高频通气ppt课件

1、.,1,High Frequency Ventilation,.,2,通气频率正常频率4倍以上(在成人 60次 min)，而潮气量接近或低于解剖无效腔容积的机械通气模式。,.,3,高频通气是一种低周期压力变化和超生理呼吸频率的肺泡通气方法，具有低潮气量、低气道压、低胸内压，不使肺泡反复启闭，不产生剪切力。使肺泡持续扩张下保持有效通气和换气低气道压可减少肺组织及气道压损伤，循环于扰小，气体弥散好，改善氧合快、可迅速提高血氧饱和度，纠正低氧血症。,.,4,.,5,High frequency jet ventilation,.,6,High frequency oscillatory ventil

2、ation (HFOV),.,7,HFOV is a ventilatory mode in which high frequency, low amplitude, pressure oscillations of gas, at 5-15 Hz (up to 900 breaths/min), are generated in the airways, together with high mean airway pressures and low tidal volumes (1-2ml/Kg). Both the inspiratory and expiratory phases of

3、 ventilation are active.,.,8,高频振荡通气（HFOV）,急性肺损伤(ALl)、急性呼吸窘迫综合征(ARDS） 小儿或新生儿呼吸窘迫综合征(NRDS) 慢性阻塞性肺病(COPD) 支气管镜检查或手术 气漏综合征 胸腔和上腹部手术,.,9,Five different mechanisms have been proposed : 1.Transit Time Profile 2.Interregional Gas Mixing 3.Augmented Dispersion (Taylor Dispersion) 4.Asymmetric Velocity Profil

4、es 5.Molecular Diffusion,.,10,The lung compartment is not a uniform structure and transit times to alveolar units will vary in proportion to the length of the bronchial airways. Proximal alveolar units with short transit times will therefore ventilate before distal units and adequate gas exchange ma

5、y occur in proximal units, by direct bulk convection, when tidal volumes are low.,1. Transit Time Profile,.,11,The time that alveolar units take tofill during ventilation depends on their compliance (C) and resistance (R) to airflow: T = R x C,2. Interregional Gas Mixing,.,12,Consequently, units wit

6、h short time constants (low compliance, low resistance) fill and empty more rapidly. At the end of expiration, alveolar units with short time constants (fast units) are empty and ready to fill, whereas units with long time constants (slow units) are still emptying. Consequently, gas moves from slow

7、units to fast units. During inspiration the opposite occurs and gas moves from fast to slow units. This movement has been namedPendelluftmovement.,2. Interregional Gas Mixing,.,13,Gas dispersion results from the interaction between the axial velocity profile and radial diffusion of gases in motion.,

8、3. Augmented Dispersion (Taylor Dispersion),.,14,Gas dispersion results from the interaction between the axial velocity profile and radial diffusion of gases in motion.,3. Augmented Dispersion (Taylor Dispersion),.,15,Turbulence, accentuated velocities and swirls of gas all occur at the bifurcations

9、 in the airways which results in greater gas dispersion. At higher frequencies, inertial effects become more marked and the velocity profiles are more exaggerated. The net effect is, that even though bulk axial flow is low with ventilatory modes such as HFOV, the altered velocity profiles and interactions which occur in a branching system, result in greater gas dispersion.,4. Asymmetric Velocity Profiles,.,16,5. Molecular Diffusion,.,17,1.