Sodium Paradoxically Reduces The Gastropressor Response In Patients With Orthostatic Hypotension

[Guest Alex]

Interesting full text article co-authored by Dr Raj in 2006.

Follow the link below for the full text

http://hyper.ahajournals.org/content/48/2/329.full

• Sodium and Sympathetic Nervous System:Sodium Paradoxically Reduces the Gastropressor Response in Patients With Orthostatic Hypotension

Abstract

Orthostatic hypotension (OH) can cause syncope that is difficult to treat. We have found that 473 mL (16 oz) of water can increase systolic blood pressure (SBP) by >30 mm Hg in many OH patients (the gastropressor response). OH patients are routinely advised to increase their sodium intake to augment their blood volume. We tested the hypothesis that the ingestion of salt with water would increase the magnitude of the acute pressor response compared with water alone in patients with OH. Patients with OH (n=9; female=5; 65±3 years) underwent a randomized crossover trial of drinking water (H₂O) and salt water (NaCl-H₂O). Noninvasive heart rate and BP were measured with the patient seated for ≥60 minutes after ingestion. The area under the curve for SBP was greater with H₂O than NaCl-H₂O for the 30 minutes (714±388 mm Hg×min versus 364±369 mm Hg×min; P=0.002) and 60 minutes (1454±827 mm Hg×min versus 812±734 mm Hg×min; P=0.048) after ingestion. The increase in SBP with H₂O was greater than with NaCl-H₂O at 30 minutes (37±6 versus 18±5 mm Hg; P=0.006) but not at 60 minutes (17±6 versus 10±6 mm Hg; P=0.4). Norepinephrine increased after H₂O (P=0.018) but not after NaCl-H₂O (P=0.195). Both oral water and salt water increase BP in patients with OH. Instead of augmenting the gastropressor response, the additional salt paradoxically attenuates the pressor response to water. These data suggest a potentially important role for gastrointestinal osmolality in the activation of the sympathetic nervous system leading to cardiovascular reflexes responsible for the gastropressor response.

Conclusion

We conclude that the oral ingestion of water can induce a large pressor response in patients with chronic OH and that this occurs at least in part as a result of activation of the sympathetic nervous system. Adding sodium to the water, likely via an increase in fluid osmolality, decreases the magnitude of the gastropressor response. This suggests an important role for gut or portal osmoreceptors in the afferent signaling of the pressor response to oral water.

Perspectives

The gastropressor response is a recently described cardiovascular control mechanism that can lead to a marked increase in blood pressure after ingestion of water. This acute response peaks within 20 to 40 minutes and resolves within 60 to 90 minutes. In this report, we show that the pressor response after water ingestion correlates with an increase in plasma norepinephrine, which strongly suggests that the pressor response is mediated by the sympathetic nervous system. The ingestion of salt water, instead of plain water, decreases the magnitude of the pressor response, which suggests that a low gastrointestinal osmolality might be required to trigger the gastropressor response. These data further our understanding of this blood pressure control mechanism. Additional research is required to determine the afferent signaling pathway for the gastropressor response.

Alex

[angelloz]

Ok Alex, thank you for posting and I have a question. I am admittedly having a problem understanding the bottom line. Which is best water or water with salt?? I believe I have problems balancing my electrolites.

[Guest Alex]

Angelloz, my understanding is that drinking pure water (vs water with added salt) leads to better results.

According to this study, in those with orthostatic hypotension, the gastropressor response (the blood pressure increase) after ingesting water is higher compared to the one acquired after ingesting water with salt added.

Alex

[kayjay]

Ok Alex, thank you for posting and I have a question. I am admittedly having a problem understanding the bottom line. Which is best water or water with salt?? I believe I have problems balancing my electrolites.

Electrolyte imbalance can potentially be dangerous. It's pretty easy to get your levels checked.

This study was of 9 people with Orthostatic Hypotension. I have POTS and Orthostatic Intolerance. I try not to drink more than 50% plain water as per Mayo Rochester instructions. As for what is best for you I would check with your doctor.

I'm not personally looking for a temporary blood pressure spike. My goal with fluid and salt intake is to stay properly hydrated.

[kayjay]

http://www.ncbi.nlm.nih.gov/pubmed/21731062

[kayjay]

http://www.sciencedaily.com/releases/2008/05/080515171020.htm

http://jama.jamanetwork.com/article.aspx?articleid=1152665