Blood pressure and mast cell disease

Blood pressure is the pressure that blood exerts upon the walls of blood vessels.  Blood pressure is mostly a function of the beating action of the heart.  It is expressed as two numbers: systolic, which measures the pressure in arteries when the heart contracts and forces out blood; and diastolic, which measures the pressure in arteries when the heart refills with blood before it beats again.

Low blood pressure (hypotension) is defined as less than 90 systolic or less than 60 diastolic (according to the American Heart Association.)

Ideal blood pressure is defined as 90-119 systolic and 60-79 diastolic.

Prehypertension is defined as 120-139 systolic or 80-89 diastolic.

High blood pressure (hypertension) is defined as 140-179 systolic or 90-109 diastolic.

Hypertensive emergency is defined as above 180 systolic or above 110 diastolic.

Hypotension is sometimes found in patients with mast cell disease.  It can be perpetual, associated with POTS or related to anaphylaxis, in which the blood pressure may drop precipitously. 

Hypertension is also sometimes found in mast cell patients.  These people might always become hypertensive when they stand.  Alternately, they might have isolated episodes of high blood pressure, rapid heartbeat, anxiety and shortness of breath.  In these instances, blood pressure can be as high as 240/140.  This was described in the past as “hypertensive MCA.”  Mast cell patients who also have POTS may have a kind of POTS called hyperadrenergic POTS (hyperPOTS), which can result in hypertension.

The interactions between mast cell disease and POTS (of either type) is thought to occur in the following fashion:

1.       Mast cells are activated and release mediators that can alter blood pressure or heart rate.

2.       These mediators relax the smooth muscle in the vessel walls.  This decreases the resistance of the vessels against the blood, allowing the blood to move more quickly. 

3.       In response to this, the sympathetic nervous system is activated.  This causes several things to occur.

4.       The vessel walls tighten to increase resistance against the blood.

5.       Heart rate increases.

6.       Norepinephrine and neuropeptide Y are released.  For patients with hyperPOTS, the amount of norepinephrine released is significantly more than necessary to regulate blood pressure.  (Often 1000-2000 pg/ml, while 600 pg/ml is diagnosed for POTS.)

 

7.       Neuropeptide Y induces mast cell degranulation.

This type of cyclical interaction is called a positive feedback loop.  Mast cells degranulate because of sympathetic activation, and sympathetic activation occurs because of mast cell degranulation.

Patients with both POTS and MCAS showed an increase in heart rate from 79-114 bpm after standing for five minutes, increased systolic pressure from 117-126 after standing for five minutes, and increased systolic pressure (157 vs 117 in control group) at the end of the Valsalva manuever.  (The Valsalva manuever is when you pinch your nose shut and try to force air outward to “clear” your ears.) 

In hyperPOTS patients, blood pressure can climb significantly during episodes.  Only 10% of patients with POTS have hyperPOTS; of this 10%, only 10% also have mast cell activation.

To determine if the patient has hyperPOTS, a catecholamine blood test is usually performed.  This measures dopamine, epinephrine and norepinephrine levels.  Patients lay down in a dark, quiet room for 30 minutes, after which time blood is drawn.  Then they walk around for 10 minutes.  Another blood sample is taken.  HyperPOTS can be diagnosed from the difference in levels between the two samples.

In hyperPOTS, methyldopa and clonidine are sometimes used.    Beta-blockers should be used cautiously in patients with mast cell disease.