12 APAPARI 2017 lung function testing en

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 29th April 2017


Overview
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Spirometry
Body plethysmography
Helium dilution
Carbon monoxide
transfer


Introduction
• 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


Indications
• Diagnosis

– Characterise impairment in physiological function
– Quantification of impairment in physiological function

• Monitoring of chronic disease
– Asthma
– Neuromuscular disease

• Establishing the effectiveness of therapeutic
intervention
– Asthma
– Bronchiectasis

• Assessing risk of an intervention
– Chemotherapy
– Anaesthetic

Spirometry
• 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:
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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


spirxpert

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


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 crosssectional area decreases,
peripheral airway resistance
increases, EPP moves
towards alveoli
• Proportion of airways
dynamically compressed
increases
• Reduction in surface area
increases number of airways
that are choked or flow
limited exponentially
• Gives rise to expiratory flowvolume 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
graphical display)
• Highly reproducible when airway function
is
stable
• Wide range of predicted values


•

What can we learn from forced
flow- volume measurements?
(1) blow out? –
How much air can the subject

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



͚͚Spiroŵetry is aŶ effort-dependent
manoeuvre that requires
understanding, co-ordination, and
co-operation by the
subject/patient, ǁho ŵust ďe
The person
making
the recordings is
Đarefully
iŶstruĐtedd
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



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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 flowvolume
• 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