Describe P and R in pulmonary vasculature

Describe the structure of pulmonary capillaries and functional advantage

• dense network of capillaries in alveolar walls
• air spaces nearly completly surrounded by flowing blood
• functional advantage- ensure large surface area for gas exchange with a very short distance btw air and blood

• pulm. artery branches accompany bronchi down center of secondary lobules as far as terminal bronchioles
• includes bronchiol arteries as well
• beyond terminal bronchioles, they break up and supply capillary bed in walls of alveoli

• endothelium has looser junctions (pick up fluid via lymphatics)
• epithelium btw alveoli have tight junctions

Why does lung tissue usually not die

• MAP: 15-18 mmHg
• diastolic: 8 mmHg
• systolic: 25 mmHg

Describe why pressure of pulm. circulation is low

• distribution is not complex in lung
• pressure head needs only to be high enough to lift blood to top of lung

Equation of PVR

PVR = (input P- output P)/blood flow

Mechansim of action of Swan Ganz catheter

1. blow up catheter in branch of pulmonary artery
2. measure backflow pressure aka pulmonary capilary wedge pressure from left atrium (average is 5 mm Hg)

• decreases in response to increased flow
  • ex: distension, recruitment during exercise

it is difficult to increase pulmonary blood pressure, so we decrease resistance

• recruitment opens up more airway vessels
• distension just increases the radius of vessels that are currently opened

• pooling of blood in lungs, leading to rise in pulmonary pressures

Effect of increased alveolar pressure on flow in lung bv's

• leads to "collapse" of capillaries, leading to decrease in blood volume

• initial decrease in resistnace leads to increased lung volume
• eventually, they have direct proportional relationship

Effect of inflation on extra-alveolar vessels

• resistance decrease as lung volume increases (radius gets larger)

• increase pulm. venous presssure
• increased left atrial pressure
• increase pulmonary blood flow
• decrease alveolar pressure
• decrease transpulmonary pressure
• increase blood volume
• increased pulm. artery pressure (diameter will expand to accomadate, leading to decrease in PVR)

• alveolar hypoxia, leads to increased PVR (vasoconstriction) (divert blood flow away from dying and to the living)
• acidemia (increased PVR)

• prostacyclin (PG I2)
• bradykinin
• nitric oxide

• blood volume storage (change from standing to lying)
• filtration (stray blood clots)
• metabolic
  • biological activation: angiotension I to II via ACE
  • biologic inactivation: bradykinin, serotonin, PGE1, PGE2, PGF2alpha