Sleeping Pattern

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J. Sleep Res. (2011) 20, 318–325
doi: 10.1111/j.1365-2869.2010.00871.x

Insomnia and cardiovascular activity

Sleep onset and cardiovascular activity in primary insomnia
MASSIMILIANO DE ZAMBOTTI, NAIMA COVASSIN, GIULIANO DE MIN T O N A , M I C H E L A S A R L O and L U C I A N O S T E G A G N O Department of General Psychology, University of Padova, Italy

Accepted in revised form 14 June 2010; received 3 December 2009

SUMMARY

The transition from wakefulness to sleep is characterized typically by a shift from sympathetic to parasympathetic regulation. Physiological functions, depending on the neurovegetative system, decrease overall. Previous studies have shown cardiovascular and electroencephalographic hyperactivity during wakefulness and sleep in insomniacs compared with normal sleepers, but there is very little evidence of this in the process of sleep onset. The purpose of this study was to compare cardiovascular and autonomic responses before and after falling asleep in eight insomniacs (who met DSM-IV criteria for primary insomnia) and eight normal sleepers. Non-invasive measures of heart rate (HR), stroke volume (SV), cardiac output (CO) and pre-ejection period (PEP) were collected by impedance cardiography during a night of polysomnographic recording. Frequency domain measures [low-frequency (LF), high-frequency (HF)] of heart rate variability (HRV) were also estimated. Decrements in HR and CO and increases in SV and HF normalized units (n.u.) were found in both groups after sleep onset compared with wakefulness. Conversely, PEP (related inversely to sympathetic b-adrenergic activity) showed increases after sleep onset in controls, but remained unchanged in insomniacs. PEP was also significantly lower in insomniacs than in normal sleepers in both conditions. These data suggest that, whereas normal sleepers follow the expected progressive autonomic drop, constant sympathetic hyperactivation is detected in insomniacs. These results support the aetiological hypothesis of physiological hyperarousal underlying primary insomnia. k e y w o r d s cardiovascular system, hyperarousal, impedance cardiography, primary insomnia, sleep onset

INTRODUCTION Primary insomnia is defined as difficulty in falling asleep, maintaining sleep or non-restorative sleep which is not due to other medical, psychiatric or sleep disorders (DSM-IV; American Psychiatric Association, 1994). In insomniacs, polysomnographic sleep monitoring shows reduced sleep efficiency because of increased sleep latency and extended periods of nocturnal wakefulness (ICSD-2; American Academy of Sleep Medicine, 2005). In addition to night-time sleep disorders, insomnia also involves daytime consequences, which may lead to significant distress and functional impairment in Correspondence: Massimiliano de Zambotti, Department of General Psychology, University of Padova, Via Venezia 8, 35131 Padova, Italy. Tel: +39-049-8276635; fax: +39-049-8276600; e-mail: massimiliano. dezambotti@unipd.it

daily activities. In particular, insomniacs often report diurnal sleepiness, fatigue, dysphoria, decreased attention and memory (for a review, see Riedel and Lichstein, 2000). Severe forms of insomnia may also enhance the risk of traffic and work accidents and psychiatric diseases, such as depression or anxiety disorders (ICSD-2; American Academy of Sleep Medicine, 2005). Epidemiological data suggest that about one-third of the general population suffers from symptoms of insomnia and that about 6% of people satisfy the criteria for a diagnosis of primary insomnia (Ohayon, 2002). Morin et al. (2006) recently interviewed a large sample (2001 subjects), reporting that 25.3% were unsatisfied with their sleep, 29.9% suffered from symptoms of insomnia and 9.5% met DSM-IV (American Psychiatric Association, 1994) and ICD-10 (World Health Organization, 1992) criteria for a diagnosis of insomnia. Ó 2010 European Sleep Research Society

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Sleep onset and primary insomnia
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