9. Análisis
9.3.1. Malas decisiones de los jefes
Following screening 40 participants were selected to complete the sleep restriction study. The following chapter outlines the characteristics of the total study population, OSA n = 20, control n = 20. It is not designed to answer any hypothesis or research questions but provides back ground information of the two groups (OSA and control) being investigated by the simulator studies.
4.1.1 Statistical analysis
Analysis is designed to identify any difference between the two experimental groups. Any differences found may be an underlying factor for differences at the driving simulator tasks.
A Two tail independent T tests was used to compare the ages and total sleep time and sleep disturbance index of each group. Data were visually checked in histograms that the assumption of normal distribution was not violated. The assumption of homogeneity of variance was assessed using Levenes test and was not violated.
BMI and % body fat are reported but not statistically compared as the control group was artificially selected to have a BMI under 28.
4.2 Physical characteristics
Mean S.d. OSA Age 63.8 7.7 Control Age 66.6 6.1 OSA BMI 34.5 6.5 Control BMI 25.5 1.7 OSA % body fat 32.4 5.5 Control % bodyfat 23.9 3.8
4.2-1 Age, BMI and percentage body fat of OSA and control groups
All participants were aged between 50 and 75, there was no significant difference between groups [t(37) = 1.22, p = 0.269]. As expected both BMI and percentage body fat were higher in the OSA group. The average BMI in the OSA group was obese at 34.5; the average BMI in the control group was slightly overweight at 25.5. Control participants were screened not to have a BMI over 28 as there would then be at risk of
then having undiagnosed OSA. BMI distribution can be seen in Figure 4.2-1. A man of average body weight would be expected to have 15 – 20% body fat, healthy range for 50 – 75 years old is considered to be 13 – 25 %. 9 control and 18 OSA participants had a percent body fat above 25%.
All participants were included in the study. Due to work commitments one OSA participant withdrew from the study before completion. The time commitment required for the study resulted in no other suitable participant volunteering. It is therefore stated in the methodology section of each chapter whether this participant is included (OSA n =20) in analysis for that chapter or not (OSA n = 19).
Figure 4.2-1 BMI distribution
4.3 OSA
All of the OSA participants were being treated using CPAP from Leicester General Hospital and attend once a year for check up appointments. They had all been receiving CPAP since their diagnosis. For between 1 and 19 years (average = 7.46 years). When asked if they ever slept without their CPAP 16 said they never would, 1 person said they sleep without it once a month, 2 people once every two to three months and 1 person very occasionally. These participants reported not using their CPAP on occasion if they were away from home and there was no facility to plug it in,
0 2 4 6 8 10 12 14 16 underwieght <19 normal weight 20 - 25 overweight 25 - 30 obese 30 -40 morbidly obese 40+ Fr eq ue nc y BMI OSA Control
putting it on. However, one person who reported falling asleep before putting it on did comment that in this scenario they would then wake in the night and apply the mask.
All the participants were happy with the CPAP and felt it was improving their quality of life. When asked what life was like before having a CPAP machine the most common complaints were falling asleep during the day, feeling stressed at work, struggling when driving and having a reduced social life, examples include:
“I had a restricted social life as I found it hard to go out in the evenings because I felt sleepy.”
“I was embarrassed to go on holiday with groups of people as my snoring would disturb them.”
“My performance at work was badly affected; I thought I couldn’t sleep well because I was stressed. It turned out I was stressed because I wasn’t sleeping well.”
“I left my job as I thought I was stressed so was unable to sleep properly.”
“I used to fall asleep in the daytime when I sat down.”
“I struggled to stay alert when driving long distances.”
“I was tired during the day and wanted to sleep all the time.”
4.4 Driving
OSA participants had held a UK driving licence for an average of 44.6 years, s.d. 7.2, with the least experienced driver having 32 years experience. Control participants had held a UK driving licence for an average of 45.2 years, s.d. 6.9, with the least experienced driver having 30 years experience. No participants were professional drivers. All participants drove for a minimum of 3 hours per week, the modal number of hours driven per week was 3- 5 hours (55% of OSA, 40% of controls). All participants drove at least 1000 miles per year with the modal response being 5000 – 10 000 miles (65% OSA, 40% control).
4.5 Trait sleepiness
All participants completed the Epworth Sleepiness Scale to assess for excessive daytime sleepiness (ESS >12). On average the OSA group had a slightly higher ESS (5.3 s.d. 3.36) compared with controls (4.7 s.d. 2.56). One OSA participant reported EDS, during the 30 minute test drive of the simulator participants rated how sleepy they felt on the KSS every 200 seconds, and a mean over the 30 minutes was calculated. The OSA participant with EDS had an average KSS of 1 during the test drive and was included in the final study population.
4.6 Habitual sleep
During screening participants were asked how long it took them to fall asleep in order to exclude anyone with insomnia. They were also asked if their bed partner currently reported anything unusual about their sleep. All control participants reported no loud snoring, choking or waking with a jolt in their sleep; all these signs would suggest undiagnosed OSA.
Figure 4.6-1 Total sleep time with standard deviation
Each participant completed a sleep diary and wore an actiwatch to assess for compliance to sleep criteria prior to the study days. Four nights of baseline actiwatch data were collected as non study nights. Sleep diary and actimeter data were combined (Copyright Cambridge Neurotechnology Ltd. Version 7.22) and mean total
0 100 200 300 400 500 600 Control OSA Sl ee p Pe rio d (m in )
Non study night
Normal sleep study night 5hr sleep
sleep time (TST) was calculated as time from initial sleep onset until final awakening for each participant, see Figure 4.6-1. On average both groups habitually slept a similar length (on non study days), controls slept for 7h 50min and OSA participants slept 7h 37 min on average. There was no significant difference between the two groups average non study night SP [t (37) = 0.931, p = 0.358, two tailed].
The TST calculated for non study nights was used to assess if participants were compliant in the study conditions having either their usual night’s sleep or 5 hours sleep as appropriate.