Exam 3 - PFT's Flashcards
How can you solve for concentration of a gas in a system?
[gas] = PPgas ÷ Ptotal
Ptotal is always 760 mmHg
What is normal PAN2?
569 mmHg
What is the Fowler Test measuring?
How does it work?
- Anatomical dead space
- The pt breathes 100 % O2, and then exhales. The first part of the exhalation should only contain O2 (dead space)
- As the person exhales longer, N2 begins to show up from the alveolar volume
- The amount of dead space is measured as the half way point between when N2 begins to show up, until the N2 percentage plateaus
Why is knowing anatomical dead space important?
- It contributes to how much Vt they require
- Tall people have an increased anatomical dead space, but still require 350 mL of alveolar ventilation
- So, they would need an increased Vt to obtain an adequate alveolar ventilation
What is the normal alveolar N2 concentration?
569 mmHg ÷ 760 mmHg = 75 %
What does the Nitrogen Washout Test measure?
The “evenness” of ventilation
How does the Nitrogen Washout Test work?
- The patient inspires 100 % O2 and the percent of N2 expired is measured with each exhalation
- Each exhalation should have a reduction in N2 content due to dilution by O2
- The test is stopped when N2 % is around 2.5%
- In a normal pt, this should happen in much less than 7 mins
When does the greatest reduction in N2% occur during the Nitrogen Washout Test?
During the first breath
What does this graph of a nitrogen washout test tell you?
- This is a normal test = even ventilation
- The y-axis is logarithmic, meaing more N2 is expired at the beginng and less at the end
What does this graph of a nitrogen washout test tell you?
- The expired N2 is not occuring in an even fashion, which is abnormal
- This means oxygen is going to all different places in the lung causing the nitrogen to be diluted at an uneven rate
- This is hallmark of an unhealthy lung (could be from large lungs with normal Vt; takes longer to washout N2; COPD)
What is flow volume loop measuring?
The airspeed and volume of a maximum effort vital capacity breath
What is the pattern of airflow speed during expiration on a flow volume loop?
Airflow speed peaks at >10 L/s in a healthy person and then begins to slow as the volume reaches RV
What is effort dependence and indepence describe on flow volume loop?
Effort dependence: airflow speed during exhaltion changes with the amount of effort provided by the patient (more effort = faster airflow)
Effort independence: as lung volumes get close to RV, airflow cannot be increased, despite an increased effort
When is the fastest rate of expiration and exhalation in volume flow loops?
- Expiration: half way through vital capacity volume
- Inspiration: skewed toward the left, less than half way of vital capacity volume
What happens to expiratory time in unhealthy patients?
Expiration takes longer
What is peak expiratory flow reliant on?
- Elastic recoil pressure (30 cmH2O normally)
- Pleural pressure: positive during forced expiration
What 2 things causes the very positve intrapleural pressure seen on forced expiration?
- Contraction of internal intercostal muscles (on the inside of rib cage and pulls ribs closer together to decrease volume)
- Contraction of abdominal muscles
What happens to elastic recoil under anesthesia?
Considerations?
- Decreased d/t paralysis and positive pressure
- Probably need to allow for a longer expiratory time on the ventilator
What would the expiratory flow volume loop look like for obstructive disease?
- The peak expiratory flow is decreased due to loss of ER
- Independent effort of expiration is abnormal
- Vital capacity is decreased d/t an increased RV (lungs are easier to fill, but they cannot exhale a normal volume)
RV is right blue line crossing x-axis, TLC is left blue line crossing x-axis
What would the expiratory flow volume loop look like for restrictive disease?
- Max expiratory airflow is decreased d/t decreased inspiratory volume (less full, less airflow speed)
- Increased ER decreases lung volumes
- Decreased vital capacity
RV is right blue line crossing x-axis, TLC is left blue line crossing x-axis
What does size of vital capacity tell us about lung disease severity?
Usually, the smaller the VC, the more severe the disease
What is the common name for these curves?
FVC - Forced Vital Capacity
