PFT ppt - Pheonix India

Report
PRESENTED BY: RASHMI BHATT
MODERATOR: Dr GIRISH SHARMA
7.
MEASUREMENT OF VENTILATORY FUNCTION
Bedside tests
Measurement of lung volumes
Measurement of expiratory flow rates
Measurement of airway hyperresponsiveness
Respiratory muscle testing
Distribution of ventilation
Gas transfer and exchange

EXERCISE TESTING

1.
2.
3.
4.
5.
6.
SEBARESE’S BREATH HOLDING TEST :
>30 sec : normal value
20-30 sec : decreased respiratory reserve
<20 sec : severe pulmonary disease
 SNIDERS MATCH BLOWING TEST:
It tests the subject’s ability to blow out a lit up matchstick
at a distance of 15 cm from the mouth, after a deep inspiration
followed by forced expiration without pursing the lips. The
ability to do so suggests an FEV1 more than 1.5 litres.
 WRIGHT’S PEAK FLOWMETER & DE BONO’S WHISTLE:
After a deep inspiration, air is blown out through peak
flow meter with force. Adults : 500L/min or more ;
males:450-700L/min ; females: 300-500 L/min
children : 200-250L/min
<200L/min: impaired cough efficiency and a higher risk of post
operative pulmonary complications

WATCH AND STETHOSCOPE TEST:
Breath sounds over the trachea are heard and the
expiration time is noted.
≤ 4sec : normal
↑ed : Obstructive airway disease
 GREENE & BEROWITZ COUGH TEST:
vigorous coughing is induced in the pre op period and
the following noted:
•ability to cough
•strength
•effectiveness
•nature of mucus
 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


The subject is first asked to breathe with a normal,
resting tidal pattern followed by maximal inspiration and
exhalation. Several lung volumes can be determined
through spirometry, except residual volume.

VITAL CAPACITY: most common measurement of lung
function. Largest volume measured after the subject
inspires deeply and maximally to TLC and then exhales
completely to residual volume, without concern for
rapidity of effort

TIDAL VOLUME: amount of air moving in and out of lungs
during normal, quiet breathing. 10 ml/kg

INSPIRATORY RESERVE VOLUME: amount of air
inspired with max effort in excess of TV

EXPIRATORY RESERVE VOLUME: volume of air
expelled by active expiratory effort after passive
expiration

RESIDUAL VOLUME: amount of air left in the lungs
after maximal expiratory effort

RESP MINUTE VOLUME: volume of air inspired per
minute (500ml*12 = 6000ml/min)

INSPIRATORY CAPACITY: TV + IRV

ALVEOLAR VENTILATION( at rest) 4.2 L/min
MALES




IRV
TV
ERV
RV
TLC
3.3 L
0.5 L
1.0 L
1-2 L
6.0 L
FEMALES
1.9 L
0.5 L
0.7 L
1.1 L
4.2 L

HELIUM DILUTION METHOD:
The subject is asked to rebreathe a known volume of
gas in a closed circuit spirometer which has helium as a
trace. Once equilibrium is attained, total system volume(
lungs+spirometer) is known. Deducting the spirometer
volume gives the FRC and further deducting the ERV gives
the RV.

MULTIBREATH NITROGEN WASHOUT TECHNIQUE:
Tracer gas used is nitrogen which is normally present
in the lungs. It is washed out by breathing 100% O2. by
measuring the exp N2 quantity, FRC can be derived, having
known the initial conc of N2 in the alveoli.

PLETHYSMOGRAPHIC VOLUME DETERMINATION:
Used for measuring FRC & RV. Uses the boyle’s law,
whereby the subject and the box behave as a closed
system. volume changes in the subject are reflected as
pressure changes in the gas tight box i.e. P1V1=P2V2

It is also used to evaluate airway obstruction by measuring
the airway resistance. Normally it is <2cmH2O L/sec.

The reciprocal of Raw known as airway conductance Gaw
can be calculated, which when divided by the FRC gives
the specific conductance which is a highly reproducible
measurement.
These parameters are recorded with respect to time i.e.
the rapidity of the effort is significant. The maneuvers are
to be completed either as rapidly as possible or within a
specified time range.
1) FORCED VITAL CAPACITY:
The subject is asked to inhale upto TLC and then
exhale as forcefully as possible for not less than 4
seconds. It is reduced in lung pathologies like pneumonia
atelectasis, fibrosis, surgical excision and muscle
weakness, abd pain or swelling. Normally, it is almost
equal to VC. A discrepancy suggests the presence of
airway obstruction and air trapping.
2) FEV1:
It measures the vol of air exhaled forcefully in 1 sec
during an FVC maneuver. Normally it varies from 3.0 to
4.5 L. value of 1.5 to 2.5 L signifies mild to mod
obstruction while less than this is suggestive of a severe
impairment. FEV1: 75-80% FVC , FEV2: 83-90% FVC,
FEV3:97% FVC.

3)
FEV1/FVC RATIO:
This parameter is a better indicator of
airway obstruction, wherein FEV1 while FVC
remains normal or only slightly reduced,
leading to a decrease in the ratio. In case of
restr
lung
disease,
both
decrease
proportionately and the ratio is more or less
the same, while TLC is dec.
<70%: mild obst,
<60% mod obst,
<50%: severe obst.
4) PEAK FLOW RATE:
The max flow rate during a forced exp
from TLC( initial 0.1 sec) in L/min or L/sec. in
normal individuals, it is ≥500L/min. it can be
used to monitor response to bronchodilator
therapy.
5)
FORCED MIDEXPIRATORY FLOW/ FEF25-75%:
It measures the air flow during the middle
half of FVC, which is the effort independent
portion. It varies with the value of FVC,
normally4.5-5.0 L/sec. sensitive indicator of
small airway obstruction.
6)
MAX BREATHING CAPACITY/ MAX VOLUNTARY
VENTILATION:
Largest vol that can be breathed per min by
voluntary effort. Measured over 12 sec and
extrapolated to 1 min. in healthy adults: 150175L/min. it is approx 35 times the value of
FEV1. ABOUT 80% of MVV can be sustained by
healthy individuals for 15 min or so.



1.
2.
3.
4.
Graphic analysis of air flows at various lung volumes to
differentiate various cause of airway disease. The loop is
plotted while the patient performs an FVC maneuver.
MID VC RATIO: the ratio of expiratory flow to inspiratory
flow at 50% of VC. Normally it is 1
The entire inspiratory portion of the loop and the
expiratory curve near the TLC are effort dependent
Fixed obstr: ratio remains 1. the airway diameter does
not change and both insp and exp flows show a plateau.
Variable extrathoracic obstr: airway collapses during insp
while exp flow is N so ratio>2.0.
Variable intrathoracic obstr: ratio<1.0 due to reduction in
exp flow only
Diffuse obstr: mid VC ratio is low





Its measurement is associated with the concept of small
airway obstruction
It is the lung volume at which airways in dependent areas
of the lungs cease to contribute to exhalation
Due to gravity dependent gradients in pleural pressure
Techniques used: bolus technique ( using xenon,argon or
helium) and the residual gas technique (using N2)
Normally CV is 15-20% of vital capacity
Useful in the patients with clinical suspicion but
normal spirometry.
 Airway hyper-responsiveness is precipitated by
the use of agents like histamine, methacholine,
cold air, exercise etc.
 After measuring the baseline FEV1, %change in
lung function is recorded
 The test is considered positive if ≤8.0µmol of the
agent produced a 20% fall in FEV1.
 It is useful to exclude asthma in patients with
similar symptoms.







Respiratory muscle strength alters the measurement
of pulm function which require patient effort.
The parameters used to measure it are PImax and
PEmax. These are recorded while the airway is
occluded, during max insp and exp effort, using
anaeroid gauges.
PImax is recorded near RV, it is -125cmH2O
PEmax is recorded near TLC, it is +200cmH20
These are static pressures measured at FRC and
measure the pressure due to the resp muscles alone,
by eliminating that due to elastic recoil of the resp
system.
Low PImax suggests an inability to take a deep insp
while a low PEmax suggests an impaired coughing
ability




ALVEOLAR-ARTERIAL O2 TENSION DIFFERENCE (PAO2-Pao2): sensitive
indicator of V/Q abnormalities. Normally it is >8mmHg and increase
with age(d/t dec in PaO2)
Dyspnoea differentiation index: to distinguish cardiac cause from
pulmonary cause of dyspnoea.
DDI = PEFR*PaO2/1000
Multiple breath N2 washout: the curve of N2 washout is single
exponential in case of uniform ventilation,
Diffusing capacity of lung using CO(DLCO): measure of the ability of
gases to diffuse from the alveoli into the capillaries. It depends upon
the gradient and the thickness of alveolo-capillary membrane. Also
suggests the no of functioning capillaries being ventilated.
technique is single breath CO test
normal value is 20-30ml/min/mmHg
it is dec in emphysema, lung resection, pulm emboli, anaemia,
fibrosis, sarcoidosis etc.
it is inc in assoc with increased pulm blood volume (supine position
exercise, left to right cardiac shunts).





Stair climbing: the ability to climb three flights of stairs
at the patient’s own pace, without stopping. Quantitative
assessment is 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
6 minute walk test: distance walked in 6 min, at patient’s
own pace. The ability to walk 180 feet in 1 min (6 minwalk distance of 1080 feet) corresponds to a VO2max of
12ml/kg/min.




NORMAL : FVC>= 80% of predicted ; FEV1>=80% of pred
FEV1/FVC>=0.75 ; DLCO>=80% of pred
MILD IMPAIRMENT : FVC: 60-79% ; DLCO : 60-79%
FEV1 : 60-79% ; FEV1/FVC ratio : 0.60-0.74
MODERATE IMPAIRMENT : FVC : 51-59% ;
DLCO : 41-59% ; FEV1 : 41-59%; FEV1/FVC : 0.41-0.59
SEVERE IMPAIRMENT: FVC≤50% ; DLCO≤ 40%
FEV1≤40% ; FEV1/FVC≤0.40

similar documents