High blood pressure (hypertension) affects up to 80% of all patients receiving haemodialysis
for chronic kidney disease (CKD). High blood pressure is a major cause cardiovascular disease
(i.e. strokes, heart attacks and heart failure) and, thereby, cardiovascular deaths in these
patients.
A significant cause of raised blood pressure in haemodialysis patients is thought to be due
to retention of salt in the body. In healthy people the kidneys excrete salt but the kidneys
of patients with CKD cannot do this, so salt has to be removed by dialysis. However dialysis
cannot remove as much salt as is necessary, and so it accumulates. This fact has been
recognized for many years, and health professionals caring for haemodialysis patients often
stress the importance of restriction of dietary salt intake.
However no research has looked in detail at the mechanisms by which salt raises blood
pressure in haemodialysis patients. It is likely that salt directly affects thirst, causing
patients to drink more and become overloaded with fluid. In addition, salt may have direct
effects on the blood vessel wall, causing failure of adequate blood vessel relaxation. Both
of these factors may raise blood pressure.
We will conduct a carefully controlled crossover study looking at the effects of a modest
reduction in salt intake on BP. During the course of the study, which will last eight weeks,
patients will receive both a 5 gram per day and a 10 gram per day salt intake. We will look
at how thirst, fluid intake, a number of markers of blood vessel function and blood pressure
differ on these two salt intakes.