The shape of the maximum expiratory flow-volume curve reflects exposure infarming

The objective of the study was to examine the effect of farming exposure. r espiratory symptoms and smoking on the shape of the MEFV-curve in 1,691 mal e farming students and 407 male controls and to relate the slope ratio with FEV1 and FEV1/FVC. Each subject underwent a medical interview and the slop e ratios from the MEFV-curve at 75 (SR75), 50 (SR50) and 25 (SR25) %FVC tog ether with FEV, and FVC were recorded. Histamine bronchial reactivity (Yan method) was measured and skin prick test with inhalant allergens was perfor med. In smokers, SR75 increased with increasing exposure to: general farmin g, swine and dairy cattle (p less than or equal to 0.020). SR50 increased w ith increasing exposure to farming(p = 0.015). In non-smokers, SR25 increas ed with increasing exposure to swine and dairy cattle(p = 0.021) and increa sed SR25 was associated with sensitisation to house dust mite(p = 0.017). D ata revealed on interaction between smoking and exposure to farming. FEV1 a nd FEV1/FVC was not associated with farming exposure or production animals. FEV1 and FEV1/FVC (p less than or equal to 0.003) were lower among subject s with bronchial hyperresponsiveness and asthma( FEV I and asthma only in s mokers). SR75 (p = 0.037) and SR50 (p = 0.024) were increased in subjects w ith asthma and SR75 was increased in subjects with bronchial hyperresponsiv eness. but only in smokers (p = 0.002). In conclusion. exposure to farming seems to influence the shape of the MEFV-curve and there are indications of interaction between exposure to organic dust and smoking. These changes ar e seen only in the slope ratios and not in FEV1 and FEV1/FVC. However. FEV, and FEV1/FVC are superior to slope ratios in differentiating healthy subje cts from those with respiratory symptoms.