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Flashcards in measuring lung function Deck (21)
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1
Q

how is spirometry done

A

Done slowly or forced
Most often as forced expiration
Fvc or ‘tiffeneau’ manoeuvre
Deep breath in, don’t hold breath, lips round outside of tube, blow out as hard and long as possible

2
Q

how is spirometry interpreted

A

FEV1/FVC ratio
For all results compare to set of predicted values
Vary by age, height and gender
Abnormal is <80% of normal predicted value
FEV1/FVC ratio should exhale >70% of FVC in first second, less than indicates obstruction

3
Q

what is a flow volume loop

A

plot of flow x time

4
Q

what does a flow volume loop indicate

A

where obstruction is located in tracheobronchial tree

5
Q

how does early airflow obstruction present on a flow volume loop

A

Peak flow many be normal, mid-expiratory flow rates are usually more affected

6
Q

how does an extra-thoracic obstruction present on a flow volume loop

A

increase of flow rate less than expected, plateaus on expiration with slight decrease
top chopped off usual graph

7
Q

why is peak flow rate used

A

Easy to perform

Easy to maintain device

8
Q

what is peak flow rate useful for

A
Asthma diagnosis, not for COPD 
Monitoring day to day variation
Picking up exacerbations
Assessing response to treatment 
Mandatory for patients on nebulised Rx
9
Q

how is peak flow seen as abnormal

A

Peak flow shouldn’t vary over a day

Compared to predicted values

10
Q

what are causes of obstruction

A

Recall flow = pressure gradient / raw

Decrease radius of an airway – mucous, bronchoconstriction, compression (a mass)

11
Q

how can lung volume be measured

A

Cannot be obtained from spirometry

Method of measurement – helium dilution, plethysmography “body box’

12
Q

what do low lung volumes diagnose

A
restrictive lung disease 
Reduced TLC, FRC and RV
Preserved tidal volume 
Reduced IRV
Reduced vital capacity (FVC and SVC)
13
Q

what is TLC, FRC, RV, TV, IRV, FVC, SVC

A
TLC total lung capacity 
FRC functional residual capacity 
RV residual volume
TV tidal volume
IRV inspiratory reserve volume
FVC forced vital capacity
SVC slow vital capacity
14
Q

what are causes of restriction and decrease lung volumes

A
Alveolar filling process eg pneumonia 
lung disease eg fibrotic 
pleural disease eg pneumothorax, large pleural effusion, fibrosis of pleural tissue (trapped lung)
chest wall disease eg kyphoscoliosis
weakness (nerve and muscle disease)
15
Q

how does hyperinflation present

A

elevated TLC (in emphysema loss of elastic recoil – CI curve plateaus at higher volume (breathing at high volume)

16
Q

what affects gas exchange

A

In alveoli, depends on adequate ventilation of alveoli, influenced by SA and thickness of membrane

17
Q

what causes abnormal gas exchange

A
Airway disorders (asthma and COPD)
Alveolar destruction (emphysema)
Fibrotic lung disease (idiopathic lung fibrosis)
Abnormal ventilatory control 
Abnormal environment eg altitude
18
Q

how is gas transfer measured

A
CO diffuses like O2, binds to Hb 
Inhale known vol of gas with low conc of CO and helium
Hold breath for known time
Measure CO and He in expired air
He dilution gives alveolar volume
19
Q

what diseases effect gas transfer

A

Pulmonary
Emphysema, alveolar filling process, lobectomy, scarring or inflammation
Around alveolar wall
Cardiovascular/haematological disease

20
Q

what is the effect of diseases on gas transfer

A

Pulmonary hypertension
Low Cardiac Output
Pulmonary oedema
Anaemia

21
Q

what other assessments of lung function are there in clinical practice

A

Assessment of airway reversibility
Assessment of ventilation
Fitness to fly
Respiratory muscle assessment