3. Airway hyper-responsiveness: Airway hyper-responsiveness to exogenous stimuli is a characteristic feature of asthma Symptoms of asthma: Wheezing dyspnea chest tightness cough in the following: After exercise with exposure to cold air during respiratory infections following inhalant exposures in workplace after exposure to allergens and other asthma triggers

4. AHR progress from a concept synonymous with variable airflow obstruction, to a physiologic measurement AHR is most commonly measured by inhalation provocation challenges The various agents which can be used for bronchoprovocation

6. Methacholine challenge testing content: Indications Contraindications Technician Training/Qualifications Safety Patient Preparation Choice and Preparation of Methacholine Dosing Protocols Nebulizers and Dosimeters Spirometry and Other End-point Measures Data Presentation Interpretation

7. Indications The main indication: asthma is a serious possibility and traditional methods, notably spirometry performed before and after BD not establish or eliminate diagnosis

8. Other indications : asthma with atypical features possibility of occupational asthma Monitoring asthma therapy Identifying specific asthma triggers Excluding a diagnosis has social impact Objective assessing of asthma severity

9. Contraindications: Absolute: Severe airflow limitation (FEV1 < 50% predicted or <1 L) Acute coronary syndrome or stroke within 3 months Severe hypertension (SBP > 200 mm Hg or DBP > 100 mm Hg) Cerebral or aortic aneurysm

10. Contraindications : RELATIVE Moderate airflow limitation (FEV1 < 60% predicted or <1.5L) Inability to perform acceptable and repeatable spirometry Pregnancy Nursing mothers Current use of cholinesterase inhibitor medication for MG Significant hypoxemia (PaO2 < 60) Recent upper or lower respiratory tract infection (within 6 wk) Failure to withhold medication that may affect test results Vigorous exercise on day of test

11. Technician Training/Qualifications technician should be: familiar with guideline capable of managing equipment proficient at spirometry Know the contraindications familiar with safety and emergency procedures Know when to stop further testing proficient in administration of BD and evaluation response

14. Safety Precautions for patient safety: Presence of medical director trained to treat bronchospasm Presence of medications to treat severe bronchospasm Oxygen must be available A nebulizer should be available for administration BD A stethoscope, sphygmomanometer and pulse oximeter should be available

15. Precautions for technician safety: Minimize technician exposure Testing room must have adequate ventilation. Using low resistance filters A laboratory fume hood dosimeter technique reduce technician exposure To stand well away from patient

16. Patient preparation Give list of item to avoid Explain the test Ask would like to urinate before the test Evaluate contraindications and medications able to understand procedure & perform reliable spirometry A brief P/E of the chest and lungs

18. Choice and Preparation of Methacholine(Provocholine) a dry crystalline powder choice for nonspecific bronchoprovocation challenge test available in100 mg vials Sterile N/S +/- 0.4% phenol is used as the diluent stored 4°C with0.125mg/ml and greater stable for 3 mo warmed to room Tem before test sterile mixing is very important unused methacholine remain in nebulizer should be discard

19. Dosing protocols different protocols have been used able to narrow the choices to two : the 2-min tidal breathing method the five-breath dosimeter method These give similar results FDA approved Provocholine for five-breath technique

20. Two-minute tidal breathing dosing protocol Prepare the following 10 doubling concentrations:

21. Two-minute tidal breathing (cont…) Remove from refrigerator 30 min before test Insert 3 ml diluent or lowest concentration,using a sterile syringe(diluent setup is optional) perform baseline spirometry Apply a noseclip Instruct patient to breathe quietly for 2 min holding nebulizer upright begin nebulization

22. Two-minute tidal breathing (cont…) after 2 min,turn off the flow meter Measure FEV ₁,30 and 90s after complete nebulization Obtain acceptable FEV ₁ at each time no more than three or four maneuvers after each dose no more than 3 min to perform these interval of two subsequent concentrations should be kept to 5 min At each dose report the highest FEV ₁

23. Two-minute tidal breathing (cont…) If the FEV ₁ falls less than 20% go to next concentration If the FEV ₁, falls more than 20% from baseline (or the highest concentration has been given), give no further methacholine administer albuterol,wait 10 min and repeat spirometry

25. Five-breath dosimeter protocol Prepare the following five concentrations:

26. Five-breath dosimeter protocol(cont..) Remove vial from refrigerator 30 min before test 2 ml of first concentration to nebulizer wear a nose clip Perform baseline spirometry Ask to hold the nebulizer upright

27. Five-breath dosimeterprotocol(cont..) At end exhalation(FRC) encourage patient to inhale slowly and deeply (about 5 s to complete the inhalation) and to hold breath (at TLC) for another 5 s Repeat this step for a total of five inhalations Take no more than a total of 2 min

28. Five-breath dosimeterprotocol(cont..) Measure FEV ₁, at 30 and 90s after the fifth inhalation Obtain an acceptable FEV ₁, at each time point no more than three or four maneuvers,take no more than 3 min interval between two subsequent concentrations should be kept to 5 min

29. Five-breath dosimeter protocol(cont..) At each dose, report the highest FEV ₁ If the FEV ₁, falls more than 20% from baseline (or the highest concentration has been given),give no further methacholine administer albuterol,wait 10 min and repeat spirometry

30. The effect of increasing the inhaled dose of histamine or methacholine in a healthy subject (red) and an asthmatic patient (blue). The provocative concentration is the amount of inhaled aganist required to drop the FEV1 by 20 percent from the baseline (PC20 FEV1), and is much less in the asthmatic than in the normal subject.

32. Optional shortening 2-min tidal breathing protocol may be shortened depending on the clinical situation subject not known to asthma, no asthma medications, with normal lung function, no response to diluent,start at 1 mg/ml when FEV ₁ fall less than 5%,in next concentration fourfold increase is quite safe

33. Nebulizers  Nebulizers for the tidal breathing method : deliver aerosol with a particle mass median diameter(MMD) between 1 and 3.6 µm The English Wright nebulizer Flow must be adjusted for nebulizer to obtain output within 0.13 ml / min +/- 10%  Nebulizers for the five-breath dosimeter method deliver 9 µl +/-10% of solution per 0.6s actuation during inhalation The DeVilbiss model 646 nebulizer

34. A-2 min tidal breathing (English wright nebulizer) B- five beath dosimetre(Devibiss model 646)

35. Spirometry and Other End-point Measures Change FEV ₁ is primary outcome for MCT Failure to meet repeatability should be to assist interpretation and not to exclude data from analysis Quality control (QC) report after each level: A = two acceptable FEV ₁ values that match within 0.10 L B = two acceptable FEV ₁ values that match within 0.20 L C = two acceptable FEV ₁ values that do not match within0.20 L D = only one acceptable FEV ₁ maneuver F = no acceptable FEV ₁ maneuvers

36. Other End-point Measures(cont…)  Raw and sGaw Airway resistance(Raw) express as specific conductance (sGaw) are alternative end point Use in patients cannot perform acceptable spirometry Usually parallel changes in FEV ₁ with MCT Raw and sGaw are more variable than FEV ₁ A larger change (e.g 45%) for a positive test

37. Other End-point Measures(cont…)  Transcutaneous oxygen Ptc o ₂ may a useful end point Use in patients cannot perform acceptable spirometry  Forced oscillation have recently been assessed do not require patient effort useful in patients cannot perform acceptable spirometry should be restricted to laboratories with expertise

38. Data Presentation Data should be presented for each step in the protocol:

39. PC ₂₀ PC ₂₀ used to summarize results for clinical purposes PC ₂₀ =provocative concentration cause 20% fall in FEV ₁ If FEV ₁ does not fall by at least 20% after 16 mg/ml PC ₂₀ should report > 16 mg/ml For manual calculation of PC ₂₀ : C ₁ = second to last concentration(concentration preceding C ₂ ) C ₂ = final concentration result 20% or greater fall in FEV ₁ R ₁ = percent fall in FEV ₁ after C ₁ R ₂ = percent fall in FEV ₁ after C ₂

43. Interpretation Factors should take into consideration when interpreting: Pretest evaluation probability of asthma Degree of baseline airway obstruction Quality of spirometry Pretest questionnaire results (modifiers) Symptoms at the end of test Degree of recovery after BD Sensitivity and specificity of MCT Repeatability of MCT

44. Curves illustrating pretest and posttest probability of asthma after a methacholine challenge test with four PC ₂₀ values.They are approximations presented to illustrate relationships and principles of decision analysis. They are not intended to calculate precise posttest probabilities in patients.

45. Relationship between airway responsiveness & asthma If clinical probability of asthma is 30-70%and PC ₂₀ >16 mg/ml, patient does not currently have asthma If PC ₂₀ < 1 mg/ml, strong confirmation of asthma When PC ₂₀ between 1 and16 mg/ml, more cautious about stating asthma When PC ₂₀ low and the “asthma-like” symptoms induced by MCT, diagnosis of asthma increase

46. methacholine dose–response curves for four individuals, one with normal airway responsiveness and one each with mild to moderate and marked airway hyperresponsiveness. These curves demonstrate hyperresponsiveness both in the increase in magnitude of the response and the ease of the response, the latter identified the leftward shift of the curve and the smaller PC20

47. Relationship (cont…) when PC ₂₀ between 1 and 16 mg/ml and no asthma symptoms several possibilities exist: Mild intermittent asthma but patient is “poor perceive” of asthma symptoms After MCT,experience chest tightness but not recognized as abnormal Patient never exercises or experiences environmental triggers of bronchospasm mild BHR is due to a cause other than asthma(URTI ) there is subclinical asthma will become clinical in future

48. Relationship (cont…) significant correlation between degree of airway responsiveness and severity of asthma PC ₂₀ does not reflect the “usual” untreated severity of asthma difficult to interpret a low PC ₂₀ with baseline airway obstruction(e.g COPD)

49. Categorical method of interpreting MCT Categorical method for clinical interpretation of MCT makes three assumptions: MCT results are either positive or negative for BHR asthma is either present or absent There is a“gold standard” for diagnosing asthma Sensitivity is fraction of patients with asthma have positive test Specificity is fraction of patients without asthma have negative test

50. Categorical method(cont..) Negative MCT is defined as nonresponse to highest concentration (PC ₂₀ > 8-25 mg/ml) positive test is defined as a PC ₂₀ < 8 or < 16 mg/ml The false-positive when PC ₂₀ is <8 mg/ml but patient does not have actually asthma Allergic rhinitis and COPD have high FP rates and poor PPV

51. Categorical method(cont…) A FN result occurs when PC ₂₀ > 8-25 mg/ml in a patient with asthma The NPV of MCT is more than 90% when pretest probability of asthma is in range of 30-70% Negative MCT rules out asthma certainly in patients have had asthma symptoms during previous 2 wk

52. Categorical method(cont…) Consider three factors before negative test rule out asthma: taking intensive anti inflammatory medications prior MCT season for aeroallergen exposure may have passed occupational asthma due to single Ag or chemical sensitizer respond only specific challenge agent