Understanding Sleep in Pregnancy via Animal Models

Animal studies are widely used to further the understanding of how various diseases, illnesses, or situations may affect the human immune system. They can provide an opportunity to control variables that are typically not controllable in human studies. The gathering of information on the sleep patterns of animals during pregnancy has been occurring since the early 1970s due to the acknowledgement that sleep was significantly disturbed in humans (Branchey and Branchey 1970). Clearer information about sleep and wake patterns was acquired with the ability to continuously monitor sleep in controlled environments throughout pregnancy as well as into postpartum. Data from one of the first studies revealed that as early as 15 h before delivery, sleep patterns in rats were modified, reflecting increased wake time and a marked decrease in REM sleep (Branchey et al. 1970). Although no hormonal data were collected from these animals, the authors contend that the observed sleep changes are most likely due to dramatic hormonal changes that occur near or at term. Nishina, Honda, Okai, Kozuma, Inoue, and Taketani (1996) studied the sleep patterns in pregnant female rats. They found increases in the number of NREM episodes, but no increases in total time of NREM sleep. Additionally, they showed a reduction in the number of REM episodes as pregnancy advanced and a prominent decrease in REM sleep during the last 4 days before delivery (Nishina et al. 1996). A protocol by Kimura et al. hoped to further elucidate the sleep-related mechanisms occurring during pregnancy (Kimura, Zhang, and Inoue 1996). Two groups of female rats (pregnant and nonpregnant) were implanted with EEG recording equipment and measured for approximately 3 weeks. Results indicate that significant increases in sleep, primarily NREM sleep, occurred in the pregnant rats. There were also similar fluctuations throughout the pregnancy similar to that in humans, more NREM sleep during the early and late periods than during the midperiod of pregnancy (Kimura et al. 1996). REM sleep was also shown to increase over the course of gestation compared to the nonpregnant rats, but this was attributed primarily to an increase in the number of REM episodes rather than time for each episode. Importantly, the authors heed caution in comparing animal studies to human studies, even though sleep has been shown to be disturbed in pregnancy in both animal and human models.

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Sleep Apnea

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