Physiology: Pulmonary Block, Chapter 4

Front 1

what are the two systems of blood feeding the lungs?

Back 1

bronchiole and pulmonary.

Bronchiole comes from the left ventricle and feeds 02 blood to the lungs. It represents a small portion of LV's output. Supply hilar lymph nodes, the pleura, pulmonary arteries and veins, vagus, and esophagus.


Pulmonary comes from the RV and represents its entire output, and is equivalent to cardiac output.

Front 2

About how many capillaries serve how many alveoli?

Back 2

there are 280 billion capillaries serving 300 million alveoli, so there are 1000X more capillaries.

Alveoli are completely enveloped in capillaries.

Front 3

Bronchiole circulation - down to what level is blood supplied to the bronchiole tree?

How does the blood pressure compare to pulmonary blood pressure?

Back 3

To the level of terminal bronchioles - after that, blood needs are supplied by the pulmonary circulation.

Blood pressure in the bronchiole circulation is equivelant to the rest of the systemic circulation and is MUCH HIGHER than pulmonary blood pressure.

Front 4

Venus return of the bronchiole circulation - where does it go?

Back 4

Some goes to the azygous system as normal, but a significant portion goes to the PULMONARY VEINS, which contain blood that's just been oxygenated in the lungs and is returning to the heart ("arterial blood").

This represents part of the normal Right to Left shunt that exists.

Front 5

What are some differences between pulmonary arteries and systemic arteries, and what result from this?

Back 5

Pulmonary arteries tend to have larger diameters and be much THINNER WALLED, much LESS smooth muscle, and are more compressible/distensible.

They're shorter too, also a reason that RESISTANCE IS LOWER.

Also, no true arterioles, which is where most of the systemic resistance comes from.

Result is that the pressure here is MUCH LOWER, and the vessels respond greatly to things like intrapleural and alveolar pressures.

Front 6

What is the big difference between the way left and right heart people think?

Back 6

left heart people (cardiolgosits) think that differences in resistance cause pressure differences.

right heart people think that resistance is determined by the effects of pressure.

Front 7

What are our pulmonary system resistance equations?

Back 7

Generally,

R = change in pressure / flow.

So, in the pulmonary system,

Pulmonary Vascular Resistance = mean pulmonary arterial pressure - mean left atrial pressure / pulmonary blood flow (also equals cardiac output).

Front 8

How do pulmonary and systemic resistances compare?

Where are the resistances located?

Back 8

Pulmonary resistance has to be about 1/10 of systemic resistance.

In the pulmonary circulation, the resistances are evenly distributed (1/3 each) between the pulmonary arteries, capillaries, and veins.

In systemic circulation, most of the resistance is found in the artery section (70%).

Front 9

What kinds of effects have a great impact on pulmonary vascular resistance?

Back 9

Passive effects far more important than smooth muscle tone.

Gravity, pulmonary volume, intrapleural/alveoli pressures, right ventricular output are all very important.

Front 10

What is a transmural pressure gradient, and what is its effect on the size of a vessel?

Back 10

Transmural pressure gradient is P(in) - P (out).

As transmural pressure goes up, the vessel distends and resistance goes down.

Decrease transmural pressure = collapse of vessel and up in pressure.

Front 11

Pulmonary vessels - how does lung volume affect their resistance?

Back 11

Two kinds of vessels are affected in opposite ways:

small vessels that surround alveoli (usually capillaries) are stretched by the filling alveoli, stretching decreases their radius, and since resistance is affected by the 4th power of radius, the resistance goes WAY UP in smaller vessels.

Large vessels, outside alveoli: they're exposed to intrapleural pressure. During inhalation, intrapleural pressure gets MORE NEGATIVE and the transmural pressure goes UP, making the vessels DISTEND and their resistance DECREASE.

They also experience radial traction from the local connective tissue.

Note that during forced expiration, these large vessels are apt to collapse due also to their exposure to IP pressure and decreasing transmural gradient.

Front 12

How do the resistances of the extra/intra alveolar blood flow combine, and at what volume is the lowest resistance found? what's the effect of changing that volume up or down on resistance?

Back 12

The resistances are in series, so they add together.

The lowest resistance is found at the FRC, and going up or down in volume from that point will raise the vascular resistance. The curve is up and down.

Front 13

What is the effect of mechanical positive pressure ventilation on the resistances of the extra/intra alveolar vessels?

Back 13

positive pressure will increase alveolar and intrapleural pressures, meaning that BOTH extra and intra alveolar vessels will tend to compress and resistance will go up.

This can lower cardiac output if the heart can't accommodate.

Front 14

What is the effect of exercise on the pulmonary vascular pressure? Asked another way, increasing blood flow to the lungs does what to pressure?

Back 14

Even though cardiac output may triple or more, the pulmonary vascular pressure rises only a tiny amount.

remember, P = Q*R, so as Q rises, R must go DOWN greatly.

2 reasons: distensibility and recruitment.

Vessels with increased flow will distend (comply) keeping pressure constant.

Also, there are a subset of alveolar capillaries that are normally closed and don't open until a slight increase in pressure forces them open = recruitment.
Up in flow = more pathways open in parallel, so resistance drops and pressure maintains nearly unchanged.

Front 15

innervation of the pulmonary vasculature: what's up?

Back 15

far less innervation of pulmonary vasculature than the systemic vessels.

see more innvervation of the larger vessels than the smaller.

sympathetic effect is unknown.
parasympathetic effect seems to be vasodilation, as is usual.

Front 16

what are the regional effects of gravity on the lung with resistance, flow, and time of flow?

Back 16

gravity causes larger pressures at anatomically lower areas, so the bottom of the lung tends to have slightly higher pressure. this is enough to cause recruitment to DECREASE the resistance in these vessels, increase flow, and decrease the mean capillary transit time.

Front 17

Interaction of gravity and extravascular pressures results in what?

Back 17

Zones! 1, 2, and 3. Note that this the interplay of alveolar pressure (PA), pulmonary arterial pressure (Pa), and pulmonary venus pressure (Pv).

For blood to flow, arterial pressure must be greater than alveolar pressure: imagine that too much air will prevent blood flowing.

Remember that Pa is going to increase as you move down the lung due to gravity effects.

Front 18

What's in zone 1?

Back 18

Zone 1 is alveolar dead space.

Alveolar pressure is too high to allow vascular flow.

PA > Pa > Pv

Front 19

What's zone 2?

Back 19

Pa>PA>Pv.

Arterial pressure is higher than alveolar, so blood will flow - and the delta P that allows this is determined by Pa-PA.

Note that because PA plays such a large role here, physical latitude in the lung allows for gravity effects that change arterial pressures, which change blood flow significantly

Front 20

What's zone 3?

Back 20

here, Pa>Pv>PA, so delta P that determines flow is Pa-Pv.

Front 21

How do exercise and positive pressure mechanical ventilation affect the zones?

Back 21

Exercise will turn all Zone 1 into Zone 2, so no more zone 1. This is from recruitment and such.

Positive pressure ventilation will dramatically increase alveolar pressure (PA), which will dramatically increase the amount of Zone 1 around, making lots of dead space.

Front 22

hypoxia: what happens? why is the effect good? what about all over the lung?

what about upping Co2?

Back 22

causes localized vasoconstriction, raising pressure and resistance.

this is good because it'll shunt blood away from the blocked area (otherwise, lack of gas exchange would lower overall O2 sat).

If global effect (high altitude/suffocation), upping pressure is good because it'll recruit more capillaries for more gas exchange.

Upping Co2 has an identical effect, not sure why.

Front 23

what is pulmonar edema, and where does fluid accumulate?

Back 23

extravasicular fluid in the lungs is pulmonary edema.

the alveoli have relatively impermeable membranes, so fluid tends to accumulate in the interstitium long before it fills in the alveoli

Front 24

pulmonary effusion - what equation determines the direction of fluid movement and what changes it?

Back 24

the starling equation:

Qf = Kf [Pc - Pif] - [Oc - Oif]

Note that a sigma "reflection coefficient" is inserted before the Osmotic terms, which refers to the ability of a membrane to prevent extravasation of solute particles.

Front 25

if fluid does get into the interstitium, how is it removed?

Back 25

lymphatics are very important - normally the rate can go up 10x to combat disease, get edema only after that's been overwhelmed.

Front 26

What kinds of conditions can cause pulmonary edema?

Back 26

think about the equation - anything that raises the final number is fluid movement and edema.

raising capillary permeability (Kf), with toxins/oxygen toxcisity.

raising capillary hydrostatic pressure (left heart failure causing buildup of pressure in the lungs)

lowering interstitial hydrostatic pressure (re-inflating a lung too fast).

lowering capillary (aka colloid) osmotic pressure (protein starvation, kidney dysfunction, etc).

also stopping lymph drainage, getting hit in the head, and high altitude.