A comparison of 2 methods of measuring rectal temperatures with digital thermometers.

BACKGROUND: Digital rectal thermometers typically have 2 distinct modes of operation: dwell or monitor, in which body temperature is displayed continuously, and predictive, in which body temperature is mathematically estimated on the basis of the curve of temperature rise that occurs after the thermometer is inserted. Although the dwell mode is generally considered more accurate, the predictive mode allows more rapid measurement. Direct comparisons of these 2 methods are lacking. OBJECTIVE: To determine if measurements of rectal temperatures obtained with the predictive mode differ significantly from those obtained with the dwell mode. METHODS: For each of 10 subjects, both dwell and predictive modes were used to measure early morning rectal temperature. For comparison of the 2 modes during states of temperature flux, 8 subjects had rectal temperatures measured after swimming in cold water. Initial predictive values were measured directly after each subject exited from the water. Initial dwell values were estimated by linear extrapolation of measured 3- and 6-minute dwell values. Paired-sample statistical methods were used to compare data. RESULTS: Measurements of early-morning temperatures obtained with the predictive mode did not differ significantly from those obtained with the dwell mode (P = .64). Predictive values also did not differ significantly from extrapolated dwell values for measurements obtained during mild temperature flux after immersion in cold water (P = .33). CONCLUSION: The predictive and dwell modes of digital rectal thermometers yield similar measurements of temperature during steady-state conditions and during states of mild temperature flux.

Hypothermia and afterdrop following open water swimming: the Alcatraz/San Francisco Swim Study.

To determine whether or not participants in open water swim events experience hypothermia and afterdrop, rectal temperature was measured for up to 45 minutes in 11 subjects following the New Year's Day Alcatraz Swim. This event was held in open water (11.7 degrees C [53.0 degrees F]) in the San Francisco Bay, and participants did not wear wetsuits or other protective clothing. Biophysical parameters, including surfacelvolume ratio, body mass index, and percent body fat were measured before the swim, and statistical analysis was done to determine predictors of temperature decrease and afterdrop duration. Applying the American Heart Association definition of hypothermia (less than 36.0 C [96.8 degrees F]), hypothermia was seen in 5 of the 11 subjects. Using a more rigorous and traditional definition (less than 35.0 degrees C [95.0 degrees F]), hypothermia was seen in only one subject. Afterdrop, defined as continued cooling following removal from cold stress, was seen in 10 of the 11 subjects. Surface/volume ratio (S/V) and body mass index (BMI) predicted the lowest recorded temperatures (P < .05; r(S/V) = -.71, r(BMI) = .72) and afterdrop duration (P < .05; r(SN) = -.75, r(BMI) = .69). These results suggest that hypothermia and afterdrop can occur commonly after recreational open water swimming, and that participants should be observed for signs of temperature decrease following removal from cold stress.