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RTT 215 - Ch. 5 (1)

Ch. 5 - Diffusing Capacity Tests (PFT)

QuestionAnswer
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