Comparison of heart rate obtained from shorter duration Holter recordings to 24-hour mean heart rate in dogs with atrial fibrillation.

The objective of this study was to evaluate the accuracy of short duration electrocardiographic (ECG) recordings extracted from ambulatory continuous ECG (Holter) to assess 24-hour mean heart rate in dogs with atrial fibrillation. In this retrospective study, Holter recordings obtained from 20 dogs with atrial fibrillation were selected for analysis. Ten out of 20 dogs were receiving drugs to control heart rate at the time of Holter evaluation. From the Holter recordings, heart rate averages were calculated for various sample durations (five-minutes, 30 minutes, one-hour, two-hours, and three-hours) for each dog. Percentage of these shorter duration ECG obtained HR averages that fell within ±10%, ±15% and ± 20% of 24-hour mean heart rate was determined for each sample duration and for each dog. Seventy five percent of heart rate averages obtained from three-hour ECG recordings fell within ±10% of 24-hour mean HR. All the heart rate averages obtained from two-hour ECG recordings fell within ±20% of 24-hour mean heart rate. Based on the results of this study it can be concluded that the duration of the ECG recording affects the prediction accuracy for 24-hour Holter mean HR. Only two and three hours of Holter recordings provided all heart rate averages within ±20% of 24-hour mean heart rate. No significant differences were noted in the prediction accuracy of shorter duration ECG recordings based on rate control therapy status. Further prospective studies are needed to assess the accuracy of HR obtained at home using various ECG recording devices to predict 24-hour mean heart rate in dogs with atrial fibrillation.

Correlating Li/O2 cell capacity and product morphology with discharge current.

The discharge rate is critical to the performance of lithium/oxygen batteries: it impacts both cell capacity and discharge-phase morphology, and in so doing may also affect the efficiency of the oxygen-evolution reaction during recharging. First-discharge data from tens of Li/O2 cells discharged across four rates are analyzed statistically to inform these connections. In the practically significant superficial current-density range of 0.1 to 1 mA cm(-2), capacity is found to fall as a power law, with a Peukert's-law exponent of 1.6 ± 0.1. X-ray diffractometry confirms the dominant presence of crystalline Li2O2 in the discharged electrodes. A completely air-free sample-transfer technique was developed to implement scanning electron microscopy (SEM) of the discharge product. SEM imaging of electrodes with near-average capacities provides statistically significant measures of the shape and size variation of electrodeposited Li2O2 particles with respect to discharge current. At lower rates, typical "toroidal" particles are observed that are well approximated as cylindrical structures, whose average radii remain relatively constant as discharge rate increases, whereas their average heights decrease. At the highest rate studied, air-free SEM shows that particles take needle-like shapes rather than forming the nanosheets or compact films described elsewhere. Average particle volumes decrease with current while particle surface-to-volume ratios increase dramatically, supporting the notion that Li2O2 grows by a locally mass-transfer-limited nucleation and growth mechanism.