Respiratory function tests

Lung anatomy and physiology

Lungs consist of – Airways– Alveoli

Airways

Conducting zone: no gas exchange occurs– Anatomic dead space

Transitional zone: alveoli appear, but are not great in number

Respiratory zone: contain the alveolar sacs

Mechanics of Breathing

Inspiration– Active process

Expiration– Quiet breathing: passive– Can become active , with forced expiration

The goals of respiration:

Provide O2 to tissue and remove Co2 through:

1. Pulmonary ventilation: outflow and inflow of air between outside and alveoli.

2. Diffusion of O2 and Co2 between alveoli and blood.

3. Transport to and from tissue

Lung Volumes

IRV

TV

ERV

RV

IC

FRC

VC

TLC

RV

Tidal Volume (TV)

IRV

TV

ERV

RV

IC

FRC

VC

TLC

RV

Volume of air inspired or expired during normal quiet breathing– About 500ml

The Inspiratory Reserve Volume IRV

The extra volume of air that can be inspired over and above the normal tidal volume , when person inspires with full force

=3000ml

IRV

TV

ERV

RV

IC

FRC

VC

TLC

RV

The extra volume of air that can be exhaled over normal tidal volume when person expires forcefully

ERV= 1100ml

Expiratory Reserve Volume (ERV)

IRV

TV

ERV

RV

IC

FRC

VC

TLC

RV

Residual Volume (RV)

IRV

TV

ERV

Volume of air remaining in the lungs at the end of maximum expiration.

RV =1200 ml

RV

IC

FRC

VC

TLC

RV

Vital Capacity (VC)

IRV

TV

ERV

The maximum amount of air a person can expel from the lungs after filling the lungs to their maximum extent and then expires to the maximum extent.

VC=4600ml VC=IRV+TV+ERV

RV

IC

FRC

VC

TLC

RV

Inspiratory Capacity (IC)

IRV

TV

ERV

The amount of air a person can breathe in beginning at the normal expiratory level and distending the lung to the maximum amount.

IC = IRV + TV IC= 3500ml

RV

IC

FRC

VC

TLC

RV

Functional Residual Capacity (FRC)

IRV

TV

ERV

Volume of air remaining in the lungs at the end of a normal expiration

FRC = ERV + RV FRC= 2300 ml

RV

IC

FRC

VC

TLC

RV

Total Lung Capacity (TLC)

IRV

TV

ERV

Volume of air in the lungs after a maximum inspiration

TLC = IRV + TV + ERV + RV

=5800ml

RV

IC

FRC

VC

TLC

RV

CLINICAL SIGNIFICANCE

VC depends on sex, age and height. VC < 80% is abnormal. As in cases of restrictive ventilation disorder RV/TLC% (residual air rate) normal : < 35% emphysema: > 40 % old person can be 50%. FRC ↑ : emphysema FRC ↓ : interstitial pulmonary fibrosis

Value of Respiratory function tests

Evaluates 1 or more major aspects of the respiratory system– Lung volumes– Airway function– Gas exchange

Why to use Respiratory function test?

Detect disease Evaluate extent and monitor course of

disease Evaluate treatment Assess risk for surgical procedures

1. Arterial blood gases2. Blood PH3. Pulse oximeter 4. Peak flow meter measuring peaked

expiratory flow rate.5. Spirometry

Investigation tools used for studying respiratory function

Factors affecting lung volume

Age Sex Height Weight Race Disease

Peak expiratory flow rate (PEFR) using the peak flow meter

Peak flow meter is a small device that measures the fastest rate of air that you can blow out of your lungs, it can detect airway narrowing, commonly used in asthma, Even by the patient himself to know

1. when he needs an emergency interference. 2. the effectiveness of a person's asthma

management and treatment plan. 3. when to stop or add medication, as directed by

physician. 4. what triggers the asthma attack (such as exercise-

induced asthma )

PEAKED EXPIRATORY FLOW

To perform this test: Loosen any tight clothing that might restrict your breathing. Sit up straight or stand while performing the tests Breathe in as deeply as possible. Mouthpiece is placed in mouth with lip sealed to prevent escape

of air Blow into the instrument's mouthpiece as hard and fast as

possible. Do this three times, and record the highest flow rate.

Why the Test is Performed? The test is commonly used to diagnose and monitor lung

diseases such as: Asthma Chronic obstructive pulmonary disease (Less accurate)

Normal Results

Normal values vary based on a person's age, sex, and size. Peak flow measurements are most useful when a person compares the number on a given day to his or her "personal best."

A fall in peak flow can signal the onset of a lung disease flare, especially when it occurs with symptoms such as:

Shortness of breath Increased cough Wheezing

SPIROMETRY

Simple, office-based

Measures flow, volumes

Volume vs. Time

Can determine:- Forced expiratory volume in one second (FEV1)

- Forced vital capacity (FVC)- FEV1/FVC

Indications of spirometry:diagnostic and prognostic

Evaluation of signs and symptoms of pulmonary diseases like asthma and COPD

Screening at-risk populations (male smokers >45 years)

Monitoring pulmonary drug toxicity

Preoperative assessment

■ Assess severity of diseases

■ Follow up response to therapy

■ Determine further treatment goals

■ Referral for surgery

■ Disability

Terminology

Forced vital capacity (FVC):– Total volume of air that can

be exhaled forcefully from TLC

– The majority of FVC can be exhaled in <3 seconds in normal people, but often is much more prolonged in obstructive diseases

– Measured in liters (L)

FVC

Interpretation of % predicted:– 80-120% Normal– 70-79% Mild reduction– 50%-69% Moderate reduction– <50% Severe reduction

FEV1

Forced expiratory volume in 1 second: (FEV1)– Volume of air forcefully expired from full

inflation (TLC) in the first second– Measured in liters (L)– Normal people can exhale more than 75-

80% of their FVC in the first second; thus the FEV1/FVC can be utilized to characterize lung disease

FEV1

Interpretation of % predicted:– >75% Normal– 60%-75% Mild obstruction– 50-59% Moderate obstruction– <49% Severe obstruction

Technique

Have patient seated comfortably Closed-circuit technique

– Place nose clip on– Have patient breathe on mouthpiece– Have patient take a deep breath – Blow out the air as fast as possible and as

hard and long as possible

Obstructive Lung Disease — Differential Diagnosis

Asthma

COPD - chronic bronchitis

Bronchiectasis

Bronchiolitis

Upper airway obstruction

Restrictive lung disease:

Pneumoconiosis Chest wall deformity Pleural adhesion and pleural effusion Interstitial lung fibrosis

Combined restrictive and obstructive in cases of cystic fibrosis

Flow-Volume Loop

Illustrates maximum expiratory and inspiratory flow-volume curves

Useful to help characterize disease states (e.g. obstructive vs. restrictive)

Spirometer pattern

Obstructive Disorders

Characterized by a limitation of expiratory airflow

Decreased: FEV1, FEV1/FVC ratio (<0.8)

Increased or Normal: TLC

Spirometry in Obstructive Disease

Slow rise in upstroke May not reach plateau

Restrictive Lung Disease

Characterized by diminished lung volume

Decreased TLC, FVC Normal FEV1 Normal or increased:

FEV1/FVC ratio

Restrictive Disease

Rapid upstroke as in normal spirometry

Plateau volume is low

Bronchial Dilation Test

Method: to determine FEV1 and FEV1/FVC% before and after ß2-agonist inhalation

Result: improved rate = after-before ×100% before Positive: >15% Reversible limitation: asthma