Fluctuations in BP cause by PM

No one seems to address the wide range of changes in BP related to PM. Doctors don't understand the Physics involved with PM. If a person has a PM that limits increases in heart rate, any exercise will cause their BP to increase. The brain needs oxygen and monitors that level by monitoring he CO2 in the blood. Hence breathing into a paper bag brings C02 back into the blood stream and cures hyperventilation. The only way to increase the the amount of oxygen reaching the brain is to get more blood there per unit time. The blood has to move from the heart to the brain. If the pulse rate is fixed the only way to get more oxygenated blood to the brain is to increase the pressure. The body increases that pressure by constricting the veins thereby decreasing the size of the system. At a given pulse rate, increasing the pressure will increase the flow of oxygen to the brain. So I postulate that a PM can cause paroxysmal hypertension which is sudden and typically short term changes in BP.
If the brain senses any type of trauma it immediately contracts the blood vessels so that it has more blood and more oxygen. The first sign of shock is pale, cold and clammy skin. That is because the brain contracts the vessels and those near the surface of the skin are small and almost close. The skin turns cold because less warm blood is reaching the surface. The blood is being horded by the brain.
The point is: if the heart rate is fixed by a PM the BP must fluctuate to maintain the oxygen level reaching the brain. A person with a pacemaker might walk into the doctors office and as a result of that exercise the BP might be high. In 10 minutes or so it might drop back to normal. Physical and mental stress can all cause this to happen.
When one looks at the vascular system it can be considered a pressure vessel but one must not overlook the fact that the vessel can change size. So heart rate is not the only thing that must be considered with regard to increases in blood pressure. Increasing the heart rate while dilating he vessel will not necessarily increase the amount of blood reaching the brain.

6 Comments

Good points.....

by Sue H. - 2012-03-02 01:03:09

Reading both posts, raises a lot of questions and if nothing else should provide a very interesting discussion. Before I got my pacer, my BP one month before was 110/70...and my family doctor was happy. One month AFTER getting pacer my blood pressure shot up to way above normal and I was put on BP meds. Coincidence? I suffer from white coat syndrome and the nurse at my pacer check always takes my BP right after I've walked into her room....result? High.....she makes note in my chart....and at follow up with Dr same day, he always shakes his head and says you're still too high and wants to add on meds to what I'm on already. Specifically slug drug beta blocker...so of course I say no and he takes BP again after I've been sitting and it is slightly higher than it should be but not so high that he insists on adding more BP drugs..... Coincidence because of pacer doing its job? Or simply a coincidence..... Interesting for sure..........would love to hear other opinions. Sue

white coat

by aldeer - 2012-03-02 06:03:14

Sue, I have the exact problem that if the nurse takes my BP right away, it will be high. If she would just let me sit for a minute or two, it will go down, but some have a routine they insist on following:) aldeer

The Way a PM Operates

by donr - 2012-03-02 12:03:54

I need to understand HOW you think a PM operates. This is to verify your assumptions in the second sentence, where it seems you are assuming that a PM can limit a person's HR. That is only true if a PM is working w/a heart w/o any capability of increasing its HR on its own - like someone who has had a complete Atrial Sinus Node ablation. They have zero capability to increase their own HR.

Anyone else will have that capability, & the PM has a lower & upper limit that it works with. The lower limit in HR is the HR below which the PM will NOT allow the heart to go. Soon as it senses that the heart is going to beat slower, it kicks in & makes the rate the minimum. The upper rate is the point at which the PM ceases to be an active participant & stops helping the heart function. All it does is monitor.

In essence, there is no brake pedal on a PM, only an accelerator.

Your profile indicates no PM model implanted, so I have no idea what info you are working with.

At this point, I am stepping off a cliff and assuming that you do not realize that there is no such thing as a "Heart Rate." Each beat of the heart is individually timed; therefore, a HR is an accumulation of a whole bunch of individual beats put together in a string, as opposed to a nice, neat periodic function like a sine wave. The time between beats can vary considerably, depending on how accurate the timer is in the Sinus Node. There is no way that a human can place a finger on a wrist pulse point & sense the length of an individual beat - they can only count the beats in a minute & get a HR in BPM.

MY cardio & I get into these discussions all the time. They lead to interesting points in the functioning of the body. Your points are well taken. I want to ensure that I truly understand your basic assumptions - for if they are incorrect, they change the entire line of reasoning.

The vascular system is complicated beyond belief - being elastic, yet having the capability of constricting & expanding at command of the central computer; serving to transport an incompressible fluid being driven by a variable speed pump that is in between positive displacement & otherwise.

Don

Theory?

by Sue H. - 2012-03-03 09:03:35

Hi Patch,

Could discuss your reasoning of why it's off base?

Would love to hear as to why you feel that way.

Sue

Good theory, but....

by shockbox340 - 2012-03-03 11:03:52

There are too many variables to really buy into this theory. First off, most pacemaker patients do not have a "fixed" heart rate. The vast majority either have some sort of AV block (in which case the sinus node is still controlling the rate and the pacemaker is sensing the atrial beat and pacing in the ventricle) or have some sort of rate adaptation algorithm turned on for heart rate variability (VVIR vs VVI, DDDR vs DDD, DDD-CLS vs. DDD, etc.)

Your body has multiple ways to control cardiac output. Heart rate is the most simple (how fast your heart beats). Another is cardiac contractility (how HARD you heart beats). This can be a huge factor - think about those times when you can feel your heart beating in your chest after a surge of adrenaline (scared, angry,etc.). The final way is via vasoconstriction or vasodilation (making the 'pipes' or blood vessels bigger or smaller to vary pressure).

Now pacemakers can 'cause' fluctuations in BP, especially when they are paced intermittantly in the ventricle. The quality of an intrinsic contraction is much better than a paced ventricular contraction (which is more like a PVC). Intrinsic ventricular contractions move more blood out of the heart and into the circulatory system than paced beats, so it stands to reason that changing from paced to sensed or vice versa will affect your blood pressure.

But here's the more important thing to consider: If you have an increase or decrease in blood pressure as a result of your pacemaker, your body will use the other parts of the system to stabilize blood pressure on the fly. So even if you have enough of a fluctuation to be symptiomatic, it should be very short lived.

Any patient that is having consistent symptoms that you think are related to pacing, talk to your doctor and your pacer tech/nurse or the company representative that does your checks. Be the squeaky wheel. There is a decent chance that adjustments can be made to minimize if not eliminate the symptoms you are feeling.

Higher heart rate

by JIMMYANDJEREMY - 2019-10-07 17:27:26

Had a pacemaker put in 3 weeks ago for low heart rate was 30 had 3rd degree electrical heart block now it can be in the high 90s without exercising if I walk from one room to another then goes back down to 70s and 80s anyone else have this

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