In excised lungs of dogs, the static pressure-volume characteristics of the vascular bed were determined with the vessels filled with dextran and again after replacement of the dextran with kerosene. Whereas the dextran was distributed throughout the entire vascular bed, the kerosene was distributed only in relatively large vessels due to interfacial tension. Volume-pressure curves obtained with kerosene were markedly different from those obtained with dextran. Utilizing both types of volume-pressure curves, it was possible to separate the vascular bed of the lung into two compartments that responded oppositely to inflation of the lung when vascular pressure was held constant: one compartment, consisting of relatively large vessels, always increased in volume; the other compartment, consisting of smaller vessels, always decreased in volume. Submitted on June 9, 1960

SUMMARY A new self administered questionnaire completed by parents was used to study the prevalences of wheeze, shortness of breath, and cough in 2503 Southampton schoolchildren aged 7 and 11 together with exacerbating factors and background information including treatment and diagnosis. The questionnaire had a response rate of 84% and was found to be highly repeatable with respect to current symptoms. The overall prevalences of wheeze and shortness of breath in the current year (1986) were 12-1% and 8.5% respectively. Social class, home ownership, parental smoking, and presence of a family pet were unrelated to symptom prevalence. According to the parents the overall diagnosis rate for asthma was 9-5%. In common with other studies, however, we found considerable evidence for undertreatment. The symptoms of wheeze and nocturnal and morning breathlessness occurred more commonly in boys, but this sex ratio decreased with increasing age. The prevalences of wheeze and shortness of breath were similar in the two age groups. In contrast, there were only small differences between the sexes with respect to cough whereas, among children without wheeze or shortness of breath, there was a fall in the prevalence of cough from 18-9% at 7 years to 8-7% at 11 years. When controlling for the other respiratory symptoms, wheeze was the only symptom significantly related to parental asthma. The fall in the prevalence of cough between the two age groups is unlikely to be related to changes in asthma prevalence and, when not associated with wheeze, may be an indicator of separate pathology.Studies of the prevelance of asthma produce widely varying rates even among European populations.' These differences may be largely explained in terms of varying definitions of asthma and undue reliance on general practitioner diagnoses. This is confirmed by the considerably greater concordance between studies with respect to particular respiratory symptoms. Reliable information can only be gained if wheeze has been defined and explained adequately to parents.2-4 In a cross section survey in Melbourne, Williams and McNicol recorded a cumulative prevalence of 19% for wheeze at 7 years.2 Anderson et al reported a prevalence of 11% for wheeze during the current year in 9 year olds in Croydon.3 Lee et al found a prevalence of 14-8%

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It was shown that in excised lungs of dogs the effect of changing the degree of inflation of the lung was to change the static volume-pressure curve of the pulmonary vascular bed in shape, slope, and position. The data show that there is no simple answer to the question: does the pulmonary vascular bed get bigger or smaller with inflation of the lung? If vascular pressure was held constant when transpulmonary pressure was changed from 0 to 30 cm H2O, vascular volume increased when vascular pressure was low and decreased when vascular pressure was high. In addition, when vascular pressure was held constant, vascular volume changed in an opposite way depending on whether transpulmonary pressure was changed from low to moderate values or from moderate to high values. Submitted on June 9, 1960