Respiratory Function Tests RFTs

Review Of Anatomy & physiology

Lungs comprised of AirwaysAlveoli

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 BreathingInspiration

◦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

IRV

TV

ERV

RV

IC

FRC

VC

TLC

RV

4 Volumes4 Capacities

◦Sum of 2 or more lung volumes

Tidal Volume (TV)

IRV

TV

ERV

RV

IC

FRC

VC

TLC

RV

Volume of air inspired or expired during normal quiet breathing

TV = 500 ml

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

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. Also called Forced vital capacity FVC

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

Factors affecting lung volumeAgeSexHeightWeightRaceDisease

CLINICAL SIGNIFICANCE VC% < 80% is abnormalRV/TLC% (residual air rate) normal : < 35% emphysema: > 40 % old person can be 50%.FRC ↑ : emphysemaFRC ↓ : interstitial pulmonary

fibrosis

Value of Respiratory function tests

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

IndicationsDetect disease Evaluate extent and monitor

course of diseaseEvaluate treatmentMeasure effects of exposuresAssess risk for surgical

procedures

PFTs

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

peaked expiratory flow rate.5. 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)

FVCInterpretation of % predicted:

◦80-120% Normal◦70-79% Mild reduction◦50%-69% Moderate reduction◦<50% Severe reduction

FEV1Forced 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

FEV1Interpretation of % predicted:

◦>75% Normal◦60%-75% Mild obstruction◦50-59% Moderate obstruction◦<49% Severe obstruction

Technique Have patient seated comfortablyClosed-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 TestMethod: to determine FEV1 and

FEV1/FVC% before and after ß2-agonist inhalation

Result: improved rate = after-before ×100%

before Positive: >15%Reversible limitation: asthma