1. At what lung volume is pulmonary vascular resistance at its lowest?
2. West Zone 1 is an example of what type of VQ matching?
a) Relative intrapulmonary shunt
b) Relative avleolar dead space
c) Normal VQ matching
d) Intracardiac shunt
3. What is the effect of positive pressure ventilation on LV transmural pressure?
c) No Change
d) Depends on preload
4. Which of the following probably best predicts fluid responsiveness?
c) Pulse pressure variability >15%
d) Heart Rate
ANSWERS & EXPLANATIONS
1. B. At FRC, the pulmonary vascular resistance is at its lowest. With increasing lung volumes, septal vessels get compressed leading to increased PVR. At lower lung volumes, corner vessels get compressed leading to increased PVR. Hence, the aggregate resistances of septal and corner vessels is the lowest at FRC (after a normal tidal breath exhalation).
2. B. West Zone 1 is more aerated with relatively less perfusion. Hence, it is an example of relative alveolar dead space. Zone 2 is an example of VQ matching with Zone 3 an example of relative intrapulmonary shunt, with blood flow in excess of avleolar ventilation.
3. B PPV decreases the transmural pressure (pressure in the ventricle - pressure out of the ventricle) where pressure out of the ventricle is the intrathoracic pressure. Hence, by increasing intrathoracic pressure with PPV, you reduce transmural pressure, which is essentially decreasing LV afterload.
4. C Pulse pressure variability (with a rise in pulse pressure with delivery of a mechanical PPV breath) of >15% has been shown to be associated with fluid responsiveness, at least in adult patients.