USE OF FLOW VOLUME CURVES IN INFANCY TO STUDY AIRWAYS RESPONSIVENESS TO HISTAMINE

Abstract

Wheeze in infancy is very common, but, little is known about airway function in this age group. We have adapted a technique (Taussig et al, J Appl Physiol 1982; 53: 1220-27) for producing partial maximum expiratory flow-volume curves in infants after light sedation. The infant sleeps supine inside an inflatable jacket which, when inflated rapidly to 3-4kPa (<100m.sec) at end inspiration, leads to forced expiration with flow limitation. Flow (integrated digitally to provide a volume signal) is measured at the facemask by pneumotachography. From the flow-volume curve, two indices are derived: (i) peak expiratory flow rate (PEF); (ii) maximum expiratory flow rate at the previously stable end-expiratory volume (VmaxFRC). The median within-subject coefficients of variation of PEF and VmaxFRC for normal infants were 6% and 11% and for wheezy infants were 8% and 11% respectively.Histamine responsiveness was measured as the change in PEF and VmaxFRC after doubling concentrations of histamine acid phosphate solution, administered for 1 min by Acorn nebuliser at 5 min intervals in 10 infants with recurrent or persistent wheeze. Where possible, tests were repeated after 24 hours. Rapidly reversible dose-dependent responses to histamine were shown at concentrations of about 4 g.1−1. The responses were reproducible and were partly preventable by nebulised salbutamol (2.5mg). Acute reversible airways obstruction, modified by bronchodilators, may play a part in the pathophysiology of wheezy infants.