Answer to Question 1
ANS: A
Plateau pressure requires the establishment of a period of no-flow for 1-2 seconds to allow pres-sure equilibration by the redistribution of the tidal volume and stress relaxation. This maneuver increases inspiratory time and if held longer than 2 seconds may cause barotrauma.
Answer to Question 2
ANS: B
The plateau pressure (Pplateau) is the pressure required to overcome only elastance. When positive end-expiratory pressure (PEEP) is applied, the alveolar pressure will rise. This will result in a higher Pplateau. If overdistention occurs the Pplateau will rise immediately. Peak inspiratory pressure (PIP) reflects the total force that must be applied to overcome both elastance and airway re-sistance offered by the patient-ventilator system. The mean airway pressure represents the aver-age pressure recorded during the entire respiratory cycle. It is influenced by PIP, PEEP, inspira-tory time, and total cycle time. The mean airway pressure is not a specific monitor for optimizing PEEP. The PIP will increase in the face of alveolar overdistention, but it is not specific enough to rely on as the sole measurement to identify overdistention. The transairway pressure is the dif-ference between the PIP and the Pplateau and represents the amount of pressure needed to over-come airway resistance (all frictional forces). The transairway pressure will not reflect alveolar overdistention because when alveolar overdistention happens both the PIP and the Pplateau will rise, and the difference between the two will remain constant unless there is an unrelated change in airway resistance.
Ventilation of the mammalian lung by negative pressure filling.
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Measuring Blood Pressure
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The forces of diffusion and electrostatic pressure. (a) In diffusion, solutes move from an area of h