Lung Function Tests And Oxygen In The Blood Flashcards Preview

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Flashcards in Lung Function Tests And Oxygen In The Blood Deck (40)
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1
Q

Describe how spirometry works

A

Subject breathes from a closed chamber over water
Volume changes with ventilation
Coupled apparatus with a pen draws a trace on a rotating drum

2
Q

Define inspiratory reserve volume

A

The extra volume that can be breathed in above the tidal volume

3
Q

Define expiratory reserve volume

A

The extra volume that can be breathed out after tidal volume

4
Q

What is vital capacity?

A

Maximum expiration to maximum inspiration

Approx 5L in a typical adult

5
Q

What is the functional residual capacity?

A

The volume of air left in the lungs at resting expiratory level

6
Q

What is total lung capacity?

A

Volume of air in the lungs at the end of maximal inspiration
Approx 5.8L in a normal adult

7
Q

Name some factors influencing the vital capacity

A

Compliance
Force of inspiratory muscles
Airway resistance

8
Q

Describe single breathe spirometry

A

Breathe out as fast and fully as possible
Typically do 3 tests and take an average
Requires the subject to understand the test

9
Q

What is a vitalograph trace?

A

Plotting volume expired against time

10
Q

When is flow maximal?

A

When volume in the lungs is maximal due to the pressure gradient

11
Q

What is FEV1?

A

The volume expired in the first second

Affected by how quickly air flow slows down if airways are narrowed

12
Q

What is the normal ratio for FEV1:FVC?

A

> 70%

13
Q

Describe an obstructive disease

A

Airways are narrowed
Lungs are still easy to fill but resistance increases with expiration
Air will come out more slowly
(FEV1 decreased, FVC relatively normal)

14
Q

If the narrowing of airways is reversible what does this suggest?

A

Asthma

15
Q

Describe a restrictive disease

A

Lungs are difficult to fill
Cannot achieve maximal volume of lungs (FVC lowered)
Air will come out at same rate so FEV1 normal
Ratio >70% generally

16
Q

How can we measure PEFR?

A

Peak flow metre
Cheap and easy to use
Blow into tube as hard and fast as possible
Arrow shoots up scale to an estimate PEFR

17
Q

Describe the flow volume loop of an obstructive disease

A

Reaches (almost) the PEFR

Then flow rate falls rapidly

18
Q

Describe a restrictive flow volume loop

A

Shape of flow curve generally the same as normal

Doesn’t reach as high a volume

19
Q

Describe the helium dilution test

A

Measuring residual volume
Helium isn’t metabolised therefore pt breathes a known volume of gas containing a known conc of helium
Helium conc diluted into the larger volume in the lungs
Measure the conc when we breathe out to work out what volume of air the helium expanded into

20
Q

How do we measure serial/anatomical dead space?

A

Nitrogen wash out
Subject takes one normal breath of pure oxygen
Breathes out via meter reading the percentage of nitrogen
The volume expired half way between just oxygen and normal concs of nitrogen is the volume of serial dead space

21
Q

What do we use the CO transfer factor for?

A

Measuring the diffusion capacity of the lung
Not done routinely
Patient inhales to total lung capacity - mixture containing CO
Hold breath for 10 sec
Rate of diffusion of CO estimated

22
Q

Is oxygen soluble in water?

A

Not very

23
Q

What is the equation for working out the concentration of oxygen dissolved?

A

Solubility of oxygen x pO2

24
Q

What does the dissociation curve of myoglobin look like?

A

Rectangular hyperbola.

Saturation = y, partial pressure = x

25
Q

Describe the T state of Hb

A

Low affinity for oxygen

Difficult for O2 to bind to Hb

26
Q

When the pO2 is low, Hb is in which state?

A

T state

27
Q

What does the dissociation curve of Hb look like?

A

Sigmoidal

28
Q

Above what approx kPa is Hb saturated?

A

9-10 kPa

PO2

29
Q

What is the normal Hb concentration?

A

2.2 mmol/L

30
Q

What is the normal Hb bound oxygen content?

A

8.8 mmol/L

31
Q

What can the tissue pO2 not fall below?

A

3 kPa

32
Q

Describe the Bohr shift

A

pH affects the affinity of Hb for oxygen
Decreased pH means more H+ bound to Hb
Hb moves into T state
Harder for oxygen to bind
(Decreased pH = increased oxygen dissociation)
Shifts curve to the right

33
Q

Which direction does an increased temperature shift the dissociation curve for Hb?

A

To the right

Extra oxygen dissociates at higher temperatures

34
Q

Describe a tissue that would have the maximal oxygen unloading

A

Low pO2
More acidic (lower pH)
Higher temperature

35
Q

What is the effect of 2,3-BPG?

A

Shifts curve to the right

Decreased affinity of Hb for oxygen

36
Q

When do 2,3 BPG levels increase?

A

Anaemia

High altitude

37
Q

What happens when carbon monoxide is in the blood?

A

Very high affinity for Hb
Reacts to form COHb - binds irreversibly
Increases the affinity of unaffected subunits for oxygen therefore oxygen not given up at the tissues
Fatal if HbCO >50%

38
Q

What is the difference between peripheral and central cyanosis?

A
Peripheral = poor local circulation 
Central = poorly saturated blood in systemic circulation
39
Q

Describe pulse oximetry

A

Place on end of finger
2 different wavelengths of light are emitted
Detects levels of Hb saturation
Only detects pulsatile arterial blood
(Gives us saturation but cannot tell us how much Hb is present)

40
Q

Where do we commonly take an ABG from?

A

Radial artery