Tiredness or sleepiness, on the other hand, is a key symptom in sleep disorders
such as obstructive sleep apnea syndrome (OSAS). Because pathological sleepiness
increases the risk of occupational injuries and automobile accidents, standard tests
have been developed and validated for assessing daytime sleepiness. In clinical
settings, tiredness/sleepiness is objectively assessed with aMultiple Sleep Latency
Test(MSLT), considering the gold standard for clinical diagnosis of pathological
sleepiness. The underlying premise of the MSLT is the physiological need for sleep
(sleep pressure), with greater sleepiness being reflected by an increased tendency to
fall asleep. The test is conducted in a sleep laboratory; individuals are required to lie
down in a dark room and attempt to sleep over four orfive sessions, each session
lasting 20–30 min, performed at two hourly intervals. Sleep latency is measured by
standard electrophysiological means and is defined as the time elapsed from lights
out to thefirst epoch of any stage of sleep. Short mean sleep latency is indicative of
excessive sleepiness (Carskadon et al. 1986 ; Carskadon and Dement 1992 ; Shahid
et al. 2010 ). MSLT has been well validated and is a useful tool for assessing
sleepiness associated with various conditions such as acute and partial sleep de-
privation, sleep disruption, circadian rhythm disorders, obstructive sleep apnea, and
other clinical conditions. A mean sleep latency of less than 5 min on the MSLT
represents severe pathological sleepiness (Shahid et al. 2010 ).
Although this is a reliable, validated, and accurate test, it may fail to measure
some aspects of sleepiness. It fails to separate sleep propensity (the ability to fall
asleep) from sleep need, as the MSLT does not capture the effect of‘arousal factors’
on sleepiness. An‘arousal factor’(e.g., anxiety or excitement) is generated inter-
nally and is independent of the environment (Johns 2009 ). Another objective test,
theMeasurement of Wakefulness Test(MWT), was devised to assess the strength
of the arousal system but is not considered a useful tool in estimating sleepiness.
Although there are some correlations between sleepiness and a decreased level of
alertness, sleepiness is not considered to be the reverse of alertness (Shahid et al.
2010 ).
Application to Parental Sleep Loss, Tiredness, and Fatigue
Although both PSG and actigraphy have been applied to measuring maternal sleep
quantity, none of the above-mentioned techniques for objectively assessing tired-
ness or fatigue have yet been applied to the experience of parental tiredness and
fatigue; however, both the MSLT and the PMVT may be relevant for capturing
information about acute sleep pressure and acute fatigue experienced as a conse-
quence of sleep loss and disruption in the period of early infancy. These tests might
provide a useful benchmark for calibrating‘safe’and‘unsafe’levels of tiredness or
fatigue in parents, and providing recommendations regarding potentially hazardous
activities such as driving, and tasks that require accurate attention to detail such as
taking or administering medications. In research they might, at the very least,
34 A.E.F. Rudzik and H.L. Ball