04 Pulmonary Circulation - Boards and Beyond

  • lower p: doesn't need to go as far

Blood O2 Content

  • fetal: less blood to lungs, not important in womb

Diffusion

  • more pressure difference of O2 in air/blood: more diffusion
  • more area: more diffusion
  • thickness: less diffusion

  • emphysema: alveoli destroyed, low DLCO
  • fibrosis: thicker, low DLCO
  • diffusion of CO same as DLCO

Diffusion-Perfusion

  • infuse 3 gases into lungs at Pa concentration, ideally reach Pa concentration
  • N2O: at length 0, no N2O diffuse into blood; diffusion rises very rapidly along capillary length to max value
  • CO: rises slowly, never gets to maximum concentration
  • O2: some O2 from veins at length 0, rise relatively rapidly until max value

  • gas must diffuse through and get carried away

  • N2O: barrier not a factor
  • N2O rapidly diffuse through
  • only determination for rate of rise of N2O is how fast blood flowing, carrying away molecules, rapid rise in partial pressure

  • barrier is major factor for diffusion
  • slow rise
  • diffusion main factor. Perfusion not a factor

  • N2O: only thing slow or speeds up concentration is blood flow rate
  • O2: same
  • CO: uptake limited by diffusion

  • diffusion limited
  • concentration of O2 in blood falls = hypoxemic

  • at rest: blood flows slowly, lots of time to pick up O2
  • exercise: blood flow faster, gets further before reach maximum, but still does even in patients exercising
  • exercise alone should not make someone hypoxemic

Pulmonary Resistance

  • alveolar: blood supplying alveolus
  • arteriolar: blood supplying lung parts outside alveoli
  • inhale: increase resistance from alveolar vessels
  • exhale: increase resistance from arteriolar vessels
  • FRC: lowest point of pulmonary vascular resistance

Pulmonary Hypertension

  • right heart cath: cath into PA from heart

  • V: energy needed to drive flow
  • I: how fast you want to go
  • R: resistance to flow
  • Ppa high in pulmonary hypertension, if any of the variables increased

  • high CO: increase flow through lungs
  • most common cause of PHTN nothing to do with lungs but with left heart

  • chronic hypoxia vasoconstrict

  • Epoprostenol: IV, must infuse constantly, cumbersome