Transcript Pulmonary Function Tests

Pulmonary Function Tests
Presenter: Dr. Sofia Patial
Moderator: Dr. Gian Chauhan
GOALS
To predict presence of pulmonary dysfunction
 To know the functional nature of disease.
 To assess the severity of disease
 To assess the progression of disease
 To assess the response to treatment
 Medicolegal- to assess lung impairment as a
result of occupational hazard.
 To identify patients at perioperative risk of
pulmonary complications

INDICATIONS OF PFT IN PAC
TISI GUIDELINES FOR
PREOPERATIVE SPIROMETRY
 Age > 70 yrs.
 Morbid obesity
 Thoracic surgery
 Upper abdominal surgery
 Smoking history and cough
 Any pulmonary disease
ACP GUIDELINES FOR
PREOPERATIVE SPIROMETRY
 Lung resection
 H/o smoking, dyspnoea
 Cardiac surgery
 Upper abdominal surgery
 Lower abdominal surgery
 Uncharacterized pulmonary disease
(defined as history of pulmonary Disease
or symptoms and no PFT in last 60 days)

Contraindications:
 Hemoptysis
of unknown origin
 Pneumothorax
 Unstable cardiovascular status, recent MI,
pulmonary embolism
 Thoracic, abdominal or cerebral aneurysms
 Recent eye surgery (cataract)
 Nausea, vomiting
 Recent surgery on thorax or abdomen
Components of PFT’s:
 Spirometry
for measuring airway
mechanics (dynamic flow rates of gases)
 Measuring lung volumes and capacities
 Measuring diffusion capacity of lung
Spirometry
PREREQUISITIES
 Prior
explanation to the patient
 Not to smoke /inhale short acting bronchodilators 4
hrs prior or oral aminophylline and long acting
bronchodilator 12hrs prior.
 Remove any tight clothings/ waist belt/ dentures
 Pt. Seated comfortably
 If obese, child < 12 yrs- standing
 Nose clip to close nostrils.
 3 acceptable tracings taken & largest value is used.
FVC
Forced vital capacity (FVC):
 Total volume of air that can be
exhaled forcefully from TLC
 Exhalation time at least 6sec for
adults & children> 10 yrs
 3 sec for children< 10 years
 Interpretation of % predicted:
◦ 80-120% Normal
◦ 70-79%
Mild reduction
◦ 50%-69% Moderate reduction
◦ <50%
Severe reduction

FEV1
Volume of air forcefully
expired in 1st second of FVC
 N- FEV1 (1 SEC)- 75-85% OF FVC

FEV2 (2 SEC)- 94% OF FVC

FEV3 (3 SEC)- 97% OF FVC
 FEV1/FVC ratio

Reduced in obstructive lung
diseases
<70%: mild obst,
<60% mod obst,
<50%: severe obst
FEF25-75
Mean forced expiratory flow in
middle half of FVC
 Reflect status of small airways
 Effort independent expiration
 N value – 4.5-5 l/sec Or 300 l/min.
 Upto 2l/sec- acceptable.
 CLINICAL SIGNIFICANCE:
SENSITIVE & 1st INDICATOR of
obstruction of small distal airways
 Interpretation of % predicted:
>79% Normal
60-79% Mild obstruction
40-59% Moderate obstruction
<40% Severe obstruction

PEFR
max. Flow rate during initial 0.1
sec of FVC .
 DETERMINED BY :
 Function of caliber of airways
 Expiratory muscle strength
 Pt’s coordination & effort
 Normal value in young adults
(<40 yrs) > 500L/min
 Clinical significance - values of
<200 L/m- impaired coughing &
hence likelihood of post-op
complication

MAXIMUM BREATHING CAPACITY:
(MBC/MVV)
 Largest volume that can be breathed per minute
by voluntary effort , as hard & as fast as possible.
 N – 150-175 l/min.
 Estimate of max. ventilation available to meet
increased physiological demand.
 Measured for 12 secs – extrapolated for 1 min.
 MVV = FEV1 X 35
 MVV altered by- airway resistance
- Elastic property
-Muscle strength
- Learning, Coordination, Motivation
RESPIRATORY MUSCLE STRENGTH
MAX STATIC INSP. PRESSURE: (PIMAX) Measured when inspiratory muscles are at their optimal
length i.e. at RV
 PI MAX = -125 CM H2O
 CLINICAL SIGNIFICANCE:
 IF PI MAX< 25 CM H2O – Inability to take deep breath.
 MAX. STATIC EXPIRATORY PRESSURE (PEMAX):
 Measured after full inspiration to TLC
 N VALUE OF PEMAX IS =200 CM H20
 PEMAX < +40 CM H20 – Impaired cough ability
 Particularly useful in pts with NM Disorders during
weaning

Flow-Volume Loop
Illustrates maximum
expiratory and
inspiratory flow-volume
curves
 Useful to help
characterize disease
states (e.g. obstructive
vs. restrictive)

Reversibility:
Indicate effective therapy
 Spirometry before & after bronchodilator
 12% or greater improvement in FEV1 and at
least 200 ml increase in FEV1 .
post FEV1-pre FEV1
 % improvement= ------------------------- x100
Pre FEV1

Bronchial Challenge:
 Detects
hyperreactive airway
 Indication- patients of seasonal or exercise
induced wheezing with normal spirometry
results
 use of agents like histamine, methacholine,
cold air, exercise etc.
 Start with NS aerosol- positive response: 10%
or more decrease in FEV1
Methacholine aerosol (0.03,0.06,16mg/ml)
Positive response- 20% or more decrease in FEV1
e.g; PD22FEV1 = 4mg/ml
NORMAL VALUES
MALES




IRV
TV
ERV
RV
TLC
FEMALES
3.3 L
0.5 L
1.0 L
1-2 L
1.9 L
0.5 L
0.7 L
1.1 L
6.0 L
4.2 L
FACTORS INFLUENCING VC
PHYSIOLOGICAL :
 physical dimensions- directly proportional to ht.
 SEX – more in males : large chest size, more muscle power,
more BSA.
 AGE – decreases with increasing age
 Strength of respiratory muscles
 POSTURE – decreases in supine position
 PREGNANCY- unchanged or increases by 10% ( increase in
AP diameter In pregnancy)
 PATHOLOGICAL:
 disease of respiratory muscles
 Abdominal condition : pain, dis. and splinting

DIFFERENT POSTURES AFFECTING VC
POSITION
 TRENDELENBERG
 LITHOTOMY
 PRONE
 RT. LATERAL
 LT. LATERAL

DECREASE IN VC
 14.5%
 18%
 10%
 12%
 10%

in post operative period if VC falls below 3
times VC– artificial respiration is needed to
maintain airway clear of secretions.
FACTORS AFFECTING FRC











FRC INCREASES WITH
Increased height
Erect position (30% more than in supine)
Decreased lung recoil (e.g. emphysema)
FRC DECREASES WITH
Obesity
Muscle paralysis (especially in supine)
Supine position
Restrictive lung disease (e.g. fibrosis, Pregnancy)
Anaesthesia
FRC does NOT change with age.
FUNCTIONS OF FRC
Oxygen store
 Buffer for maintaining a steady arterial po2
 Partial inflation helps prevent atelectasis
 Minimise the work of breathing
 Minimise pulmonary vascular resistance
 Minimised V/Q mismatch
- only if closing capacity is less than FRC
 Keep airway resistance low (but not minimal)

MEASUREMENTS OF VOLUMES
TLC, RV, FRC – MEASURED USING
 Nitrogen washout method
 Inert gas (helium) dilution method
 Total body plethysmography

1) HELIUM DILUTION METHOD:
Patient breathes in and out of a spirometer filled with 10%
helium and 90% o2, till conc. In spirometer and lung
becomes same
 As no helium is lost; (as He is insoluble in blood)

C1 X V1 = C2 ( V1 +V2)

2) TOTAL BODY PLETHYSMOGRAPHY:
Subject sits in an air tight box.
 At the end of normal exhalation – shuttle of mouthpiece
closed and pt. is asked to make resp. efforts.
 As subject inhales – expands gas volume in the lung so lung
vol. increases and box pressure rises and box vol. decreases.
BOYLE’S LAW:
PV = CONSTANT (at constant temp.)
For Box – p1v1 = p2 (v1- ∆v)
For Subject – p3 x v2 =p4 (v2 - ∆v)
P1- initial box pr. P2- final box pr.
V1- initial box vol. ∆ v- change in box vol.
P3- initial mouth pr., p4- final mouth pr.
V2- FRC

DIFFERENCE BETWEEN THE TWO METHODS:
 In healthy people there is very little difference.
 Gas dilution technique measures only communicating gas
volume.
 Thus,
 Gas trapped behind closed airways
 Gas in pneumothorax
 => are not measured by gas dilution technique, but measured by
body plethysmograph
3) N2 WASH OUT METHOD:
Following a normal expiration (FRC), Pt. inspires 100% O2 and
then expires it into spirometer ( free of N2)
 over next few minutes (usually 6-7 min.), till all the N2 is
washed out of the lungs.
 N2 conc. of spirometer is calculated followed by total vol.of
AIR exhaled.
 As air has 80% N2 →so actual FRC calculated.

PROBLEMS WITH N2 WASH OUT METHOD
Atelectasis may result from washout of
nitrogen from poorly ventilated lung zones
(obstructed areas)
 Elimination of hypoxic drive in CO2 retainers is
possible
 Underestimates FRC due to underventilation
of areas with trapped gas

TESTS FOR GAS EXCHANGE
FUNCTION
1) ALVEOLAR-ARTERIAL O2 TENSION
GRADIENT:
 Sensitive indicator of detecting regional V/Q
inequality
 N value in young adult at room air = 8 mmHg to
upto 25 mmhg in 8th decade (d/t decrease in PaO2)
 AbN high values at room air is seen in asymptomatic
smokers & chr. Bronchitis (min. symptoms)
PAO2 = PIO2 – PaCo2
R
2) DYSPNEA DIFFENRENTIATION
INDEX (DDI):
- To differentiate dyspnea due to resp/
cardiac disease
-
DDI = PEFR x PaCO2
1000
DDI- Lower in resp. pathology
 3)
DIFFUSING CAPACITY OF LUNG:
 depends upon gradient and thickness of
alveolo-capillary membrane.
 defined as the rate at which gas enters into
blood divided by its driving pressure.
 DRIVING PRESSURE: gradient b/w alveoli &
end capillary tensions.
 DL CO = Vco /(P A CO–P c CO)
SINGLE BREATH TEST USING CO
Pt inspires a dilute mixture of CO and hold the
breath for 10 secs.
 CO taken up is determined by infrared analysis
 N range 20- 30 ml/min./mmhg.
 NORMAL- 75-120% of predicted
 DL IS MEASURED BY USING CO, coz:
A) High affinity for Hb which is approx. 210 times
that of O2 , so does not rapidly build up in
plasma
B) Therefore, pulm capillary partial pressure of CO
≈0

DLCO decreases in Emphysema, lung resection, pul. Embolism,
anaemia
 Pulmonary fibrosis, sarcoidosis- increased
thickness
DLCO increases in:
(Cond. Which increase pulm. bld flow)
 Supine position
 Exercise
 Obesity
 L-R shunt
TESTS FOR CARDIOPLULMONARY
INTERACTIONS
Reflects gas exchange, ventilation, tissue O2.
 QUALITATIVE- history, exam, ABG, stair
climbing test
 QUANTITATIVE- 6 minute walk test

 1) STAIR CLIMBING TEST:
 If able to climb 3 flights of stairs without stopping/
dypnoea at his/her own pace-↓ed morbidity &
mortality
 If not able to climb 2 flights – high risk
 Quantitative assessment by measuring the max O2
uptake during exercise(VO2max).
 A 2-flight stair climb (20 steps/min) without dyspnea
is approx VO2max of 16ml/kg/min.
 VO2max≥20ml/kg/min: minimal risk
 VO2max≤15ml/kg/min: inc cardiopulmonary risk
 VO2max≤10ml/kg/min: high risk with 30% mortality
 2) 6 MINUTE WALK TEST:
 Gold standard
 C.P. reserve is measured by estimating max. O2
uptake during exercise
 Modified if pt. can’t walk – bicycle/ arm exercises
 If pt. is able to walk for >2000 feet during 6 min,
VO2 max > 15 ml/kg/min
 If 1080 feet in 6min( 180 feet in 1 min): VO2 of
12ml/kg/min
 Simultaneously oximetry is done & if Spo2 falls
>4%- high risk
BED SIDE PFT
1).Sabrasez breath holding test:
>25 sec.-normal
15-25 sec- limited CPR
<15 sec- very poor CPR (Contraindication for
elective surgery)
25- 30 SEC - 3500 ml VC
20 – 25 SEC - 3000 ml VC
15 - 20 SEC - 2500 ml VC
10 - 15 SEC - 2000 ml VC
5 - 10 SEC - 1500 ml VC
2). SINGLE BREATH COUNT:
It is a measure of the FRC.
>15 : normal
<15 : dec reserve
11-15 : mild impairment
5-10 : mod impaired
<5
: severe impairment
3). FET (WATCH AND STETHOSCOPE TEST ):
After deep breath, exhale maximally and forcefully &
keep stethoscope over trachea & listen.
N. – 3-5 SECS.
OBS.LUNG DIS. - > 6 SEC
RES. LUNG DIS.- < 3 SEC
4) SCHNEIDER’S MATCH BLOWING TEST:
Measures MBC







Ask to blow a match stick from a distance of 6” (15 cms) withMouth wide open, Chin rested, No purse lipping
No head movement, No air movement in the room
Mouth and match at the same level
Can not blow out a match
MBC < 60 L/min
FEV1 < 1.6L
Able to blow out a match
MBC > 60 L/min
FEV1 > 1.6L
MODIFIED MATCH TEST:
DISTANCE
MBC
9”
>150 L/MIN.
6”
>60 L/MIN.
3”
> 40 L/MIN.
5) GREENE & BEROWITZ COUGH TEST:
 deep breath f/by cough
 ABILITY TO COUGH
 STRENGTH
 EFFECTIVENESS
 INADEQUATE COUGH IF: FVC<20 ML/KG
FEV1 < 15 ML/KG
PEFR < 200 L/MIN.
 VC ~ 3 times TV for effective cough.
 wet productive cough / self propagated paraoxysms
of coughing – patient susceptible for pulmonary
Complication.
6) WRIGHT PEAK FLOW METER:
Measures PEFR
N – MALES- 450-700 L/MIN.
FEMALES- 350-500 L/MIN.
<200 L/min.–inadequate cough efficiency.
7) DEBONO WHISTLE BLOWING TEST:
Measures PEFR.
Patient blows down a wide bore tube at the
end of which is a whistle, on the side is a hole
with adjustable knob.
 As subject blows → whistle blows
 leak hole is gradually increased till intensity
of whistle disappears.
 At the last position at which the whistle can
be blown , the PEFR can be read off the scale.
8)Wright respirometer : measures TV, MV (15 secs times 4)
 Instrument- compact, light and portable.
 Disadvantage: It under- reads at low flow rates and over- reads
at high flow rates.
 Can be connected to endotracheal tube or face mask
 Prior explanation to patients needed.
 Ideally done in sitting position.
 MV- instrument record for 1 min. And read directly
 TV-calculated and dividing MV by counting Respiratory Rate.
 Accurate measurement in the range of 3.7-20l/min.(±10%)
 USES: 1)bed side PFT
2) ICU – weanig pts. from ventilation.
9) BED SIDE PULSE OXIMETRY
10) ABG.