5. Pulmonary Ventilation II Flashcards
Define TIDAL VOLUME (TV)
amount of AIR in a SINGLE INSPIRATION or EXPIRATION
500ml
what is FUNCTIONAL RESIDUAL CAPACITY (FRC)
volume of AIR that REMAINS IN THE LUNGS at the END of NORMAL RESPIRATION
2400ml
what is VITAL CAPACITY (VC)
Volume of AIR that CAN be EXHALED AFTER a MAXIMAL INSPIRATION
4800ml
what is RESIDUAL VOLUME (RV)
amount of AIR REMAINING IN LUNGS After MAXIMAL EXPIRATION
1200ml
what is TOTAL LUNG CAPACITY (TLC)
MAXIMUM VOLUME of AIR in the LUNGS AFTER MAXIMAL INSPIRATION
6000ml
what is AIRFLOW RESISTANCE of
Resistance of the RESPIRATORY TRACT to Airflow during INHALATION/EXPIRATION
- NOT always CONSTANT
eg asthma - increased resistance
AIRFLOW RESISTANCE influenced by
- DIAMETER or Airways
- LAMINAR (smooth) or TURBULENT (irregular) Airflow
what can we use to MEASURE LUNG VOLUMES
- PLETHYSMOGRAPH or ‘BODY BOX’
(not always user friendly) - SPIROMETRY
(SIMPLE, MOST COMMON, can be done at bedside or at home)
what can SPIROMETRY MEASURE
- EFFORT of expiration/inspiration
- AMOUNT/VOLUME of air in/out
- SPEED/FLOW of air that can be inhaled/exhaled
(take deepest breath in, exhale into sensor as hard and fast as possible pref 6 seconds, rapid inhalation)
SPIROMETRY gives us a FLOW VOLUME LOOP
describe how a NORMAL, ACCEPTABLE one should look
Expiratory Phase:
INITIAL RAPID INCREASE IN FLOW (patient emptying larger airways)
LINEAR DECLINE (emptying smaller branches)
Inspiratory: Semi-Circle below
- gives indication of EFFORT
- any OTHER type UNACCEPTABLE
SPIROMETRY also gives a TIME VOLUME CURVE which Gives us..
FEV1 (FORCED EXPIRATORY VOLUME, 1 SECOND)
- volume of air that can be Forcible blown out in 1 second after full inspiration, measured in Litres
FVC (FORCED VITAL CAPACITY)
- volume of air that can be Forcible blown out after full inspiration, measured in Litres
from FEV1, FVC we can get 4 possible SPIROMETRY OUTCOMES:
- NORMAL
- OBSTRUCTION (Obstructive Disease)
- RESTRICTION (Restrictive Disease)
- MIX OBSTRUCTION and RESTRICTION (mix obstructive and restrictive disease)
what is the CRITERIA for NORMAL SPIROMETRY for
FEV1/FVC RATIO, FEV1 Predicted %, FVC Predicted %
FEV1/FVC RATIO: 0.7-0.8
FEV1: Predicted ≥ 80%
FVC: Predicted ≥ 80%
how do you get the FEV1% Predicted and the FVC% Predicted
DIVIDE FEV1/FVC MEASUREMENTS by the AVERAGE FEV1/FVC in the Healthy Population for any person of SIMILAR AGE, HEIGHT, GENDER
what is the CRITERIA for OBSTRUCTIVE DISEASE from Spirometry
- flow-volume loop for Obstructive Disease
FEV1/FVC RATIO: < 0.7
(LESS than 0.7)
- regardless of % Predicted FEV1/FVC
Flow Volume Loop (see image)
- smaller initial increase, rapid decrease and curved off
- CONCAVE shape (curves inwards)
DISEASES associated with Airflow OBSTRUCTION
- COPD (CHRONIC OSTRUCTIVE PULMONARY DISEASE)
- ASTHMA (Uncontrolled)
- BRONCHIECTASIS
- CYSTIC FIBROSIS
CRITERIA for RESTRICTIVE DISEASES from Spirometry
FEV1/FVC RATIO: >0.8
(More than 0.8)
FEV1 % PREDICTED: REDUCED (Less than 80%)
FVC % PREDICTED: REDUCED (LESS than 80%)
FLOW-VOLUME LOOP for RESTRICTIVE Disease
SIMILAR SHAPE to Normal
but SMALLER as reduced volume
(smaller peak, steeper decline to lower volume)
(see image)
DISEASES Associated with RESTRICTIVE Defect
Pulmonary:
- LUNG FIBROSIS
- PNEUMOCONIOSIS (Coal Miner’s lung)
- PULMONARY OEDEMA (Heart Failure)
Extrapulmonary:
- THORACIC CAGE DEFORMITY
- OBESITY
- PREGNANCY
- NEUROMUSCULAR DISORDERS
CRITERIA for MIXED/OBSTRUCTIVE Spirometry
FEV1: LESS than 80% Predicted (REDUCED)
FVC: LESS than 80% Predicted (PREDICTED)
FEV1/FVC RATIO: NORMAL (0.7-0.8)
(obstructive low ratio, restrictive high so balances)
CLINICAL HISTORY also important to differentiate
eg. co-existent COPD and Pulmonary Fibrosis
how is the FLOW VOLUME LOOP when there is UPPER AIRWAYS OBSTRUCTION
BOX-SHAPE
NO initial sharp RISE
slight rise, levels off, convex curve back down at end
(see image)
possible CAUSES for UPPER AIRWAYS OBSTRUCTION
- LARGE GOITRE / ENLARGED THYROID
- LARYNGEAL CARCINOMA / THYROID CANCER
what can we use SPIROMETRY for - PURPOSE in CLINICAL APPLICATION
- DIAGNOSIS of respiratory disease
- provide SEVERITY LEVELS for a number of respiratory conditions (eg COPD)
- Evaluate PROGRESS of respiratory diseases
- TREATMENT Response
possible SIDE-EFFECTS of SPIROMETRY
- feel LIGHT-HEADED
- FACE may go RED
- HEADACHE (increase intercranial pressure)
- FAINTING - reduced venous return or vasovagal attack
- Transient (temporary) URINARY INCONTINENCE (Unintentional PASSING of URINE)
LIMITATIONS of SPIROMETRY
- DEPENDENT on PATIENT COOPERATION and EFFORT
- therefore LUNG VOLUME can be UNDERESTIMATED ONLY (never overestimated)
- usually REPEATED AT LEAST 3 TIMES to ensure Reproducibility, each FVC result within 5% or less than 150ml Variation
- STABLE ASTHMATICS have NORMAL SPIROMETRY RESULT (can only see if uncontrolled) therefore limiting USEFULNESS as DIAGNOSTIC TOOL
- Look at Flow-Volume Loop to assess quality and effort of the test (NOT always available in some commercial spirometers)
because SPIROMETRY is DEPENDENT on PATIENT COOPERATION what does this mean for the LUNG VOLUME
CAN ONLY be UNDERESTIMATED
(NEVER OVERSTIMATED)
why does SPIROMETER have Limited Usefulness as a DIAGNOSTIC TOOL
only detects ASTHMA if UNCONTROLLED
- STABLE ASTHMA has NORMAL RESULT
list some ABDOMINAL WALL muscles that are used for EXPIRATION (as well as INTERNAL INTERCOSTALS)
- RECTUS ABDOMINUS
- INTERNAL and EXTERNAL OBLIQUES
- TRANSVERSUS ABDOMINUS
RESPIRATORY MUSCLE STRENGTH can be ASSESSED by MEASURING…
- MAXIMAL INSPIRATORY PRESSURE (MIP / PImax)
reflects strength of Inspiratory Muscles - MAXIMAL EXPIRATORY PRESSURE (MEP / PEmax)
reflects strength of Expiratory Muscles
how to MEASURE RESPIRATORY MUSCLE STRENGTH (MIP & MEP)
- MECHANICAL PRESSURE GAUGE
seal lips firmly around mouthpiece
MIP / INSPIRATORY MUSCLE STRENGTH:
- Exhale Slowly and Completely
- PULL/SUCK in hard
MEP / EXPIRATORY MUSCLE STRENGTH:
- Inhale Completely
- BLOW as HARD as possible
(see reference values in images)
(higher ranges in males)
(MEP HIGHER than MIP values)
which RESPIRATORY MUSCLES tend to be Stronger (give higher values)
EXPIRATORY
MEP VALUES HIGHER
CLINICAL APPLICATIONS of RESPIRATORY MUSCLE STRENGTH
(PURPOSE)
- DIAGNOSIS of Respiratory MUSCLE WEAKNESS
- Assessment of the SEVERITY of Resp. MUSCLE WEAKNESS
- FOLLOW the COURSE of the Resp Muscle WEAKNESS - PROGRESSION
potential CAUSES of RESPIRATORY MUSCLE WEAKNESS
- NEUROMUSCULAR Diseases
- MND (Amyotrophic Lateral Sclerosis)
- Myasthenia Gravis (at neuromuscular junction)
- Polymyositis (Muscular Inflammation)
- Guillain-Barre Syndrome (Demyelination)
- systemic conditions that affect Skeletal Muscle Strength
- Thyrotoxicosis / Overactive Thyroid
- Malnutrition
what is DIFFUSION CAPACTIY (TLCO / DLCO)
Measures the ABILITY of the LUNGS to EXTRACT OXYGEN FROM INHALED AIR TO PULMONARY CAPILLARIES
DIFFUSION CAPACITY can be determined by which 2 FACTORS
- DIFFUSION
from/across alveoli, into blood capillary, into Hb - HAEMOGLOBIN LEVEL
what does HAEMOGLOBIN have a HIGHER AFFINITY for than OXYGEN
CARBON MONOXIDE
- 210 X Greater affinity
(CO also surrogate for O2)
what can be a SURROGATE MARKER to MEASURE DIFFUSION CAPACITY
UPTAKE of CARBON MONOXIDE (CO) by HAEMOGLOBIN
how to MEASURE DIFFUSION CAPACITY
- BLOW OUT all air possible, LEAVING only RESIDUAL LUNG VOLUME
- INHALE Quickly GAS MIXTURE of 0.3% CO, 10% HELIUM,
(CO surrogate for O2) - HOLD BREATH for 10 SECONDS
- Helium is Freely Distributed throughout Alveolar space but DOES NOT CROSS ALVEOLAR/CAPILLARY MEMBRANE
- CO continuously MOVES from ALVEOLI INTO BLOOD
- EXHALES and EXHALE GAS ANALYSED
- measure DIFFERENCE in CO and HELIUM CONCS. in INSPIRED and EXPIRED GAS
how is DIFFUSION CAPACITY (TLCO) Reported
as mL/min/mmHg
as a PERCENTAGE OF A PREDICTED VALUE
what can AFFECT TLCO (diffusion capacity) RESULTS from test
CIGARETTES - HIGH CO
- can lead to falsely high TLCO
DO NOT SMOKE for at least 4-6 HOURS BEFORE the test
what is the NORMAL reference range for DIFFUSION CAPACITY (TLCO)
76 - 140 %
CLINICAL APPLICATIONS.
OBSTRUCTIVE LUNG DISEASES (FEV1/FVC RATIO < 0.7)
how is TLCO for EMPHYSEMA? CHRONIC BRONCHITIS? UNCONTROLLED ASTHMA?
Emphysema:
- REDUCED TLCO
(TLCO excellent index for the DEGREE of anatomical emphysema on CT scan)
Chronic Bronchitis:
- NORMAL TLCO
Uncontrolled Asthma:
- NORMAL or HIGH TLCO
CLINICAL APPLICATIONS.
RESTRICTIVE LUNG DISEASES (FEV1/FVC RATIO > 0.8)
how is TLCO for
Pulmonary Causes - LUNG FIBROSIS, OEDEMA?
Extrapulmonary Causes - THORACIC CAGE DEFORMITY, OBESITY, PREGNANCY, NEUROMUSCULAR DISORDERS?
Pulmonary Causes - LUNG FIBROSIS, OEDEMA:
- REDUCED TLCO
Extrapulmonary Causes - THORACIC CAGE DEFORMITY, OBESITY, PREGNANCY, NEUROMUSCULAR DISORDERS:
- NORMAL TLCO
When can you have INCREASED TLCO
- ASTHMA
- POLYCYTHEMIA (high conc. RBCs in blood)
- PULMONARY HAEMORRHAGE (Bleeding in lungs, blood binds to O2)
- LEFT-TO-RIGHT INTRACARDIAC SHUNTING
- EXERCISE
what is TRANSFER COEFFICIENT (KCO) and what is the CALCULATION for it
TLCO CORRECTED for ALVEOLAR VOLUME
KCO = DLCO / VA
TRANSFER COEFFICIENT = DIFFUSION CAPACITY (DLCO/TLCO) /
ALVEOLAR VOLUME (VA)
(Proportion of the Alveolar Volume that is able to Diffuse into capilarries)
VA is ALVEOLAR VOLUME AFTER MAXIMAL INHALATION
( TLC approx 6000 ml)
what is TRANSFER COEFFICIENT (KCO) and what is the CALCULATION for it
TLCO CORRECTED for ALVEOLAR VOLUME
VA is ALVEOLAR VOLUME AFTER MAXIMAL INHALATION
( TLC approx 6000 ml)
KCO = DLCO / VA
TRANSFER COEFFICIENT = DIFFUSION CAPACITY (DLCO/TLCO) /
ALVEOLAR VOLUME (VA)
(Proportion of the Alveolar Volume that is able to Diffuse into capilarries)
effect of VA DECREASE on KCO eg in PNEUMONECTOMY
DECEREASED VA
-> INCREASED KCO
(smaller division of DLCO)
eg. pneumonectomy, VA decreases due to dicrete LOSS of alveolar units. Blood Diverted to remaining lung
Effect of VA DLCO REDUCTION on KCO eg. in PE (blood clots)
DLCO DECREASE
VA NORMAL
-> DECREASE KCO
(division of a SMALLER Numerator)
due to impairment of alveolar/capillary interface
what is the ALVEOLAR-ARTERIAL GRADIENT (A-a GRADIENT)
DIFFERENCE between :
the ALVEOLAR CONC. of O2 (A)
and
ARTERIAL CONC. of O2 (a)
what is the ALVEOLAR-ARTERIAL A-a GRADIENT used for
to Determine the REASONS for HYPOXIA (LOW OXYGEN)
/ DIAGNOSING the SOURCE of HYPOXEMIA
how do ALVEOLAR OXYGEN (PAO2) and ARTERIAL OXYGEN (PaO2) DIFFER
ALVEOLAR OXYGEN ALWAYS HIGHER (PAO2)
by at least 5-10 mmHg
even in a healthy person
A-a GRADIENT can either be…
ELEVATED or NORMAL
ELEVATED A-a gradient suggests DEFECT in DIFFUSION
eg. in ventilation perfusion MISMATCH such as PE (pulmonary embolism) ELEVATED A-a gradient as oxygen not effectively transferred from alveoli to book
- in high Altitude, NORMAL A-e gradient
ARTERIAL LOW only because ALVEOLAR LOW
CHANGES in VENTILATION during EXERCISE
VENTILATION INCREASES
- due to INCREASED TIDAL VOLUME and RESPIRATORY RATE to meet INCREASED OXYGEN DEMANDS
- MINUTE VENTILATION might INCREASE from resting values 5-6 l/min
to > 100 L/MIN - OXYGEN CONSUMPTION INCREASES LINEARLY with increasing work rate
until VO2 MAX ACHIEVED
what is VO2 MAX
and how is it expressed
MAXIMUM amount OXYGEN that an individual CAN UTILISE during PEAK EXERCISE
- expressed as ml/kg/min
(ML of O2 used in 1 MINUTE per KG of BODYWEIGHT)
VO2 MAX is determined by which 3 FACTORS
(LIMITED BY..)
- MAXIMUM ABILITY of CARDIOVASCULAR System to DELIVER OXYGEN TO Exercising Skeletal MUSCLE
- the ABILITY of EXERCISING MUSCLE to EXTRACT OXYGEN FROM BLOOD
- INCREASE EXERCISE ENDURANCE
How to measure VO2 MAX
- GRADED EXERCISE TEST eg. treadmill, stationary exercise bike
-exercise INTENSITY progressively INCREASED
- MEASURE VENTILATION, O2, CO2 conc. of inhaled and exhaled air
- VO2 MAX ACHIEVED when OXYGEN CONSTUMPTION remains at STEADY STATE
despite INCREASING WORK LOAD
(increases and then levels off - VO2 max)
VO2 MAX is the MOST objective assessment of FUNCTIONAL CAPACITY in patients with…
CHRONIC HEART FAILURE (CHF)
- LOW VO2 MAX (less 50% predicted) lower survival (less chance 2 year survival)
(therefore should be considered for transplantation)
if higher than 50% predicted, higher rates survival
