Pulmonary Circulation Flashcards
Pulmonary Circulation vs. Systemic (1 similarity, 3 differences, 2 results)
Must be equal in magnitude, but pulmonary has:
Lower pressures/resistance
Significant resistance in capillaries, not just arterioles
Thinner more compressible walls (low P)
So bigger effects of gravity/passive forces
Low hydrostatic pressure reduces filtration across capillaries (prevents edema in lungs)
Fick Principle
VO2 = Qt x (Cao2 - Cvo2)
Resistance =
Pressure gradient/blood flow (PVR = about 1.7 mm Hg/L/min)
Magnitude vs. Distribution
Magnitude of pulmonary circulation determined by cardiac output and shit, but PVR controls distribution and how much work the right heart must do to drive blood flow
Zone 1,2,3 PA, Pa, and Pv relationships
1: PA > Pa > Pv (closed)
2: Pa > PA > Pv (compressed)
3: Pa > Pv > PA (blood flow)
Ventilation Distribution
Greater at base bc has to be kept standard with perfusion. Base intrapleural pressures greater (less neg) than apical bc small fluid column. On inspiration, same pressure change throughout but the change in volume is greater starting from removing greater pressures
Vascular Pressure and PVR
Increase in pressures lead to decrease in PVR via recruitment and distension of alveolar capillaries (and large increase in flow)
Positive Pressure Ventilation Effect on Capillaries
Compress capillaries in alveoli making it harder for RH
PVR by Lung Volume
Minimal at functional residual capacity. As it gets bigger, alveolar vessels compressed so their resistance increases (although extraalveolar vessels expand bc intrapleural pressure decreases on inspiration). On expiration, opposite happens and extra alveolar vessel resistance increases
Low pO2 and acidic blood pH (high CO2)
Pulmonary a.s constrict, bypassing poorly ventilated regions. Good usually and before birth, but problem w/ high elevations
3 Reasons Interstitial Edema Develops before Alveolar
Tissue hydrostatic pressures more negative outside interstial rather than alveolar vessels
Endothelium more water permeable than alv epithelium
Type II cells pump Na out of alv and water follows
2 Chemical Sensitivities of Pulmonary Circulation
Constricted by endothelin
Dilated by NO