Under control conditions, the right ventricle operates at maximum efficiency and submaximal work output. Compliance of the pulmonary artery is a significant factor in decoupling the right ventricle from its vascular load. As the compliance decreases with acute pulmonary hypertension, the maximum stroke work against load point shifted in such a manner that the right ventricle changed its operational status from a flow to a pressure pump, resulting in a decreased stroke volume.

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Background It would be helpful if patients with asthma who require admission to hospital for an acute attack could be identified. Methods The relation between the severity of an attack of asthma as determined by admission assessment and the eventual outcome was studied in 52 asthmatic patients aged 14 to 44 years and admitted to an asthma emergency room. The patient's history, including medication and previous admissions to hospital, was recorded and a clinical assessment, including a full inspiratory and expiratory flow-volume loop, was performed on four occasions: on admission, at two hours and at 12-18 hours after the start of a standardised treatment, and two weeks later on an outpatient basis. Patients who were discharged and who had an uneventful follow up at the two week assessment were defined as good responders. Patients who had to be admitted to hospital after 12 to 18 hours or were readmitted during the two weeks, or both, were defined as poor responders. Results Thirty eight patients were good responders and 14 were poor responders (seven admitted at 12 to 18 hours, seven returned to hospital). All four patients with a raised arterial carbon dioxide tension (Paco2) ( > 6 kPa) and the three with cyanosis were in the poor responder group, and this group had lower peak expiratory flow (PEF) values (21% v 30% predicted) on admission. There was, however, considerable overlap in PEF between the two groups and no clinical measure was able to distinguish between the good and the poor responders reliably. Poor

An easy and accurate method of assessing bronchial hyper-reactivity could be of great value in identifying and classifying the degree of severity of asthma in children. The sensitivity and specificity of three methods of provocation, ie, histamine, nebulized water, and exercise, were compared in 20 asthmatic and 20 control children between ages 5 and 13 years. Three clinical categories of severity ranging from slight (Group 1) through moderate (Group 2) to severe asthma (Group 3) were identified. The three methods were compared in each subgroup for detecting a tendency to bronchospasm. An inverse correlation (-0.57) was found between the histamine dose and clinical degree of severity, whereas distilled water and exercise proved to be too insensitive for identifying Group 1 asthmatics. Histamine challenge in children is a safe and sensitive technique for identifying asthma and for monitoring the severity of the disease during follow-up.