Sixteen nonsmoking young healthy male adult volunteers (24±1.15 years, range: 22-26) were studied with polysomnography. Inclusion criteria were as the following: 1) non-smoker males, 2) no history of mental and physical disorders at present and in the past that might influence sleep architecture. Depression was ruled out by using Hamilton Rating Scale for Depression²⁷ and Beck Depression Inventory²⁸ (cut-off score of 10), 3) no heavy snoring or obesity (body mass index >28), 4) no sleep disorders such as sleep apnea syndrome, idiopathic hypersomnia, narcolepsy, and periodic limb movement disorder, confirmed with overnight polysomnography, 5) no history of drug abuse, and 6) no use of medications that may affect sleep. The study was explained to them. Then, a signed consent approved by the Institutional Review Board in Yongin Mental Hospital was obtained. The subjects were asked to abstain from ethanol and caffeine for at least 3 days prior to each sleep recording and during the experiment, Breath-ethanol concentrations were measured with a Lion Alcometer S-D2 (Lion Laboratories plc., Barry, Wales, UK).

Polysomnography was conducted for three nights. The first night was for adaptation and to rule out sleep disorders. On the second night, one transdermal nicotine or placebo patch was administered in a double blind randomized crossover design. One nicotine patch contained 14 mg of nicotine. Both nicotine and placebo patches were generously provided by Sam Yang Pharmaceutical Company as the identical shape and color. Every patch was applied at 18:00 on the upper outer arm about 4-5 hours before retiring to bed. Recording started between 22:00 and 23:00. The patch was removed the next morning. After a washout period of minimum 84 hours, the third night polysomnography was carried out and the placebo or nicotine patch was administered in a counter-balanced order. Subjects were allowed to maintain their usual lifestyle except during experimental night times.

Polysomnographic recordings were done with Grass model 78 polysomnograph, which included electroencephalography (EEG), left and right electro-oculography (EOG), submentalis electromyography (EMG), left and right anterior tibialis EMG, electrocardiography (ECG), snoring microphone, oro-nasal airflow, chest and abdominal respiratory movements, and arterial oxygen saturation.

Two channels of EEG were recorded at C3/A2 and O2/A1 according to the international 10-20 system.²⁹ EOG electrode placement was done following the standard method. ECG electrode was attached at modified lead II position. The snoring microphone was attached at the surface area nearest to the vocal cord. Oro-nasal airflow was monitored with the thermocouple positioned at the mouth and the nostrils. Chest and abdominal breathing movements were monitored with impedance pneumograph applied to the chest and abdomen at the maximum excursion of breathing. Oxymeter probe was attached at the tip of the non-dominant second finger. All recordings were done at the paper speed of 10 mm/second. Behavioral monitoring was also done with infrared closed circuit camera system.

Polysomnography data were digitized and analyzed by the digital polysomnography system, developed jointly by Division of Sleep Studies in Seoul National University Hospital and Institute of Biomedical Engineering in Seoul National University using visual C++ programming language (Microsoft visual C++, version 6.0, USA) and a high performance analog-to digital (AD) and digital signal processing (DSP) card based on a transputer in order to record and process simultaneously in real time. EEG and EKG data were sampled with a frequency of 250 Hz.

Sleep stages were scored visually in 30-second epochs from the recording, according to Rechtschaffen and Kales criteria.³⁰ Movement time epochs were not scored separately but were included in the wake stage.

All-night sleep variables were derived from the visual scoring of recordings using standard criteria and were grouped into 2 catogories: sleep continuity measures and sleep architecture measures. Sleep continuity measures included time in bed (TIB), TST, sleep efficiency in percent (TST/TIB×100), sleep latency (time from lights-out to the first occurrence of a stage 1 or 2 epoch), and REM sleep latency (time from sleep-onset to the first epoch of stage REM). Sleep architecture measures included duration and percentage of time spent asleep in the different stages of sleep (stage 1, 2, 3, 4, REM, and slow wave sleep, i.e. the sum of sleep stages 3 and 4).

For each subject, one EEG derivation (C3-A2) was selected to determine the power spectra. The spectral analysis was performed with the fast Fourier transform (FFT) algorithm. The epoch length was 2 seconds (256 points), and truncating error was reduced with applying Hanning window. In addition, the values for 15 adjacent 2-second epochs were averaged to yield power density values for 30-second periods. Thus, sleep visual scores of each 30-second epoch were synchronized with power density values. The values of adjacent 0.5-Hz frequency bins were collapsed into slow wave activity (0.5-4.5 Hz; SWA), spindle frequency activity (12-15 Hz; SFA), theta (4-7.5 Hz), alpha (8-12.5 Hz), beta1 (13-21.5 Hz), and beta2 (22-30 Hz) frequency bands. Power spectral parameters were calculated within a specific period of time. Consecutive NREM-REM sleep cycles were defined according to modified criteria of Feinberg and Floyd³¹ by the succession of an NREM sleep episode of at least 15 minutes' duration and an REM sleep episode of at least 5 minutes' duration.

For each subject, 300 continuous beats of EKGs without artifact were chosen from both stage 2 and REM sleeps and were also used for power spectral analysis. We compared the heart rate variability including LF and HF power, LHR, very low frequency power (VLF), R-R means, and R-R variance between the nights with and without transdermal nicotine patch.

Statistical software package SPSS 11.0 for windows was used. Tests for normality of continuous measures were made with the Kolmogorov-Smirnov test in conjunction with plots of the distribution and descriptive statistics. If normality was confirmed for the measures, parametric method (paired student t-test, Pearson's correlation test) was used. If normality was not confirmed, non-parametric method (Wilcoxon signed rank test) was used.

Table 1 lists the sleep parameters derived from visual scoring compared between the nights with and without transdermal nicotine patch. Among sleep continuity measures, all parameters except TIB showed significant differences between the nights. On the nights with nicotine patch, as compared to the nights with placebo patch, TST (321.8 minutes vs. 422.7 minutes, p<0.01) and sleep efficiency (72.5% vs. 91.6%, p<0.01) were decreased and wakefulness after sleep onset (WASO) (97.8 minutes vs. 23.8 minutes, p<0.01), sleep latency to stage 2 (23.7 minutes vs 9.2 minutes, p<0.01), and sleep latency to REM stage (105.1 minutes vs. 74.9 minutes, p=0.05) were increased. Among sleep architecture measures, on the nights with nicotine patch, as compared to the nights with placebo patch, percentage of stage 1 was increased (15.5% vs. 10.9%, p<0.01) and percentage of stage REM was decreased (19.7% vs. 23.4%, p<0.05). In the sleep variables for the first four consecutive cycles, non-REM sleep episode on the fourth cycle was decreased on the nights with nicotine patch compared with the placebo patch (55.4 min vs. 73.8 min, p<0.05) (Table 2).

EEG power density of slow wave activity in stage 2 and REM sleep of the first 3 NREM-REM cycles were plotted relative to the corresponding total values of each stage. During stage 2 sleep, SWA was significantly lower in nights with transdermal nicotine patch compared to nights with placebo patch (t=2.442, df=14, p<0.05) (Figure 1). The difference was confined to the first cycle of the nights. For spindle frequency activity, theta, alpha, beta1, and beta2 activity, no statistical differences were observed.

During REM sleep, SWA was significantly lower in nights with transdermal nicotine patch compared to nights with placebo patch on the first NREM-REM cycle of the nights (t=2.498, df=14, p<0.05) (Figure 2). During REM sleep, alpha activity was significantly higher in nights with transdermal nicotine patch compared to nights with placebo patch also on the first NREM-REM cycle of the nights (t=−2.673, df=14, p<0.05) (Figure 3). For spindle frequency activity, theta, beta1, and beta2 activity, no statistical differences were observed.

LF and HF power, LHR, VLF, R-R means, and R-R variance in stage 2 and stage REM sleep were compared between the nights with transdermal nicotine patch and placebo patch. However, no statistical differences were observed.

LHR, indicating sympathetic nervous system activity, was 12.7±31.2 during REM sleep in the nights with transdermal nicotine patch but not significantly higher than the nights with placebo patch (8.3±15.8). We examined the correlation between LHR and other variables including TST, sleep efficiency, WASO, and SWA. Significant correlation was found between LHR and WASO during stage 2 sleep in the nights with transdermal nicotine patch (r=0.535, p<0.05) (Figure 4), but not in the nights with placebo patch. A tendency for reverse correlation between LHR and SWA during stage 2 sleep in the nights with transdermal nicotine patch (r=−0.442, p=0.099) was observed.