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The importance of the viscoelastic properties of the tissues of the respiratory system has recently been recognized, and lung models have been produced to describe the resistive and viscoelastic properties of the lung. The pulmonary mechanics of 10 rabbits were studied using the interrupter technique to assess the effect of volume history on the resistive and viscoelastic elements of the respiratory system. The influence of the tone of the muscles of respiration was also studied. In healthy lungs, the resistive and viscoelastic elements of the lung are dependent on the volume history of the respiratory system and are significantly lower if these elements do not reach a resting position before expiration. The chest wall made a significant contribution to the resistive and viscoelastic elements of the respiratory system, which was also dependent on the lung volume history. The tone of the muscles of respiration had no effect on the resistive or viscoelastic elements of the respiratory system.

The different ventilatory pattern of HFOV and conventional ventilation (IPPV) may differently affect cerebral hemodynamics in neonates. Using color Doppler sonography we measured left ventricular output (LVO), the mean blood flow velocity (BFV,cm/s) in the median cerebral artery (MCA) and in the great cerebral vein (GCV) in 10 critically ill neonates [GA 27 (25-37) wks, weight 980 530-2500) g, age a (1-36) d] during IPPV and 3 (2-18) h after initiating HFOV (Infant Star). Indication for HFOV: Air leak (n = 8), failure of IPPV (n = 2). RESULTS: Data are medain and range. MAP = mean airway pressure (mmHg) OI = oxygenation index (OI = FiO2 × MAP × 100 / paO2). * = p < 0.05. During IPPV, LVO was low and MCA-BFV normal compared to data of 54 stable ventilated (IPPV) preterm neonates [GA 28(23-35)wks; LVO: 248(212-316), mean MCA-BFV: 10(5-28)]. During HFOV the blood flow in the MCA was oscillating synchroneously with the oscillations of the ventilator and arterial cerebral BFV was increased in all infants (increased pCO2) compared to IPPV. Venous cerebral BFV however was decreased (up to 45%), possibly due to the increased PEEP during HFOV. CONCLUSION: HFOV affects cerebral hemodynamics and may cause cerebral congestion in neonates at risk of intracranial hemorrhage.

There is evidence that morbidity and mortality from asthma as well as the prevalence of allergic diseases is increasing. As data were missing in Germany, we studied in a crossectional design 9 403 schoolchildren (age 9-11 years) in an urban and rural area of Bavaria using a questionnaire, skin prick tests and pulmonary function tests before and after cold air challenge. The responserates were: 87% for questionnaires, 77% for allergy or pulmonary function tests. Evaluation of the questionnaires gave the following prevalences: 18,1% allergic rhinitis, 19,7% atopic dermatitis, 2,5% asthma and 5,5% recurrent wheezy bronchitis. Beyond this 8,3% had recurrent wheezing and 3,4% chronic cough by night or exercise without any diagnose of asthma or wheezy bronchitis. 42 % of all german children are atopic, ie exhibit at least one positive prick test reaction for the six aeroallergens tested. Bronchial hyperreactivity was found in 9% of german children. Atopic diseases and asthma are more frequent in the urban than the rural area. In summary there is an important underdiagnosis of asthma in this pediatric population.