# Pulm: Blood flow Flashcards

1
Q

What is passive control?

A

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.

2
Q

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

A

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.

3
Q

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

A

Vgas = A x D(P1-P2)/T

A = area

D = Diffusion constant

T = thickness

P1 - P2 = gas concentration gradient

4
Q

Blood flow: Zone 1

A

Alveolar pressure (PA) is greater than arterial (Pa) and venous pressure (PV) and no blood flow occurs

5
Q

Blood flow: Zone 2

A

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

6
Q

Blood flow: Zone 3

A

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

7
Q

Where is the V/Q ratio 1?

Where is it not and why?

A

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.

8
Q

What is the normal V/Q?

why?

A

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

9
Q

A

Alveoli that are ventilated but not perfused

10
Q

What is shunt flow?

A

Perfusion without ventilation

anatomic- blood bypasses the alveoli

physiological- airway is blocked

11
Q

Under which circumstance would V/Q be infinity?

A

When there is ventilation but no perfusion

12
Q
A