Alterations in dietary sodium intake affect cardiovagal baroreflex sensitivity

Abstract

High dietary sodium intake has been linked to alterations in neurally mediated cardiovascular function, but the effects of high sodium on cardiovagal baroreflex sensitivity (cBRS) in healthy adults are unknown. The purpose of this study was to determine whether high dietary sodium alters cBRS and heart rate variability (HRV) and whether acute intravenous sodium loading similarly alters cBRS and HRV. High dietary sodium (300 mmol/day, 7 days) was compared with low dietary sodium (20 mmol/day, 7 days; randomized) in 14 participants (38 ± 4 yr old, 23 ± 1 kg/m² body mass index, 7 women). Acute sodium loading was achieved via a 23-min intravenous hypertonic saline infusion (HSI) in 14 participants (22 ± 1 yr old, 23 ± 1 kg/m² body mass index, 7 women). During both protocols, participants were supine for 5 min during measurement of beat-to-beat blood pressure (photoplethysmography) and R-R interval (ECG). cBRS was evaluated using the sequence method. Root mean square of successive differences in R-R interval (RMSSD) was used as an index of HRV. Serum sodium (137.4 ± 0.7 vs. 139.9 ± 0.5 meq/l, P < 0.05), plasma osmolality (285 ± 1 vs. 289 ± 1 mosmol/kgH₂O, P < 0.05), cBRS (18 ± 2 vs. 26 ± 3 ms/mmHg, P < 0.05), and RMSSD (62 ± 6 vs. 79 ± 10 ms, P < 0.05) were increased following high-sodium diet intake compared with low-sodium diet intake. HSI increased serum sodium (138.1 ± 0.4 vs. 141.1 ± 0.5 meq/l, P < 0.05) and plasma osmolality (286 ± 1 vs. 290 ± 1 mosmol/kgH₂O, P < 0.05) but did not change cBRS (26 ± 5 vs. 25 ± 3 ms/mmHg, P = 0.73) and RMSSD (63 ± 9 vs. 63 ± 8 ms, P = 0.99). These data suggest that alterations in dietary sodium intake alter cBRS and HRV but that acute intravenous sodium loading does not alter these indexes of autonomic cardiovascular regulation.

Keywords: baroreflex sensitivity; cardiovagal; heart rate variability; high-salt diet; hypertonic saline; plasma osmolality; sequence method; serum sodium.

Fig. 1.

Effects of dietary sodium manipulation on serum sodium, plasma osmolality, and cardiovagal baroreflex sensitivity (cBRS). A: serum sodium was significantly increased from day 7 of the low-sodium (LS) compared with the high-sodium (HS) diet. B: plasma osmolality was significantly increased from day 7 of the LS compared with the HS diet. C: overall cBRS (all sequences) was significantly increased at the end of 7 days of the HS compared with the LS diet. Values are means ± SE (n = 14). *P < 0.05.

Fig. 2.

Effects of low-sodium (LS) and high-sodium (HS) diets relative to a recommended sodium run-in diet. Overall cardiovagal baroreflex sensitivity (cBRS, all sequences) tends to demonstrate differential responses with alterations in dietary sodium intake (P = 0.10). Values are means ± SE (n = 12 participants).

Fig. 3.

Effects of acute sodium manipulation on serum sodium, plasma osmolality, and cardiovagal baroreflex sensitivity (cBRS). A: serum sodium was significantly increased from preinfusion (Pre) to postinfusion (Post) of hypertonic saline. B: plasma osmolality was significantly increased from pre- to postinfusion of hypertonic saline. C: overall cBRS (all sequences) was not different between pre- and postinfusion (P = 0.73). Values are means ± SE (n = 14 participants). *P < 0.05.