Pulmonary Blood Flow And V/q Relationships

Front 1

Pulmonary circulation

Back 1

A high flow, low pressure, and low resistance system. High pressures are not required to drive the high blood flow since resistances are so low.

Front 2

Pulmonary blood flow

Back 2

Entire cardiac output of the R heart, normally around 5 L/min

Front 3

Accommodating high flow

Back 3

In a single circulation is accomplished via low resistance.

Front 4

Pulmonary pressures

Back 4

Do not need to be high to drive flow as resistance is very low

Front 5

Pulmonary blood vessels

Back 5

More more compliant than systemic vessels, less smooth muscle.

Front 6

Pulmonary blood flow is uneven in....

Back 6

the upright lung, d/t gravitational affects.

Front 7

Zone 1

Back 7

-Lowest blood flow
-Pulmonary arterial pressure lower than alveolar air -pressure
-Pulmonary capillaries compressed

Front 8

Zone 2

Back 8

-Medium blood flow
-Pulmonary arterial pressure higher than alveolar air pressure
-Flow driven by Pa – PA

Front 9

Zone 3

Back 9

-Highest blood flow
-Pulmonary arterial and venous pressures higher than alveolar air pressure
-Most capillaries perfused

Front 10

Positive pressure breathing

Back 10

Increases alveolar air pressure further and can lead to complete closing of pulmonary capillaries in zone 1.

Front 11

Hemorrhage

Back 11

Lowers pulmonary blood pressures and can lead to complete closing of pulmonary capillaries in zone 1.

Front 12

Pulmonary vascular resistance decreases with...

Back 12

An increase in cardiac output. The decrease in resistance occurs via two mechanisms: perfusion of additional capillaries and distention of perfused capillaries.

Front 13

Capillary recruitment

Back 13

Adding additional capillaries than normal when there is higher blood flow. Prevents pulmonary edema. Increases the surface area for gas exchange.

Front 14

Capillary distention

Back 14

Highly compliant capillaries distend, by doing this they don't allow pressure to greatly increase. Prevents pulmonary edema.

Front 15

Benefits of decreasing resistance with high cardiac output

Back 15

Keeps velocity of blood flow slow in capillaries, allowing time for gas exchange; increases surface area for gas exchange; keeps pulmonary capillary pressures from increasing too much so that pulmonary edema is prevented.

Front 16

Hypoxic vasoconstriction

Back 16

Reflex constriction of pulmonary arterioles with hypoxic conditions in surrounding tissue and alveoli. This prevents wasting perfusion in alveoli that are not well-ventilated. Triggered when alveolar PO2 drops below about 70 mm Hg.

Front 17

Global hypoxic vasoconstriction

Back 17

occurs in the fetal circulation; pulmonary blood flow is only about 15% of the cardiac output.

Front 18

Physiological shunts

Back 18

Bronchial circulation and portion of coronary venous flow
Cause PaO2 to be slightly lower than PAO2

Front 19

Right-to-left shunts

Back 19

Rerouting of blood from right to left heart
Septal wall defect
Hypoxemia results as up to 50% cardiac output diverted
Not corrected by high O2 gas
PaCO2 normal as ventilation stimulated

Front 20

Bronchial circulation

Back 20

Bronchial arteries arise from thoracic aorta; perfuse bronchial tree; empties into freshly oxygenated blood in the pulmonary veins.

Front 21

Coronary venous shunt

Back 21

A small portion of coronary venous blood empties directly into the left ventricle.

Front 22

Left-to-right shunts

Back 22

Do not result in hypoxemia. In patent ductus arteriosus, the ductus arteriosus fails to close after birth and blood flows from the aorta into the pulmonary artery. Right heart PaO2 elevated.

Front 23

Patent ductus arteriosus

Back 23

The ductus arteriosus fails to close after birth and blood flows from the aorta into the pulmonary artery. Forms a L-to-R shunt. Does not cause hypoxemia, but does cause a problem if you're diverting too much from systemic circulation.

Front 24

Fetal pulmonary blood flow

Back 24

Collapsed lungs, global hypoxic vasoconstriction, high pulmonary pressures and resistance; aortic pressure lower, almost all pulmonary blood flow enters aorta through ductus arteriosus.

Front 25

V/Q Ratio

Back 25

Compares alveolar ventilation to pulmonary blood flow.
Matching ventilation to perfusion is critical for ideal gas exchange.
Mismatching seen in numerous pulmonary diseases.

Front 26

Normal V/Q

Back 26

Average for lung - alveolar/pulmonary
4L/5L = 0.8
ABGs will be normal

Front 27

V/Q distribution

Back 27

Uneven in upright lung
V/Q highest at apex, lowest at base
Greater impact of uneven blood flow
Results in regional differences in gas partial pressures

Front 28

Greater than normal V/Q

Back 28

Arterial PO2 is higher, arterial CO2 is lower.

Front 29

Lower than normal V/Q

Back 29

Arterial PO2 is lower, arterial CO2 is higher.

Front 30

V/Q ratios and the alveolar gas equation

Back 30

Small changes in V/Q ratios have a greater impact on PaO2 than PaCO2.

Front 31

V/Q defects

Back 31

Result when either ventilation or perfusion is impaired.

Front 32

Airway obstruction

Back 32

Local V/Q=0. Alveolar gas pressures are the same as mixed venous blood since no ventilation is occurring; of course with no gas exchange, the gas pressures in the blood leaving the affected alveoli remain unchanged.

Front 33

Pulmonary embolism

Back 33

Thrombus lodges in a pulmonary artery, blocking blood flow to a region of the lung; affected region V/Q = infinity as Q = 0. Alveolar gas pressures are the same as tracheal air since no perfusion is occurring; local blood gas pressures are N/A as there is no blood flow.

Front 34

Pulmonary diseases

Back 34

Often see V/Q defects, don’t have to be extreme as in 0 or infinity, but can be higher or lower than normal. There can be BOTH high and low V/Q defects present, depending on the region of the lung. Ex. pneumonia

Front 35

Pneumonia

Back 35

Fluid-filled portions of the lung that are not ventilated will have a low V/Q ratio, whereas other regions of the lung, where the infection has not yet spread, may be ventilated but have lower blood flow (high V/Q).