Latency measurements between three potentials (waves I, III, and IV/V) of the human brainstem auditory response can allow early detection of certain posterior fossa lesions. The diagnostic use of these interwave latencies requires knowledge of what factors may prolong them in the absence of disease. Hypothermia appears to be one such factor--in 5 neurologically and audiometrically normal patients, mean esophageal temperatures as high as 34.5 degrees C resulted in prolongations of central auditory conduction time. Interwave latency prolongations that were abnormal relative to an age-matched normal population were seen at 32.1 degrees +/- 0.3 degrees C in patients with both spontaneous and induced hypothermia, and these abnormalities disappeared after rewarming to normothermia. Hypothermia often accompanies intoxication and coma and should therefore be considered when brainstem auditory response abnormalities are being interpreted in these two clinical conditions.
The thermal conductivity (Λ) of 13 specimens of lightweight concrete, incorporating either Lytag, Pellite or Aglite aggregates, varying in density from 1144–1424 kg/m3 have been measured at several moisture contents between 0.03 and 19.75 per cent by volume. Although the Λ-value increased with increasing moisture content, the change was much less than that predicted by the Jakob factors. In general, the moisture factors were found to be density dependent and to increase with decreasing conductivity. A general expression has been derived relating the moisture factor to both density and moisture content by volume over the range 0–4 per cent. A comparison has been made between Λ obtained up to 6.5 per cent moisture content, corrected to 3 per cent using this expression, and experimental results at 3 per cent moisture content. Close agreement was obtained. This expression has also been used to correct the Λ-values to 5 per cent moisture content by volume and reasonable agreement has been obtained with the limited experimental data obtained at this level.
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