Next to the atmospheric pressure, the most curious pressure to understand is stored within the human circulatory system. Yes, it is the “blood pressure” fondly referred to as BP by both physicians and patients. (When worried men & women visit us and say, that they are suffering from BP, please make it a point to clarify, BP is a sign of existence of life, rather than a dreaded pathology )
Why should blood have pressure?
BP is lateral pressure exerted by flowing blood on the vessel wall (or is it the propelling pressure head ? It is to be noted, cuff pressure doesn’t measure this !) BP is generated by the heart in systole and sustained by the vascular system in both systole and diastole. BP is measured as mmHg. It can also be expressed as PSI(Pounds /sq Inch) or Pascals or ATMs. If you allow me to spoil with some physics. Pressure is force per unit area ie Newton/m². So, pressure is essentially a force. Force is mass times the acceleration. Mass is weight independent of gravity, while the acceleration of blood is essentially the force of gravity added to the velocity of blood flow. If you think gravitational waves and planetary positions might influence the mass of blood (and hence the BP) you may not be insane. (Environmental & astrological influence of BP and cardiovascular events need not a be mythology) (Oomman A, J Indian Med Assoc. 2003 ) (Robert D Brook Cardiac clinic . 2017)
How is it regulated?
Physics uttered at the bedside is sure to appear as nonsense for practicing physicians. Forget It. BP is not only a continuous variable, the neural, hormonal, cardiac control mechanisms are also in a dynamic flux. What we need to bother is, how to sustain a mean BP of around 90 mmHg within the human circulation, with robust autoregulation. (For the fellows in cardiology, it is a dangerously simplified teaching & belief that cardiac stroke volume determines systolic BP and PVR determines diastolic BP) In fact, It is the systolic pressure that confers the energy required for diastolic BP. Regulation of BP is all about large vessel stiffness, neuro-humoral tone of small vessels, water and sodium metabolism. This makes the kidney a central organ for long-term control of BP. It must also be emphasized BP is regulated in a regional and organ-specific manner. (Ex -The cuff brachial artery pressure may tell little about what is happening at the glomerular perfusion pressure )
Who are the guardians of BP?
Though general Physicians , Neurologists, Nephrologists even Endocrinologsts have more geograhcial rights cardiologists have largely taken siege over the entity of SHT because the heart happens to be a glamorous victim organ. We are witnessing an almost intoxicating number of cardiovascular trials on hypertension, right from Framingham’s days of 1970s to just released BP LLTC in 2021, trying to bring down cardiovascular risk. Based on the accrued evidence, the guardians of human BP in various global institutions bring out strategies to reduce the risk of vascular injury. Have we succeeded in this Intravascular number game.? I think we are. At what cost?
Two repeatedly asked two trivial questions
- What is normal BP & When to start treatment?
- How much lower is best for our body?
Probably, we have got an answer for the first question from this Impactful publication.
I think this study is trying to tell us, there is no normality for blood pressure in terms of risk reduction in cardiovascular disease. (Please recall, one JNC -Joint national committee was dissolved after including a controversial term pre-hypertension in healthy public few years back) What will be the implication for this study? Its core conclusion is about 5 mmHg BP reduction across any subset of adult population will reduce CVD risk considerably. I am sure this study is so intense and powerful it will take at least a decade for its conclusion to fade away. So, can we make these funny conclusions? Hereafter we need not measure BP before starting treatment. Just administer drugs to any live adult who has blood & pressure. (J or U curve need a big debate later)
Mind you, sustained 5mmhg reduction* can be brought by any of the following habits. A salt moderated fruit-rich diet, reasonable physical activity, good sleep, a stroll in the park, yoga, a deep breath, having a pet, watching a movie in a quiet evening, having a loving family, and so on so forth (Of course, 5mg Amlodipine, 40 mg of Telmisartan, or a paradise device can do the same, with an add on pride)
*There is a big catch in this landmark paper. Read the title again. The important take-home point is that this 5mmhg lowering should strictly come by pharmacological means, not by any other means. (Correct me if I am not correct)
Final message
We got the final answer from this marvelously done meta-analysis for the toughest question in cardiology. Hereafter It’s going to be a celebration time for mankind, who struggle in a hypertensive world.
Post-ample
True, sustained high BP is a major risk factor for stroke, heart failure, and CVD. However, it is also true BP can’t* do much damage to the coronary artery without the help from its naughty cousins DM & dyslipidemia. All three parameters must be optimized in unison. May I propose a rough rule? It may be called DFL index for the collective CVD target. Diastolic BP, fasting blood sugar and LDL all should converge around a unitless number of 70 to 80.
*HT is a powerful risk factor for stroke and HFpEF.
Reference
https://www.thelancet.com/action/showPdf?pii=S0140-6736%2821%2900590-0
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Dr.S.Venkatesan MD 