Hi Friend

I hope you have had a fantastic week and are doing well. I put up a social media post this week on how I use heart rate variability to really help my patients get better. This week I will explain what it actually is and how it works.

What Is Heart Rate Variability

Heart rate variability (HRV) is a measure of the variation in time intervals between consecutive heartbeats. Rather than beating like a metronome at perfectly even intervals, a healthy heart constantly adjusts the timing between beats in response to physiological demands. These beat-to-beat fluctuations are driven primarily by the autonomic nervous system (ANS), which has two main branches:

• Sympathetic (“fight or flight”) — tends to accelerate heart rate and reduce variability

• Parasympathetic (“rest and digest”) — tends to slow heart rate and increase variability

Because HRV reflects the dynamic balance between these two branches, it’s considered an important non-invasive marker of autonomic nervous system function, cardiovascular health, and overall physiological resilience.

How is HRV Measured

• We measure the time between one beat and the next (that’s called the “beat-to-beat interval”).

• Recording Those Intervals

  • To see those tiny differences, you need a device that can pick up each beat precisely:

    • Electrocardiogram (ECG): Sticks-on-skin sensors that detect your heart’s electrical signals.

    • Wearables (like some fitness watches or chest straps): Use light or electrical signals to do much the same thing.

• Looking at the Numbers

  • Once you have a list of beat-to-beat intervals—say 800 milliseconds, then 790 ms, then 810 ms, etc.—you do simple math on those numbers:

    • Average distance from the mean (called SDNN): How spread-out all your numbers are overall.

    • Average of the tiny jumps between beats (called RMSSD): Basically, how big each little change is from one beat to the next.

• Why Two Measures?

  • SDNN tells you how much your heart rhythm changes overall.

  • RMSSD focuses on the quick, breath-to-breath fluctuations that come from your body “resting and digesting.”

• Putting It in Context

  • Higher numbers mean more variation—your heart is adapting quickly, which is generally good.

  • Lower numbers mean less variation—your heart is staying very steady, which can be a sign of stress or fatigue.

HRV and chronic disease

1. Fibromyalgia

• Reduced overall variability: Patients with fibromyalgia consistently show lower time-domain indices (e.g., SDNN, RMSSD) and attenuated high-frequency (HF) power, indicating diminished parasympathetic (“rest-and-digest”) activity.

• Relative sympathetic predominance: The low-frequency (LF)/HF ratio is often elevated, reflecting a tilt toward sympathetic (“fight-or-flight”) dominance.

• Clinical correlations: Lower HRV correlates with greater pain intensity, fatigue severity, and poorer sleep quality. HRV biofeedback and paced breathing interventions have shown modest improvements in both HRV metrics and symptom burden.

2. Chronic Fatigue Syndrome (CFS/ME)

• Blunted variability at rest and on tilt: CFS/ME patients typically exhibit reduced RMSSD and reduced HF power during supine rest—and an exaggerated drop in HRV upon head-up tilt, suggesting impaired orthostatic autonomic regulation.

• Delayed recovery: After mild exercise or orthostatic challenge, HRV takes longer to return toward baseline, mirroring the characteristic “post-exertional malaise.”

• Subgroup differences: Some studies identify a subgroup with almost normal resting HRV but marked dysregulation under stressors, underlining heterogeneity in autonomic phenotypes.

3. Long COVID

• Persistently depressed parasympathetic tone: Many long COVID sufferers display chronically low RMSSD and HF power—often more pronounced than in age-matched healthy controls—pointing to sustained vagal withdrawal.

• Elevated sympathetic markers: LF power and LF/HF ratio are frequently elevated, reflecting ongoing sympathetic overactivation that may underlie tachycardia, palpitations, and orthostatic intolerance seen in post-COVID dysautonomia.

• Correlation with fatigue and brain-fog: Lower HRV metrics are associated with greater self-reported fatigue, cognitive dysfunction, and exercise intolerance. Preliminary pilot studies suggest that gentle HRV-guided breathing and graded mobilization may help restore autonomic balance over weeks to months.

4. Shared Mechanisms & Implications

1. Autonomic imbalance: Across all three syndromes, there is a consistent shift toward sympathetic dominance and vagal withdrawal—a signature of poor stress-adaptation and diminished homeostatic flexibility.

2. Neuroimmune interactions: Chronic low-grade inflammation and altered cytokine profiles (e.g., elevated IL-6, TNF-α) can disrupt central autonomic networks and impair baroreflex sensitivity, perpetuating low HRV.

3. Diagnostic and management roles:

   • Risk stratification: HRV can help identify patients at higher risk for severe orthostatic intolerance or exercise-induced symptom flares.

   • Biofeedback interventions: Techniques like slow, paced breathing (e.g., 6 breaths per minute) and HRV biofeedback have shown promise in raising parasympathetic tone and ameliorating symptoms.

   • Monitoring recovery: Serial HRV tracking—using wearable ECG or validated PPG devices—offers an objective window into autonomic recovery over months of rehabilitation.

Take-Home Points

• All three conditions—fibromyalgia, CFS/ME, and long COVID—feature chronically reduced HRV, driven by sympathetic overdrive and impaired vagal function.

• Lower HRV correlates with greater pain, fatigue, orthostatic intolerance, and cognitive symptoms.

• Interventions targeting autonomic balance (biofeedback, paced breathing, graded exercise) can boost HRV and may translate into symptom relief.

• Wearable-based HRV monitoring provides a noninvasive tool for personalised management and recovery tracking.

As you can see I take HRV very seriously so all my patients get given a hrv weekly device which I track and adjust the treatment plan for them weekly to try and get the HRV up., this forms around 20-30% of the plan. Next week I will discuss what we can actually do and what methods there are to help a low HRV. Just recording it and pacing is only the first step, we need to do better and get you feeling better!

PS I have a closed community that is launching tomorrow. It will give you daily access to therapies and weekly check in withs drs aswell as a closed forum, if interested please sign up below:

Regards

Dr Ahmed