ABSTRACT
Residency training may disrupt normal sleep/wake cycles, resulting in mood and performance deficits and alterations in biological rhythms. To characterize such disturbances and determine whether they are associated with an alteration in the day/night pattern of melatonin excretion, measurements were obtained around-the-clock in seven male subjects, each studied in two 48-h sessions. Session 1 was conducted during the week before beginning a residency, and session 2 at 6 months into a first-year surgical residency. The mean time of the end of nocturnal sleep and the timing of the temperature rhythm were both (P less than .01) approximately 2.3 h earlier in session 2 (vs. 1). The sleepiness rhythm and the overall mood score rhythm were also phase-advanced (P less than .05) in session 2. The mean value of mood around-the-clock was significantly worse due to increased anger, tension, confusion, depression, and fatigue in session 2. Vigilance, tested by simple reaction time, did not exhibit a 25-h rhythm and was worse in session 2 with an increase (P less than .05) in mean response latency less than 1 s and an increase (P less than .01) in lapse time (microsleep, greater than 1- s latency). The urinary cortisol rhythm exhibited a raised curve average value (mesor) in session 2 (vs. 1, P less than .05), but no difference was revealed in amplitude or acrophase. Urinary excretion of Na+, K+, and Cl- did not differ between sessions, though the Na+/K+ ratio peaked earlier in session 2 (P less than .05). The urinary 6-sulfatoxymelatonin rhythm did not differ in timing, amplitude, or mesor between sessions. A residency training schedule can be associated with altered timing in rhythms of sleep, sleepiness, temperature, and mood and with deterioration of mood and performance without detectable alteration of the endogenous melatonin pattern as exhibited by the excretion rate of the principal urinary metabolite.