The Cardiovascular Magnetic Resonance Imaging Group, Department of Cardiology, Rigshospitalet, Copenhagen, Denmark;
Am J Physiol Heart Circ Physiol. 2013 Oct 1;305(7):H1004-9. doi: 10.1152/ajpheart.00309.2013. Epub 2013 Jul 26.
Positive-pressure ventilation (PPV) is widely used for treatment of acute cardiorespiratory failure, occasionally at the expense of compromised cardiac function and arterial blood pressure. The explanation why has largely rested on interpretation of intracardiac pressure changes. We evaluated the effect of PPV on the central circulation by studying cardiac chamber volumes with cardiac magnetic resonance imaging (CMR). We hypothesized that PPV lowers cardiac output (CO) mainly via the Frank-Starling relationship. In 18 healthy volunteers, cardiac chamber volumes and flow in aorta and the pulmonary artery were measured by CMR during PPV levels of 0, 10, and 20 cmH2O applied via a respirator and a face mask. All cardiac chamber volumes decreased in proportion to the level of PPV. Following 20-cmH2O PPV, the total diastolic and systolic cardiac volumes (±SE) decreased from 605 (±29) ml to 446 (±29) ml (P < 0.001) and from 265 (±17) ml to 212 (±16) ml (P < 0.001). Left ventricular stroke volume decreased by 27 (±4) ml/beat; heart rate increased by 7 (±2) beats/min; and CO decreased by 1.0 (±0.4) l/min (P < 0.001). From 0 to 20 cmH2O, right and left ventricular peak filling rates decreased by -146 (±32) and -187 (±64) ml/s (P < 0.05) but maximal emptying rates were unchanged. Cardiac filling and output decrease with increasing PPV in healthy volunteers. The decrease is seen even at low levels of PPV and should be taken into account when submitting patients to mechanical ventilation with positive pressures. The decrease in CO is fully explained by the Frank-Starling mechanism.
正压通气（PPV）广泛用于治疗急性心肺衰竭，偶尔会导致心脏功能和动脉血压受损。这一解释主要基于对心内压力变化的解读。我们通过心脏磁共振成像（CMR）研究心脏腔室容积来评估 PPV 对中央循环的影响。我们假设 PPV 通过 Frank-Starling 机制降低心输出量（CO）。在 18 名健康志愿者中，通过 CMR 在呼吸机和面罩下分别施加 0、10 和 20cmH2O 的 PPV 水平下测量心脏腔室容积和主动脉与肺动脉内的血流。所有心脏腔室容积均按 PPV 水平成比例下降。在 20cmH2O 的 PPV 后，总舒张期和收缩期心脏容积（±SE）从 605（±29）ml 降至 446（±29）ml（P＜0.001）和从 265（±17）ml 降至 212（±16）ml（P＜0.001）。左心室每搏量减少 27（±4）ml/beat；心率增加 7（±2）次/分钟；CO 减少 1.0（±0.4）l/min（P＜0.001）。从 0 到 20cmH2O，右和左心室峰值充盈率分别降低了-146（±32）和-187（±64）ml/s（P＜0.05），但最大排空率不变。在健康志愿者中，随着 PPV 的增加，心脏充盈和输出减少。即使在低水平的 PPV 下也能观察到这种减少，因此在对患者进行正压通气时应考虑到这一点。CO 的减少完全可以用 Frank-Starling 机制来解释。
