PULMONARY FUNCTION

TESTS

PRESENTED BY: RASHMI BHATT

MODERATOR: Dr GIRISH SHARMA

ASSESSMENT OF PULMONARY FUNCTIONS

MEASUREMENT OF VENTILATORY FUNCTION

1. Bedside tests2. Measurement of lung volumes3. Measurement of expiratory flow rates4. Measurement of airway

hyperresponsiveness5. Respiratory muscle testing6. Distribution of ventilation7. Gas transfer and exchange

EXERCISE TESTING

BEDSIDE TESTS 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

BEDSIDE TESTS (CONTD.) 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

SPIROMETRY

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

NORMAL VALUES

MALES IRV 3.3 L TV 0.5 L ERV 1.0 L RV 1-2 L

TLC 6.0 L

FEMALES 1.9 L

0.5 L

0.7 L

1.1 L

4.2 L

GAS DILUTION METHODS

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.

MEASUREMENT OF EXPIRATORY FLOW RATES 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: 150-175L/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.

FLOW VOLUME LOOPS

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

1. Fixed obstr: ratio remains 1. the airway diameter does not change and both insp and exp flows show a plateau.

2. Variable extrathoracic obstr: airway collapses during insp while exp flow is N so ratio>2.0.

3. Variable intrathoracic obstr: ratio<1.0 due to reduction in exp flow only

4. Diffuse obstr: mid VC ratio is low

CLOSING VOLUME 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

MEASUREMENT OF AIRWAY HYPER-RESPONSIVENESS

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 TESTING

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

DISTRIBUTION OF VENTILATION AND GAS EXCHANGE FUNCTION 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).

EXERCISE TESTING 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 min-walk distance of 1080 feet) corresponds to a VO2max of 12ml/kg/min.

DEGREE OF IMPAIRMENT 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

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