心肺交互作用ppt课件

Four mechanisms participate in the cyclic changes of SV observed during mechanical ventilation.
First, during insufflation, venous return decreases due to an increase in pleural pressure. This decrease in RV preload leads to a decrease in RV output that subsequently leads to a decrease in left ventricular output. Second, RV afterload increases during inspiration because the increase in alveolar pressure is greater than the increase in pleural pressure.
With spontaneous breathing therefore, LV afterload is greater in inspiration than in expiration . A symmetrical chain of events leads to a reduced LV afterload in the course of a transient increase in ITP, such as with positive pressure inflation of the lungs. Steady increases in ITP, as effected with PEEP, similarly unload the LV with potentially beneficial consequences in presence of left heart failure, as described in greater detail below (Sect. ‘‘Effects of PEEP on cardiac output’’ in Part II).
CCM.2009
Definition: the force opposing ejection Ventricular afterload is represented by the level of transmural pressure,
in the course of systole, within either the aortic root (LV afterload) or the pulmonary artery trunk (RV after-load) The transmural rather than the intraluminal pressure must be considered because these great vessels as well as the ventricles are exposed to an extramural pressure (i.e., ITP) which is usually non atmospheric. The mechanisms whereby respiration interacts with LV and RV afterload are different.
At the onset of spontaneous inspiration, the intraluminal pressure in the aortic root decreases less than does ITP, due to the connection of this vessel with extrathoracic arteries. As a result, aortic transmural pressure increases.
However, left ventricular preload in-creases during insufflation because blood is expelled from the capillaries toward the left atrium .
Finally, left ventricular afterload decreases during inspiration because positive pleural pressure decreases the intracardiac systolic pressure and the transmural pressure of the intrathoracic part of the aorta
Conversely, patients with obstructive sleep apnea have bouts of greatly negative ITP which increase LV after-load, thus contributing to LV hypertrophy
Pump function:
Preload at a given HR Pra or CVP
Afterload Contractility.
CO
Return function:
Blood volume(vein) stressed and unstressed
Compliance Resistance
跨壁压（Ptm）
▪ 舱或血管内外压力差= 血管内收缩压− Ppl 非胸腔内血管
▪ 外压=大气压（传感器的零点） 胸ቤተ መጻሕፍቲ ባይዱ内血管
▪ 被胸膜腔内压包围
▪ 胸膜腔内压随通气周期变化 Ppl ↑ →RV前负荷↓ 自主呼吸或负压呼吸时Ppl 和血管内主动脉压力均下降
Ppl下降幅度大于主动脉压力下降幅度 Ptm实际增加→LV后负荷↑、SV ↓