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RTT 215 - Ch. 5 (1)
Ch. 5 - Diffusing Capacity Tests (PFT)
| Question | Answer |
|---|---|
| what is diffusing capacity also referred to as? | transfer factor |
| what is DLCO used to assess? | gas-exchange ability of lungs, specifically oxygenation of mixed venous blood |
| what is the most common DLCO method and most standardized method? | single-breath DLCO |
| what does DLCO measure? | transfer of diffusion-limited gas (CO) across the alveolocapillary membranes |
| what is DLCO reported in? | mL of CO/min/mm of mercury at 0 degree C, 760 mmHg, dry |
| CO combines with hemoglobin approximately ____ times more readily than O2. | 210 |
| in the presence of normal amounts of Hb and normal ventilatory function, what is the primary limiting factor to diffusion of CO? | status of the alveolocapillary membranes |
| what are the 2 components that the process of conductance across the membranes can be divided into? | 1. membrane conductance (DM) 2. chemical reaction b/t CO and Hb |
| what does DM reflect? and what does the uptake of CO by Hb depend on? | process of diffusion across alveolocapillary membrane; reaction rate/pulm capillary blood vol |
| what factors can diffusing capacity be affected by? | factors that change the membrane component, alterations in Hb, capillary blood volume |
| basically, what is the pressure gradient causing diffusion? | alveolar pressure |
| what is the equation that all methods of DLCO are based on? | DLCO = VCO/(PACO-PCCO) |
| what does the pt do in the single-breath technique? | exhales to RV, inspires a VC breath ("IVC" or "VI") |
| what does the diffusion mixture usually contain? | 0.3% CO, "tracer" gas, 21% O2, balance is N2 |
| what is usually the tracer gas? | insoluble, inert gas (He, methane, neon) |
| what are used to detect changes in CO? | rapidly responding infrared analyzers; gas chromatography |
| how much should the pt ideally inhale of the VC? | 90% within 2.5-4 secs |
| after inspiring the VC breath, how long does the pt hold the breath at TLC? | 10 secs, exhales within 4 secs |
| after a suitable ________ _______ (750-1000 mL) has been discarded, a sample of _________ ____ is collected in a small bag or by continually aspirating a sample of the exhaled gas. | washout volume; alveolar sample |
| what is the sample analyzed to obtain? | fractional CO and tracer gas concentrations in alveolar gas, FACO2, and FAtracer |
| the concentration of CO in the alveoli at the beginning of the _______ _____ must be determined as well. | breath hold |
| what does the change in the tracer gas concentration reflect? | dilution of inspired gas by the gas remaining in the lungs (RV) |
| what is this change used to determine? | CO concentration at beginning of breath hold, before diffusion from alveoli into pulm capillaries |
| what are the two times the dilution of the tracer gas is used? | 1. CO concentration at beginning of breath hold 2. determine lung vol where breath hold occurs |
| what is the difference in the amount of the CO between inspiration and expiration? | diffusion of gas thru the alveolocapillary membrane |
| the tracer gas and CO analyzers may be calibrated to real ____ ______ when sampling the diffusion mizture, and to read _____ when sampling air. | full scale; zero |
| if the analyzers have a linear response to each other, the fractional concentration of the tracer gas in the alveolar sample is equal to the ______. | FACO0 |
| systems that use the same detector for both CO and the tracer gas also need to provide _______ _______. the linearity of the system should be within ____% of full scale. | linear output; 0.5% |
| _______ _______ uses specialized infrared analyzers capable of detecting several gases simultaneously. what do these systems use as a tracer gas? | multigas analysis; methane |
| what is one advantage of multi-gas analysis? | CO and CH4 (methane) are measured rapidly and continuously |
| what tracer gas is used for gas chromatography? carrier gas? | neon; helium |
| gas chromatography is slow (60-90 secs), but is extremely __________. | accurate |
| what should the resistance of the breathing circuit be? | <1.5 cmH2O/L/sec, at a flow of 6 L/sec |
| what is used instead of a reservoir bag for the test gas? what should the maximal inspiratory pressure to maintain flow at 6 L/sec be in a demand-flow system? | demand valve; <10 cmH2O |
| the ______ method of timing the breath hold hsould be used. what does this method measure? | jones; breath-hold time from 0.3 of the I time to the midpoint of the alveolar sample collection |
| what should anatomic dead space be calculated as? | 2.2 mL/kg IBW |
| instrument VD should not exceed _____ mL for adult subjects. | 350 |
| what is anatomic and instrument VD subtracted from before the alveolar vol is calculated? | inspired volume |
| all gas volumes must be corrected from _____ to _____ for DLCO calculations. | ATPS; STPD |
| accurate measurement of inspired vols during the maneuver requires that the spirometer have an accuracy of ____% over a range of __ L. | 3.5%; 8 |
| what is absorption of CO2 usually accomplished with? | chemical absorber using baralyme or soda lyme (each produce water vapor) |
| __________ _____ is commonly used to remove water vapor. what is also used to establish water vapor content? | anhydrous CaSO4; selectively permeable tubing |
| when should DLCOsb maneuvers be performed? | after pt has been seated for 5 minutes |
| why should pt refrain from exertion immediately before the test? | exercise increases CO (increases DLCO) |
| how long should expiration to RV be? how should inspiration to TLC be? | usually 6 secs or less; rapid but not forced |
| healthy subjects and pts with airway obstruction should be able to inspire at least ___% of their VC within __ seconds. | 85%; 4 |
| what does the single-breath calculation assume? | instantaneous filling of the lung |
| what should the pt avoid excessiveness of? | positive intrathoracic pressure (valsalva maneuver) or negative intrathoracic pressure (muller maneuver) |
| what might the valsalva/muller maneuver cause the DLCO to do? | valsalva - decrease DLCO; muller - increase DLCO |
| exhalation should take less than __ secs and alveolar gas sampling should occur in less than __ secs. | 4; 3 |
| how long should the breath-hold time, measured using the hones method be? | 10 secs +/- 2 secs |
| what is one of the most common problems encountered when performing the DLCOsb maneuver? | failure to inspire 85% of previously measured VC |
| to obtain an alveolar sample, _____ _____ gas needs to be washed out. what is usually a sufficient washout time? what about with small VCs? | dead space; 0.75-1.0 L; 0.5 L |
| what is the sample volume size? | 0.5-1.0 L |
| alveolar sampling may be adjusted to begin at the point where the tracer gas and CO indicate an "________ ________." | alveolar plateau |
| ____ or more DLCOsb maneuvers should be averaged. duplicate determinations should be within __ mL CO/min/mmHg of each other, or within ___% of the largest value obtained | two; 3; 10% |
| why should no more than 5 repeated maneuvers be performed? | b/c of the effect of increasing COHb from inhalation of the test gas. |
| how long of a delay should be b/t repeated maneuvers to allow for washout of the tracer gas from the lungs? | 4-minute |
| the predicted DLCO should be corrected so that it reflects the DLCO at an Hb value of ____g% for adult and adolescent males, and to an Hb value of ____g% for women/children of either sex younger than 15. | 14.6; 13.4 |
| what does DLCO vary inversely with? | changes in alveolar O2 pressure (PAO2) |
| what does the pt do during the rebreathing technique? | rebreathes from a reservoir containing 0.3% CO, tracer gas, and air; 30-60 secs at 30 breaths/min |
| the rebreathing method can be used during ________. | exercise |
| what happens during the slow exhalation single-breath-intrabreath method? | pt inspires a VC breath of test gas containing 0.3% CO, 0.3% CH4, 21% O2, & balance N2 |
| what does the pt do during this method? | exhales slowly and evenly at approximately 0.5L/sec from TLC to RV |
| ____ is used as the tracer gas because it can be rapidly measured using an infrared analyzer. | CH4 |
| the _________ _______ can also be used during exercise. | intrabreath method |
| what is done during the membrane diffusion coefficient and capillary blood volume method? | pt performs 2 DLCOsb tests, each at a different level of alveolar PO2 |
| what can measurement of diffusion of CO at different levels of alveolar PO2 be used for? | distinguish resistance caused by alveolocapillary membrane from resistance caused by RBC membrane/Hb reaction rate |
| the membrane component of resistance to gas transfer can also be estimated by measuring the rate of uptake of ______ ______. | nitric oxide |
| what is DLNO a direct measure of? | conductance of alveolocapillary membrane |
| NO combines with Hb approximately ____ times faster than CO. | 280 |
| DLNO reflects the ________ __________ to gas diffusion in the lungs. | membrane resistance |
| the avg DLCO value for resting adult pts by the single-breath method is approximately ___ mL CO/min/mmHg (STPD) with significant variability. | 25 |
| DLCO is often decreased in _________ lung disorders, particularly pulmonary fibrosis. | resistrictive |
| what are other causes of decreased DLCO? | pulmonary edema; medical/surgical intervention for cardiopulmonary disease; radiation therapy; chemo drugs; inhalation of toxic gases |
| what is DLCO in CHF? | early stage - normal or increased; most times decreased |
| what is an exception to the extent of reduction being directly proportional to the vol of lung removed? | lung volume reduction surgery and bullectomy |
| DLCO is commonly used to monitor _____ ________. | drug toxicity |
| DLCO may be helpful in evaluating disorders such as ____________ syndrome. | hepatopulmonary |
| decreases in DLCO are termed _________ _______. | diffusion defect |
| what is the steady state (filey) technique? | breath a gas mixture of 0.1%-0.2% CO in air for 5-6 mins; last 2 mins expired gas collected in bag/balloon; ABG drawn |
| what is exhaled volume measure and analyzed for? | CO, CO2, O2 |
| what is the calculation of steady diffusing? | DLCOss= VCO/PACO |
| DLCO may be decreased in both acute and chronic ____________ lung disease, like __________. | obstructive; emphysema |
| DLCO measurements at rest have been suggested to estimate the probability of ___ ___________ during exercise. | O2 desaturation |
| what is DLCO directly related to in healthy individuals? | lung volume |
| what can analysis of this relationship help to determine? | whether a decrease is due to loss of lung volume (restriction) or from uneven V/Q (obstruction) |
| in healthy subjects, DL/VA is __-__ mL of CO transferred/min/L of VA. | 4-5 |
| how is VA measured? | by the dilution of the tracer gas used |
| what is the advantage of the intrabreath method? | not requiring a breath hold at TLC |
| what indicates a restrictive cause of decreased DLCO? obstructive cause? | decreased without a reduction in VA; if DLCO and DL/VA are decreased |
| what are 7 other physiologic factors that can influence the observed DLCO? | 1. Hb/Hct 2. COHb (increases reduce DLCO) 3. alveolar PCO2 4. pulmonary capillary blood vol 5. body position (supine increases DLCO) 6. altitude about sea level 7. asthma/obesity |
| what are the 3 methods to measure breath-hold time? | 1. jones method 2. epidemiology standardization project method (midpoint of I to beginning of alveolar sampling) 3. ogilvie method (beginning of I to beginning of alveolar sampling) |
| a ______-_________ _______ has been proposed that uses separate equations for the three phases of the maneuver. | three-equation method |
Created by:
christa_2008
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