Repeatability of methacholine challenge in asthmatic children measured by change in transcutaneous oxygen tension

Clinical Implications of Oscillatory Lung Function during Methacholine Bronchoprovocation Testing of Preschool Children

OBJECTIVE

To investigate the repeatability and safety of measuring impulse oscillation system (IOS) parameters and the point of wheezing during bronchoprovocation testing of preschool children.

METHODS

Two sets of methacholine challenge were conducted in 36 asthma children. The test was discontinued if there was a significant change in reactance (Xrs5) and resistance (Rrs5) at 5 Hz (Condition 1) or respiratory distress due to airway obstruction (Condition 2). The repeatability of PC₈₀_Xrs5, PC₃₀_Rrs5, and wheezing (PCw) was assessed. The changes in Z-scores and SD-indexes from prebaseline (before testing) to postbaseline (after bronchodilator) were determined.

RESULTS

For PC₃₀_Rrs5, PC₈₀_Xrs5, and PCw for subjects, PC₈₀_Xrs5 showed the highest repeatability. Fifteen of 70 tests met Condition 2. The changes from pre- and postbaseline values varied significantly for Rrs5 and Xrs5. Excluding subjects with Z-scores higher than 2SD, we were able to detect 97.1% of bronchial hyperresponsiveness during methacholine challenge based on the change in Rrs5 or Xrs5. A change in IOS parameters was associated with wheezing at all frequencies.

CONCLUSION

Xrs5 and Rrs5 have repeatability comparable with FEV1, and Xrs5 is more reliable than Rrs5. Clinicians can safely perform a challenge test by measuring the changes in Rrs5, Xrs5, and Z-scores from the prebaseline values.

The Tools of the Trade - Physiological Measurements of the Lungs

Pulmonary function assessment plays an integral part in the clinical management of school-aged children with respiratory disease. Pulmonary function tests (PFTs) are being increasingly applied in infants and preschool children too, albeit only in specialised centres. PFTs, when performed and interpreted accurately, provide objective outcome measures which can be used clinically to guide management, for prognostic purposes and in epidemiological research studies. They can be used to determine the nature and severity of lung disease, to ascertain response to treatment and to monitor disease progression. PFTs are rarely diagnostic in their own right with the exception of asthma, but are valuable adjuncts and before clinicians select a PFT they must know what the results are likely to be in the disease being considered. Spirometry and tests of airway calibre and function are the most widely used PFTs, as diseases in children commonly affect airway function. As such, spirometry should be a standard part of the assessment of school-age children who present to the pediatrician with chronic respiratory symptoms. This review will provide a bird's eye view of currently available PFTs in children to assist in the diagnosis and management of respiratory disorders.

Reduced vital capacity after methacholine challenge in early childhood--is it due to trapped air or loss of motivation

In a previous study we assessed the feasibility of measuring bronchial-reactivity (BHR) in young asthmatic children by the determination of PC(20)-FEV(1) along with clinical end-of-test criteria during a methacholine challenge test (MCT). The end-point was associated with a significant reduction in both flow and vital capacity values. The findings could be due to the children's loss of motivation, which may preclude use of this test. Alternatively, if it reflects air trapping during airway obstruction, it might reinforce its applicability in preschool age children.

OBJECTIVES

To elucidate the mechanism of low vital capacity at PC(20)-FEV(1) in preschool age children.

SUBJECTS

Twenty-eight children (3.3-6.9 years) with recurrent respiratory symptoms.

METHODS

An MCT was carried out using tripling doses (0.06-13.9 mg/ml) delivered by a dosimeter. Spirometry was measured at baseline and after each inhalation in duplicate sets. Whole body plethysmography was measured at baseline and at end-of-test (defined by clinical criteria) according to the recommendations for older populations.

RESULTS

Plethysmography was reliably performed by 20 children before and after MCT. At baseline, lung function was within the healthy range. At end-of-test (PC(20)-FEV(1)=4.02+/-3.47 mg/ml), the spirometry parameters and specific conductance values were markedly reduced in correlation with a significant increase in residual volume and resistance.

CONCLUSIONS

The study shows that diminished vital capacity is due to the increase in FRC at end-of-test. Our findings support the use of PC(20)-FEV(1) during BHR in young children and suggest that lung volume measurement by a plethysmograph may be feasible in early childhood. Larger studies should be performed to establish the clinical applicability of PC20-FEV1 determination in the preschool age.

Can bronchodilator response predict bronchial response to methacholine in preschool coughers?

The aim of the present study was to determine the relationship between bronchodilator response, assessed by interrupter resistance (Rint), and bronchial reactivity in preschool children with chronic cough. Thirty-eight children coughers (median age 5.0 years, range 2.8-6.4) were tested. Bronchodilator response was recorded within 4 months before methacholine challenge. Response to the latter was assessed using transcutaneous partial pressure of oxygen and Rint. Children were considered responders if a 20% fall in transcutaneous partial pressure of oxygen occurred during the bronchial challenge. Bronchodilator response was not different between responders (n = 24) and nonresponders (n = 14) [median (range) -0.11 (-0.44-0.09) vs. -0.08 (-0.21-0.10) kPa L(-1) sec; respectively]. However, none of the nonresponders had a bronchodilator response larger than -0.21 kPa L(-1) sec, this cutoff had a 100% positive and a 44% negative predictive value to predict a positive methacholine challenge. The relationship between bronchodilator response and bronchial methacholine responsiveness reached the limit of significance (P = 0.048). Furthermore, the magnitude of the bronchodilator response was correlated to the level of methacholine-induced level of bronchoconstriction (P = 0.01), and to the postchallenge bronchodilation (P = 0.04), all values expressed as % predicted. Moreover, the postbronchodilator Rint value obtained with preceding methacholine challenge was lower than the postbronchodilator value without preceding methacholine challenge in 71.4% (10/14) of the nonresponders and in only 33.3% (8/24) of the responders. Conclusions in preschool coughers bronchodilator response, assessed by the interrupter technique, was correlated to the bronchial responsiveness to methacholine. Non responders had a bronchodilator response not larger than -0.21 kPa L(-1) sec.

Methacholine and adenosine 5'-monophosphate challenges in preschool children with cough-variant and classic asthma

Bronchial challenge with different stimuli provides different information and may be used as an adjunct to understand the pathophysiology of cough variant asthma (CVA) in young children in whom the mechanism of disease is still unresolved. This study was designed to investigate the hypothesis that airway hyperresponsiveness (AHR) to methacholine and adenosine 5'-monophosphate (AMP) is similar in preschool children with CVA and classic asthma. We examined airway response to methacholine and AMP in well-defined 3-6-year-old children with CVA (n = 18), classic persistent asthma (n = 31), and healthy controls (n = 10) by transcutaneous oxygen monitorization. The number of AMP responsive children was significantly lower in the group with CVA (38.9%) than classic persistent asthma (67.7%) (P = 0.049). Mean provocative concentration of AMP causing a 15% fall in transcutaneous oxygen tension (PC15PtcO2 AMP) in children with CVA and classic persistent asthma were 234.58 and 36.35 mg/ml, respectively (P = 0.001). None of the healthy children in the control group responded to AMP. The severity of methacholine responsiveness was found similar in CVA and classic persistent asthma groups (P = 0.738). Although both asthma groups showed a similar pattern in methacholine responsiveness, preschool children with CVA were found to differ from children with classic persistent asthma with regard to response profiles to AMP challenge which may point to different pathophysiologic mechanisms of CVA in the young age group.

Airway hyper-responsiveness to adenosine 5'-monophosphate in preschool-age children with asthma

Airway hyper-responsiveness (AHR) to adenosine 5'-monophosphate (AMP) is closely associated with airway inflammation; however, not all asthmatic patients are responsive to it. This study was planned to investigate the predictive factors of AHR to AMP in asthmatic children aged between 3 and 6 yr. We performed a retrospective analysis of data from 63 asthmatic preschool-age children who were challenged by AMP in our department. All children were characterized by skin-prick tests, serum immunoglobulin E (IgE) levels, peripheral blood eosinophil percentage and bronchial challenge with methacholine (MCH) and AMP. Potential determinants for AHR to AMP were assessed within the group. AHR to AMP was found in 46% of preschool-age children with asthma, while that of MCH was 93.7%. All children responsive to AMP were also responsive to MCH. The geometric mean provocative concentration of MCH and AMP causing a 15% fall in transcutaneous oxygen tension (PC(15)PtcO(2)MCH and AMP) were 0.55 mg/ml (0.004-9.19) and 10.53 mg/ml (0.59-342.89), respectively. AMP-responsive children did not differ from non-responsive ones with respect to demographic factors, geometric mean PC(15)PtcO(2)MCH and atopic status. The median serum IgE level was significantly higher in AMP-responsive group than the non-responsive ones (p = 0.011). The peripheral blood eosinophilia was more frequent among responsive children (p = 0.019), and it was found as the only predictive factor for AMP responsiveness in preschool-age children with asthma in logistic regression model (odds ratio: 5.14; 95% CI: 1.23-21.47; p = 0.025). AMP responsiveness may be predicted by peripheral blood eosinophilia but not with atopy markers in young children with asthma.

Relationship between bronchial responsiveness and clinical evolution in infants who wheeze: a four-year prospective study

Recurrent illness involving wheezing during the first years of life is transient in most children. The role of bronchial hyperresponsiveness as a factor influencing the persistence of wheezing from infancy to school age remains unknown. In a prospective study we investigated whether infants who wheezed and subsequently developed persistent asthma differed from infants who wheezed and later became asymptomatic either in the initial degree of bronchial hyperresponsiveness or in the persistence of bronchial hyperresponsiveness with age. One hundred and twenty-nine infants with three or more wheezing episodes before 2 yr of age were followed during 4 yr with a clinical evaluation and a methacholine challenge performed every 6 mo until the child was 4 yr old and once per year thereafter. The clinical score significantly improved with time in most children. The proportion of children with persistent wheezing after 2 and 4 yr of follow-up was only 31% and 20%, respectively. Persistent wheezers had significantly lower VmaxFRC values at initial evaluation and higher SRaw values at the end of follow-up than infants who became asymptomatic. We used transcutaneous oxygen tension (PtcO(2)) to measure the response to methacholine. No significant difference in PD(15) PtcO(2) between groups with subsequently different clinical progression was observed at initial evaluation. Bronchial hyperresponsiveness persisted 4 yr later in all children but children with persistent wheezing showed significantly lower PD(15) PtcO(2) values than children who became asymptomatic, as early as 30 mo of age. However, an acceptable early PD(15) PtcO(2) cut-off point predictive for subsequent clinical progression could not be identified. The level of bronchial hyperresponsiveness in infants who wheezed was not predictive of the persistence of asthma 4 yr later.

Routine pulse oximetry during methacholine challenges is unnecessary for safety

BACKGROUND

Methacholine-induced bronchoconstriction is associated with significant hypoxemia, which can be assessed noninvasively by transcutaneous oxygen tension and pulse oximetry.

OBJECTIVES

To assess the value of the monitoring of finger pulse oximetry during routine methacholine challenges in a clinical pulmonary function laboratory with regard to both safety and the possibility that a significant fall in oxygen saturation as measured by pulse oximetry (SpO(2)) might be a useful surrogate for determining the response to methacholine.

METHODS

Two hundred consecutive patients undergoing diagnostic methacholine challenges in the pulmonary function laboratory of a tertiary-care, university-based referral hospital were studied. Methacholine challenges were performed by the standardized 2-min tidal breathing technique, and the DeltaFEV(1) was calculated from the lowest postsaline solution inhalation to the lowest postmethacholine inhalation value. SpO(2) was measured immediately prior to each spirogram, and the DeltaSpO(2) was measured from the lowest postsaline solution inhalation value to the lowest postmethacholine inhalation value. We examined the data for safety (ie, any SpO(2) value < 90). Based on previous reports, we used a DeltaSpO(2) of > or = 3 as significant and looked at the sensitivity, specificity, and positive and negative predictive values for DeltaSpO(2) > or = 3 vis-à-vis a fall in FEV(1) of > or = 15%.

RESULTS

There were 119 nonresponders (DeltaFEV(1), < 15%) and 81 responders. The baseline FEV(1) percent predicted was slightly but significantly lower in the responders (responders [+/- SD], 91.6 +/- 15%; nonresponders, 96.4 +/- 14%; p < 0.05). DeltaSpO(2) was 3.1 +/- 1.6 in the responders and 1.6 +/- 1.8 in the nonresponders (p < 0. 001). There was a single recording in one patient of SpO(2) < 90 (88). A DeltaSpO(2) > or = 3 had a sensitivity of 68%, a specificity of 73%, a positive predictive value of 63%, and negative predictive value of 77% for a fall in FEV(1) > or = 15%.

CONCLUSIONS

Pulse oximetry is not routinely useful for safety monitoring during methacholine challenge. DeltaSpO(2) is not helpful in predicting a positive spirometric response to methacholine. However, the negative predictive value is adequate to allow the DeltaSpO(2) to be used as an adjunct in assessing a negative result of a methacholine test in patients who have difficulty performing spirometry.

Bronchial challenge with carbachol in 3-6-year-old children: body plethysmography assessments

Several studies of airway responsiveness in young children (3-6 years old) have been reported, but few have attempted measurements of airway resistance by body plethysmography. Therefore, we decided to study nonspecific bronchial responsiveness following cumulative doses of inhaled carbachol in 44 children with clinical asthma (CA group), 44 children with chronic cough (CC group), 38 children with wheezy bronchitis in the first 2 years of life (WB group), and 40 controls. Specific airway resistance (sRaw) was measured in a body plethysmograph, and specific airway conductance (sGaw=1/sRaw) was calculated. Two parameters were used to assess individual bronchial responses: 1) PD100 (the dose of carbachol which induced a 100% increase in sRaw), and 2) bronchial reactivity (BR), i.e., the slope of the log-dose sGaw response to carbachol. Significant differences were observed in PD100 and BR between the control group and the three groups of young patients (P < 0.001). Moreover, PD100 of the CA group was significantly lower than in the CC group (83.1 +/- 7.8 microg vs. 108.0 +/- 10.2 microg, respectively, P < 0.05), but was similar to the WB group PD100 (94.4 +/- 8.5 microg). BR in the CA group was significantly higher than in both the CC and WB groups (0.127 +/- 0.009 cm H2O-L.sec(-1) x log microg(-1) vs. 0.073 +/- 0.006 cm H2O(-1) x sec(-1) x log microg(-1) and 0.082 +/- 0.006 cm H2O(-1) x sec(-1) x log microg(-1), respectively, P < 0.001). Repeatability and coefficients of variation were always acceptable. Continuous SaO2 monitoring in some children of the CA group demonstrated the safety of the method, which is proposed as a technique in future studies.

Repeatability of lung function tests during methacholine challenge in wheezy infants

BACKGROUND

The repeatability of lung function tests and methacholine inhalation tests was evaluated in recurrently wheezy infants over a one month period using the rapid thoracic compression technique.

METHODS

Eighty-one wheezy, symptom free infants had pairs of methacholine challenge tests performed one month apart. Maximal flow at functional residual capacity (VmaxFRC) and transcutaneous oxygen tension (Ptco2) were measured at baseline and after methacholine inhalation. Provocative doses of methacholine causing a 15% fall in Ptco2 (PD15 Ptco2) or a 30% fall in VmaxFRC (PD30 VmaxFRC) were determined.

RESULTS

Large changes in VmaxFRC were measured from T1 to T2 with a mean difference between measurements (T2-T1) of 7 (113) ml/s and a 95% range for a single determination for VmaxFRC of 160 ml/s. The mean (SD) difference between pairs of PD30 VmaxFRC measurements was 0.33 (1.89) doubling doses with a 95% range for a single determination of 2.7 doubling doses. Repeatability of PD15Ptco2 was similar. A change of 3.7 doubling doses of methacholine measured on successive occasions represents a significant change.

CONCLUSIONS

Baseline VmaxFRC values are highly variable in wheezy, symptom free infants. Using either VmaxFRC or Ptco2 as the outcome measure for methacholine challenges provided similar repeatability. A change of more than 3.7 doubling doses of methacholine is required for clinical significance.

Repeatability of methacholine challenges in 2- to 4-year-old children with asthma, using a new technique for quantitative delivery of aerosol

To determine the repeatability of bronchial responsiveness in awake young children, two methacholine challenge tests were performed on separate days in 16 children with stable asthma (mean age, 3 3/4 years). Methacholine was administered using a new method for quantitative delivery of aerosol that eliminates the effect of dilution of the aerosol by entrainment of air and enables quantitative delivery of aerosol according to body weight. Respiratory function was monitored by measurement of respiratory resistance by the interrupter technique (Rint), respiratory resistance and reactance at 5 Hz (Rrs5, Xrs5) by the impulse oscillation technique, transcutaneous measurements of oxygen (PtcO2), and specific airway resistance (sRaw). Repeatability was evaluated by determining the provocative dose that caused a defined percentage of change relative to baseline (PD%: Rint PD30, Rrs5 PD30, Xrs5 PD80, PtcO2 PD10, and sRaw PD80. Repeatability was estimated from the difference between the PD% obtained at the time of the two tests. Using the numeric value of these differences, the repeatability of Xrs5 PD60, PtcO2 PD10, and sRaw PD50 was [mean (SD)]: [0.8 (0.5)] [0.5 (0.4)] and [0.7 (0.6)] doubling doses, respectively. Rint PD30 and Rrs5 PD30 proved to be less reproducible: [1.2 (1)] and [1.6 (0.9)] doubling doses, respectively. The new method of aerosol delivery offers a means of standardizing the bronchoconstrictor stimulus, and the results show that estimates of bronchial responsiveness in young children can be obtained reproducibly within one doubling dose of methacholine.

Measurement of lung function in awake 2-4-year-old asthmatic children during methacholine challenge and acute asthma: a comparison of the impulse oscillation technique, the interrupter technique, and transcutaneous measurement of oxygen versus whole-body plethysmography

This study evaluated three techniques for testing of lung function in young awake children. We compared measurements by the forced or impulse oscillation technique (IOS), the interrupter technique (IT), and transcutaneous measurements of oxygen (tcPo2) with concomitant measurements of specific airway resistance (sRaw) during methacholine challenge in 20 stable asthmatic children, 2-4 years old. Measurements were performed with all techniques after each dose of methacholine and after inhalation of a bronchodilator. Measurements were carried out during tidal breathing using a face-mask with a built-in mouthpiece. The ranking of sensitivity was as follows: sRaw > IOS, respiratory reactance at 5 Hz (Xrs5) > tcPo2 > interrupter resistance (Rint) > IOS, respiratory resistance at 5 Hz (Rrs5). The sensitivity of sRaw and Xrs5 was not significantly different, but both were significantly more sensitive than Rint and Rrs5; the sensitivity of tcPo2, Rint, and Rrs5 was not significantly different. Measurements in eight of the subjects performed during an episode of acute asthma yielded comparable results in regard to the sensitivity of the techniques. Measurements improved significantly after bronchodilator administration; however, the response to bronchodilator tended to be less during acute asthma and was best demonstrated by a deterioration of tcPo2. All the evaluated techniques reliably reflect short-term changes in respiratory function and can provide clinically useful estimates of airway function. The techniques are non-invasive, are not dependent on the active co-operation or sedation of the subjects, and therefore are well suited for routine use in young children.

Influence of breathing pattern on transcutaneous oxygen and carbon dioxide tension during histamine provocation in children with bronchial asthma

The influence of the breathing pattern on transcutaneous blood gases was evaluated in 18 boys and 8 girls 7-18 years of age, with bronchial asthma, during bronchial provocation with histamine-HCl. Transcutaneous oxygen tension (tcPO2), carbon dioxide tension (tcPCO2) and the breathing pattern assessed by the transthoracic impedance technique were continuously monitored during the provocation. At reaction, when the fall in the forced expiratory volume in 1 s (FEV1) was 20% or more, the tcPO2 fell by 15% or more below the baseline in 22/26 and by 20% or more in 14/26 children. In some children, a marked fall in the tcPO2 was already noted after the saline inhalation and the first histamine dose steps without simultaneous changes in the FEV1. This early fall in the tcPO2 correlated to changes in the breathing pattern and was interpreted as a sign of compensatory hypoventilation secondary to the hyperventilation observed during the inhalations. We conclude that transcutaneous oxygen tension can be used as an indicator of a bronchial reaction during bronchial provocation tests in children only if one takes account of the fact that the breathing pattern during the inhalation of the challenge compound per se has an effect on the oxygen tension.

Evaluation of the interrupter technique for measuring change in airway resistance in 5-year-old asthmatic children

The interrupter technique is a noninvasive method for measuring airway resistance during quiet breathing which requires minimal subject cooperation. It, therefore, has enormous potential for use in young children unable to cooperate with conventional lung function tests. We evaluated the interrupter technique during bronchial challenge with methacholine administered by the tidal breathing method in 10 5-year-old asthmatic children. The mouth pressure/time [P mo(t)] curve obtained following brief airflow interruption during the expiratory phase of quiet breathing was analyzed to determine the interrupter resistance (Rint) using four different methods: RintC, a smooth curve fit with back-extrapolation; RintEO, calculated from the pressure change after the postinterruption oscillations had decayed (end-oscillation); RintL, two-point linear fit with back-extrapolation; and RintEI, calculated from the pressure change at the end of the period of interruption. The four Rint methods were compared for repeatability and sensitivity with the direct measurement of resistance by the forced oscillation technique (Rrs), and with an independent method of measuring the response to challenge, utilizing the change in transcutaneous oxygen tension (PtcO2). The sensitivity of the methods was defined by a sensitivity index (SI), the change after challenge expressed in multiples of the baseline standard deviation. The PtcO2 method had the lowest variability and was by far the most sensitive method (geometric mean SI 18.9), at least 1 doubling concentration more sensitive than the other techniques in every subject (P < 0.05). RintL was more sensitive than the other interrupter methods (geometric mean SI: RintL 4.2; RintC 1.0; RintEO 2.7; RintEI 3.1; P < 0.05) and similar in sensitivity to Rrs (geometric mean SI 4.6) in 7 out of 10 children in which this could be measured. We conclude that the interrupter method provides a simpler method than the oscillation technique for assessing airway obstruction in this age group.

Bronchial responsiveness and symptoms in 5-6 year old children: a comparison of a direct and indirect challenge

BACKGROUND

The level of bronchial responsiveness in those with definite asthma correlates with disease severity and markers of airway inflammation. However, in population studies no clear distinction between normal and abnormal is found. Since the outcome of wheeze in early childhood is very variable, a marker of underlying airway inflammation would be of practical value. A stimulus acting indirectly may be more appropriate than one acting directly on smooth muscle. In this study the airway response to a direct (methacholine) and indirect (hypertonic saline) challenge have been compared in 5-6 year old children with past or present wheeze to see if symptom patterns or severity could be distinguished by either test.

METHODS

Forty children with a wide spectrum of wheeze were monitored for a six month period after which their pattern and severity of symptoms were graded. Hypertonic saline and methacholine challenges were then performed on separate days. The response was assessed by both respiratory resistance (Rrs6) and transcutaneous oxygen (PTCO2). Atopic status was determined by IgE and skin prick tests.

RESULTS

The results of both challenges were similar whether assessed by Rrs6 or PTCO2. There was no difference in the response to either methacholine or saline between different symptom patterns or severity grades, nor was there any correlation with either test to atopic status.

CONCLUSIONS

Neither an indirect nor a direct challenge distinguished between past or present wheeze or degree of clinical severity in this group of children. Either wheezy children of this age do not have airway inflammation or bronchial responsiveness is not a marker for it.