Rectal and gastrointestinal temperature differ during passive heating and subsequent recovery

Area of Science:

• Exercise Physiology
• Thermoregulation
• Sports Science

Background:

• Accurate core body temperature monitoring is crucial in exercise and heat stress research.
• Rectal temperature (T_rec) is a common proxy for core body temperature, but its agreement with gastro-intestinal temperature (T_GI) under various conditions is debated.
• Investigating the influence of passive heating and recovery interventions, like ice slurry ingestion, on temperature measurement agreement is important for practical applications.

Purpose of the Study:

• To compare rectal temperature (T_rec) and gastro-intestinal temperature (T_GI) during passive heating and subsequent recovery.
• To examine the effect of ice slurry ingestion on the agreement between T_rec and T_GI during recovery from passive heating.
• To assess the reliability of T_rec as a surrogate for T_GI under these specific experimental conditions.

Main Methods:

• Twelve healthy males underwent passive heating via hot water immersion to elevate T_rec by approximately 1.8°C.
• Following heating, participants underwent a 60-minute recovery period in ambient conditions.
• During recovery, participants ingested either an ice slurry (ICE) or a control drink (CON), with T_rec and T_GI continuously monitored.

Main Results:

• During passive heating, T_rec was consistently lower than T_GI (P < 0.001).
• During recovery, T_rec became higher than T_GI (P < 0.001).
• Agreement between T_rec and T_GI was less favorable during the recovery phase compared to the heating phase, with wider Limits of Agreement (LoA) observed in the recovery period for both ICE and CON conditions.

Conclusions:

• Rectal temperature (T_rec) and gastro-intestinal temperature (T_GI) exhibit significant differences during both passive heating and subsequent recovery.
• The agreement between T_rec and T_GI is reduced during the recovery phase, irrespective of ice slurry ingestion.
• T_rec may not be a consistently reliable indicator of T_GI during the recovery from passive heat stress, suggesting caution when using T_rec as the sole measure of core body temperature in such scenarios.