呼吸机肺通气原理简介

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                    <section><section powered-by="gulangu"><section><section><p>肺通气的物理学基础</p></section><p><img src="image/20201019/19a6da88b13814e5800024e789b60abc_1.png" /></p> <section></section></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;肺通气的物理学基础为波义耳定律，即温度不变时，气体的压力与容积呈反比，压力差推动气体由高压处向低压处流动。自主呼吸时，由于呼吸肌的收缩和舒张使胸廓扩大和缩小，进而导致肺的扩张和缩小，使肺泡内压与大气压之间产生压力差，气体在外界与肺泡间流动。</p></section></section></section><section powered-by="gulangu"><section><section><p><img src="image/20201019/c374266521a9d335043feca620f4c6a2_2.jpg" /></p></section></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;</p></section></section></section><section powered-by="gulangu"><section><section><p>吸气过程</p></section><p><img src="image/20201019/19a6da88b13814e5800024e789b60abc_1.png" /></p> <section></section></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;只有吸气肌收缩时才会造成吸气运动，因此吸气是一个主动过程。膈肌是主要吸气肌。平静呼气末，膈肌位于舒张状态，呈钟形向上隆起。膈肌收缩时，隆起的中心部位下降，扩大了胸廓上下径，使胸腔容积增大，压力降低，当肺泡内压力低于大气压时，产生吸气。</p></section></section></section><section powered-by="gulangu"><section><section><p>呼气过程</p></section><p><img src="image/20201019/19a6da88b13814e5800024e789b60abc_1.png" /></p> <section></section></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;肺脏本身具有弹性回缩力，肺泡内气-液界面具有表面张力，两者，共同构成肺的回缩力。平静呼吸初，膈肌和肋间外肌舒张，肺由于其回缩力而趋向于回位，并牵引胸廓缩小，逐渐恢复到吸气开始前的位置，完成呼气过程。则，平静呼气是一个被动过程，并不需要呼气肌的参与。</p></section></section></section><section powered-by="gulangu"><section><section><p><img src="image/20201019/52b880c1fe10410f5a52a200af2d0442_5.jpg" /></p></section></section></section><section powered-by="gulangu"><section><section><p>胸式呼吸和腹式呼吸</p></section><p><img src="image/20201019/19a6da88b13814e5800024e789b60abc_1.png" /></p> <section></section></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;由膈肌舒缩产生的呼吸运动主要表现为腹壁的起伏，称为腹式呼吸。由肋间肌收缩产生的呼吸运动主要表现为肋骨和胸骨的移动，称为胸式呼吸。腹式呼吸和胸式呼吸常同时存在，何种方式占优势取决于性别、年龄、体型和健康等情况。</p></section></section></section><section powered-by="gulangu"><section><section><p>肺泡内压和胸内压</p></section><p><img src="image/20201019/19a6da88b13814e5800024e789b60abc_1.png" /></p> <section></section></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;肺泡内压的周期性升降，使之与大气压产生压力差，驱动气体进出肺泡。随着肺容积的增加，肺泡内压也逐渐升高。到吸气末，肺泡内压升高，超过大气压，肺内气体向外流动，肺容积减少，肺泡内压逐渐下降。</p><p>&nbsp; &nbsp; &nbsp; &nbsp; 胸膜腔内的压力称为内压，胸内压低压大气压，为负压，造成这种负压的原因为肺的回缩力，包括弹性回缩力和表面张力形成的回缩力。机械通气时，吸气末胸内压可升高超过大气压。</p></section></section></section><section powered-by="gulangu"><section><section><p>弹性阻力和顺应性</p></section><p><img src="image/20201019/19a6da88b13814e5800024e789b60abc_1.png" /></p> <section></section></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;气体进出肺泡除需驱动之外，尚需克服阻力。肺通气的阻力分为弹性阻力和非弹性阻力。弹性阻力包括肺和胸廓的弹性阻力。非弹性阻力主要包括气道阻力、惯性阻力和组织的黏滞阻力。</p><p>&nbsp; &nbsp; &nbsp; &nbsp; 弹性阻力和顺应性呈倒数关系，因此可表示为：1/肺和胸廓总顺应性=1/肺顺应性+1/胸廓顺应性。</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp;通常应用大注射器分步打气的方法测量胸肺静态顺应性，每步吸气后，屏气并放松呼吸肌，测定肺容积和上呼吸道压力的变化，由于测定是在屏气无气流的情况下进行的，因此称之为静态顺应性。</p></section></section></section><section powered-by="gulangu"><section><section><p><img src="image/20201019/8776fda752f00a459194e67289a64eed_9.jpg" /></p></section></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 随肺容积不同，顺序性也在发生改变。为消除肺容积对顺应性的影响，提出了比顺应性（specific compliance）的概念，即：</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 比顺应性=顺应性/功能残气量</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 机械通气时，也可应用简便的计算公式推算静态顺应性：</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 静态顺应性=呼出潮气量/（平台压-PEEP）</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 当应用无吸气平台的机械通气方式时，也就是气道内的气流未达到静止时，也可计算动态顺应性：</p><p><span>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 动态顺应性=呼出潮气量/（气道峰压-PEEP）</span></p></section></section></section><section powered-by="gulangu"><section><section><p><img src="image/20201019/1f7aa1ba900c8ffd7c0c3b15cea48e5c_10.jpg" /></p></section></section></section><section powered-by="gulangu"><section><section><p><span> </span></p></section></section></section><section powered-by="gulangu"><section><section><p><span>&nbsp; &nbsp;</span></p></section></section></section><section powered-by="gulangu"><section><section><p>气道阻力</p></section><p><img src="image/20201019/19a6da88b13814e5800024e789b60abc_1.png" /></p> <section></section></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 气道阻力是非弹性阻力的主要成分，约占80%到90%。气道阻力可用维持气体流量所需的压力差表示，即：</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 气道阻力=推动气流的压力差/气体流量</p></section></section></section><section powered-by="gulangu"><section><section><p><img src="image/20201019/01f91df793b715bbe8f24b9dcac379e2_12.jpg" /></p></section></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 气道阻力受气流流量、气流形式、和管径粗细的影响，流量快，阻力大。层流阻力小，湍流阻力大。根据Hagen-Poiseuille定律，气道阻力与气道半径的4次方呈反比。当气道内径缩小一半时，气道阻力将增大至16倍。</p></section></section></section><section powered-by="gulangu"><section><section><p>时间常数</p></section><p><img src="image/20201019/19a6da88b13814e5800024e789b60abc_1.png" /></p> <section></section></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;将肺脏视作一整体腔隙，在通气过程中，气体入肺和出肺叶符合指数变化规律。影响肺脏的力学参数包括顺应性（C）和阻力（R），通过过程的τ则等于这两者的乘积：</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;τ（s）-C*R</p></section></section></section><section powered-by="gulangu"><section><section><p>呼吸作功</p></section><p><img src="image/20201019/19a6da88b13814e5800024e789b60abc_1.png" /></p> <section></section></section></section><section powered-by="gulangu"><section><section><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 面积和距离的乘积为容积。因此，呼吸作功也可表示为：</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 呼吸功=压力*容积</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 正常呼吸作功为（2.5~3）J/min，最高可达到（10~15）J/min，若超过该界限，则需要进行机械通气支持。</p></section></section></section><section powered-by="gulangu"><section><section><p><br  /></p></section></section></section><section powered-by="gulangu"><section><section><section powered-by="gulangu"><section><section><p>欢</p></section></section></section></section><section><section powered-by="gulangu"><section><section><p>迎</p></section></section></section></section><section><section powered-by="gulangu"><section><section><p>关</p></section></section></section></section><section><section powered-by="gulangu"><section><section><p>注</p></section></section></section></section></section></section><section powered-by="gulangu"><section><section><p><br  /></p></section></section></section><section powered-by="gulangu"><section><section><section powered-by="gulangu"><section><section><p><img src="image/20201019/0cd2ef3f7891605295295294472eba14_15.jpg" /></p></section></section></section></section><section><section powered-by="gulangu"><section><section></section></section></section></section><section><section powered-by="gulangu"><section><section><p>关注我们</p><p>一起涨姿势！</p></section></section></section></section></section></section></section>