Inspiratory muscle strength and six-minute walking distance in heart failure: Prognostic utility in a 10 years follow up cohort study

Background
Maximal inspiratory pressure (PImax) and 6-minutes walk distance test (6MWD) may be more available and feasible alternatives for prognostic assessment than cardiopulmonary testing. We hypothesized that the PImax and 6MWD combination could improve their individual accuracy as risk predictors. We aimed to evaluate PImax ability as a mortality predictor in HF and whether the combination to 6MWD could improve risk stratification.
Methods
Prospective cohort from HF Clinics of three University Hospitals. PImax, 6MWD and pVO2 were obtained at baseline. The end point was all cause mortality.
Results
Consecutive 256 individuals (50% woman, 57.4±10.4years) with low ejection fraction (LVEF) (31.8±8.6%) were followed up to 10years. During a median follow-up of 34.7 (IQR 37) months, 110 participants died. Mean±SD values were: pVO2 14.9±5.1mL/kg/min, PImax 5.5±1.3kPa and 6MWD 372±118m. In multivariate Cox regression, pVO2, PImax, 6MWD and LVEF were independent mortality predictors. The pVO2 showed gold standard accuracy, followed by PImax (AUC = 0.84) and 6MWD (AUC = 0.74). Kaplan-Meier mean survival time (MST±SE) for lower (≤5.0kPa) and higher (>6.0kPa) PImax tertiles, were 37.9±2.8months and 105.0±5.2months respectively, and addition of 6MWD did not restratified risk. For intermediate PImax tertile, MST was 81.5±5.5months, but adding 6MWD, MST was lower (53.3±7.6months) if distance was ≤350m and higher (103.1±5.7months) for longer distances.
Conclusion
PImax is an independent mortality predictor in HF, more accurate than 6MWD and LVEF. Addition of 6MWD empowers risk stratification only for intermediate PImax tertile. Although less accurate than pVO2, this simpler approach could be a feasible alternative as a prognostic assessment.

### 背景
与心肺运动试验相比，最大吸气压力（PImax）与6分钟步行距离试验（6MWD）或许是更易获取、更具可行性的预后评估替代方案。我们提出假说：将PImax与6MWD联合应用，可改善二者单独作为风险预测因子的准确性。本研究旨在评估PImax作为心力衰竭（HF）患者死亡预测因子的效能，以及联合6MWD是否能够优化风险分层。

### 研究方法
本研究为前瞻性队列研究，队列来源于3所大学附属医院的心力衰竭门诊。所有受试者在基线阶段均完成了PImax、6MWD及峰值氧耗量（pVO2）检测，研究的主要终点为全因死亡。

### 研究结果
本研究共纳入256例受试者（女性占比50%，年龄57.4±10.4岁），均合并左心室射血分数降低（LVEF：31.8±8.6%），随访时长最长达10年。中位随访时间为34.7个月（四分位距IQR：37），期间共有110例受试者发生全因死亡。受试者的各项检测指标均值±标准差分别为：pVO2 14.9±5.1mL/kg/min，PImax 5.5±1.3kPa，6MWD 372±118m。多因素Cox回归分析显示，pVO2、PImax、6MWD及LVEF均为独立的全因死亡预测因子。其中pVO2展现出金标准级别的预测效能，其次为PImax（曲线下面积AUC=0.84）与6MWD（AUC=0.74）。按PImax三分位进行分组，低三分位组（≤5.0kPa）与高三分位组（>6.0kPa）的Kaplan-Meier平均生存时间（MST±标准误SE）分别为37.9±2.8个月与105.0±5.2个月；加入6MWD后未对该两组的风险分层产生额外优化。对于中间三分位PImax组，其平均生存时间为81.5±5.5个月，但在联合6MWD进行分层后，若步行距离≤350m，则平均生存时间降至53.3±7.6个月；若步行距离更长，则平均生存时间升至103.1±5.7个月。

### 研究结论
PImax可作为心力衰竭患者的独立死亡预测因子，其预测准确性优于6MWD与LVEF。仅针对中间三分位PImax组，联合6MWD可进一步优化风险分层。尽管该联合检测方案的准确性低于pVO2，但这种更为简便的检测组合可作为预后评估的可行替代方案。