Pulmonary function tests: A brief Insight- By RxVichuZ! :)

PRESENTED BY:
VISHNU.R.NAIR,
5TH YEAR PHARM.D,
NATIONAL COLLEGE OF PHARMACY(NCP).

Refer to tests, that provide OBJECTIVE & QUANTIFIABLE
measures of LUNG FUNCTION
Useful in the DIAGNOSIS, EVALUATION & MONITORING
of respiratory disease/s
Also help to evaluate :
a. Response/ efficacy of ongoing therapy
b. Side-effects of medications, that lead to pulmonary disease.

 Include:
A. DIAGNOSIS:
- Clinical manifestations of respiratory disease
- Follow-up of historical/lab findings
- Disease effects on pulmonary function
- Drug-induced pulmonary disorders.
B. EVALUATION:
- Medico-legal issues
- Rehabilitation

C. MONITORING:
- Respiratory disease progression
- Prognosis
- Occupational/ environmental exposure to toxins
- Therapeutic drug effectiveness
- Drug effects on pulmonary function.

- Test, that measures various aspects of breathing & lung function
- Standardization of spirometry  regulated by ATS & ERS guidelines
- PROCEDURE OF SPIROMETRY:
a. Patient  asked to breathe into a tube(mouth piece)
b. Mouth piece  connected to a machine(spirometer)
c. Spirometer  measures amount & flow of inhaled/ exhaled air
d. Physical forces of airflow + total amount of air inhaled/exhaled  converted by
transducers to electrical signals  displayed on a computer screen
e. Prior to conducting spirometry  the technique involved SHOULD BE
EXPLAINED & DEMONSTRATED TO THE PATIENT
f. Since spirometry results  depend on patient’s inhalation & exhalation 
importance of COMPLETELY FILLING & EMPYTING THE LUNGS OF AIR
during the test should be emphasized!!
g. Nose clips should be worn during the test(to prevent air loss through nose!)

Pulmonary function tests: A brief Insight- By RxVichuZ! :)

- There are 2 types of SPIROMETRY SYSTEMS:
A. OPEN-CIRCUIT SYSTEM:
- In this  patient has to INHALE BEFORE INSERTING THE MOUTH-PIECE
B. CLOSED-CIRCUIT SYSTEM:
- In this  mouthpiece is first inserted  patient takes several normal breaths,
before airflow is measured

- There are 2 TYPES of SPIROMETRY:
A. STATIC SPIROMETRY:
- Test, that is “VOLUME-BASED” & “SLOW”
B. DYNAMIC SPIROMETRY:
- Test, that is “TIME-BASED”
- Flow-dependant
- “FORCED”!!

Include:
1. VITAL CAPACITY(VC)
2. FORCED EXPIRATORY VOLUME(FEV)
3. FORCED EXPIRATORY FLOW(FEF)
- Via SPIROMETRY  above values, & a FLOW-VOLUME CURVE are obtained
- FLOW-VOLUME CURVE:
a. Graphical representation of INSPIRATION & EXPIRATION
b. Also known as “flow-volume loops”.

VITAL CAPACITY:
- Includes:
a. FORCED VITAL CAPACITY(FVC)
b. SLOW VITAL CAPACITY(SVC)
- FVC  refers to total volume of air EXHALED as HARD & as FAST as possible
after a MAXIMAL INHALATION
- Obtained from “DYNAMIC SPIROMETRY”
- SVC  refers to total volume of air EXHALED as SLOW as possible, after a
MAXIMAL INHALATION
- SVC  obtained from “STATIC SPIROMETRY”.

- In patients with NORMAL AIRWAY FUNCTION  FVC &
SVC are usually similar
- In COPD patients  there is trivial divergence!
- During initial stages of COPD  FVC decreases before SVC
does!

FORCED EXPIRATORY VOLUME:
- Refers to the assessment of how much air a person can exhale during a FORCED
BREATH.
- Amounts of air exhaled may be measured after:
a. FEV0.5: 0.5 seconds
b. FEV1: 1 second(clinically significant, indicator of airway function!)
c. FEV3: 3 seconds
d. FEV6: 6 seconds, respectively.
- FEV1/FVC ratio  used to estimate presence & amount of obstruction inside
airways
- In normal individuals  exhalation is approximately 50 % of their FVC in the
first 0.5 seconds, 80% in 1 second & 98 % in 3 seconds.
- In patients with OBSTRUCTIVE DISEASE  there is a decreased ratio (ratio
varies based on obstruction severity).

- According to ATS(American Thoracic Society), EPS(European Respiratory
Society) & GOLD(Global Initiative for Chronic Obstructive Lung Disease)
guidelines  the following criteria is given for diagnosis & severity grading of
COPD:
a. If FEV1/FVC ratio < 70%  indicates chronic obstruction(DIAGNOSIS)
b. For SEVERITY GRADING  FEV1 values are noted:
• If FEV1 ≥ 80% : Mild-severity
• If FEV1 = 50-80% : Moderate severity
• If FEV1= 30-50% : Severe form of disease
• If FEV1< 30% : Very severe form of disease, respiratory failure.

FORCED EXPIRATORY FLOW:
- Measures AIRFLOW RATE during FORCED EXPIRATION
- Used to measure:
a. Flow of air in medium & small airways(bronchioles & terminal bronchioles)
b. To check for large obstructions in terminal bronchioles (as in acute severe
asthma).

PEAK EXPIRATORY FLOW RATE:
- Also known as “peak flow”
- Occurs within first milliseconds of expiratory flow
- Measures maximum airflow rate
- Measured using PEAK FLOW METERS
- Applications:
a. To evaluate for large airway obstruction
b. To determine severity of asthma exacerbation
- PEFR  preferred over SPIROMETRY during exacerbation preferential
benefit!!!

DISEASE FEV1/FVC FEV1 FVC RV TLC
COPD Decreased Decreased Normal/decrease
d
Normal/Increase
d
Normal/Increase
d
Obstructive
Lung
Disease(Reversi
ble & Stable)
Normal Normal Normal Normal Normal
Restrictive Lung
Disease
Normal/Increase
d
Decreased Decreased Decreased Decreased
Combined
Obstructive &
Restrictive
Decreased/norm
al
Decreased Decreased Increased,
normal/decrease
d
Decreased

BODY PLETHYSMOGRAPHY
& LUNG VOLUMES

 Body plethysmography  refers to the method used to obtain LUNG VOLUME
MEASURES
 Lung volumes  indicate the amount of gas present in the lungs at various
stages of inflation
 In body plethysmography  patient is asked to sit inside an airtight box  asked
to inhale & exhale against a closed shutter
 Inside the box  there will be a PRESSURE TRANSDUCER
 PRESSURE TRANSDUCER  measures pressure changes within the box during
respiration
 In other words  transducer measures the intrathoracic pressure generated
when the patient rapidly & forcefully puffs against the closed mouthpiece!!!

- Above obtained details  interpreted into Boyle’s Law:
“ P1 * V1 = P2 * V2”, where
“P1”: Pressure inside the box, when the patient is seated(atmospheric pressure)
“V1”: Volume of the box
“P2”: Intrathoracic pressure, generated by the patient
“V2”: Calculated volume of patient’s thoracic cavity.
- By using Boyle’s Law  test provides a measure of FUCTIONAL RESIDUAL
CAPACITY(FRC)

 LUNG VOLUMES include:
1. TIDAL VOLUME(TV)
2. INSPIRATORY RESERVE VOLUME(IRV)
3. EXPIRATORY RESERVE VOLUME(ERV)
4. RESIDUAL VOLUME(RV)
• LUNG CAPACITIES include:
1. INSPIRATORY CAPACITY(IC)
2. EXPIRATORY CAPACITY(EC)
3. VITAL CAPACITY(VC)
4. FUNCTIONAL RESIDUAL CAPACITY(FRC)
5. TOTAL LUNG CAPACITY(TLC)

1. TIDAL VOLUME(TV):
- “Amount of air inhaled & exhaled at rest”
- TV = 0.5 litres
2. INSPIRATORY RESERVE VOLUME(IRV):
- “Additional volume of air, that a person can inhale (via forceful inspiration)”
- IRV = 3.1 litres
3. EXPIRATORY RESERVE VOLUME(ERV):
- “Additional volume of air, that a person can exhale(via forceful exhalation)”
- ERV = 1.2 litres.

4. RESIDUAL VOLUME(RV):
- “Volume of air remaining in the lung, even after forceful exhalation”
- RV = 1.2 litres

1. INSPIRATORY CAPACITY(IC):
- “Total volume of air a person can inspire after normal expiration”
- IC = (TV + IRV) = (0.5 + 3.1 ) litres = 3.6 litres.
2. EXPIRATORY CAPACITY(EC):
- “Total volume of air a person can expire after normal inspiration”
- EC = (TV + ERV) = (0.5 + 1.2) litres = 1.7 litres
3. VITAL CAPACITY(VC):
- VC = (ERV + TV + IRV) = (1.2 + 0.5 + 3.1) litres = 4.8 litres.

4. FUNCTIONAL RESIDUAL CAPACITY(FRC):
- “Volume of air remaining inside lungs after normal expiration”
- FRC = (ERV + RV) = (1.2 + 1.2) litres = 2.4 litres.
5. TOTAL LUNG CAPACITY(TLC):
- “Total amount of air contained in the lungs after maximal inhalation”
- TLC = (RV + ERV + TV + IRV) = (1.2 + 1.2 + 0.5 + 3.1) litres = 6 litres.

 Gas exchange tests  help to measure ability of gases to diffuse across alveolar-
capillary membrane
 Useful in assessing INTERSTITIAL LUNG DISEASES
 Tests  measure “PER MINUTE TRANSFER OF CO, FROM ALVEOLI TO
BLOOD”
 Why is CO USED??
- CO is a gas that is uncommon inside the lung
- It has HIGH AFFINITY for HEMOGLOBIN in RBCs!!
• In the following conditions, diffusion capacity may be lessened:
a. Reduced surface area of alveoli
b. Thickening of alveolar-capillary membrane(due to infiltration of inflammatory
cells/ fibrotic changes)

Diffusion capacity of lungs to CO (DLCO) can be measured by either of the
following tests:
A. SINGLE BREATH TEST:
- In this test  patient deeply inhales (upto vital capacity) , a mixture of 0.3 % CO,
10% helium & air  patient is asked to hold breath for 10 seconds  patient
exhales fully  concentration of C0 & HELIUM are measured (during the end of
expiration)
- The concentration, so got  compared with inspired concentration  helps to
determine the amount diffusing across alveolar membrane
- Mean value for CO : 25-30 ml/min/ mm Hg

B. STEADY-STATE TEST:
- In this test  patient breathes 0.1-0.2% concentration of CO for 5-6 minutes
- In the final 2 minutes  expired gases are collected  ABG is obtained
- Expired gas  analyzed for total volume and concentrations of CO, CO2 & O2
- ABG  analyzed for CO2
- Above values are used to calculate amount of gas transferred across alveolar
membrane per unit of time
- Females may have slightly lower values than males(due to slightly smaller lung
volumes in the former)

 As said before  diffusion capacity tests are used to assess gas exchange
 Diffusion capacity is decreased in diseases that cause ALVEOLAR FIBROTIC
CHANGES, that include:
A. IDIOPATHIC CHANGES:
- Sarcoidosis
- Environmental/occupational disease(asbestosis, silicosis)
B. INDUCED CHANGES:
- Drugs (NTU, amiodarone, bleomycin).

Include:
A. BRONCHODILATOR STUDIES:
- In this test  patient is asked to perform spirometry IMMEDIATELY BEFORE
& 15-30 MINUTES AFTER administration of an INHALED SHORT-ACTING
BETA-2 ADRENERGIC AGONIST
- According to ATS guidelines  there will be a positive bronchodilator response,
signified by an improvement of:
i. FEV1 by 12%
ii. FVC by 200 mL.

B. BRONCHOPROVOCATION CHALLENGE TESTING:
- Also known as Bronchial provocation testing(BPT)
- Measures reactivity of airways to known concentrations of AGENTS that
INDUCE AIRWAY NARROWING
- In this test  airways are challenged with increasing doses of provocative
agents, like:
i. Methacholine
ii. Histamine
iii. Adenosine
iv. Specific allergens
- Used to aid in the diagnosis of asthma(in conditions, where symptom history/
spirometry with reversibility, cannot confirm/ reject the diagnosis)
- Also helpful for studying the effect of drug therapy on airway hyperreactivity &
for research purposes.

C. EXERCISE CHALLENGE TESTING:
• Exercise-induced bronchospasm(EIB)  occurs in majority of asthmatic patients
• Rapid breathing during exercise  causes cooling & drying of airways  can
lead to EIB
• Test is done to:
i. Confirm/ rule out EIB
ii. Evaluate effectiveness of medications used to treat/prevent EIB.
• Duration of exercise is AGE & TOLERANCE dependent
• Children < 12 years of age  usually take 6 minutes
• Older children & adults  take 8 minutes to complete the test.
• After the exercise is completed  patient does “SERIAL SPIROMETRY”, at 5-
minute intervals, for 20-30 minutes  FEV1 is monitored
• A 10-15% decline in FEV1 from baseline  generally accepted as “abnormal
response”.

EXERCISE CHALLENGE TESTS USED FOR SCREENING
EIB:
METHOD ADVANTAGES DISADVANTAGES
Exercise bicycle Easily standardized, portable Relatively expensive
Treadmill Easily standardized Expensive
Free-running asthma screening
test
Familiar, inexpensive, most
asthmogenic
Not standardized, demerits of
running for 6-7 minutes, space
requirements.
Randolph C. Exercise-induced asthma: update on pathophysiology, clinical diagnosis, and treatment. Curr Probl Pediatr 1997;27:57.

- Test used to measure the distance a patient can walk on a FLAT, HARD
SURFACE in 6 minutes.
- Helps to predict morbidity & mortality for patients with CHF, COPD &
pulmonary HTN
- In this test  patient is asked to WALK AS FAR AS POSSIBLE for 6 minutes
- Stopping & resting is allowed during the test
- Normal values include:
a. For ADULTS: 500-630 metres
b. For CHILDREN: 470 +/- 59 metres
- Contraindications include:
a. UA
b. MI (in past 1 month)
c. BP > 180/100 mm Hg!

 To be precise  6MWT is used to assess amount of oxygen required for exertion
 Patients with mild-moderate pulmonary disease may have normal oxygen
saturation at rest, but POOR SATURATION with EXERTION
 If oxygen saturation is 88% or lower  it requires need for supplemental
oxygenation!

Pulmonary function tests: A brief Insight- By RxVichuZ! :)

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