Umbilical temperature correlation with core and skin temperatures at rest, in the heat and during physical activity

Figures & data

Table 1. Anatomical rationale for the relationship of umbilical temperature with intraabdominal temperature.

In non-overweight persons, the umbilicus is thinner (men, 8.1 ± 4.8 mm; women, 10.6 ± 4.9 mm) [21] than the rest of the abdominal wall, as there is little fat or muscle associated with its inner surface to insulate it from core heat (fat is a poor conductor and good insulator of heat) [14,15].

The inner surface of the umbilicus is free and separated from the abdomen only by the parietal peritoneum [16] that is tightly adherent to the umbilical ring [17] and porous so that it can transmit heat radiating from the peritoneal cavity.

As a body cavity, the umbilicus allows for cross-radiation from its opposing walls, with little heat loss, so that its surface temperatures more closely approximate core temperatures [8,9,11].

The central depression of the umbilicus moderates the effects of air currents upon its skin temperature (dependent on umbilical depth) [8].

The umbilical cord remnants (hepatic ligamentum teres, medial umbilical ligaments, urachus), attached proximally to the underside of the umbilicus and distally to intraabdominal organs, are vascularised [18–20] and can transmit intraabdominal heat along a vascular temperature gradient [11].

Figure 1. Heating garment utilised by Group B.

Figure 2. Umbilicus temperature in a silicone sleeve.

Figure 3. Average T_rectal regressed on linear and quadratic average T_umb (overall R² 0.583).

Table 2. Subject characteristics and descriptive statistics by study and phase.

Characteristics	Study A	Study B	Study C
Number of subjects	11	7	10
Age (years)	21.6 ± 0.9, 20–23	25.6 ± 5.4, 21–36	23.4 ± 2.7, 21–29
Weight (kg)	79.2 ± 6.8, 68–89	80.1 ± 8.5, 62–89	79.5 ± 6.1, 67–86
Height (cm)	86 ± 6.9, 174–196	179 ± 9.1, 165–193	181 ± 9.2, 165–196
BMI (kg/m^2)	23 ± 2.0, 20–26	25 ± 1.7, 23–27	26 ± 2.7, 22–30
Variables
Study phase I
Avg. rectal Temp.	36.9 ± 0.3, 36.5–37.3	36.9 ± 0.1, 36.7–37.1	37.0 ± 0.3, 36.5–37.4
Avg. chest Temp.	32.7 ± 0.8, 31.6–34.6	33.9 ± 0.8, 32.6–34.8	34.0 ± 1.6, 31.5–36.0
Avg. umbilical Temp.	33.4 ± 0.6, 32.4–34.5	34.5 ± 1.2, 32.5–35.7	34.6 ± 0.8, 33.3–35.7
Peak rectal Temp.	37.0 ± 0.3, 36.6–37.3	36.9 ± 0.2, 36.7–37.1	37.0 ± 0.2, 36.6–37.5
Peak chest Temp.	33.1 ± 0.8, 32.2–34.9	34.4 ± 0.6, 33.1–35.0	34.3 ± 1.5, 31.8–36.2
Peak umbilical Temp.	33.7 ± 0.6, 32.6–34.8	34.6 ± 1.2, 32.9–35.8	34.8 ± 0.9, 33.3–36.1
Study phase II
Avg. rectal Temp.	36.8 ± 0.3, 36.2–37.2	37.0 ± 0.2, 36.8–37.2	37.0 ± 0.3, 36.5–37.4
Avg. chest Temp.	35.1 ± 0.4, 34.5–35.9	36.3 ± 1.1, 33.7–36.8	35.1 ± 0.9, 33.3–36.3
Avg. umbilical Temp.	35.5 ± 0.6, 34.4–36.2	36.2 ± 0.5, 35.6–37.0	35.4 ± 0.8, 33.8–36.4
Peak rectal Temp.	36.8 ± 0.3, 36.3–37.2	37.3 ± 0.2, 37.2–37.5	37.0 ± 0.2, 36.5–37.4
Peak chest Temp.	35.4 ± 0.4, 34.6–36.3	37.4 ± 0.3, 37.1–38.0	35.6 ± 0.9, 33.9–36.5
Peak umbilical Temp.	35.8 ± 0.6, 34.5–36.5	37.2 ± 0.2, 37.0–37.5	35.9 ± 0.7, 34.4–36.6
Study phase III
Avg. rectal Temp.	37.0 ± 0.3, 36.6–37.5	37.7 ± 0.2, 37.5–37.9	37.5 ± 0.3, 37.1–38.0
Avg. chest Temp.	35.9 ± 0.2, 35.5–36.3	36.7 ± 0.3, 36.1–37.2	36.5 ± 0.4, 36.0–37.0
Avg. umbilical Temp.	36.1 ± 0.5, 35.2–36.6	36.9 ± 0.3, 36.6–37.3	37.1 ± 0.3, 36.5–37.1
Peak rectal Temp.	37.2 ± 0.2, 36.9–37.6	37.9 ± 0.2, 37.7–38.2	38.4 ± 0.4, 37.5–39.0
Peak chest Temp.	36.1 ± 0.3, 35.7–36.6	36.9 ± 0.2, 36.7–37.3	37.5 ± 0.5, 36.4–38.0
Peak umbilical Temp.	36.4 ± 0.5, 35.6–36.9	36.6 ± 0.3, 36.6–37.4	38.0 ± 0.4, 37.3–38.6
Overall
Avg. rectal Temp.	36.9 ± 0.3, 36.2–37.5	37.2 ± 0.4, 36.7–37.9	37.2 ± 0.4, 36.5–38.0
Avg. chest Temp.	34.6 ± 1.5, 31.6–36.3	35.6 ± 1.5, 32.6–37.2	35.2 ± 1.5, 31.5–37.0
Avg. umbilical Temp.	35.0 ± 1.3, 32.4–36.6	35.9 ± 1.3, 32.5–37.3	35.7 ± 1.2, 33.3–37.6
Peak rectal Temp.	37.0 ± 0.3, 36.3–37.6	37.4 ± 0.4, 36.7–38.2	37.5 ± 0.7, 36.5–39.0
Peak chest Temp.	34.9 ± 1.4, 32.2–36.6	36.2 ± 1.4, 33.1–38.0	35.8 ± 1.7, 31.8–38.0
Peak umbilical Temp.	35.3 ± 1.3, 32.6–36.9	36.3 ± 1.4, 32.9–37.5	36.2 ± 1.5, 33.3–38.6

For age, height, BMI and variables the Mean ± SD and range are reported. Temperatures are in °C.

Table 3. Results for hierarchical polynomial regressions.

	ΔR^2	R^2	Adj. R^2	Β	Std Err.	t	p
Average rectal temperature as dependent variable
Model 1	0.116	0.116	0.072				0.042
Age				0.032	0.011	2.83	0.006
Height				0.037	0.038	0.96	0.339
Weight				−0.040	0.045	−0.88	0.381
BMI				0.140	0.143	0.98	0.331
Average umbilical temperature
Model 2	0.242	0.359	0.318				<0.001
Average umbilical Temp				0.138	0.025	5.43	<0.001
Model 3	0.224	0.583	0.551				<0.001
Average umbilical Temp^2				0.095	0.015	6.44	<0.001
Average chest temperature
Model 2	0.236	0.353	0.311				<0.001
Average Chest Temp				0.121	0.023	5.33	<0.001
Model 3	0.124	0.477	0.436				<0.001
Average Chest Temp^2				0.058	0.014	4.28	<0.001
Peak rectal temperature as dependent variable
Model 1	0.078	0.078	0.032				0.163
Age				0.029	0.018	1.62	0.109
Height				0.089	0.059	1.49	0.139
Weight				−0.107	0.070	−1.53	0.130
BMI				0.358	0.222	1.61	0.110
Peak umbilical
Model 2	0.425	0.503	0.471				<0.001
Peak umbilical Temp				0.249	0.030	8.17	<0.001
Model 3	0.264	0.767	0.749				<0.001
Peak umbilical Temp^2				0.120	0.013	9.34	<0.001
Peak chest
Model 2	0.402	0.480	0.447				<0.001
Peak chest Temp				0.225	0.029	7.76	<0.001
Model 3	0.177	0.657	0.631				0.014
Peak chest Temp^2				0.083	0.013	6.31	0.014

B: unstandardised regression coefficients reported; Std Err.: is the standard error of the regression coefficient; t: t-test for regression coefficient; p: significance level of the t test for the unstandardised regression coefficient.

Figure 4. Average T_rectal regressed on linear and quadratic average T_chest (overall R² 0.477).

Figure 5. Peak T_rectal regressed on linear and quadratic average T_umb (overall R² 0.767).

Figure 6. Peak T_rectal regressed on linear and quadratic peak T_chest (overall R² 0.657).

Table 4. Correlations between rectal temperature with umbilical and chest temperature in restricted dataset.

	Average rectal temperature	Peak rectal temperature
Average umbilical temperature	0.710*
Average chest temperature	0.570*
Peak umbilical temperature		0.841*
Peak chest temperature		0.699*

Restricted dataset includes all observations in which both chest and umbilical temperature measurement are greater than or equal to 35.5 °C.

* , p <0.001.

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