04 Pulmonary Circulation

• 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