Cold air challenge of airway reactivity in children: a correlation of transcutaneously measured oxygen tension and conventional lung functions

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.

Exercise Challenge for Exercise-Induced Bronchospasm

In brief For assessing symptoms of exercise-induced asthma in active young people, the exercise challenge test has advantages over the therapeutic trial: It can be used to specifically confirm the presence of exercise-induced bronchospasm, evaluate pharmacologic control, and help improve compliance. Knowing how to interpret and use the test results helps physicians expedite effective treatment, whether the physician performs the test in the office or refers the patient to a specialty lab.

Comparison of the squeeze technique and transcutaneous oxygen tension for measuring the response to bronchial challenge in normal and wheezy infants

The aim of this study was to compare the fall in transcutaneous oxygen tension (PtcO2) as an outcome measure during bronchial provocation with histamine, with changes in airway function measured by the squeeze technique in healthy infants and those with wheezing disorders. PtcO2 was measured during histamine challenge in 20 infants, aged 6-16 months, of whom 14 had recurrent cough or wheeze (lower respiratory illness, LRI), and 6 were healthy. All were symptom free at the time of testing. The minimum value of PtcO2 after each nebulization was compared with the minimum baseline value. The response to increasing concentrations of histamine was also assessed by measuring maximal flow at functional residual capacity (VmaxFRC) by the squeeze technique. The inhaled concentration of histamine causing a 30% fall in VmaxFRC was calculated to give the provoking concentration (PC30). Baseline VmaxFRC was lower in symptomatic infants (117 mL/s) than the normal infants (322 mL/s; P < 0.005), but the PC30 was not significantly different (7.7 and 5.7 g/L, respectively). There was no difference in baseline PtcO2 between the two groups. The infants with LRI had significant reductions in PtcO2 at both the final and preceding concentrations of histamine, whereas the normal infants had a significant and smaller reduction in PtcO2 only at the provoking concentration. Reduction in PtcO2 during bronchial challenge was a less sensitive index of bronchial response in healthy infants than in infants with a history of recurrent LRI.

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

BACKGROUND

The airway response to bronchial provocation may be evaluated by monitoring the fall in transcutaneous oxygen tension (PtcO2) but the repeatability of this method has not been rigorously assessed.

METHODS

To determine the repeatability of this indirect method of assessment, bronchial challenge was performed with methacholine in nine children with stable asthma (age range 6-12 years) and was repeated 24 hours later. The response was determined by the fall both in forced expiratory volume in one second (FEV1) and in PtcO2. A modified tidal inhalation protocol was used in which quadrupling concentrations of methacholine were given, thereby reducing the time taken for the full challenge by almost half. The concentrations of methacholine that provoked a 20% decrease in FEV1 (PC20FEV1) and 15% and 10% falls in PtcO2 (PC15PtcO2, PC10PtcO2) were calculated.

RESULTS

Repeatability measures, assessed as the 95% range for a single determination, were +/- 0.96 and +/- 1.12 doubling concentration differences respectively for PC15PtcO2 and PC10PtcO2 and +/- 0.80 for PC20FEV1.

CONCLUSION

This challenge method using quadrupling concentrations and an indirect assessment of the response by PtcO2 was sufficiently repeatable for clinical use and compared favourably with repeated challenge assessed by FEV1. The PtcO2 method is simple and effort independent, and should prove particularly useful for measuring bronchial reactivity in young children.