Gas exchange

Question 1

Dalton’s law

Answer 1

The total pressure in a mixture of gases is the sum of presures exerted independently by each gas in the mixture

Question 2

What is the pressure exerted by each gas?

Answer 2

Partial pressure

Question 3

P

Answer 3

Partial pressure

Question 4

PI

Answer 4

Pressure in inspired air

Question 5

PA

Answer 5

Alveolar pressure

Question 6

Pa

Answer 6

Arterial pressure

Question 7

PB

Answer 7

Barometric pressure

Question 8

Q or Q.

Answer 8

Volume of blood (perfusion) or
Volume of blood per unit time

Question 9

Alveolar hypoventilation

Answer 9

A decrease in alveolar ventilation in relation to CO2 production

Question 10

What are the effects of alveolar hypoventilation?

Answer 10

Elevates the pulmonary pressure of CO2
Decreases the pulmonary pressure of O2

Question 11

What causes alveolar hypoventilation

Answer 11

Damage to CNS (drugs, trauma)
Peripheral nerve injury
Damage to pump (muscle paralysis, trauma to chest, bloated abdomen)
Lung resisting inflation (airway obstruction and decreased lung compliance

Question 12

Alveolar hyperventilation

Answer 12

Decreases PACO2
Increased PAO2
Occurs in response to hypoxia, acidosis or hyperthermia

Question 13

Ficks law (V. Gas)

Answer 13

V.gas = [A x D (P1-P2)] /T

Question 14

Ficks law variables

Answer 14

V.gas- rate of diffusion
A- surface area
D= diffusion coefficient
T= thickness of tissue

Question 15

How does thickness of tissue affect the rate of gas diffusion ?

Answer 15

Increased thickness will slow diffusion

Question 16

How increases the rate of gas diffusion?

Answer 16

Increased surface area

Question 17

Exercise-associated Hypoxemia

Answer 17

In strenuous exercise PVO2<40
Cardiac output is higher, blood flow is faster, less time available for equilibrium

Question 18

What is the direction if diffusion?

Answer 18

Venous blood to alveoli

Question 19

Is O2 or CO2 a better indicator of lung disease?

Answer 19

O2 because lung diseases have a minimal effect on CO2 diffusion

Question 20

Perfusion

Answer 20

Blood flow in pulmonary capillaries

Question 21

What happens with reduced alveolar ventilation?

Answer 21

Decreased PO2 and increased PCO2 in alveoli
Perfusion will reduce to match ventilation
Vasoconstriction

Question 22

What happens with enhanced alveolar ventilation?

Answer 22

Increased PO2 and decreased CO2 in alveoli
Enhanced perfusion
Dilatuon

Question 23

What does V./Q. Ratio determine?

Answer 23

Adequacy of pulmonary exchange
ideal: 0.8

Question 24

Low V./Q. Ratio

Answer 24

Overperfused and under ventilated
Blood leaving is low in O2 and high in CO2
Ex: airway obstruction and right to left shunt

Question 25

High V./Q. ratio

Answer 25

High ventilation
Blood after obstruction is higher in O2 and lower in CO2
Ex: vascular obstruction, blood doesn’t flow to thwart (dead space)

Question 26

Shunt

Answer 26

Perfusion without ventilation
Wasted perfusion
Refractory to oxygen therapy
Hypoxemia without hyoercarbia
Type 1 respiratory failure

Question 27

Dead space

Answer 27

Ventilation without perfusion
Wasted ventilation
Hypoxemia with hypercarbia
Type 2 respiratory failure

Question 28

Pneumonia

Answer 28

Large portions of blood flows to units with low V./Q.
Blood passing though right to left shunts is increased

Question 29

Isoshunt diagram

Answer 29

Plots the relationship between FiO2 and PAO2 against a set of virtual shunt lines
Used to estimate shunt % by O2 therapy

Question 30

What causes right- to - left vascular shunt to allows blood to bypass the lung?

Answer 30

Atelectasis
Acute obstruction
Acute pneumonia

Question 31

What affects PaO2 and PaCO2?

Answer 31

Inspired air
Alveolar ventilation
Alveolocapillary diffusion
Ventilation/ perfusion mismatch