Chapter 4: Blood Flow and Metabolism

Question 1

Describe both the relative flow and relative pressure in the pulmonary and systemic circulations

Answer 1

The flows are equal (5-6 liters per minute), but the pressures are very different. Systemic&raquo_space; Pulmonary

Question 2

What is the mean pressure difference across the pulmonic circulation?

Answer 2

Arterial = 15 mm Hg
Venous = 5 mm Hg

delta P = 10 mm Hg

Question 3

What is the mean pressure difference across the systemic circulation?

Answer 3

Arterial = 100 mm Hg
Venous = 2 mm Hg

delta P = ~100 mm Hg

Question 4

What effect does increasing tension in the surrounding alveolar walls have on the extra-alveolar vessels of the lung?

Answer 4

The extra-alveolar vessels are pulled open

Question 5

What tissues will you find in the extra-alveolar vessels of the lung?

Answer 5

Smooth muscle and elastic tissue

Question 6

Where does vascular constriction in response to alveolar hypoxia occur?

Answer 6

Arterioles and small arteries (not veins)

Question 7

What effect does lung inflation have on the caliber of the extra-alveolar vessels?

Answer 7

The caliber of the extra-alveolar vessels increases

Question 8

What formula describes the relationship between vascular resistance, blood flow, and pressure?

Answer 8

Analogous to Ohm’s Law (V = IR), we can describe vascular parameters with the relation:

delta P = Q x R

where delta P = arterial - venous pressure
where Q = rate of flow of blood
where R = total resistance in the systemic or pulmonary circuit

Question 9

What happens to pulmonary vascular resistance on exercise?

Answer 9

Decreases

Question 10

Why does pulmonary vascular resistance decrease on exercise?

Answer 10

Increased pressure (more flow) results in two compensating mechanisms in the pulmonary vasculature. At low pressure increases, previously closed capillary beds open up, creating more pathways for blood flow. At higher pressure increases, vessel distension accommodates increased flow and pressure, reducing resistance.

Question 11

Describe the Fick principle as it relates to relating blood flow, arterial and venous constituent concentration, and delivery of blood constituents.

Answer 11

Constituents could be oxygen, carbon dioxide, nutrients, etc. Basically, the difference in concentration of a constituent across some distance, multiplied by the rate of flow of blood across that same distance, describes the amount of that constituent consumed:

d[C]/dt = Q x ([C upstream] - [C downstream])

Question 12

In which zone(s) of the lung does alveolar pressure exceed arterial pressure

Answer 12

Zone 1 - not seen very often, means the transmural pressure is such that the capillary beds will close down

Question 13

In which zone(s) of the lung does venous pressure exceed alveolar pressure?

Answer 13

Zone 3 - flow determined by arterial/venous gradient

Question 14

What is the pressure gradient that determines blood flow in Zone 2?

Answer 14

Arterial - alveolar

Question 15

What effect would acutely increasing pulmonary venous pressure have on pulmonary vascular resistance?

Answer 15

Pulmonary vascular resistance would decrease. Looking at the relationship R = (delta P)/Q, it is clear that decreasing delta P reduces R. This can be accomplished by bringing up the venous pressure, all other things staying the same.

Question 16

What happens to the pulmonary vasculature in an individual breathing a 10% oxygen mixture?

Answer 16

Hypoxic pulmonary vasoconstriction

Question 17

What can happen to pulmonary capillaries under conditions of mechanical ventilation?

Answer 17

Too much positive pressure will compress the capillaries as the alveolar pressure rises

Question 18

Describe the mechanism by which pulmonary resistance is decreased at birth

Answer 18

At birth, baby takes first breath. Oxygenation reverses the effect of hypoxic vasoconstriction. This probably occurs when the vascular endothelium releases nitric oxide (NO, synthesized from L-arginine via NO synthase (eNOS)), which activates soluble guanylate cyclase to increase synthesis of cGMP. Cyclic GMP relaxes smooth muscle, opening the pulmonary vasulature

Question 19

Hypoxic vasoconstriction occurs in reaction to what condition?

Answer 19

Low alveolar oxygen, not arterial or venous O2 saturation

Question 20

Describe the pressure driving blood into or out of capillaries into the interstitium

Answer 20

The net pressure driving fluid flow across the capillary endothelium is a balance between hydrostatic pressure pushing out and osmotic pressure pulling in. Strictly speaking, the relation is:

delta P = K{(Pc - Pi) - sigma(PIc - PIi)}

where Pc and Pi are the capillary and interstitial hydrostatic pressures

where PIc and PIi are the capillary and interstitial osmotic pressures

where K and sigma are coefficients

We assume the K and sigma are 1 for our purposes, which makes calculations easier

Question 21

What peptides are processed in the lungs? How are they modified?

Answer 21

Angiotensin I –> converted to Angiotensin II by ACE
Angiotensin II –> Unaffected
Vasopressin –> Unaffected
Bradykinin –> Up to 80% inactivated

Question 22

What amines are processed in the lungs? How are they modified?

Answer 22

Serotonin –> almost completely removed
Norepinephrine –> Up to 30% removed
Histamine –> Unaffected
Dopamine –> Unaffected

Question 23

What arachidonic acid metabolites are processed in the lungs? How are they modified?

Answer 23

Prostaglandins E2 and F2alpha –> Almost completely removed
Prostaglandin A2 –> Unaffected
Prostacyclin (PGI2) –> Unaffected
Leukotrienes –> Almost completely removed

Question 24

Side effect of ACE inhibitor on the lungs?

Answer 24

ACE degrades bradykinin. Blocking ACE results in bradykinin build up, leads to coughing fits.