Week 3 - Lung function tests Flashcards Preview

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Flashcards in Week 3 - Lung function tests Deck (30)
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1
Q

Explain simple spirometry

A
  • Pt takes larges forces inspiration and blows as hard as they can for as long as they can
  • The results are plotted on a volume vs time on a vitalograph
  • Measurements are compared to standards accounting for age, sex and height (normogram)
  • Gives you many different readings such as TLC, FEV1/FVC etc
2
Q

What is the normal picture of a vitalograph? What does it show?

A
  • Initial rapid rise with plateau
  • Shows forced vital capacity and forced expiratory volume in 1 second
  • FEV1:FVC = 70%
3
Q

What is FVC?

A
  • Forced vital capacity

- Maximum volume which can be expired from full lungs

4
Q

What is FEV1?

A

-Forced expiratory volume in 1 second

5
Q

Describe an obstructive pattern on a vitalograph

A

-Same FVC but with decreased slope so FEV1:FVC

6
Q

Give 3 diseases which produce obstructive vitalographs

A
  • COPD
  • Asthma
  • Emyphysema
7
Q

Describe a restrictive pattern on a vitalograph

A

-Decreased FVC with not effected FEV1 producing a normal or high ratio
(lungs cannot fill)

8
Q

Give 3 causes of restrictive lung diseases

A
  • Fibrosis
  • Interstitial lung disease
  • Pneumothorax
9
Q

Define tidal volume

A

-Volume of air in and out with each breath (typically 0.5L)

10
Q

Define Inspiratory reserve volume

A

-Extra vol which can be breathed in over that at rest

11
Q

Define expiratory reserve volume

A

-Extra vol which can be breathed out over rest

12
Q

Define residual volume

A

-vol remaining in lungs after maximum expiration

13
Q

What is a capacity?

A

-two or more volumes added together

14
Q

define vital capacity

A

-max inspiration to max expiration (TV+IRV+ERV)

15
Q

Define inspiratory capacity

A

-maximum inspiration from resting expiration (TV+IRV)

16
Q

Define functional residual capacity

A

-vol air in lungs at resting expiratory level (ERV+RV)

17
Q

Define total lung capacity

A

-Vol of air after maximal inhalation (VC+RV)

18
Q

What factors influence vital capacity?

A
Inhalation factors
-Lung compliance 
-Force of inspiratory muscles
Exhalation factors
-airway resistance
19
Q

What is a disadvantage of single breath spirometry?

A

-technique greatly effects result ie very user dependant

20
Q

What are the advantages of lung-function tests?

A
  • Non-invasive
  • Cheap
  • Technically simple
  • Measures volume and flow
21
Q

If the obstructive pattern on a vitalograph is reversible what does it indicate?

A

-Asthma

22
Q

What is Peak expiratory flow rate?

A

-Simple cheap measurement screening for airway narrowing by measuring the peak flow rate when the lungs are full so there is minimal resistance

23
Q

What is a flow volume curve?

A

-A graph which plots volume vs flow using the measurements from a vitalograph

24
Q

Why when the lungs are full is flow the fastest?

A

-Airways stretched meaning minimal resistance with maximum recoil -> fastest flow

25
Q

What are the advantages of volume flow curves?

A
  • Sensitive
  • Can detect problems early in disease
  • Can discriminate where in the tract the problem lies
26
Q

Describe and explain an obstructive pattern of disease on a volume flow curve

A
  • Normal upwards slope with an indented downwards slope
  • As exhalation occurs and the airways begin to narrow, the obstruction greatly increases resistance more than usual and the flow declines
  • the narrower the airways to start the more rapidly it falls
27
Q

Describe a restrictive pattern of disease on a volume flow curve

A

-Narrowed flow volume curve as there is no problem with flow but an overall decrease in volume

28
Q

How do you measure residual volume? Describe this test

A
  • Helium dilution
  • helium is a non-toxic inert gas which cannot cross capillary membrane
  • Pt. breaths in helium from container with known He conc until equilibrium is reached
  • The new conc of He in the chamber is used to calculate FRC from which you can calcuate RV
29
Q

Describe Nitrogen washout

A
  • Measures anatomical deadspace
  • Patient takes max inspiration of 100% O2
  • O2 reaching alveoli mixes with residual volume where as air in conducting portion will be 100% O2
  • Pt exhales through one way valve and %N2 in inhaled air and volume of air calculated
  • A graph of n2 vs exhaled vol is plotted
  • initially n=0% but as alveolar air exhaled and mixes with deadspace air a plateau is reached after which only alveolar air exhaled
  • Deadspace determines from graph where area A = Area B
30
Q

Describe a test used to measure diffusing capacity of the lung

A
  • CO transfer factor
  • Measures rate of transfer of CO from alveoli to blood in ml/min/kPa
  • CO has increased affinity for Hb so only limiting factor is diffusion capcity
  • Pt. takes rapid and full inspiratory vital capacity of air containing low CO conc.
  • Breath held for 10 seconds
  • Alveolar sample collected mid expiration (discard dead space)
  • remaining conc of CO in sample measured