Is sodium restriction effective treatment of borderline and mild essential hypertension? A long-term haemodynamic study at rest and during exercise.

Blood pressure (BP) may fall during moderate sodium restriction in patients with essential hypertension (EH). Few data are available on the haemodynamic changes associated with sodium restriction and exercise data are lacking. We studied the long-term haemodynamic effect of reduced sodium intake in 19 men aged 16-51 years with mild and borderline EH. Cardiac output (CO; by Cardiogreen) and intra-arterial BP were measured at rest and during exercise before and after 9 months therapy. Sodium excretion was reduced by 75 mmol/24 h (36%) from a mean of 209 mmol/24 h and the sodium:potassium (Na:K) ratio fell by 0.75 from 2.17. Intra-arterial pressures fell by 3-5% (P less than 0.05) at rest, both supine and sitting, and during 50, 100 and 150 W bicycle exercise. Body weight and body fluid volumes (isotope dilution) remained unchanged. Haemodynamically, the fall in BP was due to reduction in CO ranging from 7-12% at rest and during exercise, while total peripheral resistance (TPR) rose by 4-10%. Stroke volume and heart rate fell by 2-9%. We conclude that moderate sodium restriction was not an efficient treatment in our patients with borderline and mild EH. The slight reduction in BP was associated with a fall in CO but without reduction of TPR. Thus, the main haemodynamic disturbance of established EH, that is an increase in TPR, was not normalized by 9 months sodium restriction.