Pulmonary vasculature: a low pressure system
General principles re fluid flow apply obv

pulmonary blood flow
- ↑ blood flow = ↑ elastic distension + recruitment of capillaries
- hence apices in upright patient = minimal blood flow = narrow capillaries = high resistance
lung volume - mechanical compression
- the sweet spot is at FRC!
- - at low lung volumes, large vessels are compressed
  - at high lung volumes, small vessels are compressed
- mostly measured in dead dog lungs
transpulmonary pressure (i.e. difference between alveolar and pleural pressure) - vascular resistance ↑ during inspiration

hypoxic vasoconstriction

sensor: oxygen sensing ?mechanism - in response to oxygen tension (so anaemia doesn't matter)
controller: regulation by endothelial modulators
- NO, prostacyclin - vasodilators
- Endothelin-1 - vasoconstriction
- effect: smooth muscle constriction
produced by ↑ resistance in small distal pulm arteries

physiological determinants

acidaemia - more reactive to hypoxia
reduced sensitivity:
- hypothermia
- iron (e.g. infusion)
- infection - sepsis, pneumonia

determined by oxygen tension (not content)

Vasodilators	Vasoconstrictors
- Nitric oxide - Milrinone - Levosimendan - Sildenafil - Vasopressin - Bosantan / ambrisantan - Prostacycline and its analogs - Calcium channel blockers - ACE-inhibitors - Adenosine	- Adrenaline - Noradrenaline - Methylene blue