IM

MOST IMPORTANT PFT

SPIROMETRY

  • A spirometer is an apparatus used to measure the volume of air inhaled and exhaled by the lungs.
  • After attaching the mouth piece, patient inhales maximally then exhales forcefully. This is recorded by the machine.

Two very important measurements by the spirometer are:

  1. FEV1: forced expiratory volume in 1 second.

    • This is the amount of air which comes out in
    • the 1st second of forced expiration.
  2. Vital capacity( also called forced vital capacity or FVC)

Remember: most of the air comes out in the 1st sec. of exhalation

FEV1/ VC

The FEV1 is used to classify the severity of obstructive lung diseases traditionally based on 0% predicted values into five levels.

  • FEV1>70% of predicted is mild
  • FEV1 60-69% of predicted I is moderate
  • FEV1 50-59% of predicted is moderately severe
  • FEV1 35-49% of predicted is severe
  • FEV1 <35% of predicted is very severe

SOME NORMAL VAUES

  • TV: 500 cc
  • F.V.C. : 5 liters(5000cc)
  • FEV1 : 4 liters (4000cc)
  • TLC: 5.7 liters (5700cc)
  • FEV1/FVC ratio : 4/5 = 75% to 80%

USES OF SPIROMETRY

  1. Diagnosis of certain lung diseases eg asthma, COPD, interstitial lung diseases (obstructive pattern vs. restrictive pattern)
  2. To see the effect of medicines being given for those diseases
  3. Pre-operatively, to assess lung function

Spirometry results in some lung diseases

1) Obstructive diseases (asthma, COPD)

  • a) FEV1 is too much reduced
  • b) FVC is slightly reduced, so
  • **c) FEV1 /FVC ratio is
    • reduced.**
  • **d) TLC is increased
    • ( air trapped inside)**
  • **eg FEV1= 1.3L, FVC = 3.2L, ratio
    • will be (1.3/3.2) x 100: 41%**

2) Restrictive diseases ( pulm. fibrosis, decreased chest movement)

  • a) FEV1 reduced
  • b) FVC equally reduced, so
  • **c) FEV1/ FVC ratio is normal **
  • d) TLC is decreased
  • Eg: FEV1 1.7L, FVC 2L, ratio * ( 1.7/2) x100 : 85%



Thera

Is the most common of the Pulmonary Function Tests (PFTs)

Is a method of assessing lung function by measuring the volume(amount)& flow(speed) of air the patient can expel from the lungs after a maximal inspiration

  • Measure airflow obstruction to help make a definitive diagnosis .

  • Distinguish between Obstructive and Restrictive diseases of the lungs.

Types of Spirometers

ParameterDescription
Bellows spirometersMeasure volume; mainly in lung function units
Electronic desk top spirometersMeasure flow and volume with real time display
Small hand-held spirometersInexpensive and quick to use
pneumotachometer (1st)
Electric Spirometry (3rd) Plethysmograph;
measures DLCO (5th)

Pulmonary function test

Lung volumes and capacities

 

Standard Spirometry Indices

The Spirometer calculates different ventilation parameters:

ParameterDescription
FVC - Forced vital capacityThe total volume of air that can be forcibly exhaled in one breath
FEV1 - Forced expiratory volume in one secondThe volume of air expired in the first second of the blow
FEV1/FVC ratioThe fraction of air exhaled in the first second relative to the total volume exhaled

Predicted Normal Values Based on Following

  • Age
  • Height
  • Weight
  • Sex
  • Ethnic Origin calculated number will be given to estimate viability

Volume-time loop

The volume versus time curve is a an alternative way of plotting spirometric results and is another useful illustration of patient performance.

Normally the whole FVC is expelled in four seconds 80% in second normally

ParameterDescription
Forced expiratory volume (FEV1)the volume of air expelled in the first second of a forced exhalation. In normal subjects 75-80% of the FVC can be expelled in the first second.
FEV1/FVCthe normal value is 75-80%. Anything below this is considered abnormal (obstructive or restrictive disease).

Flow- volume loopY

  • Spirometry is a valuable tool for analyzing the flow rate of air passing into and out of the lungs.

  • Flow volume loops provide a graphical illustration of a patient’s spirometric efforts.

Spirogram Patterns

  • Normal
  • Obstructive
  • Restrictive
  • Mixed Obstructive and RestrictiveY

obstructive and restrictive diseasesZ

Lung disease is often divided into two broad categories: obstructive disease and restrictive disease.

  • Examples of obstructive disease
    are Emphysema, Chronic Bronchitis, and bronchial Asthma.

  • Examples of restrictive diseass are abnormalities of the spine and chest and diseases within the lungs that make them less elastic (“stiffer”), such as pulmonary fibrosis.

CriteriaFEV1: % predictedFVC: % predictedFEV1/FVC
Normal> 80%> 80%> 0.7
Obstructive Disease< 80% ↓↓< 80% ↓< 0.7
Restrictive Disease< 80% ↓< 80% ↓↓> 0.7
Mixed Obstructive/RestrictiveY< 80%< 80%< 0.7

Normal Trace Showing FEV1 and FVC

Obstructive Disease

Restrictive Disease

Mixed Obstructive and RestrictiveY

Restrictive and mixed obstructive-restrictive are difficult to diagnose by spirometry alone; full respiratory function tests are usually required

(e.g., body plethysmography, etc)