Comments on "Computer-Assisted Continuous Infusion of the Intravenous Analgesic Fentanyl During General Anesthesia?An Interactive System"

This communication shows an algorithm used in the drug infusion system discussed in a recent paper1 to be incorrect. The error is corrected, and a new algorithm is presented.     

Modeling the Rate of Premature Ventricular Contractions and its Response to Lidocaine Infusion

The rate of premature ventricular contractions (PVC rate) and the dynamics of its response to the intravenous infusion of the antiarrhythmic drug lidocaine was modeled to facilitate the design of a closed-loop drug infusion system. An autoregressive moving average model structure with the lidocaine infusion rate as an exogenous input (ARMAX structure) was used. System identification experiments were performed using a canine model of myocardial infarction. The drug infusion rate was varied using a pseudorandom binary sequence (PRBS) test input to excite the system about an operating point established by an exponential infusion regimen. PVC's were detected in real time with a correlation technique. Model parameters were estimated in an offline data analysis. First-order models provided an adequate representation of the PVC rate in eight of ten runs. A second-order model was validated for two runs.     

A comparison of the noise sensitivity of nine QRS detectionalgorithms

The noise sensitivities for nine different QRS detection algorithms were measured for a normal, single-channel lead II, synthesized ECG corrupted with five different types of synthesized noise. The noise types were electromyographic interference, 60 Hz powerline interference, baseline drift due to respiration, abrupt baseline shift, and a composite noise constructed from all of the other noise types. The percentage of QRS complexes detected, the number of false positives, and the detection delay were measured. None of the algorithms were able to detect all QRS complexes without any false positives for all of the noise types at the highest noise level. Algorithms based on amplitude and slope had the highest performance for EMG-corrupted ECG. An algorithm using a digital filter had the best performance for the composite noise corrupted data.     

Automated heparin-delivery system to control activated partial thromboplastin time: evaluation in normal volunteers

BACKGROUND: Unfractionated heparin is used widely; however, control of the level of anticoagulation remains its greatest problem, with fewer than 35% of patients having activated partial thromboplastin times (aPTTs) within a range of 55 to 85 seconds in recent trials. METHODS AND RESULTS: We developed and tested a prototype of an automated heparin control system (AutoHep) in which a computer-based titration algorithm adjusted the heparin infusion to reach a target aPTT. In 1 study, 12 healthy male subjects received an intravenous infusion of heparin with the rate determined by AutoHep and were randomized to receive an initial bolus or no bolus of heparin preceding the infusion. A second study evaluated the automated blood sampling system in 12 subjects. Of the 344 end-point aPTT measurements, 78% were within +/-10 seconds of the target (prespecified primary end point), and 89% were within a +/-15-second range. The time to achieve a target aPTT was 93 minutes without and 150 minutes with an initial heparin bolus. The total percentage of time within the target range +/-15 seconds was 46 of 48 hours (96%). The automatic blood sampling system successfully obtained 96% of all scheduled samples. CONCLUSIONS: These results suggest that the AutoHep system has the potential to significantly improve aPTT control of intravenous heparin compared with current clinical practice.     

Chemical and electrochemical oxidation of copper in dielectric millimeter waveguide tubes

Chemical and electrochemical techniques are developed for oxidation of copper to constant thicknesses in 51 and 60 mm i.d. tubes up to 11 m in length. Comparison between these oxidation processes show the electrochemical process to be superior for this application. Differential double layer capacitance measurement of copper roughness after the oxidation indicates roughness factors between 3.2 and 9.9 depending on the thickness of the oxide. Potentiodynamic sweeps were used to investigate the mechanism of electrochemical oxidation in sodium hydroxide solutions saturated with copper containing complexes.