In an article published in the Journal of Hypertension, researchers from Kyoto University in Japan investigated the sleep characteristics of a community, including sleep fragmentation, sleep disordered breathing (SDB), and nocturia – and how they affect sleep blood pressure. They found that frequent nocturnal urination may represent a potential risk for circadian BP abnormalities which are risk factors for heart disease.
Sleep blood pressure and sleep characteristics
Abnormalities in circadian blood pressure (BP) variations, such as an increase in sleep BP, are risk factors of cardiovascular disease. Normal BP follows a circadian pattern that involves an early morning surge and a night time descent – meaning that for healthy individuals, their BP is higher during the day and lower when they are asleep. During sleep, a person's BP greatly drops and is not affected by other factors when uninterrupted. In contrast, a person's BP when he or she is awake varies greatly throughout the day. This makes sleep BP a more accurate marker of cardiovascular risk.
Sleep characteristics, such as sleep fragmentation, SDB, and nocturia may affect sleep BP. Sleep fragmentation is characterized by repetitive short interruptions of sleep and is one of the leading causes of excessive daytime sleepiness and tiredness. While not considered a sleep disorder, sleep fragmentation is thought to be a symptom of a sleep disorder. Sleep fragmentation can be caused by periodic leg movements, SDB, snoring, and nocturia.
SDB is a collective term for a group of disorders defined by abnormal respiratory patterns -- such as apneas or hypopneas -- and insufficient ventilation during sleep. Apnea refers to the stopping of breath for 10 seconds or more during sleep, while hypopnea refers to shallow breathing that lasts for 10 or more seconds. Both of these events disrupt a person's sleep pattern and leads to exhaustion during daytime. SDB can be classified as either obstructive sleep apnea (OSA, repetitive airway collapse), central sleep apnea (CSA, repetitive periods of insufficient ventilation), or complex sleep apnea (combination of CSA and OSA). (Related: Losing weight cures sleep apnea, scientists discover.)
Nocturia or frequent nighttime urination comes with age. As people grow older, they produce less quantities of an anti-diuretic hormone that allows people to retain fluids for six to eight hours every night. Their bladders also lose holding capacity, hence they feel the need to urinate more often. Nocturia among the elderly and even younger people can be caused by medical conditions, such as urological infections, the presence of a tumor in the bladder or prostate, bladder prolapse, or disorders that affect sphincter control. Nocturia is also associated with diabetes, pregnancy, and heart and liver failure.
Nocturia represents a risk for sleep BP abnormalities
The factors associated with BP abnormalities are not fully understood, so researchers from Japan decided to investigate the relationship between sleep characteristics and sleep BP. For their cross-sectional study, they evaluated 5,959 community participants with home-measured data on nocturnal BP change (sleep BP ? waking BP), sleep characteristics, and sleep disordered breathing. To assess sleep characteristics including the sleep fragmentation index, they relied on recordings from a wrist-wearable actigraph. They also used a finger-type monitor to assess SDB and measure the three percent oxygen desaturation index. Lastly, they asked the participants to record the number of nocturnal urinations they had each night in a sleep diary.
The researchers reported a negative mean nocturnal sleep BP change among the participants. They also found an association between the three percent oxygen desaturation index and BP change independent of the basic covariates. However, the association became insignificant after adjusting the fragmentation index. The oxygen desaturation index is the number of times per hour of sleep that the blood's oxygen level drops by a certain degree from baseline. The researchers also found that the association between the fragmentation index and BP change was insignificant after adjusting the measurement season (middle season and summer season). In contrast, the frequency of urination showed a strong and independent association with sleep BP, with smaller nocturnal BP drops in participants with frequent urination.
Based on their findings, the researchers concluded that subjective sleep estimates and frequent nocturnal urination may represent a potential risk for circadian BP abnormalities.
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