Nineteen maritime pilots and 16 controls were enrolled in the study (Figure 1, Table 1).
Maritime pilots were on average 4 years younger than controls (Table 1; 95% CI –6.139 to –1.716). Results from the independent t-test did not indicate other differences between the groups at baseline (Table 1). All participants were Dutch, of white European descent, and had the same level of education.
Table 1. Baseline characteristics.
Characteristics
|
Controls, n = 16
|
Maritime pilots, n =19
|
Age, years
|
57 ±2.9
|
53 ±3.4
|
Educational attainment, years
|
17.4 ±7.3
|
18 ±0
|
BMI, kg/m2
|
25.5 ±2.7
|
25.7 ±2.7
|
History of Diabetes
|
0 (0)
|
0 (0)
|
SBP, mmHg
|
NA
|
148.0 ±16.4
|
DBP, mmHg
|
NA
|
90.16 ±11.7
|
Medication (‘yes/no’)
|
2 (10.5)
|
4 (21.1)
|
Smoking (‘yes/no’)
|
3 (15.8)
|
3 (15.8)
|
History of hypertension
|
0 (0)
|
0 (0)
|
History of high cholesterol
|
0 (0)
|
1 (5.3)
|
CFQ
|
26.4 ±10.8
|
29 ±7.8
|
HADS Anxiety
|
4.8 ±3
|
4.0 ±1.7
|
HADS Depression
|
3.6 ±2.5
|
3.7 ±2.7
|
Data is shown as mean ±SD or No. (%).
Abbreviations: BMI, Body Mass Index; SBP, systolic blood pressure; DBP, diastolic blood pressure, CFQ, Cognitive Failure Questionnaire; HADS, Hospital Anxiety and Depression Scale; NA, not applicable.
Sleep characteristics
PSQI: Maritime pilots reported worse sleep quality on the PSQI compared to controls, especially during a workweek (Table 2). When comparing PSQI scores between workweek and rest week within maritime pilots, results of the t-test revealed that the average PSQI score for workweeks was almost twice the score for rest weeks, with values exceeding the validated cut-off point (≥7) for abnormal sleep behavior (Table 2).
Actigraphy: Subjective reports (PSQI) of poor sleep was confirmed by data from 10 days of actigraphy (mix of workdays and rest days), which indicated more awakenings and less sleep efficiency in the maritime pilot group compared to controls (Table 2).
PSG (2016/2017): Both maritime pilots and controls had normal sleep patterns, including normal amount of DST (Table 2), ruling out intrinsic sleep disorders.
Table 2. Comprehensive sleep characteristics of maritime pilots and controls.
Measures
|
|
Controls, n = 16
|
Maritime pilots, n = 19
|
p value
|
PSG
|
TST, min
|
406 ±44
|
403 ±51
|
0.86
|
|
N1, min
|
46 ±18
|
41 ±14
|
0.40
|
|
N2, min
|
232 ±36
|
215 ±36
|
0.20
|
|
DST, min
|
50 ±25
|
66 ±28
|
0.10
|
|
REM, min
|
68 ±17
|
79 ±17
|
0.10
|
|
WASO, min
|
61 ±26
|
53 ±39
|
0.48
|
|
SEF, %
|
85.8 ±7.1
|
86.1 ±9.4
|
0.91
|
|
SOL, min
|
8 ±7
|
11 ±9
|
0.32
|
Actiwatch
|
No. awakenings
|
33.5 ±11.1
|
37.8 ±10.3
|
0.24
|
|
SEF, %
|
89.3 ±4.3
|
86 ±3.8
|
0.03*
|
PSQI
(rest week vs. control
|
Overall score
|
3.2 ±1.4
|
4.5 ±2.2*
|
0.049*
|
PSQI
(workweek vs. control)
|
Overall score
|
3.2 ±1.4
|
8.8 ±2.9**
|
<0.001**
|
Data is shown as mean ±SD.
Actiwatch data and PSQI were collected in 2016 and 2017. Actiwatch data was collected for a period of 10 consecutive days, for maritime pilots these 10 days were a mix of work- and rest days. PSQI was administered twice for maritime pilots, including one workweek and one rest week.
Abbreviations: PSG, Polysomnography; TST, total sleep time; DST, deep sleep time; REM, rapid eye movement sleep; WASO, wake after sleep onset; SEF, sleep efficiency; SOL, sleep onset latency; PSQI, Pittsburgh Sleep Quality Index;
* significant at p<.05
** significant at p<.001
Home-EEG (2019): Wewere able to analyze EEG-based sleep measurements during work- and rest days in 13 maritime pilots (of the n = 19 maritime pilots, 4 had retired by 2019 when these measurements were scheduled, and could therefore no longer be measured during workdays; 2 could not be analyzed due to technical issues) (Figure 1). Maritime pilots showed less TST during workweeks compared to rest weeks (Z = –3.18; p = 0.001) as well as less DST during workweeks compared to rest weeks (Z = –2.83; p = 0.005) (Table 3). Based on the home-EEG measurements, we created hypnograms of one maritime pilot for a workweek and a rest week, illustrated in Figure 2.
Table 3. Results from the home-EEG measurements (maritime pilots only).
Measures
|
|
Rest week, n =13
|
Work week, n =13
|
p value
|
Home EEG
|
TST†, min
|
406.17 (340 – 425.98)
|
318.56 (250.21 – 352.93)
|
0.001*
|
|
DST†, min
|
51.34 (48.37 – 69.30)
|
36.75 (32.30 – 58.58)
|
0.005*
|
Data is shown as mean ±SD or median (IQR).
Home-EEG recordings were performed in 2019 in maritime pilots only using a dry single-lead EEG device (Philips, Eindhoven, The Netherlands).
Abbreviations: TST, total sleep time; DST, deep sleep time
* significant at p<.05
†= means calculated based on sleep periods within workweek or rest week respectively
Cognitive assessment
For cognitive assessment, we transformed all raw neuropsychological test scores into z-scores. Results from the independent t-test did not indicate differences between maritime pilots and controls on tests of episodic memory (WMS-IV LM recognition, RAVL total median). Small differences were observed on semantic memory and language, in which maritime pilots performed slightly better on the Boston Naming Test compared to controls. Performance on working memory and executive function (WAIS-IV, TMT, WAIS-IV Coding), and attention (TAP 2.0) did not differ significantly between the groups. Maritime pilots performed slightly better on the visual recognition memory after short compared to controls. Long-term memory consolidation, however, did not differ between the groups. All test scores were within normal age- and education-adjusted ranges based on available normative data (data not shown). All results can be found in Table 4.
Table 4. Results of cognitive assessment and memory consolidation.
Measures
|
|
Controls, n = 16
|
Maritime pilots, n = 19
|
p value
|
WMS-IV
|
LM I
|
0.16 ±1.07
|
-0.08 ±0.99
|
0.49
|
|
LM II
|
0.29 (-0.93 – 1.01)
|
0.11 (-0.61 – 0.83)
|
0.72
|
|
LM recognition
|
0.25 ±1.10
|
-0.12 ±0.94
|
0.29
|
RAVL
|
Total
|
-0.08 (-0.63 – 0.61)
|
0.77 (-1.14 – 1.09)
|
0.41
|
|
Del. Recall
|
-0.08 ±0.76
|
0.06 ±1.25
|
0.70
|
|
Del. Recognition
|
-0.10 ±1.15
|
0.21 ±0.85
|
0.37
|
|
Sensitivity A’
|
0.07 (-0.85 – 0.82)
|
0.22 (-0.30 – 0.82)
|
0.41
|
WAIS-IV
|
Coding
|
-0.10 ±0.59
|
0.21 ±1.26
|
0.37
|
Digit span
|
-0.21 ±0.62
|
0.23 ±1.24
|
0.21
|
TMT
|
Part A
|
-0.09 ±0.75
|
-0.06 ±1.15
|
0.94
|
|
Part B
|
-0.33 (-0.57 – 0.75)
|
-0.38 (-0.96 – 0.50)
|
0.24
|
Fluency
|
D-A-T
|
0.07 ±0.89
|
-0.29 ±1.13
|
0.78
|
|
Animal
|
0.38 (-0.88 – 0.73)
|
0.20 (-0.70 – 0.91)
|
0.84
|
|
Profession
|
-0.26 ±0.85
|
0.26 ±1.13
|
0.14
|
BNT
|
Short version
|
-0.11 (-0.39 – 0.31)
|
0.20 (0.10 – 0.62)
|
0.02*
|
TAP evening
|
Cued
|
-0.05 (-0.72 – 0.44)
|
-0.39 (-0.91 – 0.50)
|
0.37
|
|
Un-cued
|
-0.05 (-0.87 – 0.89)
|
-0.17 (-0.76 – 0.45)
|
0.84
|
TAP morning
|
Cued
|
-0.10 (-0.50 – 0.66)
|
-0.29 (-0.71 – 0.12)
|
0.27
|
|
Un-cued
|
-0.13 (-0.63 - 1.09)
|
-0.40 (-0.74 – 0.33)
|
0.22
|
Visual recognition Short delay (10 min)
|
Sensitivity, A’
|
-0.27 ±0.90
|
0.46 ±0.58
|
0.007*
|
|
Hits
|
-0.33 (-1.18 – 0.15)
|
0.64 (0.15 – 0.64)
|
0.03*
|
|
False alarms
|
0.19 ±1.06
|
-0.27 ±0.84
|
0.16
|
Memory consolidation Long delay (after sleep)
|
Sensitivity, A¢
|
-0.08 ±0.95
|
0.35 ±0.73
|
0.14
|
|
Hits
|
0.50 (-0.21 – 0.70)
|
-0.08 (-0.69 – 0.54)
|
0.20
|
|
False alarms
|
0.15 ±0.90
|
-0.41 ±0.76
|
0.06
|
Data is shown as mean ±SD or median (IQR).
Test results are expressed in z scores. TAP: z-scores are based on median reaction-time. Visual recognition - short-term: assessed approximately 10 minutes after targets were presented. Memory consolidation after long-term took place after one night of sleep (approximately 10 hours).
Abbreviations: WMS = Wechsler Memory Scale, LM = Logical Memory, RAVLT = Rey Auditory Verbal Learning Test, WAIS = Wechsler Adult Intelligent Scale, TMT = Trail Making test, BNT = Boston Naming Test, TAP = Test of Attentional Performance
*significant at p<0.05
18F-flutemetamol PET-CT
Amyloid PET scans were administered in maritime pilots only (n = 19, Figure 1). SUVRs in the healthy population vary around an average of 1.25 (±0.18) (40) and 1.3 (±0.09) (27). The global cortical SUVR in maritime pilots was 1.009 (±0.059; 95% CI 0.980 to 1.037), below normal values for a cognitively healthy population in this age range (27, 40). More specifically, we detected a SUVR of 0.860 (±0.098; 95% CI 0.813 to 0.907) for frontal lobes and a SUVR of 0.996 (±0.06; 95% CI 0.967 to 1.025) for temporal lobes. In addition, all scans were rated negative for the presence of amyloid deposition on visual reading. Figure 3 shows examples of amyloid PET images from two representative participants. There were no correlations between SUVRs and sleep quality (PSQI overall score and DST (for rest- and workweeks)).