None listed
Conditions
Brief summary
Fatigue causes a deterioration in cognitive performance that leads to workplace errors, injury and reduced safety. Shift work is a major source of fatigue because it disrupts the timing and duration of sleep opportunities; and therefore night workers are often chronically sleep deprived. Our work shows that 30min naps can be a powerful tool for maintaining performance during conditions of sleep deprivation. Naps can be particularly beneficial for night workers, who are on duty at times when their body rhythms naturally prime them to be asleep. However, napping can also be hazardous. Our studies show that it can have deleterious effects, in particular, `sleep inertia’, the groggy feeling and performance impairment experienced after waking where workers are extremely vulnerable to errors. This is problematic for oncall workers or health care professionals who take naps during extended hours or night shifts, but on waking need to process complex information, or engage in safety critical activities. Our recent systematic review found very few studies have investigated countermeasures that that can be implemented immediately on waking to reduce sleep inertia. Our work with caffeine gum, funded by USA and Australian Army has found it is fast acting (i.e. within 5min). It could therefore be the ideal countermeasure for the sleep inertia associated with night time naps. This study aims to answer two questions: 1. Will 200mg of caffeine (given in gum form) administered upon waking from a 30 min nap at 2:30am prevent sleep inertia when compared to placebo? 2. Will 200mg of caffeine (given in gum form) administered upon waking from a 30 min nap at 2:30am impact daytime recovery sleep between 12 and 6pm?
Interventions
Participants will undergo two 37h in laboratory sleep deprivation protocols. Participants will enter the laboratory at 11am on day 1; stay awake all night; and then sleep between 12pm and 6pm on day 2. Participants will remain in the lab until 12am.
Participants will undergo 2 conditions, with the order of conditions randomised: 1) 30min nap with 200mg caffeine gum on waking; and 2) a 30min nap with placebo gum. The 30min nap will be allowed between 2 to 2:30am.
They will visit the laboratory
Participants will undergo two 37h in laboratory sleep deprivation protocols. Participants will enter the laboratory at 11am on day 1; stay awake all night; and then sleep between 12pm and 6pm on day 2. Participants will remain in the lab until 12am. Participants will undergo 2 conditions, with the order of conditions randomised: 1) 30min nap with 200mg caffeine gum on waking; and 2) a 30min nap with placebo gum. The 30min nap will be allowed between 2 to 2:30am. They will visit the laboratory twice, a week apart, in a within groups, repeated measures design. Each person will be their own control. A 30 minute cognitive performance test battery, consisting of a 10 minute Psychomotor Vigilance Task, Karolinska Sleepiness Scale, Positive and Negative Affect Schedule, and mood Visual Analogue Scales will be administered at 8:30pm and 11pm on day 1 and at 1am, 5am, 9am, and 8:30pm on day 2. A 20 minute learning reversal decision task will be performed at 9pm on day 1 and 7:30am and 8:30pm on day 2. This computerised task is based on a go/no go paradigm. Initially four two-digit numbers are assigned to the go (response) set and four two-digit numbers are assigned to the no go (no response) set. Participants have a 750ms window to either respond or withhold a response to the number displayed on the screen. A hypothetical money reward/punishment is displayed to allow participants to determine which numbers are in the go set and which are in the no go set. After a number of trials (56, 60, or 64) the response sets are reversed for another 40 trials. A 40 minute driving simulation task (Yorke Driving Simulator) will be conducted at 7:30pm on day 1 and 6:30am, 10am, and 7:30pm on day 2. A sleep inertia test battery will be conducted post nap starting at 2:30am. Sleep inertia testing will consist of a 3 minute Psychomotor Vigilance Task, Karolinska Sleepiness Scale, and mood Visual Analogue Scales, and performed every 10 minutes (4 sleep inertia tests to map performance in the hour post nap). Venous blood sampling will be at 12:30pm on day 1 and 3:15am, 4:10am, 5:40am, and 11am on day 2 to quantify plasma caffeine concentrations for pharmacokinetic assessment, the impact of the caffeine gum on cortisol as a marker of stress and the impact of the caffeine gum on melatonin sectretion. Hourly saliva sampling will used to measure melatonin levels during wake periods. Data will be analysed using mixed models and pharmacokinetic/pharmacodynamics modelling will be used to investigate the relationship between blood (plasma) caffeine concentrations and various indices of sleep inertia.
Sponsors
Assoc Prof Siobhan Banks
Study design
Allocation
Randomised controlled trial
Intervention model
Crossover
Primary purpose
Treatment
Masking
Blinded (masking used) (Subject, Caregiver, Outcomes Assessor)
Eligibility
Sex/Gender
All
Age
18 Years to 40 Years
Healthy volunteers
Yes
Inclusion criteria
BMI between 18.5-29 kg/m2 Habitual bedtime between 2100h and 2400h Habitual wake time between 0600h and 0900h Less than 2 hours of structured high impact activity per week Currently taking a contraceptive pill or experiencing regular menstrual cycles (females) Valid driver’s licence or sufficient driving experience
Exclusion criteria
History of smoking, drug, or alcohol abuse in the past year History of psychiatric illness or sleep disorders such as insomnia and sleep apnoea Food allergies Trans-meridian travel in the 30 days prior to the study commencing Clinically significant abnormalities in blood and urine Shiftwork Habitual napping Caffeine intake exceeding 400mg per day on average Score <22 or >44 on the Composite Morningness Questionnaire Score >14 on the Beck Depression Index Score >5 on the Pittsburgh Sleep Quality Index History of cardiovascular disease History of a neurological disorder Pulmonary disease requiring daily inhaler use Kidney disease Liver disease History of psychiatric disorder requiring hospitalisation or psychiatric product for any length of time Positive urine pregnancy result Resting blood pressure above 140/90 Resting pulse >110
Outcome results
None listed