Understanding Blood Flow & Pressure | Part 2
Now that we have discussed the essence of blood and flow, we explore hypertension, if and how to treat it.
Moving On…
In Part 1 we covered a foundational set of ideas about the nature of blood and circulation, including:
What blood is.
How blood flows.
Why blood flows.
If you haven’t yet read Part 1 of this series, I would highly recommend that you stop right here, and read it first.
In this article we will dive into one of the most commonly diagnosed and treated illnesses in the modern era: high blood pressure or hypertension.
We will answer:
What is blood pressure?
Why is high blood pressure bad?
Does normalizing blood pressure improve health?
What is the best way to reduce blood pressure?
Blood Pressure
First, it’s important to understand what blood pressure is.
When we discuss ‘blood pressure,’ we refer to the force that the blood exerts on artery walls. As we know from Newton’s third law of motion, as the blood exerts a force on the artery, so too does the artery exert a force on the blood.
This reciprocal interaction between blood vessel and wall results in motion of the blood. If the arteries just kept expanding as a result of blood moving into the vessel…then there would be no force causing the blood to move along the tube.
We refer back to the image in Part 1, demonstrating the relationship between flow, pressure, and viscosity as captured by Poiseuille.
What is important to recognize is that the speed of blood flow is directly related to the difference in the pressure between two points in a vessel.
But, the blood does not exert a force on a static vessel. The vasculature of the whole body is malleable and actively controlled. Our body has evolved to release vaso-active substances which alter the tension within the artery wall to regulate flow.
For example, when you eat food…the digestive tract will respond by dilating the arteries that feed the gut…which reduces the resistance along this path…and enables the flow of larger quantities of blood. By making a path of ‘lesser resistance,’ the body controls how much blood flows to a target organ.
How Blood Pressure Is Measured
Typically, blood pressure is measured along the arm - as anyone who’s been to a family doctor or emergency department knows. The closer to the heart, the more ‘reliable’ the measurement.
In reality, when your blood pressure is measured…it is actually a measure of the pressure in the brachial artery.
There are several problems with using the brachial artery as an indicator of cardiovacular fitness. First, the brachial artery often overestimates systolic blood pressure, sometimes by up to 40 mmHg!
As it turns out, the younger you are the greater the mismatch between blood pressure in the arm, and central blood pressure coming out of the heart.
This is a bit of a digression, but suffice it to say both the method by which we measure blood pressure and the thresholds we use to assess overall health are not as concrete as your doctor or the American Heart Association may make it sound.
Furthermore, the thresholds use to define hypertension have been changing over the last 20 years. In fact, when I started medical school what I was taught as “stage 1 hypertension” had shifted by the time I had finished my training.
As you can see, the US is a bit of an outlier (since new guidelines from 2017) when it comes to definitions of “hypertension.” In Europe, if you have a systolic BP between 120-130, this is considered normal. In the US, this is considered “elevated.”
More importantly, if you are European and your diastolic BP can be up to 85 mmHg and you are considered “normal.” In the US, however, this is considered Stage 1 Hypertension. It should be noted that these diastolic thresholds are used to justify treatment of “high blood pressure” in otherwise healthy(er) young adults.
As we noted, the younger population tend to have higher blood pressure in their arms.
As you can see from the chart above, the European guidelines agree with the International Society of Hypertension.
Is High Blood Pressure Bad?
Short answer: It can be.
And, it probably is for the vast majority of people who have chronically elevated blood pressure.
Why?
In our modern time, most people have chronically elevated blood pressure because of underlying metabolic dysfunction. All of the common chronic illnesses that people have, including: diabetes, obesity, autoimmune and inflammatory conditions…are caused by the same things which can lead to high blood pressure.
What I didn’t mention is cardiovascular disease. That is because it is not only cardiovascular ‘disease’ which causes high blood pressure. It is an unfit cardiovascular system.
Just like your organs will regulate how much blood reaches them, your heart and arteries must be healthy enough to effectively supply blood where it is needed…without undue stress upon itself. People who live a sedentary life, do not put the heart and blood vessels under stress.
Going for a sprint, swimming and lifting weights do not only work out your muscles and joints.
Your heart and blood vessels expand and contract to the demands of your body, just like your muscles. In doing so, they improve and maintain what can be thought of as circulatory flexibility. Same goes for your lungs.
Two conditions are necessary for healthy blood pressure & heart rate:
Optimal conditioning of your end-organs
including: muscles, kidneys, stomach, liver, brain & skin
Optimal conditioning of your cardiovascular system
Despite what the mainstream medical paradigm will tell you, you cannot simply force your blood vessels to dilate for the purposes of reducing a number - i.e. blood pressure.
Your blood pressure is high for a reason. Unless you address that reason, you will not prevent the damage it is doing to your body.
Worse yet, by forcing your blood vessels into a state they do not wish to be in…you can add additional problems to your health.
Let’s dig further into the literature.
Does Normalizing Blood Pressure Improve Health?
To answer this question, we will look through the findings of two major studies. One published in 2013, and another in 2022.
Both of these studies wanted to explore the relationship between lifestyle, medication for blood pressure, and health outcomes.
The first study from Brown et al (2013) aimed to assess the impact of physical activity and medication on blood pressure and all-cause mortality. For this observational study consisting of over 10,000 people…the analysis was grouped into multiple categories, all of which included a sub-category of “active” or “inactive”:
On medication & controlled blood pressure
On medication & uncontrolled blood pressure
Not on medication & uncontrolled blood pressure
Normotensive: i.e. not on medication and normal blood pressure
Curves A-H
A: normotensive + active
B: normotensive + inactive
C: treated + active + controlled
D: untreated + active + uncontrolled
E: treated + inactive + controlled
F: untreated + inactive + uncontrolled
G: treated + active + uncontrolled
H: treated + inactive + uncontrolled
There are some very important observations to be made from this study.
Even if your blood pressure is normal, physical activity improves mortality as demonstrated by the difference between curves A and B
It is obviously bad for your health to be chronically hypertensive as demonstrated by the huge gap between A/B and all other curves.
Although the authors report a “significant difference” between curves C and D…upon closer inspection, you can see that they are almost identical just until after 200 months. In fact, curves C and D are closer to one another along their entire length than any other curve on that graph.
What I want to highlight from this observation is the critical importance of being active. This is the common attribute between curves C and D.
Whatever difference exists between C and D (which I’m sure, ultimately there is a difference)…the impact is likely not nearly as significant as being active.
To strengthen this point, look at this difference between curves C and E. Both are populations with treated and controlled blood pressure. But their mortality is one of the largest differences among the whole cohort.
To expand this point, being active and uncontrolled (curve D) is far better than being treated + controlled + inactive.
If the drugs used to treat blood pressure were benign, you would think that the worst outcomes would be for the population who are untreated + inactive + uncontrolled. But, this is not what we observe.
First, those with the highest mortality were inactive + uncontrolled + treated.
What is even more telling, those who were untreated + uncontrolled regardless of activity (curves F and D) had better survival rate than those who were treated + uncontrolled regardless of activity (curves G and H)
What Is Going On Here?
Whatever your opinion about the outcomes of the above study, I think the more recent publication in the Journal of the American Medical Association (JAMA) can shed some light.
In this article, the authors wanted to understand the combination of blood pressure medication and healthy lifestyle and its relationship to mortality among individuals with hypertension. Interestingly, they assessed all-cause mortality, cardiovascular mortality, and cancer mortality.
This figure from their analysis is quite informative:
A few things I want to draw your attention to:
On the Y-axis is HR, which stands for hazard ratio. Furthermore, the scale of the hazard ratio (0, 0.5, 1.0, and 1.2) is similar on all graphs
Hazard Ratio is compared with ‘healthy lifestyle score,’ and as expected every single outcome risk of mortality is lower with higher lifestyle scores.
Look at the first column (all-cause mortality) of graphs (A and D)
Although it’s not significant (at least by author reporting), the reduction in risk of mortality amongst those not using medication is better than those using medication
For example, at a lifestyle score of 6 those not using medication reduce their hazard risk below 0.5. In comparison, the medicated group achieve this reduction with a lifestyle score of 8.
The same is observed in the CVD and Cancer mortality graphs, which the cancer mortality graph being the most telling.
What does this mean? Well, one interpretation is that improving your lifestyle has a strongly beneficial impact - but simultaneously taking medications blunts the positive impact of a healthy lifestyle.
In addition to seemingly blunting the impact of lifestyle, medication use has another interesting effect on the distribution of mortality. Arguably with the exception of cancer mortality, medication use seems to make the confidence interval (the bars on either side of the dots) narrower.
Now, you might be thinking - is that a good thing? Well… yes and no.
Too illustrate what I mean, look at the confidence interval bars for the all-cause mortality charts (A and D)
If we look at the hazard ratio from graph A, for those with lifestyle scores of 5 through 7, we might question if there is even a point in increasing the quality of our lifestyle beyond 5.
But, if we look at the graph D…the narrower confidence interval demonstrates that there may indeed be a net mortality benefit from improving lifestyle from a score of 6 to 7, or 6 to 8.
So, to answer the question - yes, the narrower confidence interval are strengthening the argument in favor of lifestyle - not medication.
What Is The Best Way To Reduce Blood Pressure?
At this point you may be asking yourself “what about blood pressure medication?”
I’m not going to write an article pretending to account for the infinite complexity of each and every person who may be reading this, and tell them to do one thing or the other. That would be foolishness on par with what you may have come to expect from the common doctor.
I believe people are complicated, as is their health and personal circumstance.
However, I also believe in physiology, physics and first-principles problem solving.
Both parts of this series have been an attempt to illustrate the complexity of cardiovascular health, which I will try to boil down to a few points:
The circulatory system exists to provide energy, fuel, and nutrients to your body in one direction, and clear waste and depleted proteins in the other direction.
Every organ and body-part plays a role in altering the physical parameters of circulation which ultimately impact net blood pressure, which we measure in the arm.
Our lives and the decisions impact our organs, with consequences that determine the state of resistance and pressure that our circulatory system must adopt to account for the needs of the body.
What we ‘see’ as elevated blood pressure is the consequence of several preceding steps.
Any attempt to artificially reduce the number at the end of the causal chain (i.e. blood pressure) will not solve the problems which caused the high blood pressure in the first place.
The fallacy in the hypertension treatment paradigm is assuming that the observed consequences of high blood pressure are predominantly due to high blood pressure. This is not true.
Furthermore, I believe that if you intervene with the body’s attempt to fix itself by targeting a downstream event (e.g. high blood pressure)… you will only increase the body’s drive to fix the problem.
For example, if we treat “insulin resistance” by giving the body more insulin…then the person will become even more insulin resistant.
To close this out, let’s take a look at one of the most commonly used blood pressure medications: ACE Inhibitors. These drugs (e.g. lisinopril) interfere with a complex network of signaling involving the kidneys which impacts the state of blood vessels.
To this day, ACE inhibitors are the mainstay of blood pressure management. But, what if the liver, kidneys and lungs are doing this for a reason? What happens when you interfere?
For starters, we are observing increased rates of lung cancer in those with chronic use of ace inhibitors.
As it turns out, if you inhibit the action of a hormone that kidney cells are producing…the stimulation of those kidney cells goes up, because the body is not receiving what it is expecting to receive. This leads to worsening kidney artery pathology.
One group studied kidney resections of patients who had been placed on ACE inhibitors and observed the thickness & irregularity of the arteries compared to those who were not on ACE inhibitors.
The afferent arteriolar [smooth muscle cells] in the [ACE inhibitor/ARB] group frequently showed marked proliferative and irregular changes.
-Nagai et al, 2020
And to quote another study from Wake Forest University:
The antihypertensive…actions of the combined therapy were associated with marked worsening of [kidney] disease…data show that despite improvements in the surrogate end points of blood pressure, ventricular mass, and proteinuria, dual blockade of Ang II receptors and renin activity is accompanied by worsening of renal parenchymal disease reflecting a renal homeostatic stress response attributable to loss of tubuloglomerular feedback by Ang II.
Ok, So How Can I Reduce Blood Pressure?
You’ve made it this far, and this article is already long enough, so I’m just going to give you what I believe to be an effective strategy to reliably lower blood pressure.
Be active! If there is one thing the above studies demonstrate, it is the incalculable positive impact of being active. Even if you just put 20 pounds in your backpack and go for a walk. Do it.
Grounding/Earthing at least twice a day for 30 minutes. Feet on grass, or dirt, or concrete. This is free, and effective.
Adequate sunlight. This includes morning sunlight, and mid-day sunlight. Every day.
Avoid artificial light as much as you can, even if it means buying yourself a pair of blue-light blocking glasses. Blue light activates cortisol release, which is a stress response that ultimately impacts many things, including blood pressure.
Maintain adequate electrolyte intake, and this includes salts. Not table salt (NaCl), but all salts. Including KCl, MgCl, Calcium, etc. You need a healthy balance of electrolytes.
Partake in stress-relieving activities, whatever they may be.
Eat healthy.
The above is ordered in what I believe to be of importance.
Thank you very well written and written for the lay person, I appreciate that. It’s all about $$ isn’t it? My 90 yo mom on 8 different medications after a heart attack. Roller coaster of a ride trying to find the right balance. The great transfer of wealth 😑🙄
Interesante y sencillo. Ejercicio y comida sana. No medicamentos. Soy paciente cardíaco, de infarto hace dos años. No consumo medicamentos. Dieta sana lo mejor posible y ejercicio habitual, son profilaxis. Gracias doctor.