Conventional CPR Physiology
常规心肺复苏（CPR）生理学
Even though high-quality CPR has been shown to increase survival, it only providesabout 25% - 40% of normal blood flow to the heart and brain. Even when performing high-quality CPR, air can be drawn in during chest wall recoil, depleting the vacuum that is needed to fill the heart.
尽管已有证据表明，高质量心肺复苏（CPR）能够提高患者的生存率，但它仅向心脏和大脑提供25% - 40%的正常血流。此外，在行高质量CPR时，胸壁回弹期间，空气吸入，大幅减少心脏充盈所需的真空。
During CPR, what is circulated forward by two mechanisms: the cardiac pump mechanism and the thoracic pump mechanism.
CPR过程中，血液通过两种机制：心泵机制和胸泵机制，向前流动。
With the cardiac pump mechanism, direct compression of the heart between the sternum and the spine forces blood out. More importantly, the chest also becomes a thoracic pump. Chest compressions create a positive pressure that forces blood out of the heart and air out of the lungs. Compressions also caused a slight increase inintracranial pressure which reduces cerebral perfusion.
心泵机制指直接按压胸骨和脊柱之间的心脏，迫使血液流出。更为重要的是，胸腔也成为胸泵。胸外按压产生正压，迫使血液流出心脏，空气排出肺部。按压也导致颅内压（ICP）略微增高，减少脑血流灌注。
Then during the decompression phase, the chest wall passively recoils putting aslight negative intrathoracic pressure. This vacuum draws some blood back into the heart, pulls some air into the lungs, and fills the coronary arteries. ICP is also slightly lowered during decompression. Chest compressions create a sequence of alternating positive and negative pressures that help to circulate blood.
然后，在减压阶段，胸壁被动回弹，产生稍许颅内负压。在这种真空状态下，部分血液回流入心脏，部分空气进入肺，冠状动脉充盈。减压期间，ICP也略微降低。胸外按压交替产生一系列正压和负压，帮助血液循环。
The more blood that can be returned to the heart called preload, the more blood that can be circulated forward on the subsequent compression. Optimizing preload iscritical for maximizing the effectiveness of CPR.
回流入心脏的血液（预负荷）越多，在随后的按压下向前循环的血液越多。最优化预负荷是实现最佳CPR疗效的关键。
CPR alone does not maximize the amount of blood circulated, because just as the chest wall begins to recoil, air rushes in through the open airway and eliminates the vacuum that is needed to fill the heart. Once the negative pressure is gone, the heart stops filling. This diminished preload results in decreased cardiac output on the subsequent compression.
仅执行CPR并不能最大限度增加血液循环量，因为随着胸壁开始回弹，空气通过开放的气道气涌入，心脏充盈所需的真空消失。负压一旦消失，心脏停止充盈。预负荷减少导致随后心脏按压时，心输出量减少。
Studies also show that caregivers often make errors during the performance of CPR that compromised its effectiveness. For example, ventilating too often or with too much tidal volume causes excessive positive interest thoracic pressure that limits blood flow back to the heart and increases ICP.
研究也表明，看护人员在实施CPR时经常出错，这将降低其有效性。例如，换气过于频繁，或者潮气量（TV）过多会导致正相关胸压过大，从而限制血液回流到心脏，增加ICP。
Compressing too slow fails to generate enough pressure within the circulatory system. Compressing too fast limits preload because the heart does not have enough time to fill with blood. Finally, if the chest wall does not recoil completely, it results in decreased blood flow back to the heart.
按压过慢不能产生足够的促使血液循环的压力。按压过快则会限制预负荷，因为心脏没有足够的时间充盈血液。最后，如果胸壁未完全回弹，则会导致回流到心脏的血液减少。
Given that we only get about 25 to 40 percent of normal blood flow with conventional CPR, it's important to get it right, minimize interruption; provide proper chest compressions at a rate of 100 to 120 per minute, a depth of at least 2 inches and allow complete chest wall recoil; provide proper ventilation at a rate of less than 12 per minute, a duration of 1 second, and with no more tidal volume than is needed to produce visible chest rise.
由于通过常规CPR，我们仅获得25% - 40%的正常血流，因此需要特别注意：①正确操作，尽量减少中断；②正确胸部按压（按压频率：100-120次/分钟，按压深度：≥2英寸或50mm，胸壁完全回弹）；③正确通气（通气频率＜12次呼吸/分钟，吹气时间持续1秒，TV≤胸廓起伏所需的量）。
