Respiratory Function Tests

Question 1

What do respiratory function tests assess?

Answer 1

• The flow of air in and out of the respiratory system

- Delivery of air to the alveoli where gas exchange occurs

Question 2

What is spirometry?

Answer 2

• series of basic lung function tests
• measure expired and inspired air
• measure volume, time and flow
• it is objective, non-invasive and disease sensitive
• assess lung disease, can quantify lung impairment, monitor effects of exposures and medications

Question 3

How should a patient be positioned in spirometry?

Answer 3

• sitting upright
• feet flat on the floor with legs uncrossed and no use of abdominal muscles for leg position
• loosen any tight clothing as can give a restrictive picture on spirometry

Question 4

What is the technique for spirometry?

Answer 4

Ask subject the take a deep breath in whilst using the mouthpiece followed by a quick full inspiration. A deep breath can be taken in prior to placing the mouth tightly around the mouthpiece.
YOU CAN Ask patient to completely empty their lungs then take in a quick full quick inspiration followed by a full expiration.

Question 5

What ensures a good quality spirometry test?

Answer 5

• an explosive start
• maximal inspiration and expiration used for performance
• no glottis closure or cessation of airflow
• no coughs
• manoeuvre should meet end of test criteria (exhalation for 6s and 5ml in last 2s)

Question 6

What is tidal volume?

Answer 6

amount of air you move into and out of your lungs during rest

Question 7

What is forced vital capacity?

Answer 7

maximum volume of air into and out of lungs in a single respiratory cycle

Question 8

What is IRV?

Answer 8

volume of air you can draw into your lungs above normal inhalation

Question 9

What is expiratory reserve volume?

Answer 9

volume of air you can expel from your lungs above normal exhalation

Question 10

What is residual volume?

Answer 10

volume of air that remains in the lungs even after maximum exhalation

Question 11

On a flow loop which parts are the FVC and PEF?

Answer 11

PEF is descending expiratory slope

FVC is width of loop along x axis

Question 12

What is the significance of the percentages (25%, 50%, 75%) on the x axis on a flow volume loop?

Answer 12

Represents the volume of air you expire as a percentage of your FVC

Question 13

Which part a flow volume loop are PEF, FEF and FEV1?

Answer 13

PEF is the top of the expiratory slope
FEF is the main chunk of the expiratory slope
FEV1 is roughly 3/4 of the expiratory slope

Question 14

How do you interpret spirometry data?

Answer 14

• compare against reference/predicted values

- use subjects height, weight, age, sex, ethnic origin, smoking habits, environment

Question 15

How does bronchodilator use affect asthmatic’s flow volume loop?

Answer 15

Asthma pre bronchodilator use has a more reduced expiratory flow rate so FVC is more reduced whereas post-bronchodilator use shows improvements and increased FVC as well as a improved expiratory flow rate.

Question 16

What is the difference in flow volume loops in obstructive and restrictive diseases?

Answer 16

Obstructive - loop shifts to left, reduction in FEV1 so scooped slope
Restrictive - shift to right and narrower as FVC reduced

Question 17

There is a limitation in spirometry where ethnic group cause variation so you do not know what to define as normal for different races, how is this solved?

Answer 17

Use graphs showing age range across different ethnic groups with average/normal values for each

Question 18

What happens to carbon monoxide when it is inhaled?

Answer 18

absorbed and bound to Hb so doesn’t diffuse out

Question 19

What can a decreased TLCO indicate?

Answer 19

• decreased perfusion
  decreased ventilation
  V/Q mismatch
  anaemia

Question 20

what does an increased TLCO indicate

Answer 20

increased CO
polycythaemia
alveolar haemorrhage

Question 21

What is DLCO?

Answer 21

measures how efficient lungs are at exchanging gases and their ability to transfer gas from inhaled air to RBCs
(diffusing capacity of the lungs for CO)
- mL of CO transferred per minute for each mmHg of pressure difference across the total available functioning lung gas exchange surface

Question 22

Why is CO and helium used in spirometry?

Answer 22

CO - very small concentrations so will not lead to hypoxia, it has a greater affinity for oxygen so can measure DLCO
helium - inert gas and won’t bind to components

Question 23

How is DLCO measured?

Answer 23

• single breath hold technique
• unforced exhalation to reach residual volume -> rapid inhalation of CO/helium to reach TLC -> hold breath for 10 seconds -> unforced exhalation for less than 4 seconds and sample this exhaled breath to calculate gas populations

Question 24

What are the units of DLCO?

Answer 24

quantity of CO transferred per minute from alveolar gas to RBC (mL/min/mmHg)

Question 25

What does DLCO=

Answer 25

lung surface area available for gas exchange (Va) x rate of capillary blood CO uptake (Kco)

Question 26

What should DLCO normally be?

Answer 26

> 75% is normal up to 140%
60-74% mild decrease
40% to 59% moderate decrease
<40% severe decrease

Question 27

What can increase DLCO?

Answer 27

exercise
supine position
muller maneuver
pulmonary haemorrhage
polycythemia
left to right shunt
obesity

Question 28

What can decrease DLCO?

Answer 28

postexercise
standing
Valsalva maneuver
lung resection
pulmonary emphysema
pulmonary vascular disease
interstitial lung disease

Question 29

What are the benefits and limitations of DLCO?

Answer 29

• useful for early stage ILD detection before substantial lung reduction volume
• falsely reduced if individuals fail to inspire to TLC, can be very variable

Question 30

How is exercise testing done?

Answer 30

• 6 minute walk assess breathlessness pre and post test, PaO2 record levels
• shuttle walk, assess distance and speed without rest (like a beep test)
• cardio-pulmonary exercise, assess pre-operation fitness/SOB/exercise tolerance, increase resistance, oxygen consumption