Basic Respiratory Investigations and Lung Function Tests

Question 1

Describe an appropriate subjective inquiry with regards to a patient’s exercise tolerance

Answer 1

Ask what the patient is able to do: distance/Stairs/Shops/Daily activities and if the patient limits this activity due to the development of SOB/other problems (arthritis)

Question 2

Name two methods for objective assessment of exercise tolerance

Answer 2

1. 6 minute walk (Two cones 30 meters apart for 6 minutes - record distance)
2. CPX

Question 3

When should a haematologist be contacted in the case of polycythaemia in COPD

Answer 3

If Hb>18.5 g/dL or Hct>65% expert help should be sought from haematologists. Polycythaemia need not be of respiratory origin. Very high red cell mass makes blood much more viscous and thromboembolic risks are greatly increased.

Question 4

What adverse effects are caused by polycythaemia

Answer 4

Increased myocardial workload
Reduced perfusion
Increased risk thrombosis

DVT, IHD, CVD

Question 5

What are the ECG features of right heart strain

Answer 5

ST depression and T wave inversion in the leads corresponding to the right ventricle.

• V1 - V3
• II, III, aVF

(Compare to LV strain where ST/T wave changes occur in the LV leads: I, aVL, V5 - 6)

Question 6

What are the ECG features of RVH

Answer 6

Diagnostic criteria:
Right axis deviation of +110° or more.
Dominant R wave in V1 (> 7mm tall or R/S ratio > 1).
Dominant S wave in V5 or V6 (> 7mm deep or R/S ratio < 1).
QRS duration < 120ms (i.e. changes not due to RBBB).

Supporting criteria

• RA enlargement (p-pulmonale)
• RV strain (ST/T wave changes in II, III, aVL and V1 - V4)

Question 7

What are the ECG features of right atrial enlargement

Answer 7

Right atrial enlargement produces a peaked P wave (P pulmonale) with amplitude:

> 2.5 mm in the inferior leads (II, III and AVF)
1.5 mm in V1 and V2

Question 8

What should be done if pulmonary hypertension is suspected subsequent to review of the ECG and why

Answer 8

Established pulmonary hypertension is associated with a very high risk of perioperative heart failure and/or death, and will normally indicate cancellation of any but the most essential of surgery.

If surgery is necessary, a senior anaesthetist must be involved, ITU facilities must be available, and invasive cardiovascular monitoring should be in place.

It is also important that the higher mortality risk is included in the consent process.

Cardiac abnormalities have their own implications and are covered in other sessions.

Question 9

Interpret SaO2 of 98%

Answer 9

98% of Hb is saturated with O2 (a proportion of the available Hb)

Question 10

What is the normal O2 content of blood and what is this made up of

Answer 10

20 ml O2 per 100 mL blood

19. 7 mLO2 bound to Hb
20. 3 ml O2 dissolved in plasma

Question 11

What SaO2 will prompt further Ix (CXR/PFT)

Answer 11

SaO2 < 95%

Question 12

When are pulmonary function tests used

Answer 12

Pulmonary function tests (PFTs) can be used to define and quantify the degree of lung disease. However, they are only useful in patients with known lung disease or patients with undiagnosed respiratory compromise. These tests are generally of little use as screening tests in the general population.

Question 13

List all Lung Volumes and Capacities on PFT and state their approximate normal volume in a 70kg male

Answer 13

TLC (6000 mL)

VC (5000 mL)

IRV (3000 mL)

TV (500 mL)

ERV (1500 mL)

RV (1000 mL)

FRC (2500 mL)

Question 14

Describe the PFT findings consistent with obstructive lung disease

Answer 14

FEV1 reduced (<80% predicted normal)
FVC is usually reduced but to a lesser extent than FEV1
Measured FEV1/FVC ratio reduced (<0.7)”

Question 15

Describe the PFT findings consistent with restrictive lung disease

Answer 15

FEV1 reduced (<80% predicted normal)
FVC reduced (<80% predicted normal)
Measured FEV1/FVC ratio normal (>0.7)

Question 16

What does an FVC of < 1L mean

Answer 16

High risk patient who may well require postoperative admission to intensive care, especially following abdominal surgery. This is because there is likely to be insufficient respiratory reserve to meet postoperative oxygen requirements. In addition, coughing is likely to be ineffective and the patient will be unable to clear secretions, and they are more likely to have secretions to clear because of their chest disease.

Question 17

Define type 2 respiratory failure

Answer 17

Type 2 respiratory failure is defined as a PaO2 <8 kPa and PaCO2 >7 kPa.

Question 18

What is plethysmography

Answer 18

FRC cannot be calculated from spirometry.

Plethysmography

The patient sits in a sealed box and breathes through a mouthpiece in the centre (Fig 1). The mouthpiece is occluded, and the patient breathes against the obstruction. Compression of the lung results in reduction in the pressure in the box. Knowing the volume of the box and the pressure changes that occur allows calculation of the lung volume from the principle P1V1= P2V2.

This measures all the lung volume, and may overestimate the effective lung volume if there are cysts.

Question 19

What is Carbon Monoxide Transfer factor

Answer 19

Transfer of gases

Carbon monoxide (CO) is rapidly and totally absorbed by haemoglobin such that the limitation to uptake is due to transfer across the alveolar membrane. A small quantity of CO is added to the inhaled gas mixture and the exhaled CO levels are monitored. The inhaled/exhaled concentrations are used to derive an absorption coefficient.

In the normal lung, carbon dioxide transfer takes around 25% of the time that blood takes to transit a pulmonary capillary, but oxygen transfer can take up to 50% of the transit time. Hence reduced CO transfer means that oxygen transfer will also be reduced.

Question 20

Hw much can surgery on the thoracic cage or upper abdomen reduce lung function

Answer 20

25-30%

Question 21

How do PFT differ between asthma and COPD

Answer 21

Both have FEv1/FVC< 0.7

But FVC is usually more reduced in COPD than in Asthma

Question 22

What FEV1 and what FVC represent severe disease

Answer 22

< 50% of predicted values for both