Therapy with nasal CPAP (continuous positive airway pressure) in patients with obstructive sleep apnea syndrome (OSAS). I: Long-term acceptance of nasal CPAP

BACKGROUND: Nocturnal ventilation with nCPAP has been established as the safest and most efficient nonsurgical treatment for OSAS. Long-term results, however, are determined by the patients' compliance with therapy. The aim of this study was the objective measurement of long-term acceptability of nCPAP therapy in all patients receiving this treatment in our sleep laboratory between January 1990 and March 1995. METHODS: We prospectively investigated 41 patients (36 male, 5 female) with moderate to severe OSAS who received nCPAP therapy. Mean time of follow-up was 20.6 months, ranging from 1.2 to 53.5 months. Therapy was indicated when OSAS was confirmed by cardiorespiratory polygraphy and either (1) the patient complained of daytime sleepiness or (2) the patient possessed an apnea-hypopnea index greater than 30/h or when the mean oxygen desaturation was below 80% regardless of the presenting symptoms. The compliance with treatment was defined as a mean rate of use of over 5 hours per night calculated from the time counter on the nCPAP machine. RESULTS: 33 patients (88.5%) have continued using nCPAP until the present time but only 24 patients (59%) met our criteria for long-term acceptance and this group was identified as responders. We found no significant differences in age, body mass index, apnea-hypopnea index, and nCPAP-pressure between responders and non-responders. CONCLUSION: Although nCPAP is the safest treatment for OSAS, there is still a large group of patients with moderate to severe OSAS who are not efficiently treated with nCPAP because of the low long-term acceptability of this therapy. With respect to this group of patients, surgical approaches have to be considered as an alternative therapy.     

In vivo cerebral metabolism and central benzodiazepine-receptor binding in temporal lobe epilepsy

Positron emission tomography measured interictal cerebral glucose metabolism with [18F]fluorodeoxyglucose and central benzodiazepine-receptor binding with [11C]flumazenil in 10 mesial temporal lobe epilepsy (TLE) patients and in normal subjects. Eight TLE patients had mesial temporal, lateral temporal, and thalamic hypometabolism ipsilateral to EEG ictal onsets, with additional extratemporal hypometabolism in four. One had unilateral anterior mesial temporal hypometabolism only, and one had normal metabolism. Each patient had decreased benzodiazepine-receptor binding in the ipsilateral anterior mesial temporal region, without neocortical changes. Thus, interictal metabolic dysfunction is variable and usually extensive in TLE, whereas decreased central benzodiazepine-receptor density is more restricted to mesial temporal areas. Metabolic patterns in TLE may reflect diaschisis, while benzodiazepine-receptor changes may reflect localized neuronal and synaptic loss that is specific to the epileptogenic zone. [11C]Flumazenil imaging may be useful in presurgical evaluation of refractory complex partial seizures.     

Remote sensing of photosynthetic light-use efficiency across two forested biomes: Spatial scaling

Eddy covariance (EC) measurements have greatly advanced our knowledge of carbon exchange in terrestrial ecosystems. However, appropriate techniques are required to upscale these spatially discrete findings globally. Satellite remote sensing provides unique opportunities in this respect, but remote sensing of the photosynthetic light-use efficiency (ε), one of the key components of Gross Primary Production, is challenging. Some progress has been made in recent years using the photochemical reflectance index, a narrow waveband index centered at 531 and 570 nm. The high sensitivity of this index to various extraneous effects such as canopy structure, and the view observer geometry has so far prevented its use at landscape and global scales. One critical aspect of upscaling PRI is the development of generic algorithms to account for structural differences in vegetation. Building on previous work, this study compares the differences in the PRI: ? relationship between a coastal Douglas-fir forest located on Vancouver Island, British Columbia, and a mature Aspen stand located in central Saskatchewan, Canada. Using continuous, tower-based observations acquired from an automated multi-angular spectro-radiometer (AMSPEC II) installed at each site, we demonstrate that PRI can be used to measure ? throughout the vegetation season at the DF-49 stand (r² = 0.91, p < 0.00) as well as the deciduous site (r² = 0.88, p < 0.00). It is further shown that this PRI signal can be also observed from space at both sites using daily observations from the Moderate Resolution Imaging Spectro-radiometer (MODIS) and a multi-angular implementation of atmospheric correction (MAIAC) (r² = 0.54 DF-49; r² = 0.63 SOA; p < 0.00). By implementing a simple hillshade model derived from airborne light detection and ranging (LiDAR) to approximate canopy shadow fractions (α_s), it is further demonstrated that the differences observed in the relationship between PRI and ε at DF-49 and SOA can be attributed largely to differences in α_s. The findings of this study suggest that algorithms used to separate physiological from extraneous effects in PRI reflectance may be more broadly applicable and portable across these two climatically and structurally different biome types, when the differences in canopy structure are known.