这个低估是啥意思？

Paw is thus a fraction of Ptotal and proportional to the instantaneous Pmus during the full inspiratory cycle (Fig. 1); the gain indicates a percentage of respiratory muscle unloading, set by the clinician. Hence, if the gain is set at 75%, it means that the ventilator delivers 75% of the total pressure, the remaining 25% being assumed by the patient’s Pmus (Eq. 3): Paw equals three times Pmus along the inspiratory phase (Eq. 4). Practically, this gain can be between 5% and 85%. Indeed, assist levels close to 100% would put the patient at risk of over-assistance in case of errors in the automated calculations of respiratory mechanics resulting in overestimation of the pressure needed. Similar to NAVA, because the patient’s brain controls the desired volume, the volume delivered to the patient may show little variations when varying the level of assist [31]. Inspiration is cycled-off when flow decreases to a low pre-set level (by default set to 3 L/min). This cycling-off mechanism usually makes the end of ventilator assistance extremely close to the end of the neural inspiration. PAV+ cannot be used during non-invasive ventilation, as end-inspiratory occlusions cannot be performed in the presence of leaks. In addition, estimations of Ptotal do not correct for intrinsic PEEP , if present, which may lead to an underestimation of the delivered pressure in patients with significant hyperinflation [32].

因此，Paw是Ptotal的一部分，并且与整个吸气周期中的瞬时Pmus成正比（图1）；增益表示由临床医生设定的呼吸肌卸载的百分比。因此，如果增益设置为75%，则意味着呼吸机提供总压力的75%，其余的25%由患者的Pmus（等式3）承担：即吸气相时Paw等于Pmus的三倍（等式4）。实际上，这个增益可以在5%到85%之间。事实上，如果呼吸力学的自动计算出现错误，导致高估了所需的压力，那么接近100%的辅助水平将使患者面临过度辅助的风险。与NAVA类似，因为患者所需的吸气容量由大脑控制，所以当改变辅助水平时，输送给患者的容量可能显示出很小的变化。当流速降低到较低的预设水平（默认设置为3 L/ min）时，吸气终止呼气开始。这种切换机制通常使呼吸机辅助的终止非常接近神经调节通气辅助吸气的终止。因为在有漏气的情况下不能进行吸气末闭塞，故PAV+不能在无创通气期间使用。此外，如果存在内源性PEEP，对Ptotal的估计也不正确，这可能会导致重度阻塞性肺充气患者输送的压力被低估。

这个低估是啥意思。1.应该输送5，我们只让呼吸机输送了2

2.呼吸机输送了5，我们以为只输送了2