Gettysburg Medical View
The Clinical View
by P.E.  Hoffsten, MD
20 February 2008

HOW DOES THE BODY GET RID OF SALT?

            Heart trouble comes in two basic forms.  In one type, the arteries that supply the heart get stopped up with plaque and cholesterol.  In this type the person develops chest pain that brings them to medical attention.  But the other type of heart problem has to do with how well the heart is working as a pump and with that type of heart problem the person develops shortness of breath retains fluid with their ankles getting swollen as the day goes on.  In this second type of heart problem, the person gets up four to six times at night to pass urine.  This second type of heart problem is the one that a gentleman was recently seen for at the clinic.  It was one of those cold, snowy afternoons when not many people come out and we had some time to sit and talk.  This gentleman was having increasing problems with shortness of breath and his ankles swelled over the tops of his shoes as the day went on.  He noted that if he took his shoes off in the evening, he couldn’t get them back on again.  He had had uncontrolled high blood pressure for many years and his heart had had to pump against too much pressure too long.  Just like the old gray mare, his heart just wasn’t as strong as it used to be.  It couldn’t pump enough blood to meet his body’s needs because it had worked too long, too hard against too much blood pressure.  He wondered what he could do to quit swelling so much and quite being so short of breath.  He said he hated taking all the water pills because they made him go to the bathroom too much during the daytime.  He said that he drank lots of water because he was thirsty all the time.  I told him that it was a good thing that it was a cold, snowy afternoon because we had a lot to discuss.

            The first point to explain to him was the basic law of all metabolism.  Whatever he eats or drinks has to come out someplace or accumulate in the body.  Ideally, the adult body weighs the same day in and day out.  Ideally, it does not accumulate water such as this gentleman was doing during the day. 

            So I asked him the question, “How does your body know how much salt or how much water to put out each day?”  I pointed out to him that he really didn’t measure how much water he drank or how much salt that he ate.  So there is no measure on the “in” side. Instead, keeping balance of salt and water in his body was up to his kidneys to get rid of the salt and water that he didn’t need.  He said that made sense and so I asked him the next question, “How do your kidneys know how much salt or water to get rid of?”  He thought about that for a few seconds and said that he didn’t just have a clue. I told him that was the problem. 

            It turns out that there is a meter at the top of the heart that measures how much blood the heart is pumping and compares that to how much blood the body needs.  But when this meter was originally developed eons ago, it turns out the most common cause of a decreased heart output was dehydration or bleeding.  So the body’s defense mechanisms were designed to tell the kidneys to save all the salt and save all the water they could.  And that mechanism worked pretty good back then because those that could save salt and water the best survived and we are their descendents.  We have the same mechanisms in our bodies that they had in theirs. 

            But times have changed.  Back then there weren’t water faucets anywhere we wanted them.  There wasn’t a 7-Eleven Store with every drink that you could imagine.  There wasn’t bottled water that you could carry in your car because there weren’t even any cars.  Back then, dehydration was the likely problem if the heart wasn’t pumping enough blood.  But today, that is not the case.  Now, in modern society, the most common reason that a heart doesn’t pump enough blood is that it has worn out from too many years of high blood pressure or heart attacks.  But today the message our hearts send to our kidneys is the same one that was sent thousands of years ago.  Our bodies today still believe that if the heart is pumping enough blood, it must be because we are dehydrated and need to save salt and water.  That same mechanism tells us we are thirsty and we should drink even more. This is what was happening to the gentleman described above. 

            So I explained to him the water pills that he was taking overrode the message that his body was sending to his kidneys.  Specifically, the water pills told his kidneys to get rid of salt and get rid of water because you’ve got too much of it.  He said that he thought that water pills were “too hard on his kidneys”.  I explained that that wasn’t the case at all.  In fact, his kidneys worked very hard to filter 120 quarts of blood a day and pull it all back inside the body letting go of the waste products he didn’t need.  When he took a water pill, that just meant that his kidneys didn’t need to work so hard to bring salt back into the body so in fact, the water pills were giving his kidneys a rest.

            He then said that he didn’t like the water pills because they made him lose too much potassium and I explained that certainly was a consideration but one that can be overcome by taking extra potassium pills.  The rule is that for each 40 milligrams of furosemide (Lasix) that a person takes, they should take about 20 milliequivalents of potassium.  He said that he ate a banana each day but I explained that really has only has 6 milliequivalents of potassium and if he was taking 80 milligram of Lasix 4 times a day as he was, he would need to eat enough bananas to grow a monkey tail.  So he needed the potassium pills.

            I explained that there was one medication that he might well benefit from.  The major hormone causing salt retention in our bodies is called aldosterone. This hormone regulates our day to day salt balance and is always secreted in excessive amounts in people with heart problems.  There is a medication called aldactone that opposes the aldosterone  hormone.  Aldactone has been shown to have a remarkable life-saving and comfort benefitting effect for people with chronic heart failure.  I suggested that he would well benefit from this medication to help his water pills and not lose so much potassium.

            There is another family of hormones called the naturetic peptides.  These are hormones that the body developed to help get rid of salt and lower blood pressures.  Unfortunately, they are a relatively weak system and can be overpowered by aldosterone and the bodies other salt retaining effects.  But one of the main effects of the naturetic peptide family is to make the heart grow stronger and thicker.  Surprisingly, this is not a good thing.  When a heart is overstressed by high blood pressure for a long time, it gets so thick that it becomes stiff and difficult to fill. This leads to so-called diastolic heart failure.  There are medications that decrease this effect of the naturetic peptides.  This family of medications is called the angiotensin receptor blockers and is made up of products like Cozaar (losartan), Diovan (valsartan), Avapro (irbesartan), Atacand, Micardis, Benicar and Teveten.  These are all still brand name products and relatively expensive but are the best medications we have at this time to protect the heart against heart failure.  The gentleman in question here was already taking a substantial dose of one of these medications and it had been a significant benefit for him.

            The point that was most unpopular with this gentleman was when he was told that he had to cut down on the amount of water he was drinking if he wanted to stop the swelling in his ankles and be able to breath better.  He said that he was thirsty all of the time.  I told him that I understood his problem but that somehow or other he had to cut down on how much he drank..  Just by cutting down salt and water, he could cut down the number water pills that he had to use each day.  His best care involved:       

1.  Limit his fluid intake to a quart and a half a day.

2.  Limit his salt intake to six grams per day.  This will take the help of a dietitian. 

3.  Use the water pills enough to keep his weight stable without the swelling.  This could be anywhere from 2 up to 8 pills per day depending on how much fluid he retains.

4.  Use the Aldactone to help cut down the salt retaining effect of his body’s defense mechanisms.

5.  Keep using the angiotensin receptor blocker that he was already using to protect his heart long-term.    

This and other columns available at www.macpierre.com.