Shoemaker Michael J, Curtis Amy B, Vangsnes Eric, Dickinson Michael G
Western Michigan University Interdisciplinary Health Sciences Program.
Cardiopulm Phys Ther J. 2013 Sep;24(3):21-9.
The purpose of the present pilot study was to provide a preliminary estimate of the minimum detectable difference (MDD) and minimum clinically important difference (MCID) of the six-minute walk test (6MWT) and daily activity in outpatients with chronic heart failure (CHF).
A convenience sample of 22 adults with stable New York Heart Association Functional Class II and III CHF performed two baseline 6MWTs separated by 30 minutes of rest. Subjects then wore a triaxial accelerometer for 7 days to monitor daily activity. After 7 weeks of usual care, subjects again wore the accelerometer for 7 days and then returned to the clinic to complete the Global Rating of Change Scale (GRS) with regard to their heart disease and perform another set of 6MWTs. For the 6MWT, the MDD was calculated using the two baseline 6MWT distances. For daily activity, the MDD was calculated using two methods: (1) day-to-day test-retest reliability during baseline monitoring, and (2) baseline to follow-up test-retest reliability in those who reported no change on the GRS. The MCID for the 6MWT and daily activity was calculated using the mean and 95% confidence interval (CI95%) for those subjects who reported 'improvement' on the GRS.
The MDD at the CI95% for the 6MWT was 32.4 meters. The MCID for the 6MWT was 30.1 (CI95% 20.8, 39.4) meters. The MDD for daily activity was 5,909 vector magnitude units (VMU·hr.(-1)) The MCID for daily activity was 1,337 VMU·hr.(-1) There was good alignment of the MDD and MCID for the 6MWT, suggesting that clinically meaningful change is approximately 32 meters. However, the calculated MCID was substantially less than measurement error as represented by the MDD, indicating that the MCID was underestimated in this sample or that daily activity may be robust to change in overall disease status.
本初步研究旨在初步评估慢性心力衰竭（CHF）门诊患者六分钟步行试验（6MWT）和日常活动的最小可检测差异（MDD）及最小临床重要差异（MCID）。
选取22例纽约心脏协会心功能II级和III级的稳定型CHF成年患者作为便利样本，在休息30分钟后进行两次基线6MWT。受试者随后佩戴三轴加速度计7天以监测日常活动。经过7周的常规护理后，受试者再次佩戴加速度计7天，然后返回诊所完成关于其心脏病的整体变化评定量表（GRS），并进行另一组6MWT。对于6MWT，使用两次基线6MWT距离计算MDD。对于日常活动，使用两种方法计算MDD：（1）基线监测期间的每日重测信度，以及（2）在GRS上报告无变化的受试者中从基线到随访的重测信度。使用在GRS上报告“改善”的受试者的均值和95%置信区间（CI95%）计算6MWT和日常活动的MCID。
6MWT在CI95%时的MDD为32.4米。6MWT的MCID为30.1（CI95% 20.8，39.4）米。日常活动的MDD为5909向量大小单位（VMU·hr⁻¹）。日常活动的MCID为1337 VMU·hr⁻¹。6MWT的MDD和MCID具有良好的一致性，表明临床上有意义的变化约为32米。然而，计算出的MCID明显小于以MDD表示的测量误差，表明该样本中MCID被低估，或者日常活动可能对整体疾病状态的变化具有较强的耐受性。
