MVV - Maximum Voluntary Ventilation Flashcards
What is the definition of MVV?
the largest tidal volume and rate that can be breathed per minute by voluntary effort
How is a MVV test performed?
- patient is told to breathe in and out as fast as possible until told to stop
- performed for 12-15 seconds
What does MVV measure?
the muscular mechanics of breathing
What does it mean if a patient has a decreased MVV?
- obstructive disease (increased Raw)
- muscle weakness
- decreased compliance
- poor patient effort
What does predicated normal values mean?
all values are compared with the predicted normal values for that individual
How are predicted normal values expressed?
as percents. actual value / predicted value = % of predicted
What are predicted normal values primarily based on?
- age
- height
- sex
What is the predicted percent range for a normal PFT?
80-100
What is the predicted percent range for a mild disorder PFT?
60-79
What is the predicted percent range for a moderate disorder PFT?
40-59
What is the predicted percent range for a severe disorder PFT?
<40
What does it mean if a patient has a volume measurement (FVC) that is decreased (i.e. 65% of predicted)?
there is a mild restrictive problem
What does it mean if a patient has a flow measurement that is 83% of predicted?
there is no obstructive problem
What does it mean if a patient has a volume measurement that 80+% of predicted?
there is no restrictive problem
What does it mean if a patient has a flow measurement that is 44% of predicted?
there is a moderate obstructive problem
What He dilution?
- closed method
- initially no He in patient’s lungs. give patient a known % of He dilution. change in He% is used to determine FRC
How long should a Helium dilution procedure last for both healthy and small patients?
~2-5 minutes
Helium concentration on system stabilizes and does not fluctuate more than ___ during a ___ period
.02; 30 seconds
What criteria would cause you to stop a helium dilution procedure if it is not yet finished?
- system leak
- patient unable to continue
What is nitrogen washout?
- open method
- the FRC is washed our of the lung by having patient inspire 100% O2
- the FRC goes into a collecting spirometer and is measured to calculate it
How long should a nitrogen washout take in normal lungs?
~2-5 minutes
What does a nitrogen washout time of 7 minutes indicate?
poor distribution
What should you make sure you do before performing a nitrogen washout?
discontinue supplemental O2
How does a leak affect the FRC in both helium and nitrogen tests?
- FRC is artificially raised
- equilibration may not occur
What is the plethysmopgraph/body box?
- aka thoracic gas volume (TGV) or BP
- uses boyle’s law to determine TGV (P1V1 = P2V2)
What does the plethysmopgraph/body box do?
measures gases trapped and otherwise excluded from the FRC with the other procedures
In healthy subjects, TGV ___ FRC
equals
How is a BP test performed?
- patient performs open-glottis panting 1-2 breaths per second
- shutter is suddenly closed at end-expiration
- panting continues against a closed shutter
- airflow is not possible against a closed shutter
Airflow is not possible against a closed shutter, thus mouth airway pressure ___ alveolar pressure
equals
How is airway resistance measured?
measure the changes in pressure vs flow in the body box
What is normal airway resistance?
0.6-2.8 cmH2O/L/sec
How is compliance determined?
by volume change per unit pressure change (60-100 ml/cmH2O)
What two primary parameters are used for calibration of the body box?
- pressure verified with a mercury or water manometer
- flows verified with a rotameter
What are the advantages of the body box?
- TGV not affected by lung ventilation
- quicker test
- easily repeatable
What are the disadvantages of the body box?
- patient may be unable to enter box due to physical limitations
- claustraphobia prohibits patient from entering box
- patient may be unable to pant acceptably
What must specific things are calibrated during your calibration of the BP?
- mouth pressure transducer
- flow transducer
- cabinet pressure transducer
What is the purpose of a gas analyzer?
- determine FRC
- measures DLCO
What are the methods of calibration?
- utilize known gas value
- mechanical lung analog
- test known subjects
What is the known gas values calibration method?
- utilizes different precise gas values
- high concentration of gas source
- high concentration diluted with room air (accuracy, linearity)
What is the mechanical lung analog method?
calibrated syringe with known constant and known variable lung volumes
What is biological testing?
- calibration by using a person who gets similar lung volumes each time
- pretty common component of quality control
What are the two names of oxygen analyzers?
- galvanic (fuel cell)
- polarographic (clark electrode)
What is the name of the helium analyzer?
wheatstone bridge (thermal conductivity)
What is the name of the nitrogen analyzer?
geisler tube ionizer
What is a mass spectrometer used for and what does it measure?
- stress testing
- He, N2, O2, CO2
What is chromatograph or infrared absorption use for and what does it measure?
- DLCO testing
- Ne, O2, N2, CO
How are gas analyzers calibrated to “zero?”
by running a gas through it that is free of that particular gas (i.e. 100% O2 would read 0% on an He or N2 analyzer)
What is a known concentration of a gas used to do during calibration?
set the second or third point of calibration
