Postural Orthostatic Tachycardia Syndrome (POTS) is a condition characterized by an abnormally large increase in heart rate when moving from a lying down to standing up position. This is accompanied by symptoms like lightheadedness, palpitations, tremors, headache, fatigue, nausea, abdominal pain, chest pain, exercise intolerance, and cognitive deficits. The hallmark symptom of POTS is an increase in heart rate of at least 30 beats per minute (bpm) within 10 minutes of standing or head-up tilt testing. While these symptoms can be debilitating during the day, many POTS patients report an improvement in their symptoms at night.
Lower Heart Rate and Blood Pressure at Night
One of the main reasons POTS symptoms tend to improve at night is due to the natural circadian dipping of heart rate and blood pressure. During the night, the body’s heart rate and blood pressure decrease by 10-20%. This is a normal phenomenon called “nocturnal dipping” that allows the heart and blood vessels to rest.
In POTS patients, this nighttime dipping of heart rate and blood pressure is often impaired or exaggerated. Their heart rates do not decrease at night as much as healthy individuals. However, their heart rates still tend to be lower at night compared to the daytime. The average decrease is estimated to be around 5-10 bpm. This lowering of heart rate overnight correlates with an improvement in symptoms. Lower heart rates at nightdon’t trigger as many POTS episodes.
Reasons for Lower Heart Rate at Night
- Lying down position reduces gravitational stress on the cardiovascular system
- Parasympathetic nervous system activity increases at night
- Hormonal changes overnight such as increase in melatonin
- Lower core body temperature
- Improved circulation while lying flat
In addition to lower heart rates, blood pressure also dips at night in POTS patients. One study found an average reduction in systolic blood pressure of 8 mmHg overnight. This blood pressure dipping contributes to reduced POTS symptoms.
Less Orthostatic Stress
A critical reason that POTS symptoms diminish at night is that patients are lying down for prolonged periods. This avoids orthostatic stress which is the main trigger for POTS episodes.
Orthostatic stress refers to the effects of gravity on the body’s cardiovascular system when moving from lying to standing. The upright posture causes blood to pool in the legs and abdomen, reducing venous return to the heart. This makes it more difficult for the heart to pump against gravity.
In POTS patients, this orthostatic stress triggers tachycardia, mediated by increased sympathetic nerve activity and reduced venous return. Being in the supine position overnight avoids this gravitational stress on the circulation.
Benefits of Supine Position
- Prevents venous pooling in legs and abdomen
- Improves venous return and cardiac output
- Minimizes orthostatic stress on the heart
- Lessens need for sympathetic compensation
- Allows cardiovascular system to rest
The simple act of lying down for 6-8 hours overnight gives a necessary break to the cardiovascular system and minimizes episodes of POTS.
Changes in Fluid Balance
Fluid shifts that occur when lying down also help minimize nighttime POTS episodes. During the day upright, fluid pools in the legs and abdomen. At night while lying in bed, this fluid redistributes back into the thoracic cavity.
This improves central venous pressure, allowing for better filling of the heart chambers. It also increases stroke volume and cardiac output. The fluid shifts into the chest also increase plasma volume. This reverses the hypovolemia that contributes to POTS while upright.
Overnight Fluid Shift Benefits
- Increases central venous pressure
- Improves cardiac preload
- Increases stroke volume
- Reverses hypovolemia
- Raises plasma volume
These overnight fluid shifts reduce the cardiovascular instability characteristic of POTS. The fluid rebalancing acts to minimize nighttime POTS episodes.
Hormonal Changes During Sleep
Changes in hormones during sleep, such as melatonin, also act to dampen POTS symptoms at night. Melatonin is the primary hormone that regulates the sleep-wake cycle. Levels begin to rise in the evening around 9 pm, peaking in the middle of the night.
In addition to its sleep effects, melatonin also has favorable cardiovascular actions. It has anti-adrenergic effects, working to lower norepinephrine. This acts as a sympatholytic, reducing sympathetic outflow to the heart and vessels. The resulting decreases in heart rate and blood pressure lessen POTS symptoms.
Melatonin’s Benefits in POTS
- Lowers heart rate
- Decreases blood pressure
- Reduces sympathetic tone
- Antioxidant and anti-inflammatory effects
- Improves sleep quality
Given these cardiovascular benefits, melatonin supplementation has been investigated as a treatment for POTS patients. Taking melatonin during the daytime decreased upright heart rate and improved symptoms in a study.
Autonomic Changes During Sleep
In addition to melatonin, there are other changes in the autonomic nervous system overnight that help diminish POTS episodes.
During non-REM sleep, sympathetic nervous system activity and catecholamine release are reduced compared to wakefulness. There is an overall dominance of parasympathetic tone. This acts to lower heart rate and blood pressure into the normal “dipping” overnight.
Additionally, release of vasopressin is increased during non-REM sleep. Vasopressin is a hormone with vasoconstrictive effects. The increase in vasopressin overnight helps maintain vascular resistance when lying down. This prevents blood from pooling excessively.
Autonomic Changes That Improve POTS
- Lower sympathetic activity
- Increased parasympathetic tone
- Reduced catecholamine release
- Increased vasopressin release
These autonomic alterations during sleep serve to minimize the hemodynamic instability characteristic of POTS. The more stable overnight cardiovascular changes result in reduced POTS episodes.
Circadian Rhythm Factors
POTS symptoms following a circadian rhythm, being worse in the daytime and improving overnight, points to an interaction with the body’s intrinsic 24-hour cycles.
The circadian system helps regulate many cardiovascular parameters to follow a daily pattern. Heart rate, blood pressure, vascular tone, blood catecholamine levels, and heart rate variability all vary between night and day.
The circadian master clock in the brain helps synchronize these cardiovascular rhythms. In POTS patients, this circadian regulation seems to be disrupted. Their circadian cardiovascular rhythms lack the normal day-night variation.
However, there still appears to be some residual circadian influence overnight, accounting for the improvement in symptoms. POTS patients retain a slight dipping of heart rate and blood pressure.
Circadian Factors Improving Nighttime POTS
- Slight heart rate dipping overnight
- Minimal nocturnal BP dipping
- Some parasympathetic dominance at night
- Possible improved heart rate variability
Although diminished compared to normal, some circadian effect persists to minimize POTS at night. Enhancing circadian mechanisms may hold promise to better control day-night POTS differences.
Lower Stress Hormones
Many POTS patients also have elevated levels of stress hormones such as epinephrine, norepinephrine, and cortisol. The heightened sympathetic activation and stress response contribute to tachycardia and high blood pressure.
Cortisol in particular follows a strong circadian rhythm, with peak levels in the morning that decline throughout the day. Cortisol concentrations drop to their lowest overnight.
The overnight reduction in stress hormones likely attenuates POTS symptoms. Lower circulatory levels of epinephrine, norepinephrine, and cortisol overnight dampen sympathetic outflow. This reduces heart rate and blood pressure spikes that can trigger POTS episodes.
Benefits of Reduced Stress Hormones
- Lowers epinephrine and norepinephrine
- Reduces sympathetic activity
- Lessens HR and BP increases
- Minimizes POTS episodes
The decrease in stress hormones overnight works to stabilize the cardiovascular system in POTS patients. This nighttime hormonal change improves POTS symptoms.
Lower Body Temperature
Core body temperature is another circadian biomarker that dips during nighttime sleep. Body temperature decreases by about 0.5 to 1°F overnight.
This reduction in body heat lessens cardiovascular strain. Lower temperatures cause a mild vasodilation, improving blood flow. In POTS patients, even small improvements in peripheral circulation can alleviate symptoms.
The body’s decreased metabolic activity during sleep also reduces body heat. This metabolic downshift slightly lowers oxygen demand and carbon dioxide production, which can minimize POTS episodes.
How Lower Body Temperature Helps POTS
- Mild vasodilation improves circulation
- Lessens cardiovascular strain
- Lowers oxygen demand and CO2 production
- Small enhancement of cardiac output
Though subtle, the overnight reduction in core body temperature contributes to improved POTS symptoms by optimizing cardiovascular function.
Improved Sleep Quality
Sleeping lying down also often improves sleep quality in POTS patients. Throughout the night, POTS patients are able to achieve longer periods of sustained, uninterrupted sleep.
Poor sleep quality during the daytime commonly occurs due to POTS episodes waking patients from naps. The constant interruptions lead to fragmented, unsatisfying daytime sleep.
Conversely, nighttime slumber in bed allows for deeper, more restorative sleep. This helps POTS patients awaken feeling more refreshed and energetic. Improved sleep quality amplifies the overnight recovery from POTS symptoms.
Benefits of Improved Sleep Quality
- Longer uninterrupted sleep
- Increased slow wave and REM sleep
- Deeper and more restorative sleep
- Wake up feeling more refreshed
The differences in sleep quality between night and day amplify the variation in POTS symptoms. Getting continuous high quality sleep makes a big difference in how patients feel overnight.
More Time Spent Reclined
POTS patients often feel better when they are reclining or able to frequently sit or lie down. Being upright for long periods tends to make symptoms worse.
During the night, POTS patients spend all their time reclined in bed, usually at least 6-8 hours. This allows an extended rest period off their feet without orthostatic stress.
Spending longer durations reclined provides greater respite for the cardiovascular system. Blood can redistribute back to the thorax without gravity forcing it into the abdomen and limbs. The heart can pump without working against the pressure of standing up.
Benefits of Prolonged Reclined Time
- Minimizes effects of orthostatic stress
- Allows fluid redistribution to thorax
- Reduces workload on the heart
- Lets the cardiovascular system rest
The simple benefit of remaining still and reclined for longer sustained periods overnight aids recovery from POTS symptoms.
Avoidance of Triggers
Being at home and asleep also helps POTS patients avoid triggers that commonly exacerbate their symptoms during the day.
Factors frequently reported to worsen POTS include being in warm environments, large meals, alcohol, menstruation, emotional stress, lack of sleep, and prolonged standing.
Staying home overnight eliminates exposure to heat, big meals, and alcohol. Sleeping replaces physical and mental stress with rest. And recumbence avoids extended upright activity.
Nighttime Avoidance of POTS Triggers
- Heat exposure – home thermostat controlled
- Big meals – fasting during sleep
- Alcohol – none while asleep
- Mental stress – mind able to rest
- Upright posture – lying in bed
Being at home asleep prevents POTS patients from encountering many environmental and lifestyle factors that commonly worsen symptoms during the day.
Take Daytime Naps
Given that nighttime sleep provides significant symptom relief, taking daytime naps can provide periodic recovery periods. Getting extra sleep during the day allows POTS patients to gain some of the overnight benefits.
Trying to nap in the reclined position can help minimize disruptions from orthostatic stress. Naps also allow the mind and body to rest, providing a brief retreat from symptom triggers. Quality daytime napping serves as short respite periods to take the edge off POTS episodes.
Tips for Maximizing Daytime Nap Benefits
- Nap in reclined position with legs elevated
- Limit naps to 20-30 mins to avoid grogginess
- Take naps earlier when most tired
- Create relaxing nap environment
- Use white noise or earplugs
- Avoid stimulation before napping
Though not as effective as nighttime sleep, well-planned daytime napping can provide periodic relief from debilitating POTS symptoms.
Conclusion
The mechanisms behind nighttime improvements in POTS are complex and multifactorial. Lying down minimizes orthostatic stress while facilitating fluid shifts back to the thoracic cavity. Cardiovascular parameters like heart rate, blood pressure, and sympathetic activity dip overnight. The circadian system and hormonal changes also act to stabilize POTS symptoms in the evening. Furthermore, triggers are avoided and sleep quality increased while sleeping at home in bed.
Daytime remedies like napping can provide periodic relief, but nighttime sleep gives extended duration symptom recovery. Tapping into these regenerative nighttime states allows POTS patients to recharge both physically and mentally to face challenges the next day.