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Tuesday, March 11, 2014
High Blood Pressure
Diuretic and muscle elasticity
I am just curious of the mechanics of diuretics.
I am aware that diuretics are used to reduce the blood volume in the arteries by flushing out excess water and hence the blood pressure readings would be lower. Does this mean that whilst you are on diuretics, you should drink less water as well?
Secondly, I am also aware that arteries become less elastic as we age. This loss of elasticity can cause spikes in blood pressure due to positional changes etc as the arteries take longer to get back to normal. My understanding is that age alone is not responsible for arteries losing their elasticity. Arteries are like muscle and just like skeletal muscles when we don`t drink enough fluids our muscles get stiff and cramped and spasmed. The arteries are no different, they need enough fluids otherwise, the are not going to be healthy.
So , I am a bit puzzled why diuretics are given to treat high blood pressure , perhaps in the short term they may help , but wouldn`t they produce unhealthy arteries in the long term.
It is true that diuretics work in part by reducing blood volume and thereby reduce the pressure in the vascular system. Diuretics work by increasing the amount of salt lost by the kidney. Water always follows salt, so a loss of salt in the body leads to a loss of water and thereby blood volume. Your blood pressure is influenced by the amount of salt you eat, not by the amount of water you drink.
The kidney adjust the total amount of salt in the body by excreting just the right amount in the urine. The kidney adjusts the amount of water excretion (urine volume) according to the blood level of salt. Diuretics "nudge" the kidney to increase the amount of salt in the urine. That leads to a lower level of salt in the blood, and a more water excretion (greater urine volume). The amount of water one drinks has almost no effect on blood pressure.
By a different mechanism, diuretics also reduce the amount of salt in the arterial wall and keep them less tense and more elastic. However, that effect is not well understood.
Because of this direct effect on the arteries, diuretics can reduce blood pressure even if the amount of salt in the body is kept constant. Very high salt intake, however, can override all the effects of a diuretic and increase blood pressure. As you can see, the mechanism by which diuretics lower blood pressure is somewhat complicated.
At any rate, it has very well been shown that long term use of diuretics reduces blood pressure and reduces the risk for stroke and heart disease. There is no evidence that diuretics harm the arteries.
Max C Reif, MD
Professor of Medicine
Director of Hypertension Section
College of Medicine
University of Cincinnati