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: Pulmonary ventilation: outflow and inflow of air between outside and alveoli. Diffusion of O2 and Co2 between alveoli and blood. Transport to and from tissue

Lung Volumes IRV IC VC TLC TV ERV FRC RV RV

Tidal Volume (TV) Volume of air inspired or expired during normal quiet breathing About 500ml IRV IC VC TLC TV ERV FRC RV RV

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 IC VC TLC TV ERV FRC RV RV

Expiratory Reserve Volume (ERV) The extra volume of air that can be exhaled over normal tidal volume when person expires forcefully ERV= 1100ml IRV IC VC TLC TV ERV FRC RV RV

Residual Volume (RV) Volume of air remaining in the lungs at the end of maximum expiration. RV =1200 ml IRV IC VC TLC TV ERV FRC RV RV

Vital Capacity (VC) 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 IRV IC VC TLC TV ERV FRC RV RV

Inspiratory Capacity (IC) 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 IRV IC VC TLC TV ERV FRC RV RV

Functional Residual Capacity (FRC) Volume of air remaining in the lungs at the end of a normal expiration FRC = ERV + RV FRC= 2300 ml IRV IC VC TLC TV ERV FRC RV RV

Total Lung Capacity (TLC) Volume of air in the lungs after a maximum inspiration TLC = IRV + TV + ERV + RV =5800ml IRV IC VC TLC TV ERV FRC RV 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

Investigation tools used for studying respiratory function Arterial blood gases Blood PH Pulse oximeter Peak flow meter measuring peaked expiratory flow rate. Spirometry

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 when he needs an emergency interference. the effectiveness of a person's asthma management and treatment plan. when to stop or add medication, as directed by physician. 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