Optical carrier wave shocking: detection and dispersion.

Carrier wave shocking is studied using the pseudospectral spatial-domain (PSSD) technique. We describe the shock detection diagnostics necessary for this numerical study and verify them against theoretical shocking predictions for the dispersionless case. These predictions show a carrier envelope phase and pulse bandwidth sensitivity in the single-cycle regime. The flexible dispersion management offered by the PSSD enables us to independently control the linear and nonlinear dispersion. Customized dispersion profiles allow us to analyze the development of both carrier self-steepening and shocks. The results exhibit a marked asymmetry between normal and anomalous dispersion, both in the limits of the shocking regime and in the (near) shocked pulse wave forms. Combining these insights, we offer some suggestions on how carrier shocking (or at least extreme self-steepening) might be realized experimentally.

Two minute walking distance in cystic fibrosis.

We have evaluated the 'two minute walking distance' in children with cystic fibrosis as an objective measurement of exercise tolerance. There was a strong correlation between walking distance and height in 89 normal children (r = 0.72). Fifty children with cystic fibrosis showed a similar correlation (r = 0.56) with a mean result of 94% of that expected for height compared with the normal children. There was a training effect in the normal children with the second walk being significantly better than the first, but this was not evident in children with cystic fibrosis. The test was reproducible with no significant change in 12 children retested after one to three months. Sixteen children with cystic fibrosis admitted for treatment of chest disease showed a significant improvement in walking distance with treatment. Children as young as 5 years old can perform a walking distance test. It seems to be an objective way of assessing exercise tolerance and can help in evaluating response to treatment.

Face mask physiotherapy in cystic fibrosis.

The use of the 'PEP' mask with forced expiratory coughing was compared with conventional physiotherapy over a one month period. No difference was shown in symptom scores, sputum production, or simple lung function tests. The mask was well accepted and allowed independent treatment by older patients.

Familial neural crest tumours.

It is known that some cases of neural crest tumours are hereditary. We report the clinical and cytogenetic findings in a three-generation, extended family, four members of which developed single or multiple neural crest tumours (ganglioneuroma, ganglioneuroblastoma or neuroblastoma). To our knowledge, this is the first report of a family with three generations affected. No constitutional cytogenetic abnormality was found in the two members tested. We also review the literature on familial neural crest tumours, with emphasis on those affecting more than one generation. It is important that a detailed family history, with particular reference to tumours, is obtained in all cases of childhood cancer.

Nyctalopia and conjunctival xerosis indicating vitamin A deficiency in cystic fibrosis.

Thirty-one Cystic Fibrosis patients were investigated for clinical and biochemical evidence of Vitamin A deficiency. All had been prescribed oral pancreatic enzyme replacements and twice the recommended daily requirement of Vitamin A (5000IU). None were aware of any ocular symptoms, but 3 out of 31 (10 per cent) were found to have frank conjunctival xerosis and six (19 per cent) to have abnormal dark adaptation. There was no correlation between the above findings and abnormal liver function or clinical disease severity. All patients with cystic fibrosis should have regular Vitamin A estimations with ophthalmological assessment if serum levels fall below 30 microgram/dl.

Night blindness and conjunctival xerosis caused by vitamin A deficiency in patients with cystic fibrosis.

Forty three patients with cystic fibrosis, aged 8-44 years (median 16 years), were examined for evidence of vitamin A deficiency. Eight patients had abnormal dark adaptation tests and three had conjunctival xerosis. Serum vitamin A and retinol binding protein concentrations were significantly lower in the affected patients who were also more likely to have abnormal liver function tests. Five patients were treated with 100,000-200,000 IU water miscible vitamin A orally and their daily vitamin supplements were increased to maintain normal concentrations. In four patients dark adaptation tests were repeated. Three were normal, but one patient required three further doses of water miscible vitamin A and a daily supplement of 12,000 IU vitamin A before her dark adaptation threshold returned to normal. Adolescents with cystic fibrosis are liable to develop night blindness and conjunctival xerosis, particularly if they have liver disease or fail to take daily vitamin supplements.