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Blood pressure reading influences: Unsung factors and effects

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Unsung factors that affect a blood pressure reading are things that many don’t think about, which have a short term effect on a blood pressure reading.  They affect the actual reading at the time of the measurement.  They blood pressure readingdiffer from flaws in technique that affect the accuracy of a reading.  The main concern though, is that the reading obtained, though accurate, might be quite different from the 24 hour BP average, which is the best predictor of complications of hypertension.

These factors vary from person to person, and they apply to blood pressure readings at a person’s home or in a clinical setting.  The effects can vary between people.  Some might raise the blood pressure (BP) in one person, lower it in another, or have no impact at all.

There are some noteworthy scientifically proven factors of this sort.  It is practical to group them into categories.  They are as follows:

  • The 24-hour time cycle
  • One’s emotional state
  • Temperature
  • Activity
  • Oral nutritional intake
  • Bladder volume status
  • Drug intake

The 24-hour time cycle effect

The one factor that affects blood pressure readings in virtually everyone on a daily basis is the 24 hour time cycle.  More precisely, it is the 24-hour sleep-wake cycle.  Blood pressure has a daily pattern.  In the normal blood pressure readingstate it tends to be lowest during sleep and begins to rise a few hours before awakening. It generally reaches its steady state and high point in the mid afternoon and begins falling in the late afternoon.   

The medical term for this 24 hours cycle of blood pressure behavior is the blood pressure circadian rhythm.  Another name for it is blood pressure diurnal variation 

People whose blood pressure dips to its lowest point during sleep, which is the norm, are labeled dippers.  Those whose blood pressure doesn’t dip while sleeping are termed non-dippers.  There is evidence of a greater incidence of certain complications from high blood pressure affecting the heart and blood vessels in non-dippers.

The impact of emotional state on blood pressure 

It is well known and proven that stress, anxiety and anger cause an increase in blood pressure in both, persons with, and without hypertension.  The effect of stress and anxiety on a blood pressure reading is the presumed basis of the white coat syndrome.  White coat phenomenon, white coat syndrome and white coat hypertension are synonyms.  The terms refer to the temporary spike in a patient’s blood pressure in the doctor’s office or other clinical setting.  The anxiety is presumably due to the expected or actual encounter with the doctor and/or other personnel that wear a white coat.

The effect of temperature on blood pressure

There are various examples of how the ambient (surrounding) temperature of a person undergoing a blood pressure reading affects the obtained result. 

One is the seasonal variation in BP which several research studies from the early 1980s through the late 1990s have demonstrated.  That research was in different parts of the world.  In countries with seasons the persons studied had higher systolic and diastolic blood pressure readings in the winter months than in the summer months and in cold weather compared to hot weather in general.

Research has shown comparable effects on BP from short-term exposure to hot and cold temperatures.  BP variation caused by weather fronts is an example.  Thus, it is likely that if the room temperature in a patient’s home is significantly different from that in a doctor’s office there might be a notable difference in the blood pressure reading in the two places. 

In some instances the temperature effect might be mistaken for white coat phenomenon in some patients if the temperature is warmer in a patient’s home than in the doctor’s office or clinic. Conversely, the impact of a warmer temperature in a clinical setting than at home might explain some cases of masked hypertension – blood pressure elevation at home but not in the clinical setting.

There are also reports of hot baths or hot showers temporarily lowering blood pressure.   The proposed mechanism of vasodilation from heat exposure as being the cause of the drop in BP lends some credence to the reports.  But to date they lack scientific proof.

Effect of activity on a blood pressure reading

In the absence of certain disease states physical activity usually causes a rise in one’s blood pressure.  That is why you should be sitting and not moving for at least 5 minutes before checking your blood pressure or having it checked.

Bladder volume and its effect on blood pressure

Studies have shown that bladder distention from drinking fluids or having fluids instilled into the bladder via a catheter causes a rise in blood pressure. Therefore, it is wise to void before a BP measurement if the urge exists.

The effect of oral ingestion on blood pressure

Eating food or drinking nutrient containing fluids generally causes a drop in the blood pressure if the reading is at a time when the stomach contents have begun to empty into the duodenum. The degree of BP drop depends on a number of factors.  They include the following:

  • size of the meal
  • composition of the meal
  • consistency (degree of density or thickness) of the meal
  • body position after the meal

In general, to eliminate this factor as an influence on a blood pressure reading, the measurement should be before meals, and the interval between it and the last full course meal should be four or more hours.

The effect of drugs on blood pressure readings

Drug effects on a blood pressure reading are from a perspective of the definition of a drug in a broad sense of the word.  In a broad sense a drug is a nonfood substance which when ingested alters normal bodily functions.  Drugs in this category and their potential effects on blood pressure are the following:

  • Alcohol – Consumption usually causes a rise in BP. Small amounts in some people might cause a slight drop.  Alcohol withdrawal causes BP to rise.
  • Nicotine – Causes blood pressure to rise.  That is why one should not smoke a cigarette within 30 minutes prior to undergoing a blood pressure reading.
  • Caffeine – In some, it can cause a rather marked rise in BP.  The effect might last from 30 minutes to two hours.
  • NSAIDS – Can raise BP.
  • Antidepressants – Can raise BP.
  • Decongestants in cold medications (Sudafed; Neo-Synephrine) – Can raise BP.
  • Herbal supplements – Can raise BP. The most notable ones are ephedra (now banned) and licorice. There is a long list of others herbs that might cause the BP to rise. But they usually do so when their use is at doses greater than normal.  Some herbs in fact, at safe doses, lower BP.
  • Illicit street drugs – Can raise BP.  The most common ones are:
    • Amphetamines including methamphetamine
    • Anabolic steroids
    • Cocaine
  • Stimulants (such as Ritalin) – Can increase BP.
  • Other prescription medicines (consult your physician) – Might increase or lower BP




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