Respiratory Function Tests RFTs Review Of Anatomy physiology

Respiratory Function Tests RFTs

Review Of Anatomy & physiology �Lungs comprised of v. Airways v. 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 approximately 300 million alveoli in each lung. § Their total surface area is 40 -80 m 2

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

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

The Inspiratory Reserve Volume IRV The IRV IC VC TV TLC ERV FRC RV RV extra volume of air that can be inspired over and above the normal tidal volume , when person inspires with full force IRV= 3000 ml

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

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

Vital Capacity (VC) l IRV IC VC TV TLC ERV FRC RV RV l l 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=4600 ml VC=IRV+TV+ERV

Inspiratory Capacity (IC) l IRV IC VC TV TLC ERV FRC RV RV l l 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= 3500 ml

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

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

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 1. 2. 3. 4. 5. 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 (FEV 1) - Forced vital capacity (FVC) - FEV 1/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 FEV 1, FEF 2575%) ◦ 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 l 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 ◦ 80 -120% ◦ 70 -79% ◦ 50%-69% ◦ <50% of % predicted: Normal Mild reduction Moderate reduction Severe reduction

FEV 1 � Forced expiratory volume in 1 second: (FEV 1) ◦ Volume of air forcefully expired from full inflation (TLC) in the first second ◦ Measured in liters (L) ◦ Normal people can exhale more than 7580% of their FVC in the first second; thus the FEV 1/FVC can be utilized to characterize lung disease

FEV 1 Interpretation ◦ >75% ◦ 60%-75% ◦ 50 -59% ◦ <49% of % predicted: Normal Mild obstruction Moderate obstruction 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 � Restrictive Disorders ◦ Characterized by a limitation ◦ Characterized by reduced of expiratory airflow so that lung volumes/decreased airways cannot empty as lung compliance rapidly compared to normal Examples: (such as through narrowed ◦ Interstitial Fibrosis airways from ◦ Scoliosis bronchospasm, inflammation, etc. ) ◦ Obesity Examples: ◦ Lung Resection ◦ Asthma ◦ Neuromuscular diseases ◦ Emphysema ◦ Cystic Fibrosis

Obstructive Disorders l l l Characterized by a limitation of expiratory airflow Decreased: FEV 1, FEV 1/FVC ratio (<0. 8) Increased or Normal: TLC

Spirometry in Obstructive Disease l l Slow rise in upstroke May not reach plateau

Restrictive Lung Disease l l Characterized by diminished lung volume Decreased TLC, FVC Normal FEV 1 Normal or increased: FEV 1/FVC ratio

Restrictive Disease l l Rapid upstroke as in normal Spirometry Plateau volume is low

Bronchial Dilation Test �Method: to determine FEV 1 and FEV 1/FVC% before and after ß 2 -agonist inhalation �Result: improved rate = after-before × 100% before Positive: >15% �Reversible limitation: asthma