programs to improve aerobic capacity in people post stroke have been recommended.
Low cardiovascular fitness in stroke survivors may not only lead to low social participation, effecting quality of life, but may also worsen underlying cardiovascular and metabolic risk factors such as hypertension, obesity, diabetes and dyslipidemia, resulting in an increased risk of recurrent stroke.
Neurological deficits associated with stroke often lead to significant physical disability, resulting in low ambulatory activity and poor cardiovascular fitness. ICG is a reliable, non-invasive, repeatable method of measuring cardiodynamic data in stroke patients. This is the first study to report cardiac responses during a 6MWT in stroke patients. Correlation between 6MWD and CO and CI were higher (r s= 0.66 and 0.63, respectively (p<0.01)). Correlations between 6MWD and HR, and between 6MWD and SV were weak, with correlation coefficients Spearman’s rho (r s) =0.46, and 0.42, respectively (p<0.05). HR recorded at the end of the 6MWT was 60.8☑0.6% of the predicted maximal heart rate and perceived exertion score was 5☒. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) both returned to baseline within 2 minutes post 6MWT. Sub-group analysis showed that the increase in cardiac output was predominantly contributed by an increase in heart rate in participants diagnosed with stroke for less than 1 year, whereas both stroke volume and heart rate contributed similarly to the increase in cardiac output in participants with diagnosis of stroke for longer than 1 year. After completion of the 6MWT, all parameters had returned to baseline by a mean of 3.5 min. After commencement of the 6MWT, the increase in SV took 30 sec before the rise approaching a plateau, whereas HR, CO and CI continued to rise steeply for 90 sec before leveling off to a steady rise. Mean measured data for each subject at rest, and at the end of the better performed 6MWT were, respectively: HR 78☑1 and 100☑8 bpm CO 5.5☑.2 and 8.9☒.6 l/min, SV 71.3☑6 and 89.3☑8.6 ml/beat and CI 3.0☐.6 and 4.9☑.3 l/min/m 2. The 6 minute walk distance (6WMD) covered in the two 6MWTs was 246☑26 and 255☑30m respectively (p>0.05). There were no differences in the measured data between the first and second 6MWT (mean intraclass correlation coefficient (ICC) range: 0.87–0.95). The mean duration of stroke after diagnosis was 14.4☑9.1 months. Twenty-nine patients (mean age 55.6☑0.9 years) completed the study. Oxygen saturation, perceived exertion score (modified Borg scale) and the distance covered at the end of each 6MWT were recorded. Heart rate (HR), cardiac output (CO), stroke volume (SV) and cardiac index (CI) were measured by ICG using the PhysioFlow ® PF07 Enduro TM at 1-second intervals for 10 minutes prior to, during and for 10 minutes after each 6MWT. Patients diagnosed with stroke were invited to participate in a 6MWT on consecutive days. This is a cross-section observational study that investigated the cardiodynamic response to a 6-minute walk test (6MWT) in patients after stroke using impedance cardiography (ICG).
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