Resp - Cj - Alveolar Ventilation & Diffusion

Front 1

What is the primary reason for ventilation?

Back 1

Maintain O2 Partial Pressure Gradient in the Lung

Front 2

Define Total Ventilation

What is it AKA?

Back 2

The total amount of air entering/leaving the lungs per minute.

AKA - Minute Ventilation

Front 3

What two factors contribute to Total (Minute) Ventilation?

Back 3

Tidal Volume and Respiratory Frequency

Front 4

How does the body control it's own Total Ventilation?

Back 4

By "selecting" an appropriate tidal volume and respiratory frequency to minimize work.

Front 5

What is equal between "Dead Space Air" and Inspired Air?

Back 5

Equal Gas Composition

Front 6

Does Dead Space Air participate in gas exchange?

Back 6

No.

Front 7

In a disease state, what change is likely to be seen in the relationship between anatomical dead space and physiologic dead space?

Back 7

In disease, physiologic dead space may be greater than anatomical dead space.

Front 8

Define alveolar ventilation rate:

Back 8

the volume of air reaching the alveoli per minute.

Front 9

What three variables must be know in order to calculate Alveolar retention rate?

Back 9

It can be calculated if the tidal volume, dead space volume and respiratory frequency are known.

Front 10

How can you calculate the dead space volume?

Back 10

By calculating the dilution of the product of the alveoli
(P of CO2) by the dead space gas during expiration of mixed gas.

*Confusing concept for me*

Front 11

What value is inversely proportional to the alveolar ventilation rate?

Back 11

The Arterial P of CO2

Front 12

How can we determine the existence of hyper/hypo ventilation?

Back 12

Measure the arterial P of CO2

Front 13

what can be caused by hypoventilation?

Back 13

Arterial Hypoxemia

Front 14

Why is the ventilation of a lung greater at it's base, compared to it's apex?

Back 14

The base of the lung is more compliant

Front 15

What are the factors that most directly effect rate of diffusion across a membrane (blood-gas barrier)?

Back 15

Surface area of membrane
Thickness of membrane
Difference in Partial pressures
Solubility of the gas
Molecular weight of the gas

Front 16

Equilibration of capillary PO2 with alveolar PO2 due to diffusion is so fast that the lung has what?

Back 16

a large diffusion reserve (spare capacity for diffusion)

Front 17

Diffusion is challenged by what?

Back 17

thickening of the blood-gas barrier
exercise
alveolar hypoxia (dropping PP02 in the alveoli)

Front 18

What is utilized when diffusion across the blood-gas barrier is challenged?

Back 18

Diffusion Reserve

Front 19

When can:
-Thickening of the blood gas barrier
-Alveolar Hypoxia
-Exercise
Cause hypoxemia?

Back 19

When they occur in combination
(They will usually not cause hypoxemia alone)

Front 20

What is hypoxemia?

Back 20

An abnormally low concentration of O2 in the blood

Front 21

How can you measure diffusion capacity?
Why?

Back 21

Using carbon monoxide
Because carbon monoxide is "diffusion limited" and measures on the properties of the blood-gas barrier.

Front 22

Describe the purpose of ventilation

Back 22

To maintain the partial pressure gradient of O2/CO2
ventilation also helps with controlling the pH of the blood

Front 23

Describe the relationship between total ventilation, tidal volume and respiratory frequency.

Back 23

Total Ventilation = Tidal Volume x Respiratory Frequency

7500ml/min = 500ml x 15/min

Front 24

Explain what is meant by the terms ‘dead space’

Back 24

Dead space represents the area of the conducting zone. Some air will remain here, and not take part in blood-gas exchange.

Front 25

Describe the two mechanisms by which alveolar ventilation can be varied. Explain which mechanism is more likely to be effective.

Back 25

We can increase Tidal Volume
We can increase Respiratory Rate

Increasing Tidal Volume is more effective, because it has no positive effect on Vd. Increasing Respiratory rate would continually multiply by Vd; causing significant waste.

Front 26

Describe the relationship between the arterial PCO2 and the alveolar ventilation rate. Predict the change in arterial PCO2 for a given change in alveolar ventilation rate.

Back 26

Air has 0% CO2 (effectively)
If you have a high alveolar ventilation rate, then the CO2 in the arteries has a place to diffuse.
Alveolar Vent. Rate and Arterial PCO2 are INVERSELY PROPORTIONAL.

Front 27

Describe how the arterial PCO2 can be used as an indicator of hypoxemia due to hypoventilation.

Back 27

If you have HYPOVENTILATION, then the Arterial PCO2 will rise.

If Arterial PCO2 is high, then PO2 must be low = Hypoxemia

Front 28

Explain the relationship in health and disease between anatomic dead space, alveolar dead space and physiologic dead space.

Back 28

Anatomic Dead Space + Alveolar Dead Space (Disease) = Physiologic Dead Space.

Alveolar Dead Space is not normal, and it's presence suggest pathology.

Front 29

Explain why the difference between alveolar and end-tidal PCO2 can be used to predict the volume of physiologic dead space

Back 29

*CONFUSING TO ME*
Air sitting in the dead space does not participate in gas exchange, and thereby does not accumulate CO2.

Air in the blood-gas exchange area DOES accumulate CO2.

By measuring the dilution (mixture) of C02 between these two types of air will give information on how much dead space their is.

Front 30

Describe and explain the variation in ventilation from lung apex to lung base.

Given a change in intrapleural pressure which will expand more, apex or base?

Back 30

The apex of the lung is well expanded (due to gravity) whereas the base of the lung is not well expanded (due to being supported by the diaphragm). The apex and base of the lung are at different points on the compliance curve. Given a change in intrapleural pressure, the base will expand MORE than the apex.

Front 31

Describe Fick’s Law of diffusion. Predict how changes in surface area, barrier thickness or partial pressure difference would affect the rate of diffusion of gas across the blood-gas barrier.

Back 31

Diffusion is favored when:
There is a significant difference in partial pressures
There is a great deal of surface area
There is a thin barrier

Front 32

Explain why slowed diffusion across the blood-gas barrier does not by itself typically cause hypoxemia.

Back 32

Because the blood spends .75 seconds in the aveolar capillary, and is usually loaded in about 1/2 that time. SLOWED diffusion will not cause hypoxemia, it still reaches the point of saturation.

Front 33

Describe what is meant by a gas being ‘diffusion-limited’ or ‘perfusion-limited’.

Back 33

CO = diffusion limited
NO2 = perfusion limited

A gas that is perfusion limited can easily cross the blood-gas barrier, but is not quickly bound by blood.

A gas that is diffusion limited is one that blood will readily take up, but cannot cross the blood-gas barrier quickly enough to saturate.

Front 34

Explain why carbon monoxide can be used to measure diffusion capacity.

Back 34

Because blood will ALWAYS take up CO, understanding it's Arterial PP gives a measure of how well the diffusion aspect is working. If Arterial PP of CO is low...it mean's something is wrong with diffusion.

Front 35

Describe factors not related to the blood-gas barrier that affect the rate of diffusion of carbon monoxide/oxygen into the capillary blood.
(2)

Back 35

The distance the gas must travel to reach the interior of the RBC

The Rate of Reaction of the gas with the hemoglobin to form a compound

Front 36

List typical values of tidal volume and respiratory frequency.

Why are these values selected?

Back 36

Tidal Volume Typically = 500ml
Respiratory Frequency Typically = 15/min

These values represent minimal work required of the body to ventilate.

Front 37

What is represented by Tidal Volume? What is it's mathematical abbreviation?

Back 37

The amount of air brought in with one breath
Vt

Front 38

What is "Elastic" work?
What is "Frictional" work?

Back 38

Elastic work is the work required to expand the lungs
Frictional work is the work required to overcome airway resistance

Front 39

Define ‘alveolar ventilation’.

Back 39

‘alveolar ventilation’ represents the amount of air that reaches the gas exchange area of the respiratory tract.

Front 40

Be able to calculate the alveolar ventilation rate given values of tidal volume, dead space volume and respiratory frequency.

Back 40

Alveolar ventilation = (Tidal Volume - Dead Space Volume)
multiplied by respiratory frequency

Va = (Vt - Vd) x n
5250 ml/min = (500ml - 150ml) x 15

Front 41

What are the typical values for tidal volume and dead space?

Back 41

Vt = 500 ml (Tidal Volume)
Vd = 150 ml (Dead Space)

Front 42

Be able to calculate the physiologic dead space volume using the Bohr equation.

Back 42

(Cannot type-set the equation in this format)
Sorry...if you are me...look at your equation sheet...if you aren't me. I think you are pretty, what are you wearing?

Front 43

Which gas diffuses better? O2 or CO2?
(In blood)

Back 43

CO2

Front 44

Describe the circumstances in which a slowed rate of diffusion across the blood-gas barrier can cause hypoxemia.

This is example of what, perfusion or diffusion limitation?

Back 44

In cases where the challenge to diffusion is so server, that the blood never reaches saturation. (i.e. never gets to 100 mmHg PPO2)
-diffusion limitation

Front 45

Effect of pulmonary fibrosis on diffusion capacity.
What test might you use to aid in diagnosis of this disease?

Back 45

Alveolar walls thicken, and diffusion is inhibited

The single breath CO diffusion capacity test.