The Missing Vital Sign

Every clinician in any specialty will tell you the same thing: stress makes autoimmune disease worse. A fact that is clear to patients too. Ask someone with lupus or rheumatoid arthritis what preceded their last flare and a large fraction will describe a work deadline, a stressful relationship a move.

And then, having agreed that stress is central, medicine does essentially nothing to address it. We say "try to reduce your stress," which is roughly as actionable as telling someone with hypertension to try having lower blood pressure. We don't measure it. We don't characterize it. We don't tailor anything to it.

I've come to think this is one of the largest unexploited opportunities in the care of chronic inflammatory disease. Not because stress management is a new idea — it's an ancient one — but because we have finally reached the point where the underlying system can be measured, and once you can measure something, you can practice medicine on it.

What the autonomic nervous system does

Your autonomic nervous system is the part of your nervous system that runs everything you don't consciously control: Heart rate, Blood pressure, Digestion, body temperature, sweating, immune signaling and even Pupil size changes. Body temperature. It is, in a real sense, the operating system beneath the applications.

The Autonomic nervous system has two principal branches or neuronal circuits.

The sympathetic branch which is the accelerator — the fight-or-flight system. Heart rate up, blood pressure up, blood shunted to muscle, digestion suspended, inflammatory readiness increased. It exists to get you through the next four minutes.

And the parasympathetic branch which is the brake — rest, digest, and repair. It runs largely through the vagus nerve, and although it is commonly thought to merely be the absence of stress, in reality it’s an active state in which the body does its maintenance: digestion, tissue repair, immune regulation, memory consolidation.

For health optimization, the goal is not the absence of the sympathetic branch, but rather, theflexibility to shift appropriately between the two and to recover promptly once a stressor has passed. A well-regulated system escalates fast when it needs to and comes back down quickly when it doesn't.

Chronic illness, over and over, presents as a loss of that flexibility.

Why "stress" is the wrong unit

Here's the clinical problem with treating stress as a single quantity.

Everyone is stressed. That is the ambient condition of modern life, and telling people to have less of it is not a treatment plan. What actually differentiates people who stay healthy from people who don't is not how much stress they encounter — it's how their system handles it.

. Two patients both describing "stress and fatigue" may have opposite physiologies:

• One has an excessive sympathetic tone — wired, poor sleep onset, elevated resting heart rate, chronically braced.
• One has inadequate sympathetic response — blood pressure drops on standing, lightheadedness, exercise intolerance, a system that can't mount the response when it's needed.
• One has adequate response but impaired recovery — they can perform, but a workout or a hard day costs them two days of recovery instead of a few hours.
• One has poor parasympathetic tone — never fully downshifts, poor digestion, unrefreshing sleep.

These require different or even opposite interventions.

What COVID unmasked

Long COVID ironically did the field of medicine a favor : it made autonomic dysfunction impossible to ignore.

A large population of previously healthy people acquired a viral illness and emerged with profound fatigue, exercise intolerance, orthostatic symptoms, brain fog, and disturbed sleep — a recognizable dysautonomic picture, in numbers too large to dismiss. Post-viral autonomic dysfunction was well described since the 1990s, , but unfortunately, it wasn't taken seriously in most clinics.

What COVID revealed is that this pattern was always present in chronic illness. I see it in my rheumatology patients constantly: severe fatigue that doesn't track with inflammatory markers, and poor responses to exercise in patients who are doing everything they were told to do. Those patients were being managed as though the problem were deconditioning or motivation, but inmany cases, it was neither.

What testing actually gives us

We now have instruments capable of characterizing these different conditions with real granularity, rather than inferring from symptoms alone. Broadly, autonomic assessment looks at how the cardiovascular system responds to controlled challenges, such as changes in posture, controlled breathing, and other standardized maneuvers. Metrics including beat-to-beat variability provide measurements that reflect the balance and responsiveness of the two branches.

The output is not a score. It's a map to let us know which branch is over- or under-active, how quickly does the system responds, and how quickly does it recovers.

That map changes three things in practice.

It changes the exercise prescription. This is the most immediately useful application of autonomic nervous system testing. Movement is medicine, and I want essentially every patient exercising. But the right dose and type depend entirely on recovery capacity. For a patient with impaired recovery, the standard advice — push harder, be consistent, muscle through it — pushes a patient one step forward and then two steps back until the program collapses and the patient concludes they've failed. But they haven't failed,the prescription was wrong. Knowing where someone actually sits lets us build a program they can sustain, and sustainability is the whole ballgame.

It changes which interventions we reach for. The neuromodulatory toolkit is larger than most patients realize, and different tools act on different parts of the system:

• Breathwork, particularly extended-exhale patterns, directly engage parasympathetic tone
• Vagus nerve stimulation, both non-invasive devices and behavioral approaches
• Gentle, rhythmic movement — yoga, tai chi, walking — which appear to act on regulation in ways distinct from cardiovascular training
• Weighted vests and gravitational loading. My colleague Dr. Brennan Spiegel has written on how gravity and gravitational stimulus affect health; there's an interesting neuromodulatory dimension to this work that touches the autonomic system directly
• Thermal therapy — sauna and cold exposure — which are potent autonomic challenges and, for that reason, need to be dosed rather than maximized
• Sleep architecture, which is both an input to and an output of autonomic function

It changes what we can study. This is where I'm most excited, and where I want to be most careful with my language.

We're designing a research trial to take patients with lupus and rheumatoid arthritis, map their autonomic function, and then assign one group to a protocol specifically tailored to their individual pattern of dysfunction while the other receives our standard excellent care. The question is simple and unanswered: does tailoring to the autonomic map actually improve outcomes?

I believe it will, but I will wait for stronger evidence to finalize the claim. That's the difference between a hypothesis and a result, and this field suffers when people blur the two.

The honest framing

Autonomic testing is not a diagnostic test for autoimmune disease. It doesn't replace inflammatory markers, imaging, or antibody panels. It's a complementary layer that helps explain a category of symptoms — fatigue, exercise intolerance, poor recovery, orthostatic trouble — that conventional rheumatologic workups routinely fail to account for.

Nor is neuromodulation a replacement for disease-modifying therapy. If you have active inflammatory disease, you need treatment for the inflammation. What this work offers is a second axis, addressing a set of symptoms that frequently persist even when the inflammatory disease is well controlled — which is one of the most common and most demoralizing situations my patients face. My labs are normal and I still feel terrible. Asentence deserves a real answer rather than reassurance.

Why this matters to me

For twenty years I've told patients that stress management matters, knowing that I was handing them something vague and asking them to do the hardest part alone. It's the gap between knowing a thing is true and being able to act on it.

Measurement closes that gap. It converts "manage your stress" into a specific description of what in your regulatory system isn't working, and a specific plan for it — which can be followed, adjusted, and evaluated like any other treatment.

That's what a clinical tool is. I’m excited for the research to follow and the many people I hope we can help using this approach.

Disclaimer: This article is educational and is not medical advice. Autonomic testing and neuromodulatory interventions should be undertaken in consultation with a qualified physician. Research described as planned or ongoing has not produced published results, and no outcome is implied or promised.