Calibration of sap flow estimated by the compensation heat pulse method in olive, plum and orange trees: relationships with xylem anatomy.

The compensation heat pulse method is widely used to estimate sap flow in conducting organs of woody plants. Being an invasive technique, calibration is crucial to derive correction factors for accurately estimating the sap flow value from the measured heat pulse velocity. We compared the results of excision and perfusion calibration experiments made with mature olive (Olea europaea L. 'Manzanilla de Sevilla'), plum (Prunus domestica L. 'Songal') and orange (Citrus sinensis (L.) Osbeck. 'Cadenero') trees. The calibration experiments were designed according to current knowledge on the application of the technique and the analysis of measured heat pulse velocities. Data on xylem characteristics were obtained from the experimental trees and related to the results of the calibration experiments. The most accurate sap flow values were obtained by assuming a wound width of 2.0 mm for olive and 2.4 mm for plum and orange. Although the three possible methods of integrating the sap velocity profiles produced similar results for all three species, the best results were obtained by calculating sap flow as the weighted sum of the product of sap velocity and the associated sapwood area across the four sensors of the heat-pulse-velocity probes. Anatomical observations showed that the xylem of the studied species can be considered thermally homogeneous. Vessel lumen diameter in orange trees was about twice that in the olive and plum, but vessel density was less than half. Total vessel lumen area per transverse section of xylem tissue was greater in plum than in the other species. These and other anatomical and hydraulic differences may account for the different calibration results obtained for each species.

Comparison of APACHE II, TRISS, and a proposed 24-hour ICU point system for prediction of outcome in ICU trauma patients.

The APACHE II system for predicting outcomes in critically ill patients is now being used to evaluate quality of care for patients in surgical intensive care units, including trauma patients. The trauma data, however, on which the APACHE outcomes are based, were derived from only 364 ICU trauma patients. We compared the outcome predictions by APACHE II, TRISS, and a proposed 24-hour ICU point system in 1,000 ICU patients. [table: see text] p less than 0.025 by unpaired t test for predictive power of ICU point system versus APACHE II. Values of more than 15.5 represent poor agreement between the outcomes estimated from the model and the observed outcomes; a low value represents good agreement. The APACHE system significantly overestimated the risk of death in the lower ranges of predicted risk and underestimated the deaths in the higher ranges. Although TRISS was not developed for ICU trauma patients, it tended to perform better than APACHE II in our sample. The 24-hour ICU point system performed well, with accurate agreement between the outcomes estimated from the model and the observed outcomes.