Mechanics I: Spirometry and Pulmonary Function Tests- Johnson Flashcards
What is spirometry?
- measure lung capacity/volume
- has to be able to be expelled from the lung to be measured by lung spirometry
- an early diagnostic tool for COPD
What is the leading cause of chronic obstructive pulmonary disease (combination of emphysema and bronchitis)?
SMOKING
What are the 4 different types of lung volume?
- tidal volume
- inspiratory reserve volume
- expiratory reserve volume
- residual volume
What is tidal volume?
- the amount of air that goes into and out of the lungs at a single breath; typically 500 mL
- varies with sex, age, body structure
Air that moves into lung with each quiet inspiration, typically 500 mL
What is inspiratory reserve volume?
- the amount of breath that you take in above the tidal volume to maximally inspire
- you require more muscle than just your diaphragm
Air that can still be breathed in after normal inspiration
What is expiratory reserve volume?
at the end expiration, the amount of air we can force out calling on the abdominal muscles
Air that can still be breathed out after normal expiration
What is residual volume?
the amount of air left over after forced expiration
Air in lung after maximal expiration; RV and any lung capacity that includes RV cannot be measured by spirometry
What are the 4 different lung capacities?
Remember capacities are the sum of 2 or more physiological lung volumes.
- inspiratory capacity
- vital capacity
- functional residual capacity
- total lung capacity
What is inspiratory capacity?
- the amount of air you can take in
- tidal volume plus the inspiratory reserve volume
What is vital capacity?
-the amount of air that can be moved into and out of lung on maximum effort (followed by maximum expiration or maximum inspiration)
TV plus IRV plus ERV (every volume but RV)
Maximum volume of gas that can be expired
after a maximal inspiration
What is functional reserve capacity?
comprised of expiratory reserve volume and residual volume
Volume of gas in lungs after normal expiration
What is total lung capacity?
- vital capacity plus residual volume OR
- all four volumes summed together
What is dead space volume? How is it different from residual volume?
the amount of air that remains in the conducting airway
-does not participate in gas exchange nor does it reach the alveoli (residual volume is in the alveoli)
What constitutes the FRC? What begins at FRC?
- FRC is the combination of residual volume and expiratory reserve volume
- inspiration
this is the amount of air that you have in your lungs at the onset of diaphragmatic contraction waiting for pressure change to occur so that tidal volume will come in; if you decide to inspire above tidal volume you can taking in the inspiratory reserve volume leading to total lung capacity
Simple water-seal spirometer vs. conventional
a drum rotates with a pen that is recording fluctuations in the moving drum; when a person breathes into the spirometer air will fill the chambers
the floating drum is suspended in water and when person breathes in and out, air will fill the chamber getting inspiration and expiration as you are breathing into the machine
this will be detected on the paper for you to calculate lung volumes
Compare plethysmography (body box) with helium dilution.
- these two techniques produce the same results in normal subjects but dissimilar results in patients with obstructive lung disease due to trapped air as a result of premature airway closure
- both measure FRC
What is plethysmography?
- body box measures the amount of AIR REMAINING in the lungs after normal exhalation including gas that gets trapped during premature airway closure; the subject breathes in an airtight box (pt should have a nose piece so there is no escaping of air; air will only go through the mouthpiece into the spirometer)
- trapped air distorts the actual volume and FRC volume would appear to be LARGER
- Boyle’s law indicates that the product of pressure and volume are constant (at a constant temperature)
- pressure transducers detect pressure inside the box and inside the mouth so you can measure volume changes in lung during expiration and inspiration
What is helium dilution technique?
- is used to calculate the FRC
- you cannot expire RV into spirometer so you need to use a known conc of helium
- Known concentration of helium gas, [He] is added to spirometer of a known volume.
- At FRC, the subject is then connected to box; an unknown volume (FRC in the lungs) will be measured.
- [He] plateaus. Concentration in spirometry will be equal to that in the lungs of the subject.
- Results in a new concentration of the inert gas [He] which is measured.
- Subsequently, the change in concentration of the inert gas [He] is used to determine the FRC volume in which the inert gas has been distributed.NOTE: Less accurate measurement than box body; trapped gas due to disease state would result in larger measurement of FRC by body box than the Helium dilution technique (under estimate FRC in OPD patients). Helium equilibration in markedly obstructed airways may not have occurred during the test (long time constant airways).
Why do you to use helium dilution to measure FRC? What is the FRC comprised of?
- FRC is the residual volume and the expiration residual volume which is the one that can be entered into a spirometer
- have to have a known volume of helium
- subject has on a nose piece and they come to a normal expiratory level (not forced) and then the mouthpiece is opened and you allow the gas from the spirometer containing the helium to enter into and equilibrate with the air that is in the lungs—this will be the FRC
- the dilution of the gas from the original concentration will give you the volume that was required to produce the new concentration that is measured; as a result you can calculate the volume in the lung associated with FRC
the person NORMALLY exhales to FRC (if forced you’re measuring RV)
How much nitrogen is in the air?
70-80% percent
What is the nitrogen washout technique?
in this technique you are connected to the FRC
at the start of the lung the subject has 80% of nitrogen in the lungs
then the subject breathes 100% oxygen; the subject does this for a period of time and then you can figure out the FRC
-the concentration of nitrogen in the exhaled gas volume is collected, measured and FRC is calculated
Compare the nitrogen washout in normal vs. abnormal subjects with pulmonary disease
- both have changes in the nitrogen washout
- the relationship of washout is normally linear on a semilog plot unless uneven ventilation occurs in some lung regions (in abnormal subjects with pulmonary disease)
What is the forced vital capacity maneuver?
- a pulmonary function test that can give you indication towards obstructive, and restrictive types of pulmonary disease and that the lung is functioning normally
- person can be sitting or standing
- this is an effort dependent test!; must be repeated a few times to obtain the best reproducible results
- volume of gas vs time graph in which forced expiratory volume in 1 sec is measured which is similar to the forced vital capacity taking a ratio or the two
Vital capacity is the maximum of air that can be inspired or expired in one effort when you are forcefully; it is the maximum volume of gas that can be expired after a maximal inspiration
Compare the ratio of forced expiratory volume in 1 sec to forced vital capacity in normal, obstructive, and restrictive pulmonary subjects.
normal: 80%
obstructive: less than 80% as something is impeding air flow; main issue is time==slow rate
restrictive: the total amount of air you can move in and out of lungs is greatly reduced although the ratio may be normal or greater than 80%===more of a volume issue
What are the 4 major test results you can get from a spirogram with volume to time display?
- forced vital capacity; volume in liters
- the forced expiratory volume in 1 second
- The ratio of the FEV in one second to forced vital capacity
- the average mid-maximal expiratory flow (MMEF) of more commonly referred to as the FEF25-75 is where you will get the majority of air out
What does the expiratory flow volume loop display?
provides an instantaneous flow rate plotted against volume for both inspiration and expiration; it is continuous
Flow rates above the horizontal line in the expiratory flow volume loop are what in lung respiration? What about below the line?
above: expiratory
below: inspiratory
What points represent maximal inspiration and maximal expiration?
- maximal inspiration occurs at TLC
- maximal expiration occurs at RV
Peak expiratory flow rate that occurs within the first second is how much of the total air expired in a normal individual?
80%
FEF25, FEF50, FEF75 are essentially effort independent because of?
dynamic airway closure
What percentage of air is the residual volume that always remains in the lungs?
25%
What are the 3 major determinants of maximal flow during inspiration?
- force generated by the inspiratory muscles; inspiratory force generated is greatest at the RV and then force decreases as lung volume increases above RV
- the increase of static recoil pressure of the lung as the lung volume increases above RV and as lung elastic fibers are stretched
- airway resistance which decreases with increasing lung volume as airway caliber increases
What are the determinants of maximal expiratory flow?
- first 20% of the forced vital capacity maneuver is where maximal amount of air (80%) will come out–this is effort dependent and repeated several times to ensure it is the patient forcing the air out
- effort independent phase when the airways pressure gradients dissipates and the pressure outside the airway will exceed the pressure inside the airway
- At this point, even with increasing effort the flow rate further decreases as lung volume decreases towards RV
80% of the total lung capacity will be expired during the first second. What is this called?
peak expiratory flow rate
T/F. Women have a higher peak expiratory flow rate than men.
False- they have less
FVC and FEV1 peaks
Females ~18; Males ~27
What are the important elements that demonstrate a normal forced vital capacity maneuver?
- rapid rise (peak expiratory flow rate–effort dependent)
- smooth decrease in expiratory flow (effort independent)
- a decrease in flow to the baseline (RV)
What are the values obtained from the forced vital capacity maneuver?
So the patient breathes in as much air as they can and then forcefully expires; a volume vs. time chart is plotted
- FVC (mL; volume)
- FEV in 1 sec (sec; time)
- FEV in 1 sec/FVC (ratio of 80% is indicative of normal lung function
In those with active asthma or emphysema what is seen differently on their spirogram compared to a normal individual?
- higher residual volume: air is being trapped (retained) as there is obstruction
- higher functional residual capacity
- low vital capacity
What is emphysema?
- alveolar air spaces are dilated and there is destruction of alveolar walls
- no elastic recoil of lung as elastic fibers are destroyed
- lung is very compliant (easy to distend but empties slowly due to loss of recoil)
think of old gym shorts that stretch to fit in but don’t tighten back up once in
What is the significance of the diaphragm in a patient with emphysema compared to a normal subject?
- less curvature of the diaphragm
- diaphragm is less efficient at generating pressure
- low pressure gradient and thus reduced air flow
What does the TLC, FRC, and RV values look like for a patient with emphysema?
the patient has a chronic over-inflated lung and thus TLC, FRC, and RV are all high
What does the FEV in 1 sec, FVC, and the FEV1/FVC values look like for a patient with emphysema?
because emphysema is an obstructive disorder, the patient works hard to push air out and thus there is slow rate of air flow (compromised expiratory flow) so FEV, FVC, and FEV1/FVC are all low
What does the volume changes look like in a compliance curve for an individual with emphysema?
volume accumulates over time as the distending pressure increases
What is restrictive lung disease?
a condition marked most obviously by a reduction in total lung capacity; reduction in the elasticity and compliance of the lung tissue due to excess connective tissue; stiff and non-compliant lungs
huge decrease in the total amount of air the lungs normal have (3L compared to normal 5L)
What does the TLC, FRC, RV, FEV in 1 sec, FVC, and the FEV1/FVC values look like for a patient with restrictive lung disease?
low TLC, FRC, RV because you have lower volume of air to begin with
Low FVC but often a NORMAL FEV1/FVC
What is bronchitis?
- chronic cough with mucus production most months of the year
- mucus secretions and continuous inflammation of the bronchi tend to narrow the airways
- obstruction to airflow thus increasing the resistance of the airways
- slow air rate as it is harder to move the air out
What does the FEV in 1 sec, FVC, and the FEV1/FVC values look like for a patient with bronchitis?
low FEV1
low FVC
low FEV1/FVC
due to greater resistance in pushing air out due to obstruction
How can bronchitis RARELY cause a high RV unilike asthma and emphysema (always cause high RV)?
this is because the air flow obstruction found in bronchitis is due to increased resistance, which does not generally cause the airways to collapse prematurely and trap air in the lungs.
What is asthma?
- constriction of the smooth muscle causing significant narrowing of the airway (not in bronchitis)
- edema and mucus production is also present (in bronchitis)
How is asthma’s airway hyper-responsiveness (increase in bronchial smooth muscle tone) reversible?
- bronchodilators/things that cause relaxation of the airways can be used to open up the airways
- you can manage asthma as opposed to emphysema which progresses (is out of your control)
Compare the maximal expiratory air flow, FVC, FEV1 and the FEV1/FVC ratio of an asthmatic to a normal subject. Why are the values as such?
Decreased maximal expiratory air flow, FVC, FEV1 and the FEV1/FVC ratio. The diagnostic is a decreased FEV1/FVC ratio.
Significant effort required to create an extremely negative pleural pressure, and consequently fatigue easily.
Over-inflation also reduces the curvature of the diaphragm, making it less efficient in generating further negative pleural pressure.
What leads to increased airway resistance in asthmatics?
broncho-spasm
-increased smooth muscle tone causes airways to close at abnormally high lung volumes, trapping air behind occluded or narrowed small airways
Describe the inspiration volume, FRC, TLC, and use of muscle in an acute asthmatic.
- breathe at high lung volumes
- exhibit an elevated FRC
- inspire close to TLC
- use accessory muscles of respiration
How does age affect the respiratory system?
increasing age adversely affects the structure and function of respiratory system due to progressive loss of elastic recoil; costal cartilage calcification, decreased intervertebral spaces, and greater spine curvature
Lung function declines with a loss in FEV1 of what volume per year?
~30 mL
Why does FRC increase with age?
decrease in elasticity
What is the significance of decreased expiratory muscle strength during contraction with increasing age?
less force generation for pressure gradients thus decreased air flow
What is the result of ventilation-perfusion mismatch with increasing age?
decreased arterial tension
What contributes to a decrease in PaO2 with increasing age?
- loss of alveolar gas exchange surface
- reduced pulmonary blood flow resulting in decreased diffusion capacity
What is the most important pulmonary function test?
vital capacity which is the maximal amount of of air that a subject can inspire or expire in a single effort
T/F. Pulmonary function tests (spirometry and flow volume loops) can detect abnormalities in function prior to the appearance of symptoms.
TRUE
QUICK NOTES!!!
Obstructive lung disease (OPD) is characterized by high lung volumes (RV increased due to trapped air) and airway resistance and reduced expiratory flow rates. Emphysema is a specific type of COPD, characterized by increased lung compliance.
In OPD, the FEV1/FVC ration is decreased, whereas in restrictive lung disease, the FEV1 and the FVC are proportionately reduced resulting in a normal FEV1/FVC ratio.
Restrictive lung disease is characterized by decreases in lung volume, normal expiratory flow rates and resistance, and a marked decrease in lung compliance.
Events that occur early in the FVC maneuver reflect large airway function and effort dependent.
Events that occur late in the FVC maneuver are indicative of small airway function and effort-independent.
