Ventilation and Perfusion Flashcards
1
Q
What percentage of oxygen in arterial blood diffuses into tissues?
A
25%
2
Q
Gas exchange begins where in the airway?
A
- 17th division; respiratory bronchioles.
- alveolar ducts appear at this level.
3
Q
Anatomical dead space is:
A
- the part of the airway proximal to the respiratory bronchioles that does not participate in gas exchange (the conducting pathway).
4
Q
Anatomical dead space contains about what percentage of tidal volume?
A
30% of tidal volume.
5
Q
What percentage of tidal volume participates in gas exchange?
A
about 70%
6
Q
Rate of CO2 diffusion at the alveoli in comparison to oxygen diffusion:
A
- CO2 diffusion 200X faster.
- pulmonary capillaries have constant back and forth diffusion of CO2.
7
Q
In the peripheral tissues, normal PO2 is roughly:
A
40mm Hg
8
Q
In the peripheral tissues, normal PCO2 is roughly:
A
46mm Hg
9
Q
The alveolar-arterial gradient is a measure of:
A
- A-a O2 gradient
- the difference between the alveolar concentration of oxygen and the arterial concentration of oxygen.
10
Q
The alveolus contains which gases?
A
- inhaled nitrogen, oxygen, water
- exhaled CO2
11
Q
Alveolar pressure (PA) is equal to:
A
- Barometric pressure (Pb)
- Sum of the partial pressures of N2, O2, H2O, and CO2.
12
Q
Is there a difference between the partial pressure of CO2 in the alveolous and in arterial blood?
A
- No.
- CO2 is so diffusible that the partial pressures are equal.
13
Q
Alveolar Gas Equation to determine alveolar O2 level:
A
14
Q
FIO2 normal value =
A
- fractional concentration of inspired O2 .
- 0.21 when breathing normal air at any elevation.
15
Q
PH2O normal value when air is fully saturated =
A
- water vapor pressure
- 47 mmHg when air is fully saturated
16
Q
Respiratory quotient (R) normal value:
A
- the ratio of CO2 production to O2 consumption
- usually 0.8
17
Q
The alveolar level of oxygen depends on (4):
A
- fraction of oxygen in inspired air (FiO2)
- barometric pressure (Pb)
- water vapor pressure (PH2O)
- amount of CO2 in alveolous (PaCO2/R)
18
Q
Equation to determine PAO2 at sea level under normal conditions:
A
PAO2 = 0.21(760 - 47) - 1.25(PaCO2)
19
Q
Simplified equation to determine PAO2 for a person breathing at sea level:
A
PAO2 = 150 - 1.25(PaCO2)
20
Q
The alveolar-arterial (A-a) O2 gradient equation:
A
PAO2 - PaO2 (from ABG)
21
Q
In a young healthy person, the A-a O2 gradient is normally:
A
<15 mmHg
22
Q
Normal A-a O2 gradient in the elderly:
A
- increases with age to about 30 mmHg
23
Q
Calculate the A-a O2 gradient:
pH=7.40, PaCO2=40, PaO2=95
on room air at sea level
A
5 (Normal)
- PAO2 = 150 - 1.25(40)
- PAO2 = 150 - 50 = 100
- A-a O2 gradient = 100 - 95 = 5
24
Q
Calculate PIO2 at a barometric pressure of 596 (high altitude/plane):
A
- PIO2 = 0.21(Pb-47)
- PIO2 = 0.21(596-47)
- PIO2 = 115
25
Calculate the A-a O2 gradient:
## Footnote
**Pb = 596, PaCO2=40, PaO2=60 on room air**
5 (normal)
* **PAO2 = 0.21(Pb - 47) - 1.25(PaCO2)**
* **PAO2 = 0.21(596 - 47) - 1.25(40)**
* **PAO2 = 115 - 50**
* **PAO2 = 65**
* **A-a O2 gradient = 65 - 60 = 5**
26
Calculate the A-a O2 gradient:
## Footnote
**PaCO2= 68, PaO2=60**
**on room air at sea level**
5 (normal)
* **PAO2 = 150 - 1.25(68)**
* **PAO2 = 85**
* **A-a O2 gradient = 65 - 60 = 5**
27
An increase in arterial PCO2 leads to:
* alveolar hypoventilation
* Arterial CO2 diffuses into the alveolus and displaces oxygen.
28
The three causes of hypoxemia with a normal A-a O2 gradient:
1. low barometric pressure (high altitude)
2. decreased FiO2 (fire, CO toxicity)
3. increased arterial CO2 (alveolar hypoventilation)
29
Zones of the lung exist because:
* gravity dependence of pulmonary perfusion.
* gravity leads to blood flow being better in the base of the lungs than in the apex of the lungs.
30
Draw the Regional Ventilation to Perfusion Ratios in the Normal Lung graph:
31
Blood flow (perfusion) is highest in what part of the lung?
base of the lung (Zone 3).
32
Ventilation is highest in what part of the lung?
* slightly higher in the base of the lung (Zone 3) than in the other zones.
33
V/Q ratio definition and importance:
* alveolar ventilation (V) to pulmonary blood flow (Q) ratio.
* Ventilation and perfusion matching is important to achieve ideal exchange of O2 and CO2.
* Normal V/Q = 0.8.
34
Normal V/Q ratio value:
0.8
35
In what region of the lung does ventilation = perfusion?
* an area in the middle region of the lung
36
As you go toward the upper part of the lung, what occurs to V/Q (ventilation/perfusion ratio)?
* increases.
* more ventilation (V) than blood flow (Q).
37
As you go to the lower part of the lung, what occurs to V/Q (ventilation/perfusion ratio)?
* decreases
* more blood flow (Q) than ventilation (V).
38
If you have an alveolus that is not well ventilated, the defense mechanism of the body is:
* hypoxic pulmonary vasoconstriction.
* perfusion impaired to non-ventilated alveolus so that impaired ventilation is matched with impaired perfusion.
* blood diverted to well-ventilated alveoli.
39
Hypoxic pulmonary vasoconstriction in pneumonia:
* Perfusion less in consolidated part of the lung since pus/fluid blocking gas exchange.
* blood diverted to other areas of the lung that are better ventilated.
40
Overall purpose of hypoxic pulmonary vasoconstriction:
* match ventilation to perfusion
* allows for less of a decrease in systemic arterial oxygen saturation levels.
41
V/Q Mismatch in Pneumonia effect on PaO2:
* Ventilation and Perfusion are not matched.
* Regions of poor ventilation but preserved perfusion.
* PaO2 levels decrease; hypoxia.
42
Calculate A-a O2 gradient:
## Footnote
**PaCO2: 32, PaO2:60 on 21% FIO2**
**room air at sea level**
50 (elevated; abnormal)
* **PAO2 = 150 - 1.25(32)**
* **PAO2 = 150 - 40 = 110**
* **A-a O2 gradient: 110 - 60 = 50**
43
Anatomical shunt:
* Septal defects in the heart.
* Deoxygenated blood mixes with oxygenated blood.
* No matter how well you oxygenate the alveoli, oxygen levels in the blood will still remain low.
44
Physiologic shunt in the lung:
* bloodflow normal, ventilation zero.
* V/Q ratio is zero.
* No gas exchange; increased A-a gradient.
## Footnote
**AIRWAY OBSTRUCTION**
45
A physiologic shunt in the lung can be due to:
* airway obstruction
* acute respiratory distress syndrome
46
Dead space ventilation in the lung:
* ventilation normal; bloodflow zero.
* V/Q ratio is infinite.
* No gas exchange; increased A-a gradient.
**BLOODFLOW OBSTRUCTION**
**(PULMONARY EMBOLISM)**
47
The three conditions that cause hypoxemia with an increased A-a gradient:
1. V/Q mismatch
2. Shunting
3. Dead space ventilation
48
V/Q mismatch, shunting, and dead space ventilation all cause hypoxemia with an increased A-a O2 gradient. What distinguishes V/Q mismatch from shunting and dead space ventilation clinically?
* Supplemental O2 corrects the hypoxemia in V/Q mismatch but NOT in shunting/dead space ventilation.
49
Consequences of V/Q Mismatch:
* Low PaO2 (Hypoxemia)
* Increased A-a Gradient
* Hypoxemia is corrected with supplemental O2
50
Consequences of physiologic shunting (4):
1. Low PaO2 (Hypoxemia)
2. Increased A-a Gradient
3. Low PaCO2 (Hypocapnia)
4. Not corrected by oxygen therapy
51
Why do you have Low PaCO2 (Hypocapnia) in physiologic shunting?
* open capillaries around a poorly ventilated alveolus.
* CO2 will just diffuse across out of the capillary.
52
Alveolar Ventilation (VA) is the volume of air per minute that:
* enters or exits the alveoli of the lung and participates in gas exchange.
53
Dead space ventilation (VD) is the volume of air per minute that:
* enters the conducting airways and does not participate in gas exchange.
54
Total ventilation (VE)=
* VE= VA+ VD
* = alveolar ventilation + dead space ventilation.
55
Minute ventilation =
* = respiratory rate X tidal volume.
56
What two conditions are always associated with Dead Space Ventilation?
1. **Low PaO2 (Hypoxemia)**
2. **High PaCO2(Hypercapnia)**
* CO2 cannot diffuse across to the alveoli since xit never passes alveoli.
57
As alveolar ventilation decreases, what occurs to PO2 and PCO2?
1. PO2 drops (hypoxemia)
2. PCO2 increases (hypercapnia)
