Haemodynamic adjustment to weight reduction--separate effects of energy versus salt restriction

Repeated invasive haemodynamic investigations were performed in two matched groups of patients before and after weight reduction. The patients in Group I had an individually adjusted energy restricted diet and daily dietary sodium supplementation to keep the sodium intake unchanged from baseline. In Group II the patients had the same energy reduced diet but also sodium restriction from 183 +/- 48 to 87 +/- 34 mmol/24 h (P less than 0.001). The energy intake was reduced by about 50% in both groups and the mean reduction in body weight in Group I was 9.2 kg and in Group II 8.8 kg. In Group II the patients had significant reduction of cardiac output, cardiac index, heart rate and blood pressure. No increase in total peripheral resistance was noted. The patients in Group I had a significant reduction of heart rate only. We suggest that the failure of a blood pressure to fall was caused by the relative increase in blood volume observed in patients on a normal sodium intake during weight reduction. The cardiovascular response observed after concomitant sodium and energy restriction is consistent with a reduction of sympathetic nervous system activity and this conclusion is supported by reduced circulating norepinephrine and urinary excretion of norepinephrine.