exist如何理解？谢谢

Setting inspiratory assist during NAVA 

Different methods for NAVA titration starting from PSV or based on a thorough physiological assessment in NAVA mode exist and are summarized in Table 1. Before starting any titration, adequate EAdi catheter placement according to published recommendations [65] and the manufacturer’s positioning tool (using a calculated distance and ECG artefacts in the signal) and EAdi signal quality should be confirmed. If EAdi is abnormally low or absent despite correct catheter placement, ventilator over-assistance, excessive sedation, central apneas, severe diaphragm weakness or pre-existing neuromuscular diseases should be considered as possible reasons for low EAdi. Direct phrenic nerve lesions could hamper NAVA application if no inspiratory EAdi can be measured, but this is quite rare.

NAVA时吸气辅助水平的设置

对NAVA滴定的不同方法来自PSV或基于对NAVA模式的彻底的生理评估，并总结在表1中。在开始滴定之前，应根据已发表的建议和制造商的定位工具（使用计算出的距离和信号中的心电图杂音）行适当的EAdi导管放置和并确认EAdi信号质量。如果EAdi信号异常低或尽管导管放置正确，但EAdi信号仍不存在，则应考虑EAdi信号低的可能原因，如：呼吸机过度辅助、过度镇静、中枢性呼吸暂停、严重膈肌无力或已先存在的神经肌肉疾病。如果直接的膈神经损伤导致吸气性EAdi不能测量，就可能妨碍NAVA应用，但这种情况相当罕见。

 exist如何理解？已存在的？NAVA mode exist 已存在的NAVA模式？

 in the signal只是修饰ECG artefacts的吧？ artefacts如何理解？

谢谢