Killam MD on Hypertension Part 2

    Hypertension (HTN) and its treatment can be easily understood with a couple of simple models. Most people in East Houston have an intuitive understanding of the dynamics of pumping fluid through pipes! If the pressure in the system is too high, then the pipes are too full, simple! The cardiovascular system is a little more complicated than the pumps and pipes at the chemical plants. Our system is more dynamic because variable amounts of fluids are being added to the system on a regular basis. This is why we have kidneys, to regulate the volume in the system. By maintaining a constant volume in the system, the kidneys regulate our blood pressure on a day-to-day basis. Picture your body as a bucket of water with a faucet pouring fluid in all the time at varying rates. We take in an average of 2.5 liters of salt water per day in food and fluid. Everything we eat was once 90% salt water if it was once living! Without kidneys, the bucket would quickly overflow or explode. The simplest way to think of how your kidneys control the volume is to imagine them as a hole in the side of the bucket. The bucket fills up to the level of the hole then the water spills out keeping the volume in the bucket constant. IF the hole in the side of the bucket is the same size as the opening in the faucet, then it wouldn't matter whether the faucet is wide open or not open at all, the volume in the bucket will remain constant. If the hole is at a higher level than average, the bucket is fuller than average and the pressure in the system is too high. A thiazide diuretic essentially lowers the position of the hole in the side of the bucket thus decreasing the constant volume in the system and lowering the pressure. For that reason, thiazide was the first blood pressure medicine widely used, in the late 1950's and remains the cornerstone of blood pressure treatment still today.

    Adrenaline, produced during physical or emotional stress, causes the heart to beat faster and the blood vessels to constrict, which raises blood pressure, and some people just make too much all the time. Propanol was the next blood pressure medicine used in the early 1960's and was the first of it’s class called Beta-Blockers (BB). Beta- Blockers block adrenaline receptors, which cause the heart to beat slower and softer and blood vessels, to relax, which lowers blood pressure. In 1967 the VA published convincing data, from a large study, showing that lowering blood pressure, with the combination of thiazide and Beta-Blockers significantly reduced the mortality and morbidity associated with hypertension, namely cardiovascular heart disease, heart attacks, congestive heart failure (CHF), and stroke. No other combination has proven more effective at prolonging life since. The most commonly used Beta-Blockers today are Metoprolol and Carvedilol. In the 1970's a third class of anti-hypertensive were developed, called calcium channel blockers (CCB). By blocking calcium channels on the smooth muscles around the arteries, it causes them to relax and become more compliant which reduces the pressure transmitted during the heart's contraction cycle, lowered systolic blood pressure. The most commonly used CCB today are Diltiazem, Nifedipine, or amlodipine. Several studies done at that time showed that they reduced, the likelihood of having a second heart attack in patients with coronary artery disease.

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