chapter 4 Flashcards
Describe pulmonary circulation
pulm art accompany airways as far as the terminal bronchioles - break up to supply capillary bed that lies in walls of alveoli
- oxygenated blood collected from capillary bed by small pulm veins (run between lobules) and form the 4 large veins
What is the mean pulm art pressure?
what is pressure difference from inlet to outlet of the pulm and systemic systems?
15 mmHg
pulm: 15-5 mmHg = 10 mmHg
systemic: 100-2 = 98 mmHg
Factor of 10 difference!
Describe the difference between alveolar vs extra alveolar vessels
- Alveolar vessels exposed to alveolar pressure (include capillaries and slightly larger vessels in corners of alveolar walls)
- caliber determined by relationship between alveolar pressure and pressure within them
- exposed to alveolar pressure and compressed if this increases - Extra-alveolar vessels: arteries and veins that run through the lung parechyma
- exposed to pressure less than alveolar and pulled open by the radial traction of surrounding parenchyma - large vessels near hilum are outside lung substance and exposed to intrapleural pressure
What is equation for vascular resistance?
vasc resistance = (input pressure - output pressure)/blood flow
PVR = (15-5)/6L = 1.7 mmHg*min/litre
What happens to PVR when pulmonary arterial pressure increases? when pulmonary venous pressure increases?
PVR DECREASES
The decrease is because of recruitment and distension
What is the predominant mechanism for fall in PVR at high vascular pressures?
distension
What is critical opening pressure (for pulm vessels)?
Applies to EXTRA-ALVEOLAR vessels
When the lung is completely collapsed and the pulmonary artery pressure has to be raised several centimeters of water above downstream pressure before any flow at all occurs. This is because the smooth muscle tone of the vessels is so effective.
In contrast, when lung volume is high the PVR is low
Drugs that cause contraction of the muscle and increase PVR:
Drugs that can relax smooth muscle in the pulmonary circulation:
serotonin histamine and norepinephrine
acetycholine and isoproterenol
What is Fick principle?
. .
VO2 = Q(CaO2 - CVO2)
The volume of blood passing through the lungs each minute
VO2 = oxygen consumption CaO2 = O2 concentration in blood leaving CVO2 = O2 concentration in blood entering lungs
What is the difference in pressure between the top and bottom of lung in the pulmonary arterial system?
30 cmH2O or 23 mmHg in lung that is 30 cm high
Explain the 4 zones of the lung
- Zone 1:
- PA > Pa > Pv
- alveolar pressure above pulmonary arterial pressure - capillaries are squashed flat
- does not occur under normal conditions
- ventilated but unperfused lung is dead space - Zone 2:
- Pa > PA > Pv
- blood flow determined by difference between arterial and alveolar pressures
- Starling resistor (sluice or waterfall effect)
- increasing recruitment of capillaries occurs down this zone - Zone 3:
- Pa > Pv > PA
- flow is determined by the arterial-venous pressure difference
- increase in blood flow in this region is chiefly from distension - Zone 4:
- at low lung volumes when extra-alveolar vessels are narrowed
Also note: blood flow decreases along the acinus
Which O2 determines hypoxic pulmonary vasoconstriction?
Alveolar not arterial blood!
Marked vasoconstriction when the alveolar PO2 is reduced below 70 mmHg
What causes vasoconstriction of the pulmonary circulation
- hypoxic pulmonary vasoconstriction (from PAO2 - alveolar)
- low blood pH causes vasoconstriction
- ANS increases sympathetic outflow which causes vasoconstriction
What is Starlings law (water balance in lung)
net fluid out = K[(PC-Pi) - omega (piC-pii)]
K = filtration coefficient Pc = capillary hydrostatic pressure Pi = interstitium hydrostatic pressure piC = capillary osmotic pressure pii= interstitial osmotic pressure
List functions of pulmonary cicrulation
- gas exchange
- reservoir for blood
- filter blood
- biological activation of ACEI to ACEII
- Inactivates vasoactive substances: bradykinin
- Removes seronin, prostaglandin E2 and F2a, norepinephrine, leukotriene - Metabolizes vasoactive and bronchoactive substances: arachidonic acid
- makes luekotrienes (lipoxygenase pathway)
- makes thromboxane A2 and prostaglandins (cyclooxygenase pathway) - clotting mechanism - mast cells containing heparin
- secretes special immunoglobulins (IgA)
- synthesis of phospholipids (like dipalmitoyl phosphatidylcholine - component of surfactant)
- protein synthesis for structural framework
- carbohydrate metabolism
