Body Plethysmograph Measurements Before and After Methacholine Challenge in Early Childhood
Condition: Asthma
MeSH terms: Asthma
Study type: Observational

Summary: 
      In our previous study of Methacholine Challenge Tests (MCT) in preschool children, we found
      that wheeze detection was associated with significant reduction in flows and vital capacity
      values. We hypothesized that this finding is associated with trapped-air rather than the
      children's loss of cooperation/concentration.

      Objectives: To test this hypothesis by attempting plethysmography measurements during MCT.
    

Detailed description: 
      In young children that cannot perform adequately spirometry methacholine challenge test (MCT)
      is continued until any of the following clinical signals occurred: appearance of audible
      wheeze, a fall of >5% in O2-saturation, or an increase of >50% in respiratory rate and/or
      heart rate. In our previous study [1] we assessed the feasibility of determining PC20-FEV1 in
      relation to audible wheeze detection during MCT in asthmatic preschool children. We found
      that at end of test (EOT), the reduction in flows of the forced expiratory flow volume (FEFV)
      curves was accompanied by reduction in forced vital capacity (FVC) though reductions in flows
      were higher than the reduction in volume. We hypothesized that this finding is associated
      with trapped-air rather than the children's loss of cooperation or concentration. We have
      also thought that determining lung volume by whole body plethysmograpy, has the advantage of
      measuring airway resistance in relation to FRC. Hence, plethysmographic measurements of lung
      volumes during MCT may shed light on the physiological relation between airway obstruction
      and hyperinflation at the end of MCT when audible wheeze is detected. However,
      plethysmography requires the patient's cooperation and coordination to perform brief panting
      maneuvers against closed airways. So far, only airway resistance has been measured in the
      plethysmograph [10], as it is believed that young children will not comply with the
      occlusions needed for lung volume measurements within the plethysmograph.

      The aims of the present study were twofold: a) to test if young children are capable of
      performing plethysmographic maneuvers required for FRC measurements; and b) to investigate if
      the reduction in vital capacity at maximal reduction in flows of the FEFV curves, found at
      wheeze detection during MCT, is due to true elevation of FRC and air trapping, or is
      artificially related to patients' loss of motivation/cooperation.

      Methods:

      Lung volumes and airway resistance will be measured in a commercial, whole body ZAN500
      constant volume body plethysmograph (ZAN-Messgeraete GmbH, Germany). The plethysmograph is
      equipped with a graphic display for preschool children to increase cooperation. The chair can
      be adjusted so that the child can comfortably sit up straight with a nose-clip, and reach the
      mouthpiece without flexing the neck.

      The plethysmography procedure will be performed according to recommendations. The test events
      will be explained to the child in detail outside of the plethysmograph. After that, the
      measurements will be carried out in the same sequence that was explained to the child. FRC
      will be measured by allowing for 2-3 breathing attempt series of superimposed straight lines
      (separated only by thermal drift). The best test out of two technically accepted series was
      analyzed.

      MCT will be performed according to the ATS guidelines for the Methacholine Challenge Test.
      Tests will be performed in a designated room at the Pediatric Pulmonary Unit, Meyer
      Children's Hospital, Haifa, Israel. A parent and the investigating team will be present
      throughout the test. Tests will be performed with triple doses of fresh Methacholine
      solutions (0.057 to13.395 mg/ml) dissolved in saline. Solutions will be driven by a KoKo-PDS
      dosimeter (Ferraris Respiratory, Louisville, CO) via mouthpiece while the child was sitting
      upright with a nose-clip and breathing at least 10 deep breaths. Five-minute intervals will
      be taken between concentrations until the maximal concentration or the end point will be
      reached (see below). Oxygen saturation and heart-rate will be monitored continuously by
      pulse-oximetry (Ohmeda Biox 3700 Pulse Oximeter, USA). Auscultation for 20-seconds over the
      trachea and two zones of both lungs (upper front and lower back) will be performed according
      to recommendation. The following indices will be considered as EOT: appearance of audible
      wheeze, a fall of 5% in O2-saturation, or an increase of 50% in respiratory rate and/or
      heart rate. Nebulized Albuterol (2.5mg) was administrated after lung function measurements.

      Spirometry: FEFV curves will be measured with a KoKo PDS commercial spirometer (Ferraris
      Respiratory, Louisville, CO), using the program incentives targets (peak expiratory flow
      rates or vital capacity). Calibration was performed before the testing sessions. The curves
      will be monitored on the computer screen to ensure best effort. On-line rejection of curves
      will be based on published quality control for older and preschool children including visual
      inspection for "non-cooperation" errors, which included poor effort, incomplete expiration,
      cough and glottis closure. Acceptable curves had to show a rapid rise to peak flow, and a
      gradual, smooth decline of flow down to residual volume.

      Sequence of lung function tests: Baseline measurements included spirometry followed by
      plethysmography. After baseline measurements MCT will be performed. A duplicate spirometry
      set will be performed immediately after auscultation and during the interval between
      inhalations. Plethysmography will be repeated following the last spirometry at EOT and after
      auscultation.
    

Observational model: Defined Population
Time perspective: Other
Keywords: Plethysmograpy; preschool; methacholine challenge; spirometry; asthma