Adults with obstructive sleep apnea syndrome (OSAS) display substantial heart rate changes associated with obstructive events, and recent reports suggest similar heart rate changes in children with OSAS. These rate changes could assist screening of young patients for OSAS. Six-hour polysomnographic recordings were obtained from seven children with OSAS (mean age: 4.5 years; apnea index: 19.5 +/- 5.1) and from seven primary snorers without OSAS who served as controls (mean age: 4.7; apnea index: 0). Scatterplots of each cardiac R-R interval against the preceding interval (Poincaré plots) were used to assess beat-to-beat cardiac variability at different heart rates. Beat-to-beat variation at slow rates was significantly increased in children with OSAS relative to controls, while variation at fast and intermediate heart rates was significantly reduced in these children. We conclude that OSAS alters beat-to-beat variation in characteristic fashions in children, that the variability changes occur at all heart rates but are most significant at slow heart rates, and that these heart rate patterns could assist in screening of suspected cases of OSAS.

The flow hydrograph, thickness of the winter ice cover, and stream morphology are three climate-influenced factors that govern river ice processes in general and ice breakup and jamming in particular. Considerable warming and changes in precipitation patterns, as predicted by general circulation models (GCMs) for various increased greenhouse-gas scenarios, would affect the length and duration of the ice season and the timing and severity of ice breakup. Climate-induced changes to river ice processes and the associated hydrologic regimes can produce physical, biological, and socioeconomic effects. Current knowledge of climatic impacts on the ice breakup regime of rivers and the future effects of a changing climate are discussed.Key words: breakup, climate change, global warming, greenhouse effect, hydrology, ice, ice jam, impacts, prediction, river ice.

Ventilatory responses to peripheral chemoreceptor stimuli are absent in patients with Prader-Willi syndrome (PWS) during wakefulness. Because arousal from sleep after rapidly developing hypoxia may require intact peripheral chemoreceptor function, we hypothesized that blunted hypoxic arousal responses during sleep Stage 3/4 would be present in PWS. Thirteen patients with PWS (mean age, 23.4 +/- 3.7 +/- SEM yr; 46% male; body mass index [BMI], 28.9 +/- 1.6 kg/m2) and 11 matched control subjects (mean age 28.0 +/- 5.4 yr; 54% male; BMI, 28.8 +/- 3.1 kg/m2) were studied. An abrupt decrease in inspired O2 tension to 80 mm Hg was introduced until arousal occurred or for a maximum of 3 min. One of the 13 patients with PWS and seven of the 11 control subjects were aroused by the hypoxic challenge (p < 0.02). During hypoxia, heart rate increased by 9 +/- 2% in the PWS group versus 22 +/- 4% in the control group (p < 0.005). Respiratory rate did not change in the PWS group (4 +/- 2%; p = NS), but it increased by 13 +/- 2% in the control group (p < 0.02). We conclude that abnormal arousal and cardiorespiratory responses to hypoxia are frequent in PWS. We postulate that intact peripheral chemoreceptor function is an important component underlying arousal mechanisms to rapidly developing hypoxia during sleep.

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Supplemental oxygen during sleep may be useful as a temporary palliative treatment in children with obstructive sleep apnea syndrome (OSAS) associated with significant hypoxemia. However, supplemental O2 may also blunt hypoxic ventilatory drive and worsen ventilation. To assess the safety of the use of supplemental O2 in children with OSAS, we studied 16 children ages 2-8 (mean: 4.28 +/- 2.88 yr) with OSAS secondary to adenotonsillar hypertrophy. Patients underwent two overnight polysomnograms within 1 mo, one on room air (RA) and one while receiving supplemental O2 via nasal cannula titrated by 1/4 lpm increments to achieve SpO2 > 95% during the first hour of sleep. Oxygenation measurements were significantly improved during supplemental O2 nights (average SpO2 increased from 89.5 +/- 4.8% on RA to 97.7 +/- 1.8% on supplemental O2 [p < 0.00001]) while alveolar ventilation remained unchanged (PETCO2 > 50 mm Hg: 3.6 +/- 8.9% total sleep time on RA and 3.3 +/- 6.3% total sleep time on supplemental O2 [p = NS]). Supplemental O2 significantly reduced hypopnea density, obstructive apnea index, and paradoxical breathing. The density and average duration of central apneas remained unchanged. In addition, supplemental O2 increased the percentage of REM sleep time and decreased the number of microarousals. We conclude that supplemental O2 might be a safe and beneficial temporary treatment in children with OSAS.

Greater opportunity now exists compared to 35 years ago for civil engineers to apply river ice knowledge to practical problems of planning, designing, and operating hydro-power facilities, water intakes, bridges, and other infrastructure along ice-covered rivers. This is due to major advancements made during this period in understanding the physical processes of river ice formation, growth and breakup, in developing instrumentation for acquisition of information on winter environments, and in developing numerical modelling tools. An increasing number of journal articles, as well as papers presented at the river ice workshops of the CGU Committee on River Ice Processes and the Environment (CRIPE) and the ice symposia of the International Association for Hydro-Environment Engineering and Research (IAHR) attest to the advancement in river ice science and engineering knowledge that has occurred during the past 35 years. This paper reviews the developments in river ice science and engineering from a Canadian perspective and briefly discusses future directions.

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Surges are the most violent and spectacular events that occur during the ice breakup. Upon the release of an ice jam, water and ice held by the jam are suddenly free to move. The resulting surge generates increased water stages and higher flow velocities, such that the water wave and ice run pose a risk to downstream structures, people, and aquatic life. Climate-induced changes to river ice processes, such as enhanced mid-winter jamming or increased spring flows, could result in more frequent occurrence of major and damaging surges. To address a dearth of related quantitative data, a remote water-level reporting method has been developed and used to obtain field measurements on ice-jam generated surges. The results are consistent with the few available data but only partly conform to existing theories.Key words: breakup, celerity, ice jam, release, river, surge, wave.