12 APAPARI 2017 lung function testing en

• Spirometry – Measure dynamic lung volumes and flow rates during forced ventilatory manoeuvres • Plethysmography – Measure static lung volumes TLC, RV.. Effort independent measures of

APAPARI Workshop Hanoi 2017

Lung function

tests

Dr Michael Lim

Division of Paediatric Pulmonary and Sleep

Khoo Teck Puat - National University Childrens Medical

Institute (KTP-NUCMI) National University Hospital Singapore 29 th April 2017

• Spirometry

– Measure dynamic lung volumes and flow rates during

forced ventilatory manoeuvres

• Plethysmography

– Measure static lung volumes (TLC, RV) Effort

independent measures of airway obstruction may also be generated

• Gas diffusion techniques

– To measure static lung volumes, and to determine the efficiency of gas exchange

• Diagnosis

– Characterise impairment in physiological function

– Quantification of impairment in physiological function

• Monitoring of chronic disease

• Uses forced ventilatory manoeuvres to assess maximal flow rates and dynamic lung

volumes

• Flow and time measured

• Volumes derived from these

• Flow measured using pneumotachometer (measures pressure change across a fixed resistance) or speed of rotating fan

• Two curves:

– Flow volume curve

– Volume time curve

Flow depends on:

• Elastic recoil of the lung

• Dimensions of the airway

• Stiffness of the airway

• Lung volume (airway supported open in inflated lungs, but narrows down as the lung empties)

• (Density and viscosity of the gas)

Physiology behind forced expiratory

manoeuvres

• Flow limitation theory

– Dynamic compression of the

airways

– Wave speed theory

P mo=pressure at mouth

P br=pressure inside the

airway P pl=intrapleural

pressure

P alv=intra alveolar pressure P

L.el=elastic recoil pressure of

the lung

spirxpert

Wave speed theory

• Flow in elastic tubes limited by the ability of elastic tubes to propagate pressure waves

• Bulk flow cannot occur at speeds above which

pressures driving the flow can be propagated along the tube (tube wave speed)

• At tube wave speed – choke point

• Increasing driving pressure above choke point does not lead to increased flow

• Max flows proportional to density of gas, airway wall

compliance, and surface area of lumen

Wave speed theory (2)

• As lung volume diminishes,

total small airways cross-

sectional area decreases,

peripheral airway resistance

increases, EPP moves

airways that are choked or

flow limited exponentially

• Gives rise to expiratory

flow-volume loop

After medication, without predicted value

Flow [l/s]

Vol [l]

Spirometry – measures changes in

flow and volume

• Non-invasive

• Cheap, easy, quick to do

• Widely available (but not always with

What can we learn from forced

flow- volume measurements?

(1)

• How much air can the subject blow out? – can be reduced in restrictive disorders, or if there is airway narrowing precipitating early airway closure (e.g asthma or CF)

• How fast is the air expelled? – can be

reduced

with airway narrowing

• Pattern of change in flow-volume curve (insp

& exp) can indicate site of obstruction

What can we learn from forced

flow- volume measurements?

(2)

• RespoŶse to treatŵeŶt ;e.g β2agonist)

• Change with age or growth

• Progression of disease

͚KSpiroŵetry is aŶ effort-dependent

manoeuvre that requires understanding, co-ordination, and

co-operation by the subject/patient, ǁho ŵust ďe

Đarefully iŶstruĐted͛

The person making the recordings is

every bit as important as the

spirometer!

How do we get from a spirogram (volume-time graph) to a flow-volume curve?

Static lung volumes and capacities

based on a volume–time spirogram

IVC: inspiratory vital capacity

IRV: inspiratory reserve volume VT: tidal volume (TV)

ERV: expiratory reserve volume RV:

residual volume

IC: inspiratory capacity

FRC: functional residual capacity TLC: total lung capacity

• Forced Vital Capacity (FVC)

• Forced Expired Volume in 1 second (FEV1) (can do FEV0.5 or FEV0.75 in small children)

• FEV1/FVC

• (Inspiratory flows/volumes)

• Maximum expiratory flow when x% of the FVC has been exhaled (FEFx%) or x% of the FVC

remain to be exhaled ( MEFx% , now deprecated) – 25% 50% 75%

• Flows at 25% of FVC exhaled = FEF25 or MEF75

• Maximal mid-expiratory flow (MMEF) - average expiratory flow over the middle half of the FVC – may be more sensitive index of obstructive small airways disease as it reflects flow rates once the dynamic compression-wave has reached the small diseased airways

Quality control and practical

aspects (1)

• Demonstration and careful instruction

• Observe the subject

• Inspect raw data – timebase and

flow-volume

• Minimum 3 attempts, maximum of 8 – but may need more, especially in preschool

children

Quality control and practical

aspects (2)

• Noseclips, Yes or No?

• Filters may be used

• Posture, seated or

standing?

• Use of incentive spirometry

• FEV1 and FVC - the two largest should be within 0.2 L of each other

Common problems

• Leak between lips and mouthpiece

• Occlusion of the mouthpiece by the tongue

• Obstruction of the mouthpiece by pursing the lips or closing the teeth

• Incomplete inspiration

• No pause at or near TLC

• Hesitant start of the forced expiratory manoeuvre

• Expiration not maximally forced / with variable

effort

• Incomplete expiration

• Cough during the forced expiratory manoeuvre

Young Children

• Cannot inspire to TLC

• Cannot sustain expiration to RV

• Show inconsistency of effort, unrelated to

willingness to co-operate

Spirometry in young children

Spirometry in young children

• FEV1 occurs at different points in the VC in

children of different heights

• The same is true of FEV0.5 etc

• ͚KNorŵal͛ ǀalues of FEV1 /FVC are not constant through childhood

Pattern recognition in flow-volume

Case 1

• 7 year-old boy presents with history of recurrent pneumonia, never needing hospital admission

• Presents with a blue spell

Fixed upper airway obstruction

tracheal stenosis

Subglottic stenosis - before and after treatment

Variable upper airway obstruction

laryngeal polyp

Vocal cord dysfunction

Bronchomalacia

Baseline and After with Predicted Value

Less than 80%

What is the FVC?

Normal Restrictive Pattern Obstructive Pattern Mixed Pattern