Pulmonary circulation Flashcards
Systemic capillaries
-high pressure
-capillaries receiving blood from left ventricle/aorta and return to right side of the heart through veins
Pulmonary capillaries
-low pressure
-receive blood from right ventricle/pulmonary artery and return oxygenated blood to left atrium
-extensive branching to facilitate gas exchange
Resistance of pulmonary capillaries
-low resistance, capillaries are highly distensible and compressible (7x more compliant than systemic) to accommodate changes in right heart output
Total blood volume in pulmonary capillaries
~10%
Contraction and relaxation of pulmonary capillaries
-responds to neural or humoral factors to alter resistance and determine contraction and relaxation
Ex. exercise: vascular resistance decreases (pressure increase). Capillary bed from 70ml at rest to 250ml to maximize gas exchange
Lung blood sources
-lungs receive blood from 2 sources:
1.Bronchial circulation
2. Pulmonary circulation
Bronchial circulation
-part of systemic system (so High pressure!)
-provides nourishment and arterial perfusion from trachea to terminal bronchioles
Where does bronchial circulation arise?
Comes from aorta or intercostal arteries
How much cardiac output does bronchial circulation receive?
1% of cardiac output
Mix of systemic and pulmonary circulation
- 1/3 of venous blood returns to right atrium via azygous vein
- 2/3 to pulmonary vein and left atrium, which mixes with O2 rich blood
Pulmonary circulation
-receives total (100%) output from right ventricle for gas exchange (reoxygenate the blood and release CO2)
-provides perfusion to structures distal of terminal bronchioles; nutrients from mixed venous blood
Pressure of pulmonary circulation
-low pressure, high volume
Gas exchange properties
1.Presence of oxygen in alveoli
2. Flow of blood to pulmonary capillaries
Optimal gas exchange ratio
Alveolar ventilation (oxygen) (V)/ Pulmonary perfusion/flow (blood) (Q)
**optimal=1 but normal average=0.8
VQ mismatch
-where there is an inadequate amount of V or Q
What influences Blood flow distribution (Q)?
-influenced by gravity
-results in a vertical gradient dependent on the position of the animal
- volume pressure flow is mostly higher in caudal/ventral regions compared to cranial/dorsal regions
Blood flow distribution (Q) exception in horses
-flow is actually higher in the dorsal region of lungs instead of the ventral region of other animals
Reason for blood flow distribution exception in horses
Hypothesized that a large vertical lung height and the dorsal distance relative to the heart requires higher pulmonary arterial pressure (Pa) to drive blood flow (Pa in horse is higher than Pa in dog)
- Minimizes the effect of gravity
Intense exercise in a race horse
-huge increase in pulmonary pressure (more than 60mm Hg vs 35mm Hg in other species)
- can result in capillary rupture (exercise-induced pulmonary hemorrhage)
Gravity, alveolar size, and alveolar ventilation
-transpulmonary pressure drives distention
-greater the pressure, greater the pull, larger the alveoli=greater ventilation
-therefore larger alveoli more dorsally will have greater ventilation
Respiratory zones
-3 conceptual zones affected by pressures in the lungs
-Zone 1,2,3
Factors that effect respiratory zones
1.Arterial pressure (Pa)
2.Alveolar pressure (PA)
3. Venous pressure (Pv)
Respiratory zone 1
PA > Pa > Pv
Large alveoli (large transpulmonary pressure)
-results in reduced blood flow due to compressed capillary from alveoli
High ventilation (V), low blood flow (Q) = V/Q ratio is very high
Pathology of Respiratory zone 1
-does not normally exist in healthy lungs (physiological dead space)
- can theoretically occur near the apex/dorsal region
Ex. pulmonary embolism or late-stage COPD involving capillary damage or emphysema
Wasted ventilation
-respiratory zone 1
-lots of gas (V) but not enough blood flow (Q) to facilitate gas exchange
Respiratory zone 2
Pa> PA > Pv
-alveoli open and filled with air
-sufficient systole pressure forces deoxygenated blood into capillaries towards alveoli to facilitate gas exchange
**Results in appropriate amount of oxygen and blood flow= best functioning zone of the lung where blood flow (Q) closely matches with ventilation (V) V/Q= ~1 (or 0.8)
Optimal gas exchange
-respiratory zone 2
-balance of alveolar ventilation and pulmonary blood flow
Respiratory zone 3
Pa > Pv > PA
- Alveoli is small (low transpulmonary pressure)
- High blood flow
- High perfusion (Q), low ventilation (V)
**Results in V/Q ratio is very small
- Partially functioning zone of the lung, could theoretically occur near the caudal/ventral area
Pathological examples resulting in respiratory zone 3
-Pulmonary hypertension (high Pa) or bronchoconstriction/atelectasis (low PA)
Wasted perfusion
-respiratory zone 3
-lots of blood flow (Q) but not enough gas (V) to facilitate gas exchange
Modification examples to V/Q zones
-boundaries between the zones are dependent on physiological conditions (**Not fixed anatomical landmarks)
Examples:
1.low blood pressure (Eg. Hemorrhage reduce Pa) will increase zone 1
2. high blood pressure (pulmonary hypertension; increase Pa) will increase zone 3
3. Forceful inspiration will shift zone 3 to zone 2 by expanding the alveoli (increase PA). Will also see a small shift from zone 2 to zone 1.
4. Exercise: increase in cardiac output results in increase in Pa (zone 1 to zone 2), coupled with forceful respiration (PA) (zone3 to zone 2)
**Maximize zone 2 to support aerobic demand
5.Change in anatomical position will influence V/Q capacities
Shunt vs. dead space
Shunt: zone 3; V/Q «1
Dead space: zone 1; V/Q»_space;1
**whereas health zone= zone 2= V/Q=1
V/Q»1
-ventilation exceeds blood flow so oxygen present but no blood flow to facilitate gas exchange
V/Q«1
-blood flow exceeds ventilation (primarily due to obstruction) so blood flow there but no oxygen
VQ mismatch
-results in hypoxemia (low oxygen in systemic blood)
Right to Left shunt
-the pneumonic region (collapsed alveoli) receives no ventilation so blood flow through that region does not pick up any oxygen
- the blood from this region mixes with oxygenated blood from healthy alveoli which reduces overall PO2 returning to the heart
**Results in deoxygenated blood leaving from the right ventricle returning to the heart/left ventricle as still poorly oxygenated blood= hypoxemia
Does oxygen supplementation improve hypoxemia?
-no because there is no way to overcome the obstructed alveoli (even if more oxygen is supplied)
