Lecture 2 - Respiratory tests

Question 1

What is low PaO2 called, and what is high PaCO2?

Answer 1

Hypoxia and hypercapnia, respectively

Question 2

What are the ways we can assess ventilation?

Answer 2

• Blood gases
  
  • PaO2
  • PaCO2
• Lung volumes/flows
  
  • Spirometry
  • PEFR
• Exhaled Nitric Oxide (eNO)

Question 3

What does spirometry measure?

Answer 3

How much and how fast

Question 4

In spirometry, how is the air in the lungs divided into volumes?

Answer 4

• Tidal volume (~500ml) (V_T) - Volume of air that moves in and out during normal quiet ventilation.
• Inspiratory reserve volume ~3L. An extra 3L can be inspired if the external intercostal muscles are contracted too.
• Expiratory reserve volume ~1.5L. An extra 1.5L can be expelled if internal intercostal muscles and abdominal muscles are contracted for maximal active expiration.
• Residual volume ~1L. Even after maximal expiration, our lungs are still partially inflated.

Question 5

The volumes of the air in the lungs can be grouped in capacities.

List them.

Answer 5

• Vital capacity ~5L - Maximal breath in to maximal breath out (ERV + VT + IRV)
• Total lung capacity ~6L. If you breath all the way in, you hold about 6L in your lungs (VC + RV).
• Inspiratory capacity - Tidal volume + IRV
• Functonal residual capacity ~2.5L. Volume in lungs at end of tidal expiration (RV + ERV)
  
  • Represents “equillibrium point” for respiratory to change volume from FRC need to do work

Question 6

Label

Answer 6

Question 7

How is residual volume measured?

Answer 7

Can’t be measured directly by spirometry, need to use helium dilution

Process: Breathe on spirometer, then add known amount of He.

Measure conc. at TLC (=VC + RV)

• Calculate volume He has distributed into = spirometer + VC + RV
• Measure spirometer & VC, RV = difference
• RV can also be measured by body plethysmography

Question 8

In spirometry, how do we measure “how fast”?

Answer 8

• Forced measurements give us information about flow
• We use a forced vital capacity (FVC)
• Or a forced expiratory volume in one second (FEV1)​

Question 9

When does the FEV1 become affected?

Answer 9

It gets reduced in diseases which cause resistance to airflow (airways obstruction) OR Small lungs (scarred or fibrotic lungs)

Question 10

What FEV1/FVC ration defines obstruction?

Answer 10

Value <0.70 defines obstruction

Question 11

What are the three variables affected the “Normal”/Predicted values

Answer 11

• Height
• Age
• Gender

NOT WEIGHT - however will be effected if morbidly obese

The FVC, FEV1 will be ≥80% predicted

Question 12

What determines the quality of a spirometry measurement

Answer 12

• Technician dependant/Subject dependent
• Need an acceptabe effort
  
  • Sharp peak
  • Gradual return to 0 flow
  • At least 4 seconds
• 3 acceptable attempts within 5% of each other
• Often more easily seen on Flow-volume tracings

Question 13

What value to volume loops have?

Answer 13

May show the presence of specific patterns of upper airway obstruction. Specific patterns in other disease processes confirm but add little to spirometry numbers.

Question 14

What is the units for PEFR

Answer 14

L/min (NOT VOLUME) it’s a rate

It gives the peak flow rate for expiration

Question 15

Is an individual absolute value for someones PEFR useful?

Answer 15

Not really useful if its just one value, since there’s a wide range of normal. But it’s the changes in PEFT from a persons normal value which are useful for assessing disease progresson. e.g. worsening asthma, there’s a decrease in PEFR.

Can use changing PEFR to change/assess therapy.

Question 16

What are the indications for pulmonary function tesing

Answer 16

1. Objective assessment of pulmonary symptoms
2. Categorization of the type and severity of physiologic abnormalities
3. Documentation of progression of disease
4. Documentation of the patient’s response to therapy.
5. Preoperative assessment
6. Screening for sub clinical disease

Question 17

How are lung conditions categorised

Answer 17

As either obstructve or restrictive

• In restrictive conditions their is an inability to stRetch the lungs due to increased lung stiffness, this decreases lung volume
  
  • e.g. Lung compliance-related disease (pulmonary fibrosis/edema; chest wall compliace (kyphoscoliosis); pleural and respiratory muscle disease.
• In obstructive conditions there is a resistance to airflOw
  
  • e.g. Chronic obstructive lung disease (chronic broncitis and emphysema), asthma

Question 18

What happens to FVC, and FEV1, and the FEV1/FVC in restrictive lung disease?

Answer 18

• FVC Decreased
• FEV1 often decreased proportionate to FVC
• FEV1/FVC Normal or Increased
• May need lung volume measurements (RV, FRC, TLC) to confirm.

Question 19

Describe the changes seen in FEV1/FVC, FEV1 and FVC in obstructive lung disease

Answer 19

• FEV1/FVC <0.7 defines obstructive disease
• FEV1 usually decreased
• FVC may be decreased
  
  • e.g. if expiration incomplete due to air trapping
• Can have simulataneous obstruction and restriction

Question 20

Pic of common patterns