Gas exchange; ventilation and perfusion relationship: Johnson

Question 1

There has to be a relationship between ventilation and perfusion for what to occur?

Answer 1

gas exchange

so gas exchange CANNOT if either ventilation or perfusion is missing

Question 2

What is the goal of the respiratory system?

Answer 2

to ensure that ventilation and perfusion are matched as much as possible for efficient gas exchange

Question 3

What is the major determinant of gas exchange in the pulmonary system?

Answer 3

the ratio of ventilation to perfusion

Question 4

What is the most common cause of arterial hypoxemia?

Answer 4

mismatching of ventilation and perfusion

the PAO2 is 100 but PaO2 is less than 100

Question 5

When the ratio of ventilation to perfusion is greater than 1, what does that mean?

Answer 5

ventilation exceed perfusion

Question 6

The best gas exchange occurs where in the lungs?

Answer 6

at the base

• the best blood flow and ventilation occurs at the base of the lung
• the alveoli at the base has better compliance and started with a lower air volume; gravity causes blood flow to be highest at the base

Question 7

How does the ratio of V/Q change from base to apex of lung?

Answer 7

base: lowest ratio
apex: highest ratio

Question 8

Why can account for O2= 150 torr and CO2= 0 torr?

Answer 8

airway is completely open but there is a blood clot and the perfusion is blocked

• CO2 cannot equilibrate with the alveolar air and be expelled
• O2 cannot mix with the blood as the O2 cannot be extracted from the air if the blood cannot come in contact with the air

Question 9

If partial pressures of CO2 and O2 mimic their respective values in alveolar air pressure, what does this means?

Answer 9

there is no perfusion

Question 10

If partial pressures of CO2 and O2 mimic their respective values in mixed venous blood, what does this means?

Answer 10

absent ventilation

Question 11

What are physiological shunts? What is the V/Q ratio for shunts?

Answer 11

• complete blockage of airway, all ventilation is diverted to adjacent alveolus
• perfusion is equally distributed between both units
• this results in mixed venous blood with no gas exchange

V/Q=0

Question 12

What occurs during emphysema?

Answer 12

• lung parenchyma loses its ability to recoil: a huge increase in compliance (reflective through the large alveolar air spaces)
• destruction of blood capillaries
• very poor gas exchange

have regions of lung that have normal V/Q ratio and other regions where there are high V/Q around 10

Question 13

What occurs during chronic bronchitis?

Answer 13

Disease of the airway

Excessive inflammation and obstruction to airflow

Associated with smoking

• some region in the lung that have ability to perform normal lung function (normal v/Q ratio)
• some other regions have limited gas exchange due to low amounts of ventilation even though there is high amount of perfusion causing problems with gas exchange

Question 14

Regions where you cannot have gas exchange is physiologically similar to what other space in the lung?

Answer 14

dead air space

Question 15

What is hypoxia vasoconstriction?

Answer 15

• causes the vasculature in pulmonary side to constrict leading to pulmonary HTN and can also serve as a an autoregulatory mechanism
• it has the ability to divert blood to areas where ventilation is available (where alveoli have O2) so in this way the pt has compensatory mechanism that kicks in to help him or her to produce the best possible gas exchange and bringing V/Q to normal ratio

Question 16

Does a normal V/Q value always indicate normal lung?

Answer 16

NO because there are compensatory mechanisms

Question 17

High V/Q ratio are typically found where in the lung? Low V/Q ratio?

Answer 17

• High V/Q: apex

- Low V/Q: base

Question 18

High PO2 environment is found where in the lung?

Answer 18

apex

-this can affect the distribution of pulmonary tuberculosis

Question 19

High blood perfusion occurs where in the lungs?

Answer 19

base

Question 20

Describe the blood perfusion in Zone I, II, and III due to gravitational forces.

Answer 20

Zone I: very little blood perfusion; right underneath the heart

Zone II: has blood that is most reflective of PaO2

Zone III: best blood flow; follows a pressure gradient; no collapse capillaries

Question 21

What is the alveolar-arterial difference (AaDO2)? What difference would a perfect lung have? What about a normal individual?

Answer 21

refers to the difference between the partial pressure in the alveolar air and in the arterial blood

perfect lung would have a different of 0

normal lung should be <15 mmHg; <25 is the upper limit of normal

Question 22

An increase in AaDO2 is the hallmark of what?

Answer 22

inefficient or abnormal gas exchange

Question 23

What does PaO2 mean in an arterial blood gas?

Answer 23

PaO2 is the amount of O2 dissolved in the plasma not the O2 bound to hemoglobin

Question 24

What are some factors that contribute to AaDO2????

Answer 24

venous admixture due to anatomic shunt ??

Some bronchial and mediastinal veins drain into pulmonary veins (bronchopulmonary anatomoses) that result in venous admixture.

Oxygenated and deoxygenated blood mixing causes a reduction in the PaO2

Question 25

PAO2= 77 mmHg
PACO2= 45 mmHg

Would you expect hypoventilation or hyperventilation?

Answer 25

hypoventilation

CO2 too high and O2 is too low

Question 26

What is atelectasis?

Answer 26

when you partial collapse of the alveoli; there are patches of alveoli with no O2 and as a result that impacts gas exchnage losing the ability for efficient gas exchange

these patches could be due to mucus plug, airway edema, foreign body, tumor in the airway)

Question 27

How can congenital heart defects, anatomic shunts, tetralogy of Fallot, and Guillain-Barre syndrome induce hypoxia?

Answer 27

congenital heart defects cause cyanosis (bluish discoloration of lips and fingers) which is characteristic of hypoxia

Anatomic shunts (hypoxemia)

Tetralogy of Fallot: pulmonary valve stenosis, ventricular septal defect (hole between right and left ventricles) and overriding aorta

Guillain-Barre
syndrome: diaphragm weakness cannot allow efficient pressure gradient for air to flow into the lung in the first place for gas exchange to even occur

Question 28

Hallmark of hypoventilation is a normal AaDO2. Gas exchange and perfusion to the alveolus are normal; that is, the lung is functioning normally.????

Answer 28

?????

Question 29

Anesthesia and sleeping pills can cause what?

Answer 29

hypoventilation and thus increased PaCO2/ PACO2 and decreased PaO2/PAO2

Question 30

For the different causes of hypoventilation, what should be done?

Answer 30

fix the underlying cause to restore gas exchange because the lung itself is normal