Relation of airway responsiveness to methacholine to parent and child reporting of symptoms suggesting asthma: PATIENTS AND METHODS Part 2
Methacholine inhalation challenges were undertaken in all consenting children by using Wright’s nebulisers with an outputof0.13 mL/min and particle size 1.5 ^m aerodynamic mass median diameter. The child inhaled nebulized normal saline followed by increasing concentrations of methacho-line chloride by tidal breathing for 2 mins using a face mask. Spirometry was undertaken before, and at 30 s and 90 s after, each inhalation. If the child reported no recent symptoms of asthma, the first methacholine concentration given was 0.25 mg/mL followed by fourfold increments of 1.0 and 4.0 mg/mL, and finally 8.0 and 16.0 mg/mL. If FEV1 fell more than 6% from the baseline value, doubling rather than fourfold increments were then used until FEV1 fell more than 20% from the lowest postsaline value, whereupon the test was terminated. If the child reported a recent history of symptoms consistent with asthma, inhalations were started at a methacholine concentration of 0.06 mg/mL and increased by doubling rather than fourfold concentration increments. Online shopping will cost you less money and will take less time, because you can find efficient actos diabetes with generous discounts at the pharmacy that proved its reputability and desire to help by offering best level of service and most efficient drugs.
The provocation concentration of methacholine causing a 20% fall in FEV1 (PC20 FEV1) was calculated by linear interpolation between the last two points of the log dose response plot of FEV1 (as percentage of postsaline value) and methacholine concentration, and was expressed in noncumulative units. Methacholine challenge was not undertaken if the baseline FEV 1 was less than 1.0 L or the FEV 1/VC ratio was less than 0.7, but the child was instead given inhaled salbuta-mol 5 mg/mL nebulized undiluted for 2 mins, and FEV1 and VC repeated 10 mins later.
Statistical analysis: To assess the relation of the response to methacholine to various symptoms, receiver operating characteristic (ROC) curves were constructed. These curves plot the sensitivity (y-axis) against 1-specificity (x-axis) of the test when different cut-points of responsiveness were used to determine a ‘positive’ or a ‘negative’ test result. ROC curves were plotted for parent- or child-reported diagnoses or symptoms, using PC20 values of <1, <2, <4, <8 and <16 mg/mL as the cut-points for determining a positive result for hyperresponsiveness. The significance of the difference of the area under the ROC curve from 0.5 was examined by 2 ‘ X analysis. Bonferroni’s adjustments were used to correct for the performance of multiple comparisons. The PC20 providing the optimum balance of test sensitivity and specificity with different levels of symptoms was determined visually by determining the cut-points providing the closest point on the observed curve to the ‘ideal’ point where sensitivity and specificity are both 100%.