A Guide to HRV: The Impact of Hydration

In this video, we're going to talk about the impact of hydration on your autonomic nervous system function — in particular, how to manage the what, when and how of fluid intake to regulate and improve your autonomic nervous system function, improve your heart rate variability, and ultimately improve your symptoms.

As a baseline, we should have somewhere between 2 and 3 liters (68–96 oz) of fluids a day. When we're dehydrated, it gives an additional stressful trigger to the autonomic nervous system — something we should just take away from the continuing inputs that trigger the autonomic nervous system into a fight-or-flight mode.

Patients with complex chronic illness may be susceptible to orthostatic intolerance, which is a condition characterized by worsening symptoms when standing up. If you are one of those patients who frequently feels a lot worse when standing — for example, if you develop palpitations, shortness of breath or lightheadedness when standing up — fluid management is going to be critical in improving your symptoms.

This is because when we stand up, there is a gravitational shift where blood is pulled down from the head and the heart — the core circulation — into the lower limbs, which are huge reservoirs of blood. As the blood empties away into your lower limbs, you can experience activation of the fight-or-flight response, because the body doesn't like to be dehydrated, and it doesn't like to be in a situation where it has to experience lower blood pressure states. With that sympathetic activation, you can then experience palpitations, shortness of breath, dysfunctional breathing, dizziness and lightheadedness. So fluid management in this context is very important.

How should we apply fluid management? What should we drink, how should we drink it and when should we drink it?

We should drink fluids — plain old H2O is the very basal level of fluid that we should drink. Ideally, fluids should be drunk first thing in the morning, or front-loaded. Why front-loaded? Front-loading is the concept that you take the fluids to empower yourself for the day ahead: between 500 ml and a liter (16–32 oz) by breakfast.

The other aspect of fluid management is understanding what to drink. I said H2O, or plain old water. But if that is not tasty enough for you, you could add a bit of salt and maybe a bit of cordial. I would avoid, in the majority of patients, any strong caffeinated drinks.

I also advise isotonic electrolyte tablets. These are specific tablets that you can drop into your 500 ml (16 oz) bottle or glass, which fizz up and give you what's called an isotonic solution — the same concentration as your blood in terms of its sodium and potassium. When you drink this, the absorption and distribution into your blood supply is very rapid. So for some patients who are particularly affected, I get them to pop one of these isotonic electrolyte tablets before they get up in the morning.

I might not ask patients to take much fluid beyond dinner time — let's say 7 or 8 o'clock — because what we don't want is for a patient to not drink anything all day, feel at the end of the day that they then have to drink the 3 liters (96 oz) and consume it all at dinner time, and then have to wake up once or twice a night to pass that water.

So we've got what to drink, and when to drink it, which is front-loaded. The third thing is how to drink it. In a patient who is about to engage in activity that you know will be physically challenging, it's useful to drink your fluid as a bolus — a quick shot of fluids, if you like, if you can consider 500 ml (16 oz) a shot. You try to gulp it all at once, or in a very short time, and ideally cold. The reason for cold specifically is that the cold allows for some vasoconstriction, which allows us to have a bit more blood pressure. So not only are you getting more fluid in because you're taking it externally, you're increasing the core circulation by squeezing the blood vessels with cold, to get more blood back to your heart.

To recognize your level of hydration or dehydration, I think it's important to pay attention to a few things. One is the color of your urine. It should be a pale yellow color, and if it's getting any deeper or darker than that, you're likely dehydrated. The second thing is to feel your mouth and your tongue — how dry it is — because dehydration often shows in the tongue. And the third is to look at your skin: the plumpness of your skin and the dryness of your skin. Those are the three things you could do to assess your dehydration. The easiest, of course, would be to check the color of your urine.

So to recap, I think we should focus on the role of hydration in improving your autonomic nervous system health — in particular, hydrating well using the principles of what to drink, when to drink and how to drink your fluids, and how this will have an overall beneficial impact on your autonomic nervous system and heart rate variability, and ultimately improve your symptoms.