Effects of sensor selection on exercise stroke volume in pacemaker dependent patients

The effects of sensor selection and sensor blending on the cardiovascular response to graded exercise was evaluated in 10 patients (age 74 +/- 2 yrs; 7 men and 3 women) implanted with a dual sensor rate adaptive VVIR pacemaker (Vitatron Topaz model 515). Patients underwent three graded exercise tests (GXT) with sensor programming randomly assigned. For a given graded exercise text the pacemaker was programmed into activity sensing (ACT), QT sensing, or dual sensing (ACT = QT). Data were recorded at rest and during each stage of the graded exercise text. Oxygen uptake (VO2) was measured continuously using a Q Plex I system. Heart rate (HR), stroke volume (SV), and cardiac output (Qc) were measured by impedance cardiography. Systolic time intervals were calculated from simultaneous recordings of the ECG, phonocardiogram, and the impedance cardiogram. In response to the GXT no differences in peak VO2 were observed across the three sensor settings. Regardless of the sensor setting Qc increased linearly with each increment in VO2. The HR response to ACT only pacing was significantly higher than in the other two pacing conditions. During ACT only pacing SV failed to rise in response to exercise. The increased exercise Qc during QT and ACT = QT pacing were mediated by significant increases in both HR and SV. The QT and dual pacing conditions were also associated with longer diastolic filling times. The data indicate that the mechanisms responsible for the increase Qc during exercise were different for ACT versus ACT = QT or QT sensor-driven pacing.     

Reliability and error estimations of mechanical shock recorders and impact indicators

There have been significant developments in the electronics industry over the past decade which have led to the development of a variety of electronic measuring devices that can be placed in packages to both record and save shock and vibration data related to shipment. Most of the earlier devices were purely mechanical in nature and used a paper graph or a visual indicator to quantify shock levels. There are many of these types of mechanical devices that are still being used today because of their low cost. This study was performed to determine the reliability and error for various types of commercial mechanical shock recorders and impact indicators. The results are presented in the form of mean per cent errors in measuring shock values. The study concluded that the Impact-O-Graph recorder measured shock values more accurately than the Impact Register and that the Omni-G, Mag 2000 and Shockranger were similar in accuracy and were better than the Shockwatch when used in a variety of packages judged to be typical for instrumented shipment.     

Flame propagation,extinguishment and environmental effects on combustion

Homogeneous and heterogeneous combustible-oxidant systems are defined, and the influence of temperature, pressure, gravity, composition of the oxidant, and irradiation on flammability characteristics of each system are explained. The chemical reactions and physical mechanisms of flame extinguishment are reviewed briefly in connection with the two combustible-oxidant systems.     

Automated system administration with feedback regulation

The automation of system administration tasks requires a notion of convergence towards a stable state. Some simple models for such convergence with feedback, utilizing the system administration robot cfengine, are examined. Statistical analysis of computer systems can provide information which may be used to regulate the way in which they are used in the future without the need for excessive human intervention. © 1998 John Wiley & Sons, Ltd.