Cardiovagal Function (3 of 16)

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In this video Dr. Singer discusses the role of cardiovagal function as a key component of autonomic function testing.


Alright, on to cardiovagal function. We are interested in cardiovagal function for a number of reasons. We know cardiovagal function is impaired early in the autonomic neuropathies, including diabetic and amyloid neuropathies, so it’s very sensitive and the reason for that is rather simple. Just like a length-dependent neuropathy starts in nerves that are longest, so nerves that supply the foot, so the vagal nerve is the longest cranial nerve and so it’s early affected in nerve disease as well, and it’s very sensitive and contains a lot of parasympathetic fibers that we’re interested in studying. It is also convenient because there’s nothing easier than assessing cardiovagal function.
You really, all you need is a 3-lead EKG and some form of standardized stimulus and you can derive cardiovagal function. There are a number of ways to do that. The ones that are highlighted here in red are the ones that we do as part of the autonomic reflex screen. Why? Again, it goes back to sensitive, specific, reproducible, and all those other attributes, and so those are the ones I will be focusing on here.

When one looks at the underlying physiology it actually gets quite complicated. You can write a book about possible and real actual components and constituents to the response to deep breathing. It goes back to reflexes such as the Hering-Breuer reflex, the Bainbridge reflex may be involved. There is some component of the Baroreflex that has a contribution. There may also be some central neural coupling and even cardiac stretch reflexes may play a role. While interesting, for practical reasons all you need to know, that taking deep breath in and out results in modulation of the cardiovagal outflow from the nucleus ambiguous, and that results in respiratory sinus arrhythmia. Increase in heart rate when you take a deep breath in and decrease in heart rate when you breathe out. And that’s what we quantify here. We do think that the lung stretch reflex is actually the major component but really, it doesn’t matter, you assess cardiovagal function either way.

And, this is how we do it. On the top panel you see beat-to-beat heart rate, in the bottom panel respiration, and we look at the best 5 consecutive responses to 5 breaths. So, we do a total of 8-10 breaths and then choose the best 5 consecutive heart rate responses and quantify those. We basically look at the difference between the maximum and minimum heart rate, do that 5 times and take the average. Why are we doing the best consecutive 5? Well, back then, that was thought to be the best way of doing it, the most unbiased way of doing it, and all our normative data are derived based on that and so we are stuck with that now. Maybe taking the highest 5 would have been just as good but this is what we have normative values on and so that’s what we are using.

And again, there are a number of factors other than disease that can affect heart rate responses to deep breathing. Age clearly important variable. Posture is important. Your heart rate response is acutely diminished when you obtain in the standing position, so have your subjects in a standardized position, and do we all know if the data that are derived is supine, so we all have to be lying supine when we do the test. The rate of breathing plays a role. We have compromised on 6 breaths, 5 seconds in, 5 seconds out, that seems to give the maximum heart rate response for the majority of people. The depth of breath is very, very important. If patients do not take a maximum breath in and out, you have spuriously low responses. It’s very important. There are good studies that support that, even 80% is not good enough; 100% effort. And again medications.

Again, there are normative values…if you can see the age effect here…gender does not really seem to play a significant role in heart rate responses to deep breathing. And the other values are listed here, and they are published. Here is an example of a normal heart rate response, heart rate in red on top and a blunted virtually absent heart rate response to deep breathing on the bottom in the patient with diabetic autonomic neuropathy.

Dr. Wolfgang Singer, M.D.
Wolfgang Singer, MD

Associate Professor of Neurology
Mayo Clinic Rochester, MN

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7 thoughts on “Cardiovagal Function (3 of 16)”

  1. I have had a positive tilt table test years ago which no one followed up on it . I have been symptomatic with heart palps , sob, chest pain low BP since that time and recently developed htn since June and exacerbated symptom and put on two med meteoplol
    And amlodipine
    I have chronic neck pain and abnormal cervical and thoradic mri
    Who should I see to treat these symptoms the cardiology has no idea what is wrong and just treats the symptoms

  2. I was diagnosed with POTs with “cardiovagal autonomic impairment”. All the doctors seem to fixate on the POTs when I ask questions about the cardiovagal autonomic impairment. My questions are, 1) what specific symptoms are attributed to this (POTs has a list of symptoms that have slight variations with the other dysautonomias…what distinguishes it from others? Is it a separate type of dysautonomia or an effect?) 2) can salt/fluid/levine protocol stave/improve the symptoms like POTs?, and 3) you mention that this is highly sensitive and could indicate diabetic and amyloid neuropathies…Is this something that doctors should be monitoring for if someone has cardiovagal autonomic impairment? Thank you!

    1. Great questions!
      1. Cardiovagal autonomic impairment is a broad term to describe a problem with the relationship between the heart and the vagus nerve (main nerve which innervates the heart). Unless the impairment is further explained it would be difficult to distinguish between symptoms of POTS and cardiovagal autonomic impairment. For instance, one type of impairment might be too little norepinephrine released and therefore causing a lack of stimulation to the heart. Another impairment might be too much norepinephrine which may have not enough stimulation. Too much stimulation could cause a high heart rate, too little could cause a lower heart rate but without more information it is difficult to distinguish. As Dr. Singer points out in the video not much is really known about the physiology but there are ways to generally test if the reflex is intact. In POTS, there is also little we really know about the pathophysiology, and this is something that needs greater research.
      2. Yes! The first line treatment for autonomic disorders including POTS is Salt, Fluids and Exercise. For most POTS patients we recommend 5-9 grams of salt (as long as you don’t have hypertension) and 2 liters of fluid daily. The exercise should begin very slowly and gradually grow over time as starting an exercise regime is difficult for most patients. In some cases, working with a cardiac rehabilitation program can be helpful.
      3. It is reasonable to rule out diabetic and amyloid neuropathies – this should be evaluated by your physician based on results of testing and case history.
      Keep in mind everything here should be discussed with your doctor as we offer educational information only. Hope this helps. If you have further questions please email us at

  3. I have had 3 TTTs. One w/cardiologist who said I was “borderline”, one with neurologist who said “orthostatic hypotension” and just yesterday with Autonomic Neurologist at Mayo FL. He said “No OH, but Cardiovagal Impairment.”. I have been taking Droxidopa for 6 months since first neuro said I have OH. So confusing. I have not had follow up with Mayo doctor yet – in 2 weeks. What is the tx for this condition. I’ve never heard of it before. I was DX with SFN via biopsies 6 months ago as well. I also has a positive qsart 6 months ago but Mayo said my Qsart this week was negative. ???

    1. Ashleigh Goforth

      Cardiovagal impairment refers to an abnormality with the function of the heart and vagus nerve. In general, it means there is some dysfunction of the autonomic nervous system. Cardiovagal function is impaired early in autonomic neuropathies but is a vague term without further clarification. We encourage you to speak to the physician who gave the diagnosis for clarification of what this means in your case. Autonomic disorders are heterogenous, meaning each person may have different symptoms and different treatment plans. If you have further questions, please feel free to email us at

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