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## Basic Pulmonary Mechanics during Mechanical Ventilation

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**Basic Pulmonary Mechanics during Mechanical Ventilation**Equation of Motion dP=Rx Flow +dV / C st**Points of Discussion**• Equation of motion • Airway pressures • Compliance • Resistance • Pressure-Time • Flow-Time • Pressure-volume loop • Flow-volume loop**Spontaneous Breathing**Exhalation Inspiration**Precondition of Inspiration**Gas Flow Pa • Pa<Pb • Spontaneous breath • Pb>Pa • Mechanical ventilation Pb**Lung Mechanics**transairway pressure transrespiratory pressure transthoracic pressure volume compliance= Dvolume/ Dpressure resistance = Dpressure / Dflow flow**Tube + Spring Model**Resistive Forces Elastic Forces**Airway Resistance**“The Feature of the Tube” D P R = D F Pressure Difference= Flow Rate x Resistance**Compliance**Volume D V D P Pressure D V Cs= D P Pressure Difference = Volume Change/ Compliance**Compliance and Resistance**D P R = D F D V Cs= D P**Equation of Motion**DYNAMIC CHARACTERISTICS: dP = dV / Cdyn RESISTANCE: dPresistive= R x Flow STATIC COMPLIANCE: dPdistensive = dV / Cst dP = dPresist. + dP dist. dP = R x Flow + dV / C st**Equation of Motion**dP=Rx Flow +dV / C st**Components of Inflation Pressure**Pplateau (Palveolar) Begin Inspiration PIP } Transairway Pressure (PTA) Paw (cm H2O) Inspiratory Pause Expiration Time (sec) Begin Expiration**Exhalation Valve Opens**Begin Inspiration Inflation Hold (seconds) Pplateau (Palveolar Paw (cm H2O) Time (sec) PIP } Transairway Pressure (PTA) Paw (cm H2O) Expiration Time (sec) Begin Expiration PIP Distending (Alveolar) Pressure Airway Resistance Expiration Begin Inspiration Begin Expiration**Spontaneous vs. Mechanical**Mechanical Inspiration Paw (cm H2O) Spontaneous Expiration Expiration Inspiration Time (sec)**PIP vsPplat**PIP PIP PPlat High Raw PPlat Normal Paw (cm H2O) PIP PIP PPlat High Flow Low Compliance PPlat Time (sec)**Mean Airway Pressure**Lengthen Inspiratory Time Increase peak pressure Increase PEEP Increase Rate Increase Flow**Inspiratory Flow Pattern**Total cycle time TCT Peak Expiratory Flow Rate PEFR Beginning of expiration exhalation valve opens Peak inspiratory flow rate PIFR Inspiration Inspiratory Time TI Expiratory Time TE Flow (L/min) Time (sec) Beginning of inspiration exhalation valve closes Expiration**Flow vs Time**Inspiration Time (sec) Flow (L/min) Expiration**Flow Patterns**SQUARE DECELERATING ACCELERATING SINE**Flow Patterns and Effects of Volume**ACCELERATING SINE DECELERATING SQUARE**Mechanical vs Spontaneous**Mechanical Spontaneous Inspiration Expiration**Volume vs. Time**Inspiratory Tidal Volume Volume (ml) Inspiration Expiration TI Time (sec)**FRC and PV Loop**Normal Compliance TLC VOLUME FRC FRC Negative Positive 0 DISTENDING PRESSURE**Components of Pressure-Volume Loop**VT Expiration Volume (mL) Inspiration PIP Paw (cm H2O)**PEEP and P-V Loop**VT PEEP PIP Volume (mL) Paw (cm H2O)