Pulmonary Vascular Physiology Flashcards
(35 cards)
How is the blood supplied/circulated to the lungs?
Through a dual blood supply:
- Pulmonary circulation
- Bronchial circulation
Where does pulmonary circulation occur?
From the right ventricle
How much of the blood flow is pulmonary circulation?
100%
How much is the bronchial circulation and where is it from?
2% of Left ventricular output, which perfuses lung tissue itself.
Describe the root of the pulmonary circulation?
- Blood leaves the right ventricle via a single large artery, the pulmonary trunk, which divides into the two pulmonary arteries, one supplying the right and one supply the left lung.
- In the lungs the arteries continue to branch and
connect to arterioles, leading to capillaries that unite into venules and then veins. - The blood leaves the lungs via four pulmonary veins, which empty into the left atrium
How long does a RBC take to pass through the pulmonary circulation?
5 seconds (quite slow)
what is the difference in vessel wall thickness between pulmonary and systemic circulation?
Pulmonary - Thin
Systemic - Thick
what is the difference in muscularization between pulmonary and systemic circulation?
Pulmonary - Minor
Systemic - Significant
what is the difference in need for redistribution between pulmonary and systemic circulation?
Pulmonary - Not in the normal state
Systemic - Yes
What is systemic circulation?
Provides the functional blood supply to all body tissue. Via the aorta, which then divides into
progressively smaller vessels. The smallest arteries branch into arterioles, which
branch into roughly 10 billion very small vessels, the capillaries, which unite to form
larger-diameter vessels known as venules. The arterioles, capillaries & venules
are collectively referred to as the MICROCIRCULATION.
What is Pouiseuille’s Law?
Resistance = (8 x L x Viscosity)/ ( Pie x r^4)
What is the importance of Pouiseuille’s Law?
Shows that a small change in radius causes a big change to resistance due to the r^4
What is Ohm’s Law?
V = IR
Voltage across circuit = Current X resistance
How do we use Ohm’s Law for pressure across Pulmonary Circulation?
V = IR
Pressure across circuit (mPAP - PAWP) = Cardiac Output x Resistance (PVR)
mPAP (mean pulmonary arterial pressure)
PAWP (Pulmonary arterial wedge pressure ;eft atrial pressure)
CO (cardiac output)
PVR (Pulmonary vascular resistance)
What happens to the mean pulmonary arterial pressure when we exercise?
On exercise mPAP remains stable in normal subjects but CO increases significantly. This is possible because the resistance falls
How can we reduce resistance?
- Recruit more capillaries
- Distend some vessels (bulging of vessels)
What is Type I respiratory failure defined by?
- pO2 < 8kPA
- pCO2 <6 kPA
What is Type II respiratory failure defined by?
- pO2 < 8kPA
- pCO2 >6 kPA
What are some causes of hypoxaemia (O2 levels are low)
- Hypoventilation (reduced ventilation/ air coming in)
- Diffusion impairment
- Shunting
- V/Q mismatch
What is hypoventilation the cause of?
- Type I Respiratory failure
(failure to excrete the CO2) - Failure to ventilate the alveoli
- Muscular weakness
- Obesity
- Loss of respiratory drive
What are the three different diffusion impairments?
- Gaseous diffusion: pulmonary oedema (Diffusion in alveoli)
- Membrane diffusion: Interstitial fibrosis
(from alveoli to blood vessel) - Blood diffusion: Anaemia (through the blood vessel wall)
What is the V/Q mismatch?
Ventilation/ Perfusion mismatch
What is the V/Q mismatch like in the lungs?
Perfusion increases as we go down the lungs as at the top of the lungs there is very little flow
What are the pressures like at the top of the lungs?
The alveolar pressure Pa is greater than the arterial and venous pressure. Therefore very little flow/ perfusion
