Respiratory Function Tests RFTs

Review Of Anatomy & physiology Lungs comprised 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

The Alveoli There are approximately 300 million alveoli in each lung. Their total surface area is 40-80 m2

Mechanics of Breathing Inspiration Active process caused mainly by contraction of diaphragm . Accessory muscles may used during exercise and distress Expiration Quiet breathing is a passive process but can become active , with forced expiration

Lung Volumes 4 Volumes 4 Capacities Sum of 2 or more lung volumes IRV TV ERV RV IC FRC VC TLC 4 Volumes 4 Capacities Sum of 2 or more lung volumes

Tidal Volume (TV) Volume of air inspired or expired during normal quiet breathing TV = 500 ml 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 IRV= 3000 ml 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. Also called Forced vital capacity FVC 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

Factors affecting lung volume Age Sex Height Weight Race Disease

CLINICAL SIGNIFICANCE VC% < 80% is abnormal 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

Indications Detect disease Evaluate extent and monitor course of disease Evaluate treatment Measure effects of exposures Assess risk for surgical procedures

PFTs Arterial blood gases Blood PH Pulse oximeter Peak flow meter measuring peaked expiratory flow rate. Spirometry

Peak flow meter measuring peaked expiratory flow rate PEFR This is extremely simple and cheap test It describes maximal airflow rate in a given time. It measures the airflow through the bronchi and thus the degree of obstruction in the airways. Is best for monitoring the progression of disease

Cont….. it can detect airway narrowing, commonly used in asthma, Even by the patient himself to know when he need 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 )

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.

Normal values vary based on a person's age, sex, and size Normal person can empty their chest from full inspiration in 4 sec or less Prolongation to more than 6 sec indicates airflow obstruction 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

Old version spirometer bell kymograph pen New version portable

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

What information does a spirometer yield? A spirometer can be used to measure the following: FVC and its derivatives (such as FEV1, FEF 25-75%) Forced Inspiratory vital capacity (FIVC) Peak expiratory flow rate Maximum voluntary ventilation (MVV) Slow VC IC, IRV, and ERV Pre and post bronchodilator studies

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

ive Vs Restrictive Defect Obstructive Disorders Characterized by a limitation of expiratory airflow so that airways cannot empty as rapidly compared to normal (such as through narrowed airways from bronchospasm, inflammation, etc.) Examples: Asthma Emphysema Cystic Fibrosis Restrictive Disorders Characterized by reduced lung volumes/decreased lung compliance Examples: Interstitial Fibrosis Scoliosis Obesity Lung Resection Neuromuscular diseases Cystic Fibrosis

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