The temperature of the air within the external auditory meatus compared with esophageal temperature during anaesthesia and surgery

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 2: physiological measurements

In this, the second of four historical reviews on human thermoregulation during exercise, we examine the research techniques developed by our forebears. We emphasise calorimetry and thermometry, and measurements of vasomotor and sudomotor function. Since its first human use (1899), direct calorimetry has provided the foundation for modern respirometric methods for quantifying metabolic rate, and remains the most precise index of whole-body heat exchange and storage. Its alternative, biophysical modelling, relies upon many, often dubious assumptions. Thermometry, used for >300 y to assess deep-body temperatures, provides only an instantaneous snapshot of the thermal status of tissues in contact with any thermometer. Seemingly unbeknownst to some, thermal time delays at some surrogate sites preclude valid measurements during non-steady state conditions. To assess cutaneous blood flow, immersion plethysmography was introduced (1875), followed by strain-gauge plethysmography (1949) and then laser-Doppler velocimetry (1964). Those techniques allow only local flow measurements, which may not reflect whole-body blood flows. Sudomotor function has been estimated from body-mass losses since the 1600s, but using mass losses to assess evaporation rates requires precise measures of non-evaporated sweat, which are rarely obtained. Hygrometric methods provide data for local sweat rates, but not local evaporation rates, and most local sweat rates cannot be extrapolated to reflect whole-body sweating. The objective of these methodological overviews and critiques is to provide a deeper understanding of how modern measurement techniques were developed, their underlying assumptions, and the strengths and weaknesses of the measurements used for humans exercising and working in thermally challenging conditions.

Core temperature is not elevated at rest in people with relapsing-remitting multiple sclerosis

PURPOSE

To reassess the notion that people with multiple sclerosis (MS) do not demonstrate an elevated resting core temperature when measured using best-practice precision thermometry.

METHOD

Across two international data collection sites (Australia and USA), twenty-eight relapsing-remitting MS patients and 27 aged-matched controls (CON) were exposed to either 30 °C, 30% relative humidity (RH) (Sydney) or 25 °C, 30% RH (Dallas). Resting rectal (T_re) and esophageal (T_eso) temperature and resting oxygen consumption (VO₂) was measured in MS (n = 28) and CON (n = 27) groups who completed the 25 °C and 30 °C trials. Tympanic membrane (T_tym) temperature was measured in MS (n = 16) and CON (n = 15) groups in the 30 °C condition. A modified fatigue impact scale (MFIS) questionnaire was used to assess subjective measures of psychosocial, physical and cognitive fatigue in the 30 °C condition.

RESULTS

Irrespective of ambient temperature, no group differences were observed for T_re (MS: 37.07 ± 0.30 °C; CON: 37.18 ± 0.30 °C; P = 0.29), T_eso (MS: 36.84 ± 0.42 °C; CON: 36.92 ± 0.29 °C; P = 0.36) or resting VO₂ (MS: 3.89 ± 0.18 ml⋅kg^-1⋅min^-1; CON: 3.98 ± 0.17 ml⋅kg^-1⋅min^-1; P = 0.67). Similarly, no group differences were observed for T_tym (MS: 36.52 ± 0.38 °C; CON: 36.61 ± 0.33 °C; P = 0.55) in the 30 °C condition. Resting T_re did not correlate with subjective measures of fatigue: physical: r = -0.11, P = 0.67; cognitive: r = -0.14, P = 0.60; and psychosocial: r = 0.05, P = 0.84.

CONCLUSION

Contrary to recent reports, resting core temperature is not elevated in relapsing-remitting MS patients compared to healthy controls when measured using precision thermometry. Furthermore, no association was observed between resting T_re and any subjective measures of fatigue in a subset of participants with MS.

Impact of operator technique and device on infrared emission detection tympanic thermometry

Preliminary data on the use of infrared emission detection (IRED) tympanic thermometers suggest that operator technique may be important in IRED readings. No systematic investigation of specific technique and available IRED devices has previously been performed. In a prospective, blinded trial, 40 healthy adult subjects using six IRED thermometers with two techniques were examined in random sequence. Differences between IRED tympanic, oral, and rectal temperatures were compared using ANOVA. Significant differences were observed between all temperatures, the IRED devices, and the method of probe insertion. Differences between oral or rectal temperatures and IRED tympanic readings were reduced by an ear tug (as for routine otoscopy) for all but one device. An "ear tug" results in increased IRED readings that may improve accuracy of tympanic thermometers using IRED.

The effect of ambient temperature extremes on tympanic and oral temperatures

Exposure to ambient temperature extremes immediately preceding emergency department triage may affect tympanic membrane temperatures taken with infrared emission detection thermometers. In a prospective, unblinded study, 20 healthy subjects, on 2 separate days, underwent 15-minute exposures to hot (43.5 degrees C) and cold (-5 degrees C) temperature extremes in an environmental control room (ECR). Tympanic and oral temperatures were taken at baseline and at 2-minute intervals for 20 minutes after exiting the ECR. Rectal temperatures remained stable during the exposures. Oral temperatures rose significantly after hot exposure (P less than .05; max 0.4 degrees C) and briefly decreased after cold exposure (max 0.5 degrees C). Tympanic temperatures were elevated for 20 minutes after hot exposure (max 0.8 degrees C) and decreased briefly only in male subjects after cold exposure (max 0.7 degrees C). Individuals demonstrated wide variability in their temperature responses. Tympanic and oral temperatures taken within the first 20 minutes after exposure to outdoor temperature extremes may fail to accurately reflect the patient's true temperature.

Estimation of body sites temperatures from tympanic measurements

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.