Download - Respiratory function tests. Lung anatomy and physiology Lungs consist of – Airways – Alveoli
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:
1. Pulmonary ventilation: outflow and inflow of air between outside and alveoli.
2. Diffusion of O2 and Co2 between alveoli and blood.
3. Transport to and from tissue
Lung Volumes
IRV
TV
ERV
RV
IC
FRC
VC
TLC
RV
Tidal Volume (TV)
IRV
TV
ERV
RV
IC
FRC
VC
TLC
RV
Volume of air inspired or expired during normal quiet breathing– About 500ml
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
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.
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
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
1. Arterial blood gases2. Blood PH3. Pulse oximeter 4. Peak flow meter measuring peaked
expiratory flow rate.5. Spirometry
Investigation tools used for studying respiratory function
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
1. when he needs an emergency interference. 2. the effectiveness of a person's asthma
management and treatment plan. 3. when to stop or add medication, as directed by
physician. 4. 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