Firefighters Have Cerebral Blood Flow Reductions in the Orbitofrontal and Insular Cortices That are Associated with Poor Sleep Quality

Figures & data

Table 1 Demographic Characteristics, Sleep Parameters, and Cognitive Function Test Results of the Participants

	Firefighters (n = 37)	Controls (n = 37)	t	p
Age, years	42.8 ± 9.4	37.9 ± 12.2	−1.94	0.06
Male, number	35	34	Χ^2 = 0.21	0.64
Body mass index, kg/m^2	25.3 ± 2.6	24.5 ± 2.9	−1.26	0.21
Waist circumference, cm	84.8 ± 7.1	84.4 ± 8.2	−0.22	0.82
Self-Report Questionnaire
Athens Insomnia Scale	7.0 ± 2.3	7.1 ± 2.6	0.24	0.81
Pittsburgh Sleep Quality Index	6.6 ± 1.9	6.6 ± 2.4	−0.024	0.98
Fatigue Severity Scale	24.9 ± 9.5	29.9 ± 11.6	2.00	0.05
Epworth Sleepiness Scale	16.9 ± 3.5	17.8 ± 4.0	0.95	0.35
Karolinska Sleepiness Scale	4.5 ± 1.7	4.4 ± 1.9	−0.23	0.82
Actigraphy-Measured Sleep Parameters
Mean Sleep Efficiency (%)	82.1 ± 6.4	86.1 ± 4.1	3.19	0.002*
Mean Sleep Latency (minutes)	7.2 ± 2.1	6.9 ± 2.2	−0.58	0.56
Mean Total Sleep Time (minutes)	339.2 ± 46.4	350.8 ± 52.7	1.00	0.32
Mean Wake After Sleep Onset (minutes)	67.6 ± 26.6	49.2 ± 14.8	−3.67	0.001*
Cognitive Function Tests
Paired Associate Learning, memory score (standardized z-score^†)	−0.46 ± 0.85	-	2.11	0.038*
Paired Associate Learning, total errors (standardized z-score^†)	0.21 ± 0.65	-	−1.05	0.30
Spatial Working Memory, strategy score (standardized z-score^†, ‡)	−0.80 ± 0.98	-	3.46	0.001*
Spatial Working Memory, total errors (standardized z-score^†)	0.52 ± 1.04	-	−2.21	0.031*

Notes: Values are mean ± standard deviations. ^†Standardized z-scores were calculated using the means and standard deviations of the control group. ^‡Strategy scores were reversed so that higher scores represent better performance. *Statistical significance at p < 0.05.

Table 2 Brain Regions That Showed Significant Group Differences in Cerebral Blood Flow

Brain Regions	Cluster Size (Voxels)	Peak t value	Peak MNI Coordinates (mm)
Controls > Firefighters
Cluster 1	618	4.34	(62, −38, 0)
Middle temporal gyrus, right
Lateral occipital cortex, right
Cluster 2	172	4.50	(30, 24, −10)
Orbitofrontal cortex, right
Cluster 3	110	3.78	(38, −14, 4)
Insular cortex, right
Firefighters > Controls
None

Notes: There were five clusters that showed significant reductions of the cerebral blood flow (CBF) in the firefighter than in control groups, after adjusting for age and global mean CBF (uncorrected p < 0.005, contiguous voxels > 100). The x, y, z values represent peak coordinates on a 2×2×2 mm³ MNI template.

Abbreviation: MNI, Montreal Neurological Institute.

Figure 1 Brain regions that showed lower absolute cerebral blood flow in the FF group than in the control group are displayed in the axial, sagittal and coronal sections. Whole brain voxel-wise analyses were performed after adjusting for age and global mean cerebral blood flow of the grey matter. The color bar represents voxel-level t values. The numbers below the brain slices indicate z, x, y coordinates in the Montreal Neurological Institute space.

Abbreviations: L, Left; R, Right; A, Anterior; P, Posterior.

Figure 2 Relationship between sleep efficiency (left panels), wake after sleep onset (WASO) (right panels) and cerebral blood flow (CBF) of the significant three clusters. Mean sleep efficiency for 7 days, as measured by wrist-worn actigraphy, has a positive linear association with the CBF of the cluster 2 that is located in the right orbitofrontal cortex (β = 0.21, p = 0.002). Mean WASO for 7 days, also measured by wrist-worn actigraphy, has a negative linear association with the CBF of the clusters 2 (β = −0.22, p = 0.001) and 3 (β = −0.18, p = 0.012), which are located in the right orbitofrontal and insular cortices, respectively. A regression line and beta coefficients are from the multivariate regression model including the following variables: the CBF values extracted from each cluster as the dependent variables; sleep efficiency or WASO as an independent variable; age, sex, and mean global CBF as covariates. The CBF of each cluster is displayed in the values adjusted for age, sex, and mean global CBF. *p < 0.013.

Figure 3 Relationship between the sleep efficiency and performance in the Spatial Working Memory (SWM) task of the CANTAB. Higher sleep efficiency showed a positive linear association with the higher strategy score of the SWM (β = 0.28, p = 0.010). A regression line and beta coefficients are from the regression model including the following variables: The strategy score of SWM as the dependent variable; sleep efficiency as an independent variable; age, sex, and education level as covariates. *p < 0.013.