.-The objective of this study was to determine whether acute volume loading elevates T-wave alternans (TWA) in dogs with structurally normal hearts. TWA predicts sudden cardiac arrest in patients with left ventricular dysfunction and congestive heart failure. However, volume load and ventricular stretch may themselves precipitate arrhythmias. It is unclear to what extent volume load causes TWA. In six male mongrel dogs [25.8 kg (SD 4.2)] under general anesthesia, we measured TWA during progressive atrial pacing to 160 beats/min. Pacing was performed at baseline, at the midpoint and peak of a saline infusion designed to induce acute CHF, and then during diuresis. Dog 1 was hypothermic throughout the protocol and excluded from analysis. For dogs 2-6, 102 ml/kg (SD 30) were infused over 315 min (SD 50), causing pulmonary capillary wedge pressure to rise from 9.6 (SD 3.5) to 21.2 mmHg (SD 1.6) (P Ͻ 0.01), and heart rate variability to fall (P Ͻ 0.01). TWA magnitude (Valt) rose in all dogs with volume load (P Ͻ 0.001). Compared with baseline, TWA at peak infusion had higher magnitude [Valt 3.4 (SD 1.95) vs. 0.5 V (SD 0.35); P ϭ 0.011] and occurred at lower heart rates [128 (SD 6) vs. 151 beats/min (SD 12); P ϭ 0.008]. Net volume load was linearly related to Valt (P Ͻ 0.01), with each 10 ml/kg net volume load increasing Valt by 0.23 V. Acute volume overload elevates TWA in normal canine hearts. Although dramatic, however, this effect may contribute clinically to abnormal TWA only in patients with marked volume overload. Future studies should examine the interaction of fluid overload, myocardial disease, and arrhythmia susceptibility.
For many years, measurement of body temperature in routine medical practice was limited to oral, rectal and axillary sites. Recent introduction of infrared non-contact thermometers for the auditory canal requires the establishing of temperature relationships between the ear and more traditional thermometry sites. Since an auditory canal is exposed to the environment, the infrared readings from it are influenced by ambient temperature. A linear model of thermal gradients in the vicinity of an ear canal allows us to find simple formulas connecting temperatures taken from the ear with those from traditional core sites like bladder or pulmonary artery, in addition to rectal and oral. The formulas contain environment coupling coefficients. Their values have been found experimentally by measuring body temperatures from subjects in a walk-in environmental chamber and from multiple clinical studies. The derived coefficients are used in the Thermoscan PRO-1 Instant Thermometer to calculate core, oral and rectal equivalent temperatures.
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