In the canine model, measurement of chronic intrathoracic impedance with an implantable system effectively revealed changes in thoracic congestion due to heart failure reflected by LVEDP. These data suggest that implantable device-based impedance measurement merits further investigation as a tool to monitor the fluid status of heart failure patients.
These data support the conclusion that threshold is a voltage mediated response. Thus, voltage thresholds, not energy, current or pulse duration is the most relevant parameter for safety margin determination. Atrial parameters should be followed during electrolyte imbalances. Correlation in humans is needed.
An oxygen saturation sensor, for the purpose of chronically controlling the heart rhythm produced by a pacemaker, should be specific to oxygen saturation and should be minimally affected by the harsh blood environment. For the sensor type we tested we found: (1) one sensor failure in 205.5 canine-months of chronic implantation (n = 11, range 4 to 50 months); (2) hematocrit-induced error of less than 5 percentage points of SvO2 over the range of 50% to 80% SvO2 and 15% to 45% hematocrit; (3) carboxyhemoglobin (HbCO)-induced error of less than 4 percentage points of SvO2 with HbCO up to 20%; (4) a fibrotic sheath-induced error of less than 3 percentage points of SvO2 in the range of 50% to 80% SvO2 due to fibrotic sheath thicknesses up to 0.22 mm; (5) no significant error induced by velocity variations local to the sensor; (6) no significant error due to temperature in the range of 30 degrees to 42 degrees C; and (7) that the sensor could be as close as 0.3mm to the ventricular wall and still only produce an error of 5% SvO2.
The objective of this pilot study was to determine if three common anesthetic drugs have differing effects on the measurement of defibrillation thresholds (DFT) in dogs. The drugs compared were pentobarbital, isoflurane, and halothane. We used six dogs, which were surgically instrumented, in a chronic study design. Each dog had two internal defibrillation patches placed on its heart, which were used to deliver the defibrillation energy. DFT was determined while each dog was anesthetized under each of the listed drugs in a crossover design. This pilot study suggests that differences in DFT due to the anesthetic drugs is not significant in studies with low numbers of animals (halothane 14.5 +/- 1.0, isoflurane 14.2 +/- 1.0, pentobarbital 12.8 +/- 1.0; P = NS; mean +/- SE). The variation in DFT between individual animals is much larger than the difference in DFT due to the drugs.
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