Exam 6: Pulmonary Gas Exchange

Question 1

What is Dalton’s Law?

Answer 1

The sum of thee partial pressures of all the gases in a mixture determines the total pressure of the mixture

Question 2

What is Henry’s Law?

Answer 2

The pressure of a gas in a liquid is determined by the concentration of the gas and its solubility

Question 3

What is the FIO2 on top of Mount Everest?

Answer 3

0.21

Question 4

What are the 4 factors that determine diffusion of gases across the alveolar barrier?

Answer 4

Thickness of the membrane
Surface area of the membrane
Diffusion coefficient of the gas in the substance of the membrane
The partial pressure difference of the gas between the 2 sides of the membrane

Question 5

Which step in the diffusion process is rate limiting?

Answer 5

Partial pressure difference
Diffusion distance through tissue water
Cross-sectional area
Molecular weight and gas solubility

Question 6

Describe the oxygen tension gradient between ambient air and the cell

Answer 6

Oxygen tension decreases between ambient air and the cell
Dry gas: 159 mmHg
Intracellular 5-40 mmHg
O2 is not limiting until PO2 is less than 1 mmHg

Question 7

What is the normal arterial oxygen tension?

Answer 7

85-100 mmHg

Question 8

What is the normal alveolar oxygen tension?

Answer 8

104 mmHg

Question 9

Why is the arterial oxygen tension less than the alveolar oxygen tension?

Answer 9

Hemoglobin carries oxygen in the arterial blood

PaO2 of dissolved oxygen will be less than the PO2 of gas in the alveoli

Question 10

What is the normal value for PaO2?

Answer 10

85-100 mmHg

Question 11

What is the normal vale for PaCO2?

Answer 11

40 mmHg

Question 12

What is the normal value for PvO2?

Answer 12

40 mmHg

Question 13

What is the normal value for PvCO2?

Answer 13

40-45 mmHg

Question 14

What is the alveolar gas equation?

Answer 14

PAO2 = PIO2 - PaCO2 / R

Question 15

What is the D(A-a)O2?

Answer 15

The alveolar-arterial oxygen difference

Represents a measure of ventilation/perfusion inequality

Question 16

What are the causes of hypoxemia?

Answer 16

Decreased V ̇A
Decreased FIO2
Anatomic shunt
Ventilation/perfusion inequalities
Diffusion impairment

Question 17

Define intrapulmonary shunt

Answer 17

Blood goes through the lungs normally but does not undergo gas exchange because the alveoli are not well ventilated
Perfused but not ventilated, low V/Q mismatching

Question 18

Describe the relationship between oxygen content and partial pressure for whole blood

Answer 18

Oxygen content is a function of both Hgb saturation with oxygen and the partial pressure of dissolved oxygen
The partial pressure only contributes a small amount to total oxygen content but is important because oxygen must first dissolve in the blood in order to become saturated

Question 19

What factors cause a right shift in the oxygen-hemoglobin dissociation curve?

Answer 19

Increased carbon dioxide concentration
Increased blood temperature
Increased 2,3-biphosphoglycerate

Question 20

What factors cause a left shift in the oxygen-hemoglobin dissociation curve?

Answer 20

Decreased pH/hydrogen ions

Question 21

What is the Bohr effect?

Answer 21

Shift in the oxygen-hemoglobin dissociation curve to the right in response to increases in blood carbon dioxide and hydrogen ions has a significant effect by enhancing the release of oxygen from the blood in the tissue and enhancing oxygenation of the blood in the lungs

Question 22

What is nitric oxide?

Answer 22

NO

Produced by vascular endothelial cells and causes vasodilation

Question 23

How does NO affect carriage of oxygen?

Answer 23

Hgb transports NO along with O2
When Hgb gets to tissues it can release NO to regulate local blood supply through hypoxic vasodialtion and thus allowing more efficient transport of O2

Question 24

How is CO2 carried in the blood?

Answer 24

The presence of carbonic anhydrase within the RBC catalyzes the reaction between CO2 and water and accelerates the process of CO2 transport
HCO3- is the predominant CO2 transfer form

Question 25

What are the 4 ways to assess oxygenation in a patient?

Answer 25

Mucous membrane color Arterial blood gas analysis Pulse oximetry Co-oximetry

Question 26

A normal dog is given propofol to induce anesthesia. It halves his alveolar ventilation but does not affect his CO2 production. What would you predict his PaCO2 to be? Assuming that R = 0.8, what will has PAO2 be?

Answer 26

PAO2 = PIO2 – PaCO2 / R PIO2= (760-47) x0.21= 150 So PaCO2 is normally 40 mmHg, but because the ventilation is cut in half while production of CO2 is the same, PaCO2 is building up in the body by doubling the normal amount= 80 mmHg PaO2= 150-(80/0.8) = 50mmHg

Question 27

A dog is anesthetized and has a pulmonary and systemic arterial catheters placed. The oxygen content of the dog’s pulmonary arterial and systemic arterial blood are 14 and 16 mL O2/dL of blood, respectively. Assuming that blood leaving a functional alveolus has a content of 20 mL O2/dL, what is this animal’s shunt fraction? (hint: shunt fraction is calculated as Qs/QT)

Answer 27

Shunt fraction (Qs/Qt)= (CAO2 – CAO2)/(CAO2-CVO2) = (20-16)/(20-14) =4/6=2/3 =67%

Question 28

Will oxygen supplementation improve arterial oxygenation in a patient with a right-to-left-shunt?

Answer 28

Right to left shunt: right side should be low pressure side, if blood is going to the left, there is an elevated pressure in the pulmonary system; oxygen supplementation will not improve arterial oxygenation because the problem is getting blood to the pulmonary system to accomplish perfusion; the pressure needs to be relieved to fix the problem.

Question 29

What is FIO2?

Answer 29

Fraction of inspired oxygen

Question 30

Your patient is on 1 L/min of 100% oxygen. What is the FIO2? If you increase the flowrate to 2L/min, what is the FIO2?

Answer 30

It is 1 in both cases because oxygen is at 100%

Question 31

What role does myoglobin play in oxygen transport?

Answer 31

Myoglobin acts as a facilitator for oxygen delivery from blood to mitochondria Myoglobin is a single heme unit and is the reason muscles are red