respiratory function tests rfts. review of anatomy & physiology lungs comprised of airways ...
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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