View
214
Download
0
Category
Tags:
Preview:
Citation preview
Diffusion Capacity of Diffusion Capacity of LungsLungs
DR.LAXMAN KUMAR SONIDR.LAXMAN KUMAR SONI Dept. of Pulmonary Medicine, Dept. of Pulmonary Medicine,
Dr.SNMC , JODHPURDr.SNMC , JODHPUR
Physiology of diffusion Terminology Measurement of diffusion capacity Importance in respiratory diseases
PhysiologyPhysiology
Primary function of lung: gas exchange by Simple passive diffusion followingFick’s law of diffusion
TerminologyTerminology•North America: “Diffusing capacity”historical term
•Europe: “Transfer factor” beacause measurment of CO uptake reflects a no. of process(not just diffusion ) and its submaximal value and thus,not truly a capacity.
Components of diffusion pathway
• Gas space within the alveolus • Alveolar lining fluid – surfactant
rich • Tissue barrier – alveolar capillary
membrane • Plasma layer • Diffusion into and within the RBC • Uptake of CO by hemoglobin
Pathway for diffusionPathway for diffusion
Why CO is preferred?
Gas used for measure diffusion capacity have :
1.Lower solubility in pulmonary membrane and 2.High capacitance in blood. these gases include Oxygen ,NO and CO.
• Oxygen In addition to perfusion oxygen transfer limited by such as ventilation perfusion mismatching , shunting , and there is also accurately measurement of Po2 during capillary transient is very difficult .
• NO NO is highly reactive with oxygen so requires special equipment, and have potential cardiovascular side effect and still NO is under research setting.
CO
Not normally present in alveoli/blood Transfer is diffusion limited rather
than perfusion limited Avidly binds to Hb(210 times of
Oxygen) Less affected by other factors
DLO2=1.23 * DLco
Determinats Of CO uptakeDeterminats Of CO uptake
1/DLCO=(1/DM)+(1/QVc)1/DLCO=(1/DM)+(1/QVc)
DM-Membrane condunctivity(reflects DM-Membrane condunctivity(reflects diffusion properties of alveolar diffusion properties of alveolar capilary membrane)capilary membrane)
Factors affecting carbon monoxide diffusion Factors affecting carbon monoxide diffusion capacity of the lung (DL,CO)capacity of the lung (DL,CO)
Extrapulmonary reduction in lung Extrapulmonary reduction in lung inflation (reduced VA) producing inflation (reduced VA) producing changes in DM or QVc that reduce changes in DM or QVc that reduce DLCO DLCO • Reduced effort or respiratory muscle Reduced effort or respiratory muscle
weakness weakness • Thoracic deformity preventing full Thoracic deformity preventing full
inflation inflation
Diseases that reduce QVc and thus reduce Diseases that reduce QVc and thus reduce DL,CO DL,CO
• Anaemia Anaemia • Pulmonary emboliPulmonary emboli
Other conditions that reduce QVc and thus Other conditions that reduce QVc and thus reduce DL,COreduce DL,CO
• Hb binding changes (e.g. HbCO, increased Hb binding changes (e.g. HbCO, increased
FI,O2) FI,O2) • Valsalva manoeuvre (increased intrathoracic Valsalva manoeuvre (increased intrathoracic
pressure) pressure)
Diseases that reduce (in varying Diseases that reduce (in varying degrees) DM and QVc and thus reduce degrees) DM and QVc and thus reduce DL,CO DL,CO
• Lung resection (however, compensatory Lung resection (however, compensatory
recruitment of QVc also exists) recruitment of QVc also exists) • Emphysema Emphysema • Interstitial lung disease (e.g. IPF, Interstitial lung disease (e.g. IPF,
sarcoidosis) sarcoidosis) • Pulmonary oedemaPulmonary oedema• Pulmonary vasculitisPulmonary vasculitis• Pulmonary hypertensionPulmonary hypertension
Diseases that increase QVc and Diseases that increase QVc and thus increase DLCO thus increase DLCO
• Polycythemia Polycythemia • Left-to-right shunt Left-to-right shunt • Pulmonary haemorrhage (not Pulmonary haemorrhage (not
strictly an increase in QVc, but strictly an increase in QVc, but effectively an increase in lung Hb) effectively an increase in lung Hb)
• AsthmaAsthma
Other conditions that increase QVc and Other conditions that increase QVc and thus increase DLCO thus increase DLCO
• Hb binding changes (e.g. reduced FIO2) Hb binding changes (e.g. reduced FIO2) • Muller manoeuvre (decreased intrathorasic Muller manoeuvre (decreased intrathorasic
pressure as in asthma) pressure as in asthma) • Exercise (in addition, a possible DM Exercise (in addition, a possible DM
component) component) • Supine position (in addition, possibly a slight Supine position (in addition, possibly a slight
increase in DM) increase in DM) • Obesity (in addition, a possible DM component) Obesity (in addition, a possible DM component)
VA: alveolar volume; DM: membrane conductivity; Vc: volume of VA: alveolar volume; DM: membrane conductivity; Vc: volume of pulmonary capillary bloodpulmonary capillary blood
Physiological Factors influencing DLCOPhysiological Factors influencing DLCO
Hb levelHb level
DLCO directly correlates with Hb DLCO directly correlates with Hb
1g/Dl decrease Hb – 4% decrease DLCO1g/Dl decrease Hb – 4% decrease DLCO
1g/Dl increase Hb – 2% increase DLCO1g/Dl increase Hb – 2% increase DLCO
COHb levelCOHb level Increase in COHb reduces DLCO in two ways Increase in COHb reduces DLCO in two ways
• Decreases available binding sites on Hb Decreases available binding sites on Hb
• Reduces differential driving Pressure across ACM Reduces differential driving Pressure across ACM
1% Increase in COHb decreases DLCO by 1% 1% Increase in COHb decreases DLCO by 1%
Alveolar volume (VA) •increase in LV - increase in DLCO
expansion of lung - thinning of ACM, increase
in diameter of corner vessels
therefore correct DLCO for volume•KCO=DLCO/VA ( KCO-trasfer cofficient of lung)
Ex.. COPD, Asthma (“increased” DLCO)
Circadian rhythm DLCO drops 1-2%/hr between 9.30am-9.30pm
Gender & Ethnicity lower in women for a given height lower in African-Americans, Asians
Body size: DLco varies with BSAbetter predicted by height & weight 2DLcO=BSA(M) (18.84) -6.8
Age: DLco declines in linear fashion with age
Exercise 30-40% increase recovery after high-intensity ex - 24 hrs
Body position increase on supine
Menstrual cycle highest just before, least 5-10 days after
Measurement of diffusing capacityMeasurement of diffusing capacityMethods Single breath-holding method Single expiration method Rebreathing method Steady state method Riley-Lilienthal method
Indications Specific indications not defined
• variety of testing procedures in use• complexity of physiologic determinants
of CO uptake Most commonly used in evaluation of
• diffuse interstitial lesions• suspected emphysema• pulmonary vascular obstruction
Useful in diagnosis as well as follow up
Single breath method
• Most widely used and best standardized of the various methods
ProcedureProcedure Unforced exhalation to RVUnforced exhalation to RV
(limited to 6 seconds)(limited to 6 seconds)
Rapid inhalation of a diffusion gas mixture to Rapid inhalation of a diffusion gas mixture to TLC TLC (from spirometer/demand valve/reservoir)(from spirometer/demand valve/reservoir)• 0.3% CO0.3% CO• 10% He 10% He (tracer gas)(tracer gas)• 21% O221% O2• Balance NitrogenBalance Nitrogen
Breath hold at TLC for 10 Breath hold at TLC for 10 +/-+/- 2 seconds 2 seconds
Rapid exhalationRapid exhalation(should not exceed 4 sec)(should not exceed 4 sec)
Alveolar gas is collected after a washout Alveolar gas is collected after a washout volume (0.75-1.0 L) has been discardedvolume (0.75-1.0 L) has been discarded(If VC is <2.0 L, washout volume may be reduced to 0.50L)(If VC is <2.0 L, washout volume may be reduced to 0.50L)
Sample gas volume should be 0.50 – 1.0 LSample gas volume should be 0.50 – 1.0 L(If VC <1.0L, a sample of <0.50L can be analyzed if deadspace (If VC <1.0L, a sample of <0.50L can be analyzed if deadspace volume has been cleared)volume has been cleared)
Sample is analyzed for the fractional CO and He Sample is analyzed for the fractional CO and He (tracer (tracer gas)gas) concentration concentration
Change in He concentration reflects dilution by gas in lungs at RVChange in He concentration reflects dilution by gas in lungs at RV
This change is used to determine the initial CO concentrationThis change is used to determine the initial CO concentration
Summary of the procedureSummary of the procedure
Spirometry, lung volumes
Acceptability CriteriaAcceptability Criteria Volume-Time tracing should show smooth, Volume-Time tracing should show smooth,
rapid inspiration rapid inspiration (<4 sec) from RV to TLC(<4 sec) from RV to TLC
Expiration should be rapid Expiration should be rapid but not forced; 4 but not forced; 4 seconds or lessseconds or less
Dead space washout should be 0.75 – 1.00 L Dead space washout should be 0.75 – 1.00 L (0.5 L if VC is less than 2.0 L)(0.5 L if VC is less than 2.0 L)
Alveolar sample volume should be 0.5 to 1.0 LAlveolar sample volume should be 0.5 to 1.0 L
Inspired volume should be at least Inspired volume should be at least 85% 85% of of previously recorded best VCpreviously recorded best VC
Breath hold time should 10 sec +/- 2 sec (No Breath hold time should 10 sec +/- 2 sec (No Valsalva or Mueller maneuver)Valsalva or Mueller maneuver)
Expiration in <4 s (and sample collection time Expiration in <4 s (and sample collection time <3s)#, with appropriate clearance of VD and <3s)#, with appropriate clearance of VD and proper sampling/analysis of alveolar gas proper sampling/analysis of alveolar gas
The average of two or more acceptable test The average of two or more acceptable test should be reported. Duplicate determinations should be reported. Duplicate determinations should be within 10% of highest value or 3 ml should be within 10% of highest value or 3 ml CO/min/mm HgCO/min/mm Hg
Repeatability and Number ofTests
Obtain at least 2 acceptable tests Repeatability requirement – 2 acceptable
tests• within 3 units, OR• 10 % of the highest value
Report the average of 2 acceptable tests that meet repeatability requirement
More than 5 tests are not recommended
Eur Respir J 2005; 26: 720–735
• Average DLAverage DLcocosb valuesb value
25 ml CO/min/mm Hg (STPD)25 ml CO/min/mm Hg (STPD)
Inspiratory maneuver 14%He, 18%O2, 0.27%CO)
breathhold
Deadspace washout(0.75 L)If VC<2L, reduce to 0.5L
Sample collection volume0.5-1LIf VC<2L, reduce to 0.5L
AdvantagesAdvantages
No invasive measuring proceduresNo invasive measuring procedures Analysis of only two gases is requiredAnalysis of only two gases is required Test is easily and rapidly performedTest is easily and rapidly performed
DisadvantagesDisadvantages
Difficult breathing maneuverDifficult breathing maneuver Not practical during exercise testingNot practical during exercise testing Less than maximal inspired VC Less than maximal inspired VC
volumes affect measurement volumes affect measurement accuracyaccuracy
V/Q mismatches can affect the V/Q mismatches can affect the resultsresults
Calculation of DLCOCalculation of DLCO
DLCO = VA X ln FACOi
T X (PB-47) FACOF
T = time of breath holdPB = barometric pressure47 = water vapour pressure at 37oC
KCO = DLCO VA
Technical factors influencing DLCO
PIO2• Inversely related• DLCO increases by 0.31% per mm Hg decrease in PIO2• USA:FiO2 0.21• Europe: FiO2 0.17• Discontinue suppl. O2 > 5 min before procedure
Other Technical variables
•Inspired volume•Duration and condition of breath hold•Deadspace washout volume•Method of gas analysis•Method of measuring VA
Equipment quality controlEquipment quality control
Gas-analyser zeroing Done Gas-analyser zeroing Done before/after each test before/after each test
Volume accuracy Tested daily Volume accuracy Tested daily Standard subject or simulator testing Standard subject or simulator testing
Tested at least weekly Tested at least weekly Gas-analyser linearity Tested every 3 Gas-analyser linearity Tested every 3
months months Timer Tested every 3 months Timer Tested every 3 months
Reporting
Average of at least 2 acceptable and repeatable tests
Report includes:• Measured DLco• Predicted and percent predicted DLco/VA or
Kco• Any adjustments for Hb, COHb or VA
If using continuous analyzers, manual adjustments must be noted on report so interpreter can review and verify the adjustments
Eur Respir J 2005; 26: 720–735
Severity for diffusion disordersSeverity for diffusion disorders
% of predicted% of predicted
NormalNormal 80 – 10080 – 100
MildMild 60 – 7960 – 79
ModerateModerate 40 – 5940 – 59
SevereSevere 20 – 3920 – 39
Very severeVery severe < 20< 20
The The ReportReport
Unit of DLco
Traditional: mL (STPD).min‐1.mmHg‐1 SI units: mmol.min‐1.kPa‐1
Traditional = SI x 3
Eur Respir J 2005; 26: 720–735
Diseases causing alterations in DLCODiseases causing alterations in DLCO
Increased DLCO True increase Polycythemia Alveolar haemorrhage L-R shunts Exercise Pseudo-increase Bronchial asthma
Decreased DLCO
ILD• early though nonspecific manifestation• monitoring progress & Rx• monitoring people at risk COPD• of emphysema• correlates with severity• predicts exercise limitation• predicts mortality
Pulmonary embolism• unexplained dyspnoea + reduced DLCO• correlates with severity of obstruction• reductions persist for 3 yrs
CCF• Increased in early CCF• Decreased in advanced & chronic cases• correlates with NYHA class
Misc Anemia, CRF Alcoholism, smoking RHD, PPH etc.
Steady‐State Method Pt. breathes a mixture of 0.1% CO in air
for several min through one way valve system
During last 2 min exhaled gas is collected and analyzed
ABG also drawn and analyzed for Pco2 Can be measured during tidal breathing,
anesthesia,sleep, and exercise Results are markedly affected by uneven
distribution of ventilation or V/Q abnormalities
AdvantagesAdvantages• Natural breathing maneuverNatural breathing maneuver• Allow greater variety of clinical Allow greater variety of clinical
conditionsconditions DisadvantagesDisadvantages
• More complex and difficult to perform More complex and difficult to perform (PACO)(PACO)
• PPCCCO back pressureCO back pressure
• More affected by V/Q abnormalitiesMore affected by V/Q abnormalities
Rebreathing Method Pt rebreathes the test gas from reservoir,
the volume of which equals pt’s FEV1
Rebreathing continues for 30‐45 s, at controlled rate of 30 per min
More variable
Requires considerable patient cooperation to attain rapid respiratory rate required
AdvantageAdvantage
Least affected byLeast affected by• V / Q abnormalitiesV / Q abnormalities• Changes in the subject’s lung volume at the Changes in the subject’s lung volume at the
time of measurement time of measurement
DisadvantagesDisadvantages
Complexity of the instrumentation Complexity of the instrumentation and equations requiredand equations required
Affected by PAffected by PCCCO buildupCO buildup Need for subject cooperation with Need for subject cooperation with
breathingbreathing PPCCCO back pressureCO back pressure
Interpretation
• Relationship between DLCO and lung volume is not linear, so DLco/VA or DLco/TLC do not
provide an appropriate way to normalize DLco for lung volume
• Conceptually, low DLco but high DLco/VA: extraparenchymal abnormality (e.g. pneumonectomy or chest wall restriction)
• Low DLco and low DLco/VA: parenchymal abnorm
THANK YOUTHANK YOU
Recommended