Figure 1.
The thermoneutral experiment started in the morning on day one. After one hour a blood sample was taken and subsequently the [18F]FDG tracer was injected followed by the PET-CT scan one hour later. In the afternoon of day one, the shivering experiment was conducted, which started with a baseline period of 45 minutes during 31°C followed by 90 minutes of mild cold exposure (31°C) to determine the ambient temperature at which shivering occurred. The mild cold experiment on day two consisted of 45 minutes baseline (31°C) followed by 150 minutes of cold exposure. Blood samples were taken at the end of the baseline period and 90 and 150 minutes after the onset of cold exposure. The [18F]FDG tracer was injected 90 minutes after the onset of cold exposure, followed by the PET-CT scan one hour later.
Table 1.
Subject characteristics.
Figure 2.
Visual Analog Scale (VAS) of thermal sensation and comfort during the mild cold experiment.
This figure illustrates the thermal sensation (A) and comfort (B) of both subjects during the mild cold experiment.
Table 2.
Metabolic, cardiovascular and thermoregulatory parameters during mild-cold experiment.
Figure 3.
Comparison of CIT, BAT activity and skeletal muscle intrinsic mitochondrial uncoupling between the monozygotic twin and young adult men.
Boxplots indicating the median and interquartile range of CIT (A) and BAT activity (B) found in young adult men during previous studies [6], [17], [18], [29] (CIT n = 43; BAT activity n = 45). C) Boxplot showing the skeletal muscle mitochondrial proton leak in young adult men (n = 30) from a previous study (n = 8) and unpublished results (n = 22). In each boxplot subject A is indicated as a black square and subject B as an open square. The whisker bars represent the 5th (lower) and 95th (upper) percentile.
Figure 4.
Brown adipose tissue and respiratory muscle activity during the thermoneutral and cold exposure experiment. A, D
) PET images during thermoneutral (left) and cold (right) conditions showing [18F]FDG-uptake e in brown adipose tissue (BAT; red arrows) and respiratory muscles (RM; white arrows). B, E) Transaxial slices of subject A (5 mm thick) of thoracic area (upper) and supraclavicular area (lower) demonstrating BAT activity (red arrows) and RM activity (white arrows). C, F) [18F]FDG-uptake (SUVmean) in BAT, white adipose tissue (WAT), skeletal muscle (SM), and respiratory muscles (RM) during thermoneutral and cold conditions.