Pulmonary function tests
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Pulmonary Function Tests. J.B. Handler, M.D. Physician Assistant Program University of New England. ARDS- adult respiratory distress syndrome DL CO - diffusion capacity for carbon monoxide Ht- height Wt- weight SOB- short of breath Pred- predicted Meas- measured

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Pulmonary function tests

Pulmonary Function Tests

J.B. Handler, M.D.

Physician Assistant Program

University of New England


Abbreviations

ARDS- adult respiratory distress syndrome

DLCO- diffusion capacity for carbon monoxide

Ht- height

Wt- weight

SOB- short of breath

Pred- predicted

Meas- measured

PFT- pulmonary function test

ABG- arterial blood gas

Abbreviations


Pft s indications

PFT’s: Indications

  • Detect abnormalities and severity of lung function in presence of disease.

    • Monitor course of disease.

  • Baseline pulmonary function prior to surgical, medical or radiation therapy.

  • Differentiation of obstructive vs restrictive disease.

  • Evaluate response to therapy, reversibility.

  • Determine the preoperative risk of thoracic surgery.


Lung volumes

Lung Volumes

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Lung volumes1

Tidal Volume (TV): amount of air inhaled and exhaled at rest; normal= 500-750 ml.

Inspiratory Capacity (IC): beginning of normal inhalation to maximum inspiration.

Lung Volumes

IC

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Lung volumes2

Inpiratory Reserve Volume (IRV): Volume measured from “top” of the TV (point of normal exhalation) to maximum inspiration.

Expiratory Reserve Volume (ERV): Volume measured from the “bottom” of the TV (point of normal inhalation) to maximum expiration.

Lung Volumes

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Lung volumes3

Residual Volume (RV): The amount of air left in the lungs following full exhalation to the ERV..

Functional Residual Capacity (FRC) = ERV + RV: amount of gas remaining in the lungs at the end of the tidal volume.

Lung Volumes

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Lung volumes4

Vital Capacity (VC): volume of air measured from full inhalation to maximum exhalation

Total Lung Capacity (TLC): summation of the RV + vital capacity.

Lung Volumes

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Spirometer

Spirometer


Spirometry

Spirometry

  • Forced Vital Capacity (FVC)- Following full inspiration, patient exhales as rapidly as possible, forcibly and completely- volume of air exhaled is measured; takes 5-6 seconds with majority in 1 second. Wide range of normal (see below).

  • Volume obtained is expressed as a % of predicted normal. Normals are based on volumes obtained from thousands of healthy individuals of similar age, sex, ht and wt and race. Normal 80% of predicted.


Spirometry1

Spirometry

  • FEV1:Amount of air forcibly exhaled in the 1st second of the FVC maneuver (80% of FVC volume). Normal 80% predicted; wide range of normal (see below).

  • Volume obtained is expressed as a % of predicted normal. Normals are based on volumes obtained from thousands of healthy individuals of similar age, sex, ht and wt and race. Normal  80% of predicted.


Spirometry2

Spirometry

  • FEV1/FVC: Very important ratio; when reduced, helps identify presence of obstructive disease. Percentage reduction correlates with severity of obstruction; normal is 75-80+%. Normal (or ) in patients with restrictive disease.

  • Obstructive airway disease: Asthma, COPD.

  • Restrictive disease: Interstitial lung disease, kyphoscoliosis, pleural disease & others).


Peak expiratory flow rate

Peak Expiratory Flow Rate

  • Measured using simple hand held device.

  • Occurs within the first milliseconds of forced expiration and is a measure of maximum airflow rate.

  • Wide variation in normal ranges (age, ht and sex) adult males: 400-700L/minute.adult females: 300-600L/minute.

  • Effort dependent.

  • When abnormal- indicator of large airways obstruction.


Peak expiratory flow rate1

Peak Expiratory Flow Rate

  • Clinical use: Assessment of patients with asthma.

  • Patient determines “personal best” PEFR when most healthy, between asthma attacks.

  • PEFR often precedes symptoms.

  • Guide for responsiveness to meds, worsening of episodes, when to get help, etc.


Diffusion capacity

Diffusion Capacity

  • Tests gas exchange across the alveolar-capillary membrane.

  • Per minute transfer of gas- Carbon Monoxide measured from alveoli to blood; DLCO.

  • Decreased if thickened alveolar capillary membrane (pulmonary fibrosis, ARDS), or following loss of surface area of the alveoli.

  • Most useful and decreased in interstitial lung disease (lecture to follow).

  • Normal mean is 25-30 mL/min/mmHg.


Application of pft s

Application of PFT’s

  • Obstructive disease: asthma, COPD, bronchiectasis.

  • Pattern: FVC normal or decreased mildly.FEV1 decreased; reduction reflects severity.

  • FEV1/FVC decreased- reflects severity.

  • Response to bronchodilator indicates reversible component.


Application of pft s1

Application of PFT’s

  • Restrictive disease: pulmonary fibrosis, sarcoidosis, kyphoscoliosis, neuromuscular disease, others.

  • Pattern: FVC decreased, often markedly.FEV1 decreased, often markedly.

  • FEV1/FVC normal or increased.

  • No response to bronchodilator.


Problem solving

Problem Solving

22 y.o male with cough, SOB, and wheezing.

  • FVC – 3.63L (pred), 3.23L (meas), 89% pred

  • FEV1- 3.24L (pred), 2.24L (meas), 69% pred

  • FEV1/FVC 69% (meas)Post bronchodilator:

  • FVC- 3.23L

  • FEV1- 2.70L (meas) 83% pred

  • FEV1/FVC 84% (meas)

  • Interpretation: mild obstructive airways disease with post bronchodilator reversibility.

  • Diagnosis: Asthma


Problem solving1

Problem Solving

  • 45 y.o black man with progressive shortness of breath.

  • FVC- 3.05L (pred), 0.81L (meas), 22% predicted

  • FEV1- 2.9L (pred) 0.69L (meas), 24% predicted

  • FEV1/FVC 97% (meas)

  • No change post bronchodilator

  • Interpretation: Severe restrictive disease; no evidence of airway obstruction.

  • Diagnosis: Sarcoidosis


Pulse oximetry

Pulse Oximetry

  • Measures per cent oxygenation of hemoglobin (oxyhemoglobin).

  • Non-invasive; measures absorption of light passing through tissue, then calculates O2 saturation of arterial blood.

  • Measured via electrodes placed on skin- fingertips, ear lobes.

  • Normal = 97%


Arterial blood gas measurement

Arterial Blood Gas Measurement

  • Requires arterial puncture

  • pH of arterial blood

  • PO2: partial pressure of oxygen (mmHg)

  • PCO2: partial pressure of carbon dioxide (mmHg)

  • HCO3: calculated- bicarbonate; proportional to dissolved CO2 in blood.


O 2 hemoglobin dissociation

O2-Hemoglobin Dissociation

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