Physiologic Effects of PPMV

Physiologic Effects of PPMV A. Ventilation and Respiratory System Mechanics 

Lung inflation occurs when pressure and flow, applied at the airway opening, interact with the respiratory system compliance—lung and chest wall, and airway resistance—to effect gas flow (7,8). The interactions of pressure, flow, and volume can he expressed by the simplified equation of motion  

Driving pressure = (flow x resistance) + (volume/system compliance) 

Intrinsic Positive End-Expiratory Pressure and the Ventilatory Pattern 

Although the ventilator can supply positive end-expiratory pressure (PEEP), it can also develop within the alveoli because of either inadequate expiratory time or collapsed airways during expiration (or both). Often called intrinsic PEEP or air trapping, it depends on three factors minute ventilation, the expiratory time fraction, and the respiratory systems expiratory time constant (the product of resistance and compliance) (9). As minute ventilation increases, the expiratory time fiaction decreases, and the time constant lengthens, the potential for intrinsic PEEP to develop increases (9). 

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