Physiology-(2) Alveolar Ventilation

Front 1

Back 1

Front 2

What are the PO2 & PCO2 values for the normal airway, alveolus, pulmonary artery and pulmonary vein?

Back 2

Airway:
PO2: 149 mmHG
PCO2: 0 mmHg
Alveolus:
PO2: 100 mmHg
PCO2: 40 mmHg
Pulmonary artery:
PO2: 40 mmHg
PCO2: 45 mmHg
Pulmonary vein:
PO2: 100 mmHg
PCO2: 40 mmHg

Front 3

What is the normal pulmonary artery & vein O2 saturation, [HCO3-] & pH?

Back 3

Pulmonary artery:
O2 sat.: 75 mmHg
[HCO3-]: 22-28 mmHg
pH: 7.35-7.45

Pulmonary vein:
O2 sat.: 97 mmHg
[HCO3-]: 22-28 mmHg
pH: 7.35-7.45

Front 4

Define anatomic dead space?

Define alveolar dead space?

Define physiological dead space?

Back 4

Anatomic dead space is a volume of air that doesn't contribute to gas exchange (mouth, pharynx, larynx, trachea, bronchi, bronchioles - all conducting airways)

Alveolar dead space is the air volume within alveoli which are poorly ventilated or ventilated but w/ no or poor perfusion.

Physiological dead space is anatomic dead space + alveolar dead space.

Front 5

Define wasted ventilation?

Define minute ventilation?

Define alveolar ventilation?

Back 5

Wasted ventilation is the air volume within the physiological dead space.

Minute ventilation is the volume of air moved into the lungs per unit time...tidal volume x frequency [ V(E) = V(T) x f ]

Alveolar ventilation [V(A)] is minute ventilation [V(E)] minus ventilatory dead space [V(d)]. [ V(A) = V(E) - V(d) ]

Front 6

What are the (2) methods for measuring dead space?

Which one is more accurate?

Back 6

1) Fowler's single breath N2 washout
&
2) Bohr method

The Borh method is more accurate b/c it accounts for the total physiological dead space whereas the Fowler method only accounts for anatomical dead space and NOT alveolar dead space

Front 7

On a Fowler method graph when determining dead space, where do we estimate total dead space?

Back 7

1/2 way point of the slope

Front 8

How do you calculate dead space using the Bohr method? (equation)

How do you interpret the results?

Back 8

V(d) / V(t) = [ P(a)CO2 - P(E)CO2 ] / [ P(a)CO2 ]

V(d): physiological dead space volume
V(t): tidal volume
P(a)CO2: partial pressure of arterial CO2
P(E)CO2: partial pressure of expired CO2

The normal V(d) / V(t) ratio is ~0.3 which is about 1/3 of ventilation not-participating in gas exchange. (150 ml of 500 ml total)

This value can increase significantly w/ disease.

Front 9

What is the relationship between alveolar ventilation and alveolar partial pressures/blood partial pressure of CO2?

Back 9

↑ventilation = ↓P(A)CO2...increase ventilation rate by 2 will decrease P(A)CO2 by 1/2

Front 10

What is the alveolar gas equation used to calculate the mean partial pressure of O2 in the alveoli?

Back 10

P(A)O2 = P(I)O2 - [ P(A)CO2 / R ]

P(I): inspired partial pressure O2
R: ~0.8 in normal conditions

Front 11

A patients alveolar partial pressure of O2 is 99 mmHg & a partial pressure of CO2 at 40 mmHg. What is their Inspired partial pressure of O2? (just know how to set the equation up)

Back 11

P(A)O2 = P(I)O2 - [ P(A)CO2 / R ]

99 = P(I)O2 - [40 / 0.8 ]
P(I)O2 = 149

Front 12

Plotting alveolar partial pressures for PO2 & PCO2 on one graph will show what relationships?

Back 12

↑ventilation = ↓PCO2
↑ventilation = ↑PO2

Front 13

Define:
Hypoventilation?
Hyperventilation?
Hypercapnia?
Hypocapnia?
Eupnea?
Hypopnea?
Hyperpnea?

Back 13

Hypoventilation: ↓alveolar ventilation w/ ↑P(a)CO2
Hyperventilation: ↑alveolar ventilation w/ ↓P(a)CO2
Hypercapnia: ↑CO2 in blood
Hypocapnia: ↓CO2 in blood
Eupnea: normal breathing
Hypopnea: ↓ventilation in response to ↓metabolic CO2 production
Hyperpnea: ↑ventilation in response to ↑CO2 production