If house dust mite allergen (Der p I) is an important cause of asthma, there should be a direct relationship between level of exposure to this allergen and asthma severity. To examine this, we studied six large random samples of children in different regions of New South Wales, Australia. We measured recent wheeze by questionnaire, airway hyperresponsiveness (AHR) by histamine inhalation test and sensitization to house dust mites by skin prick tests. Current asthma was defined as the presence of recent wheeze and AHR. We measured Der p I levels in the beds of approximately 80 children in each region. In regions where Der p I levels were high, more children were sensitized to house dust mites, and these children had significantly more AHR and recent wheeze. After adjusting for sensitization to other allergens, we found that the risk of house dust mite-sensitized children having current asthma doubled with every doubling of Der p I level. There was a modest correlation between AHR and Der p I exposure in individuals (r = 0.23, p < 0.03). These data suggest that house dust mite allergens are an important cause of childhood asthma and that reducing exposure to these allergens could have a large public health benefit in terms of asthma prevention.

We assessed the clinical and biochemical effects in asthmatic children of fish oil supplementation and a diet that increases omega-3 and reduces omega-6 fatty acids. Thirty nine asthmatic children aged 8-12 yrs participated in a double-blind, randomized, controlled trial for 6 months during which they received fish oil capsules plus canola oil and margarine (omega-3 group) or safflower oil capsules plus sunflower oil and margarine (omega-6 group). Plasma fatty acids, stimulated tumour necrosis factor alpha (TNFalpha) production, circulating eosinophil numbers and lung function were measured at baseline and after 3 and 6 months of dietary modification. Day and night symptoms, peak flow rates and medication use were recorded for 1 week prior to laboratory visits. Plasma phospholipid omega-3 fatty acids were significantly greater in the omega-3 group at 3 and 6 months compared to the omega-6 group (p<0.001). In the omega-3 group TNFalpha production fell significantly compared with baseline (p=0.026), but the magnitude of change between groups did not reach significance (p=0.075). There were no significant changes in clinical outcome measures. Dietary enrichment of omega-3 fatty acids over 6 months increased plasma levels of these fatty acids, reduced stimulated tumour necrosis factor alpha production, but had no effect on the clinical severity of asthma in these children.

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The effect of lobectomy on lung function was investigated in 16 patients in whom comprehensive lung function tests were performed before and between six weeks and six months after lobectomy. The operation was well tolerated even by patients with quite severe airways obstruction. The effect of lobectomy on forced flow rates was in keeping with the change in lung volumes. There was no alteration in the distribution of ventilation and the diffusion capacity remained unchanged. The changes in the pressure volume curves were difficult to explain. All patients, even those with nearly "complete" hyperinflation of the remaining lung, had appreciable increases in maximal intrapleural pressure at full inspiration.

Serum levels of TNF-alpha and IL-5 were not related to peripheral eosinophilia and asthma severity in these children but were related to their own cellular production ex vivo. This study confirms that eosinophilia is the index of inflammation that is most closely related to the clinical severity of childhood asthma.