Pulm: Blood flow

Question 1

What is passive control?

Answer 1

It controls the amount of pulmonary resistance there is. Normally, some pulmonary capillaries are collapsed. When pulmonary artery pressure increases, these capillaries are recruited and distended. This reduces the pulmonary resistance.

Question 2

What happens to the vessels as lungs inflate from a very low volume?

Answer 2

Resistance in extra-alveolar vessels first decreases due to traction caused by distension of the vessles. As inflation continues, resistance begins to rise as alveolar vessels are compressed between the large alveoli.

Question 3

How do you calculate the diffusion of a gas across the pulmonary membranes?

Answer 3

V_gas = A x D(P₁-P₂)/T

A = area

D = Diffusion constant

T = thickness

P₁ - P₂ = gas concentration gradient

Question 4

Blood flow: Zone 1

Answer 4

Alveolar pressure (P_A) is greater than arterial (P_a) and venous pressure (P_V) and no blood flow occurs

Question 5

Blood flow: Zone 2

Answer 5

arterial pressure (P_a) exceeds alveolar pressure, but alveolar pressure exceeds venous pressure (P_V). Blood flow occurs in this zone, but alveolar pressure compresses the venules (venous ends of the capillaries)

Question 6

Blood flow: Zone 3

Answer 6

Both arterial (P_a) and venous pressures (P_V) are greater than alveolar pressure and blood flow fluctuates, depending on the difference between arterial and venous pressures.

Question 7

Where is the V/Q ratio 1?

Where is it not and why?

Answer 7

The V/Q ratio is 1 in the middle portion of the lung.

It the upper portion of the lung the V/Q ratio is >1 because there is a higher ventilation rate than blood flow rate.

In the lower portion of the lung, the V/Q ratio is <1 because there blood flow rate is higher than the ventilation rate.

Question 8

What is the normal V/Q?

why?

Answer 8

0.8

Mostly because of the blood that feeds the bronchioles which enters the systemic flow without going back to the lungs to pick up more oxygen first

Question 9

what is physiological dead space?

Answer 9

Alveoli that are ventilated but not perfused

Question 10

What is shunt flow?

Answer 10

Perfusion without ventilation

anatomic- blood bypasses the alveoli

physiological- airway is blocked

Question 11

Under which circumstance would V/Q be infinity?

Answer 11

When there is ventilation but no perfusion