Spirometry Flashcards
what is…
Tidal volume
Expiratory reserve volume
Inspiratory reserve volume
Residual volume
Inspiratory capacity
Vital capacity
Functional residual capacity
Total Lung capacity
What are the significant pulmonary structures and pressures?
What are the sequence events during inspiration
- Diaphragm and inspiratory intercostals contract
- Thorax expands
- Pleural pressure becomes more subatmospheric
- Increase in transpulmonary pressure
- Lungs expand
- Alveolar Pressure becomes subatmospheric
- Air flows into alveoli
What is transpulmonary pressure?
Alveolar pressure minus Pleural pressure
(Pleural pressure is negative at rest)
What determines airflow during expiration?
Where is resistance greatest? Least?
When is overall airway resistance least?
Flow= (Palv-Patm)/airway resistance
Resistance greatest at medium sized bronchi, least after terminal bronchioles
overall airway resistance least (or conductance greatest) at larger lung volumes
What is compliance?
Is it higher or lower in Emphysema
Is it higher or lower in fibrosis
Change in volume over change in pressure
Higher compliance in Emphysema
Lower compliance in fibrosis
Why do we measure compliance at points of zero airflow?
Because at zero airflow, alveolar pressure is ZERO. meaning pleural pressure=transpulmonary pressure.
Remember Ptranspulmon=Palv-Ppleural
so Ptranspulmon=Ppleural
This lets us measure compliance of the lungs
For expiration why is there an effort dependent and effort independent portion?
No matter the effort all flows will become the same flow in the effort independent portion. This is because the pressure in the airways dissipates as it meets resistance, to the point where it equals the pressure outside in the thoracic space meaning collapse. So while you may be using more effort and increasing your thoracic pressure to push the air out, you also increase that pushing against the outflow tracts.
What is FEV1?
What is FVC?
How much volume you can get out in 1 second
How much total volume can you get out. Functional vital capacity
What is the general concept of obstructive disease vs. restrictive disease?
Obstructive disease is you can’t get the air out. Restrictive disease is you can’t get the air in.
Where does a Flow volume loop derive from and how?
You take tangents of the Volume time Curve to generate the flow volume loop graph.
For a flow volume loop. What is above the x axis and below. What does each measure?
Above is expiration below is inspiration.
Expiration flow rates: Intra-thoracic airways
Inspiration flow rates: Extra-thoracic airways
Marked decrease in the mid lung volumes are indicative of…
Asthma/issues in the smaller airways. remember the table of airway resistance versus lung volume? Peak at maximal lung volume then dropping w expiration and smaller lung volumes.
Flowrate at 50 percent?
Should be similar for inspiration and expiration. If problems blowing out then ratio between FEF50 and FIF50 will be less than one. If extra-thoracic airway issue, then the bottom curve will become truncated and be much less (shallower).
What do expiratory phase patterns look like for normal vs. obstructive disease vs. restrictive disease?
Obstructive disease will always have lower flow rates and will have scalloping (impaired more at the lower airways because only a little bit of edema or whatever will make much more resistance vs, larger airways.
Restrictive disease will have restricted total lung capacity. (Scarred). So TLC is lower. No disproportionate decrease (no scalloping). Residual volume will be normal and flow rates are maintained.
What are loop patterns and describe:
Fixed obstruction
Variable Extrathoracic
Variable intrathoracic
Fixed obstruction: Upper airway
Variable Extrathoracic: Upper airway but still >4mm of diameter. Expiration not effected.
Variable intrathoracic: Maybe think tumor.
How do you read spirometry?
Look only at FEV1/FVC ratio. FEV1. FVC.
Always look at ratio first.
Ratio of FEV1/FVC must be close to 100% of predicted to be normal. Anything outside 95% confidence interval is low.
how long does it take a normal person to expire FVC
6 seconds
A NOT LOW ratio of FEV1/FVC means what
A LOW ratio of FEV1/FVC means what
Not low-seen in normal ventilatory function and restrictive processes
Low- seen in obstructive processes.
When is a test normal?
When the ratio is within the range of .70-.87 depending on demographics.
AND
if the FVC is normal (> or equal to 80% of predicted wthin the 95% confidence level)
IF the FEV1/FVC ratio is low. How bad is it?
If >70-99% mild
If 60-69% moderate
If 50-59% moderately severe
IIf 34-49% severe
if
(Obstructive Ventilatory Defect)
What patients to check for bronchodilator responsivity?
What is considered bronchodilator responsivity?
Pt. with slow FEV1/FVC ratio or suspected of asthma/COPD
Bronchodilator responsivity is when FVC or FEV1 increases at least 12% AND 200mLs
How do you decide if someone has a restrictive ventilatory defect?
Reduced TLC is the true hallmark.
%predicted TLC, 70% to LLN is mild
%predicted TLC 60-69% is moderate
%predicted TLC
If cannot obtain lung volumes, grade FVC via the obstructive FEV1 criteria. Degree of restriction is based upon percent of predicted FVC.
70 79, 60 69, 50 59, 34 49, less than 34
mild, moderate, moderately severe, sever, very severe
What are the acceptability and reproducibility criteria for spirograms
Acceptability
• Free from artifacts: Cough,
early termination
• Good start: Extrapolated
volume is
0.15 L, whichever is greater
or time to PEF is
• Satisfactory exhalation: 6
sec of exhalation and/or a
plateau in the volume-time
curve
Repeatability
• After three acceptable
spirograms: Are the two
largest FVCs within 0.2 L of
each other? Are the two
largest FEV1s within 0.2 L of
each other?
• If both of these criteria are
not met, test until: Both are
met or a total of 8 tests
• Save the 3 best maneuvers
What are examples of unacceptable spiragrams
Extrapolated volume
hesitation while exhaling
cough
exhalation not completed
