Pulmonary Function Tests

Report
PULMONARY FUNCTION TESTS
Made by: Meenal Aggarwal
Moderator: Dr. Ajay Sood
Lung Volumes & Capacities
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Respiratory minute volume (at rest): 6 L/min
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Alveolar ventilation (at rest): 4.2L/min
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Maximum voluntary ventilation: 125-170 L/min
Pulmonary Function Tests : Introduction
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Aim: to identify abnormal lung function in hope of
altering patient’s outcome by reducing risk of intra/post
op ventilatory impairments
Enables us to:
◦ Assess the presence and severity of respiratory dysfunction
◦ Follow the progression of impairment
◦ Document the response to therapy

2 major groups of tests:
◦ To detect abnormalities of gas exchange
◦ To assess mechanical ventilatory functions of lungs & chest wall
Clinical Spirometry
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Inventor: John Hutchinson
Vital Capacity:
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The largest volume measured after the subject inspires
deeply and maximally to TLC and then exhales
completely to RV
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Normal values are lower in supine than in sitting
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Abnormal: when <80% seen in restrictive ds:
• Lung pathologies (pneumonia, atelectasis, pulmn fibrosis)
• Loss of lung tissue (Following surgical resection)
• Diminished effort (muscle paralysis, abdominal swelling, )
Time Expired Spirogram

After a maximal inspiratory effort subject exhales as
forcefully and rapidly as possible
Forced Vital Capacity:
Exhaled volume if recorded with respect to time
 Reflects flow resistive properties of the airways
 Practice attempts given, 3 acceptable tracings required
 Normal: Exhalation takes at least 4 sec, should not be
interrupted by coughing, glottic closure or any mechanical
obstruction
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FEV1 (Forced Expiratory volume in 1sec):
Either in Lt or FEV1/FVC percentage
 Normal: 75-80 %

Abnormal: Mild obst <70%
Moderate obst <60%
Severe obst <50%
 Restrictive diseases: dec TLC, dec FVC, so dec FEV1 but
ratio FEV1/FVC either normal or increased

Disease state
FVC (L)
FEV1 (L)
FEV
1/FVC
(%)
Airway obstruction (asthma,
chronic bronchitis)
N
Dec
Dec
Stiff lung (pneumonia, pulmonary
edema, pulmonary fibrosis)
Dec
Dec
N
Resp muscle weakness (MG,
myopathies)
Dec
Dec
N
PEFR: (Peak Expiratory Flow Rate)
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Maximum flow rate obtainable at any time during FVC
maneuver
L/sec or L/min
Usually measured as the average flow of gas expired after initial
200ml (k/a FEF 200-1200 or MEFR)
Can be measured with a handheld flow meter (serves as a bed
side test) or a pneumotachygraph
Markedly affected by obstruction of large airways
Responsive to bronchodilator therapy so used to monitor
therapeutic response in acute asthma
N value: 500Lts/min or more
If < 200Lts/min, suggests impaired cough efficiency and
likelihood of post op complications
Also affected in muscle weakness
 Variable as highly dependent on patient effort
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FEF25-75%: (a/k/a Forced Mid-Expiratory Flow)
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Middle half of FVC doesn’t require high degree of efforts
k/a Effort independent (not truly as marked reductions in
effort will reduce it)
Negative effort dependence: flow rates can actually decrease
with truly maximum efforts compared from a slightly
submaximal effort (d/t dynamic airway compression)
N value: 4.5 – 5 L/sec
Sensitive indicator of early obstruction in small distal airways
Reduced even in restrictive ds, but FEV1/FVC is Normal
Maximum Breathing Capacity:
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a/k/a MVV (Maximum Voluntary Ventilation)
Largest volume that can be breathed per minute by voluntary
effort
Instructed to breathe as hard and fast as possible for 12 sec,
and then extrapolated to 1min
Reduced in obstructive diseases
Other factors: elasticity of lungs, resp muscle strength, patient
co-operation
Correlates well with FEV1 (MVV= FEV1 X 35)
Normal: 150-175L/min
< 80% indicates gross impairment in resp function
Respiratory Muscle Strength:
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All Above parameters are affected by muscle strength
Evaluated by maximum static respiratory pressures (pressures
generated against an occluded airway during a maximal forced
inspiratory or expiratory effort)
Measured with Aneroid gauges (at FRC, to nullify effect of
elastic recoil)
PImax (near RV) : -125cm H2O
If < -25 cm H2O, severe inability to take a deep breath
PEmax (near TLC) : +200 cm H2O
If < +40 cm H2O, severely impaired coughing ability
Useful in evaluating patients with Neuromuscular disorders
Gauge
Methods for Measuring Residual Volume
•
Body plethysmography
•
Helium dilution method
Physiological Determinant of Maximum
Flow Rates
3 factors:
• Degree of effort (PEmax: at TLC, PImax: at RV)
• Elastic recoil pressure of lungs (PL):
Max at TLC: 25-30cm H2O
Min at RV: 2-3 cm H2O
Is opposed by elastic recoil of chest wall (Pcw)
Net recoil Prs: PL + Pcw (zero at FRC)
• Resistance to flow provided by airways (Raw): determined by
size of airway, so min at TLC, max at RV
Gaw (conductance, 1/ Raw, is related to lung volume linearly)
Flow – Volume Relationships:
Useful as all determinants of flow are dependant on volume
• During FVC, flow rises to a max at a volume close to TLC
• Gradually:
•
Lung volume decreases
Airways become narrower
Resistance increases
Flow rates decrease
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In Obstructive ds, flows are decreased over full range
Airway Compression & Flow Limitation:
 Value in coughing
Sites & Mechanisms of Decreased Airflow in Diseases:

D/t alterations in any 3 of the parameters (PEmax, PL,
Raw)
Disease
PEmax
Raw
PL
Neuromuscular weakness
Dec
N
N
Emphysema
N
N
Dec
Asthma, Bronchitis
N
Inc
N
Peripheral Airway Disease
N
N
N
Measurement of Airway Obstruction
Airway Resistance: (Raw)
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Technique: patient pants once or twice per second through a
mouth piece with a nose clip in place (to bypass max resistive
areas-nose, nasopharynx)
Also panting maneuver keeps larynx dilated
Subject sits in a constant volume body plethysmograph (body
box)
Lung volume & Raw can be measured using changes in the box
pressure and volume (using Boyle’s law)
Normal Raw: 2cm H2O L/sec
Head flexion causes increased Raw (measured) as it reduces
the caliber of hypopharynx, so be as errect as possible during
maneuver
Forced Expiratory Maneuvers (FVC, FEV1, PEFR):
•
Tells whether obstruction is present
Flow-Volume loops:
Allows to discriminate b/w upper airway obstructive lesions
• Subject inhales fully to TLC and then performs FVC maneuver,
followed immediately by a max inspiration as quickly as
possible to TLC
• Whole inspiration and expiration near TLC are effort
dependent (Normal = 1.0)
• Mid VC ratio: ratio of expiratory flow to inspiratory flow at
50% VC
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Help to localize site & nature of obstruction
Upper airway obstruction: inspiratory flow reduced more than
expiratory, so mid VC ratio >1
Fixed airway obst : both inspiration and expiration reduced to
same extent so plateaus of constant flow, so ratio = 1
Variable obstruction: Lesion whose influence varies with the
phase of respiration
Extrathoracic: l/t increased obst during forced inspiration, mid
VC ratio >2
Intrathoracic: Increased obstruction during forced inspiration,
mid VC ratio is low
Tests of Early Lung Dysfunction
Small airway disease, minimal airway dysfunction, early
obstructive lung disease
 It is a fore runner of chronic bronchitis & emphysema
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Alveolar –Arterial Oxygen Tension Difference:
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Detects regional V/Q mismatch
PaO2 =measured easily
PAO2 = PiO2 – PaCO2 / R
Difference : PAO2- PaO2
Normal value at room air: 8 mm Hg
Increases with age (occurs d/t dec PaO2)
Frequency Dependence of Compliance:
In normal lung: compliance not dependent on respiratory
frequency
 In small airway obstruction, d/t asynchronous behaviour of
lung units where some areas of lung are moving out of phase
with others, the compliance decreases with a high respiratory
rate
 If it falls to <80% : k/a compliance to be frequency dependent
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Multiple- Breath Nitrogen Washout:
Mild obstructive airway disease leads to uneven distribution of
ventilation, measured by SBNW
 Normal : lung behaves as a single compartment and produces
a fast single exponential curve for N2 wash out
 Abnormal : Lung appears to have more than one ventilatory
compartment (d/t uneven dist of ventilation)
So different units have their N2 diluted at different rates, and
so producing a tail on the washout curve
 Very sensitive test, but requires computerization for analysis
of curve
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Single Breath N2 Washout:
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Described by Fowler in 1949
Expired N2 conc was measured after inspiration of 1 L of O2
from FRC
The change in N2 concentration b/w 750-1250 ml of expired
volume in seen
Modified method: Instead of just 1 L, patient makes a full
inspiratory effort in 100% O2. the alveolar nitrogen slope with
this method is less steep (as now whole lung is filled with O2,
c/f 1L in which only lung bases are filled leading to an inc Apex
base difference, so steeper slope)
The slope of alveolar nitrogen plateau is larger in old subjects
(reflecting uneven evntilation)
<2% normal, Even Upto 10% in smokers
Closing Volume:
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Lung volume at which the airways in the dependent areas in the
lungs begin to close
Occurs because lower portions of lungs are subject to Ppl
pressure in excess of airway pressure, l/t closure of airways
Technique: tagging of these lung areas by giving them a different
concentration of a tracer gas c.f. apex.
2 methods: Bolus gas (uses He)
Resident gas (uses N2)
First a gradient is created, and then expiratory levels of gas are
plotted. The volume at which phase 3 begins is known as closing
volume
Closing capacity = closing volume + RV
Increases with age, in smokers
Bed-Side PFT’s
1. Snider’s Match Blowing Test:
Mouth wide open
 Match held at 15 cm distance
 Chin supported
 No head tilting
 Match stick & mouth at same level
Cannot blow out a match:
 MBC < 60 L/min
 FEV1 <1.6 L
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* Modified Snider’s test:
3 inches: MBC >40 L/min
 6 inches: MBC >60L/min
 9 inches: MBC >150 L/min
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2. Forced Expiratory Time:
FET < 3 sec (restrictive disease)
 FET > 6 sec (obstructive disease)
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3. Seberese’s Single Breath Count:
Patient is asked to take a deep breath followed by counting, till
the time he cannot hold breath
 Shows trends of deteriorating/ improving lung functions
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4. Seberese’s Breath Holding Time:
Subject is asked to N tidal inspiration & hold breath
• Normal >= 40 sec
• < 15 sec C/I for surgery
•
5. Cough test:
Observe for ability to cough (strength & effectiveness)
 Wet productive cough = prone for pulm complications
 Inadequate cough= FVC < 20 ml/kg, FEV1 < 15ml/kg
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6. De Bono’s Whistle Test:
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Wide bore tube with a whistle at end and an adjustable leak
hole at the side, whistle blows only when air flow exceeds a
certain value
7. Wright’s Peak Flow Meter:
Normal males: 450- 700 l/min
 Females: 300-500 l/min
 Values< 200 l/min suggests impaired cough efficiency
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Peak flow meter
Indications for PFT in Surgical Patients:
Patient factors:
• Known Chronic pulmonary disease
• Heavy smoker (>1 pack/day)
• Chronic productive cough
• Recent respiratory infections
• Advanced age (>70 yrs)
• Obesity (>30% over ideal wt)
• Thoracic cage deformity (kyphoscoliosis)
• Neuromuscular disease (MG)
Procedure:
• Thoracic or upper abdominal surgery
• Pulmonary resection
• Prolonged anesthesia
Pre-op Measures to Improve Lung Function:
Goal: to reduce intra/post op pulmonary complications
4 basic modalities:
• Smoking cessation: after 2-4 wk (reduced secretions, airway
reactivity & improved mucociliary clearance)
• Treatment of bronchospasm (Beta 2 agonists, antichol,
theophylline)
• Removal of secretions (AB therapy, adequate hydration,
mucolytics, postural drainage, chest percussions)
• Motivation & Stamina (incentive spirometry)
Thank You

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