A Hidden Breathing Problem May Help Explain Chronic Fatigue's Exhaustion

• The study participants — The research team followed 57 adults with ME/CFS who were between 25 and 60 years old, along with a control group consisting of 25 sedentary but healthy adults. Both groups were carefully matched by age, sex, body mass index (BMI), and physical activity level to eliminate confounding variables.

• Both groups completed two days of cardiopulmonary exercise testing (CPET) — This is a structured system that measures oxygen use, breathing, CO₂ levels, and heart function while exercising on a stationary bicycle. Unlike most fitness tests, CPET isn't just about performance; it reveals how the lungs, heart, and muscles work together during exertion. This makes it especially useful for uncovering hidden abnormalities that might not be obvious in routine physical tests.

• The researchers were particularly interested in two breathing patterns — They looked closely at hyperventilation (HV), which is defined as breathing faster or deeper than needed, leading to abnormally low levels of CO₂ in the blood, and dysfunctional breathing (DB), which refers to irregular or unstable breathing (such as rapid shallow breaths or oddly fluctuating patterns), as opposed to the smooth, efficient breathing expected during exercise.

These breathing issues can produce symptoms that look remarkably similar to ME/CFS itself, including breathlessness, mental fog, dizziness, and worsening fatigue.

• Breathing abnormalities were far more common in ME/CFS than in sedentary individuals — A total of 71% of ME/CFS patients had at least one ventilatory abnormality — dysfunctional breathing, hyperventilation, or both — compared with just 32% of sedentary controls. Notably, nine ME/CFS patients exhibited both hyperventilation and dysfunctional breathing, while none of the controls had both issues. This points to a distinct, disease-related disruption in respiratory control.

• Dysfunctional breathing was present in nearly half of ME/CFS patients — 42.1% of ME/CFS participants met criteria for dysfunctional breathing — a pattern marked by erratic, unstable respiratory rhythms — compared with just 16% of sedentary controls. This irregularity may help explain symptoms such as dizziness, fatigue, and autonomic instability often seen in ME/CFS.

• Hyperventilation was also significantly more frequent — Roughly 32% of ME/CFS patients were found to hyperventilate — breathing out more carbon dioxide than their metabolic demand requires — while only 4% of control participants did. This imbalance can lower CO₂ levels and trigger a cascade of symptoms, including shortness of breath, tingling, and lightheadedness.

• Nine of the ME/CFS patients had both dysfunctional breathing and persistent hyperventilation simultaneously — This combination did not occur in any participant in the control group. The overlapping patterns were also associated with more intense shortness of breath as well as worsened symptoms like dizziness, heart palpitations, chest pain, mental fog, and profound fatigue.

• The overlap matters even more when you look at efficiency — Ventilatory efficiency is measured by something called the VE/VCO₂ ratio. Think of it as the cost of breathing — how much ventilation it takes to get rid of a unit of CO₂. A healthy VE/VCO₂ ratio is under 30, however, the ME/CFS group had VE/VCO₂ slopes of 34.7 on average. Those without hyperventilation had lower slopes, around 28.1.

Simply put, the higher the slope, the harder the body needs to work just to keep breathing steady. And the harder the respiratory system works, the less energy is left over for everything else.

• The most important takeaway? Breathing problems are both measurable and modifiable — The authors suggest that therapies aimed at improving breathing patterns, such as diaphragmatic breathing, respiratory physiotherapy, or pulmonary rehabilitation, may offer relief. Unlike medications, these methods are safer, support the nervous system, and reduce the load on respiratory muscles, especially during physical activity.

"Nearly half of our chronic fatigue subjects had some disorder of breathing — a totally unappreciated issue, probably involved in making symptoms worse," Dr. Benjamin Natelson of the Icahn School of Medicine, the study's senior author, said.

"Identifying these abnormalities will lead researchers to new strategies to treat them, with the ultimate goal of reducing symptoms."

• Carbon dioxide plays several essential roles in the body — It's not just a waste product that your body needs to expel; rather, it plays a vital role in pain management and chronic nervous system overload. CO₂ also supports a calmer stress response and allows the brain to process pain in a more regulated, controlled way. In fact, when we exhale, we actually release more oxygen than CO₂.

• One of CO₂'s most important jobs is helping transport oxygen — When you breathe, oxygen doesn't automatically enter your muscles, brain, and organs; rather, your body relies on CO₂ to actually use oxygen by signaling red blood cells to release oxygen from the bloodstream to areas of the body where it is needed most. This process is called the Bohr effect.

• What happens when you don't have enough CO₂? When CO₂ levels are healthy, oxygen is released easily where it is needed most. When CO₂ levels drop too low, oxygen stays tightly bound to the blood and becomes less available to the tissues.

This helps explain why deep/rapid breathing or overbreathing, such as when you hyperventilate, does not always make people feel better. In some cases, it can actually worsen symptoms by lowering CO₂ too much, reducing oxygen delivery to the brain and muscles.

• The medical term for low CO₂ in the blood is hypocapnia — This often results from overbreathing or when breathing is too fast, too deep, or simply excessive for the body's needs. Hypocapnia can cause a wide range of symptoms, including dizziness, chest tightness, muscle cramps, anxiety, and pain sensitivity.

• Hypocapnia also causes blood vessels in the brain to narrow — This reduces blood flow to areas involved in emotional regulation and pain processing, and creates a powerful feedback loop: Pain and stress alter breathing, altered breathing lowers CO₂, and low CO₂ makes pain and stress feel even worse.

• What happens when you have low CO₂ tolerance? Basically, low CO₂ tolerance can lead to discomfort. Even a slight rise in CO₂ can trigger air hunger, rapid breathing, or feelings of panic. As a result, they may breathe more than their body actually needs — often without realizing it. Over time, this pattern of overbreathing can keep the nervous system locked in a state of heightened alert.

• Low CO₂ tolerance is especially common in people with chronic, hard-to-explain conditions — In addition to ME/CFS, Foster also says that people with illnesses like Ehlers-Danlos Syndrome (EDS), Postural Orthostatic Tachycardia Syndrome (POTS), and hypermobility are also prone to this condition. And because the breathing system is overreactive, the nervous system remains stuck in survival mode.

• One simple way to estimate CO₂ tolerance is a gentle breath-hold test — While this test is not diagnostic, it can offer useful insight into how the breathing system is functioning. Foster describes how to do this protocol:

"You begin by sitting comfortably and breathing normally for a minute or two. Then you take two gentle, quiet breaths through your nose and, after your second exhale, you hold your breath. You are not holding until you cannot bear it any longer.

You are simply holding until you feel the first clear urge to breathe or any small shift in your body that tells you it is time to stop. That might be a twitch in your diaphragm, a swallow, or just a subtle discomfort that breaks the stillness.

Your time is then measured in seconds. A breath hold of less than ten seconds usually indicates very poor tolerance. Ten to twenty seconds is still considered low. Twenty to forty seconds is the range where some people begin to function a little better, but there is often still room for improvement. If you can hold for forty to sixty seconds, you are doing well."

• What makes this test so valuable is it provides insights on how your nervous system is functioning — A shorter breath-hold time often signals heightened sensitivity to CO₂. Even small increases can trigger an exaggerated breathing response, locking the body into patterns of overbreathing. In contrast, a longer hold time suggests greater tolerance and stability, supporting more efficient oxygen delivery and calmer day-to-day regulation.

1. Test your CO₂ tolerance with a simple breath-hold — Before you start fixing anything, it helps to get a clear picture of where you stand. I recommend doing the basic breath-hold test mentioned above.

Another good test that can tell you if your symptoms are due to a CO₂ deficiency is to breathe into a paper bag. If your symptoms begin to ease with this approach, it may suggest that breathing too much, and therefore low CO₂ levels, could be playing a role in how you're feeling. For safety reasons, never use a plastic bag, as it can be dangerous. A paper bag is important, ideally around 6 × 15 inches, since bags that are much smaller or larger may not work as intended.

Hold the paper bag lightly over your nose and mouth using your hands, and breathe normally into it for a short period. As you breathe, some of the air you exhale stays in the bag, which gently increases CO₂ levels and may help ease symptoms.

2. Start CO₂ tolerance training using nasal breathing and light breath holds — You don't need fancy tools to change how your body responds to CO₂. You just need a consistent, safe routine that tells your nervous system it's okay to breathe less.

I recommend starting with gentle nasal breathing throughout your day. Try to keep your mouth closed unless you're speaking or exerting yourself. Then, add in light breath holds — short pauses after your exhale — during calm moments. These aren't intense. You're not pushing into discomfort. You're just helping your body get used to slightly higher CO₂ levels.

3. Stop mouth breathing and focus on slow, silent breaths — Mouth breathing throws your entire breathing chemistry off. It dries your airways, triggers overbreathing, and drops your CO₂ too quickly. If you're breathing through your mouth during sleep, it's worth addressing.

Try this during the day: Slow your breath down. Breathe in and out through your nose. Your breath needs to be so quiet you barely feel it. Each breath should be low — diaphragmatic — not high and fast in the chest. Think of this as “invisible breathing.” You’re retraining your brain to stop panicking about every small rise in CO₂.

If you snore or breathe through your mouth at night, consider mouth taping as a temporary support tool (if it feels safe for you). The goal is always to return to calm, nasal breathing — especially during rest.

4. Track your breathing response to activity and stress — Start noticing when your breathing goes off. Is it after meals? During conversations? When you stand up too quickly? If you have ME/CFS, your body might be reacting to stressors with subtle hyperventilation, even if you're sitting still.

This awareness matters. Many people think breathlessness means they're "out of shape." But if your VO₂ max is normal, the problem isn't your fitness — it's your breathing regulation. Watch for patterns: sighing, yawning, rapid shallow breaths, feeling "air hungry," or even breath-holding during stress.

Once you recognize your triggers, you can intervene. Use a short nasal breathing break. Take a moment to ground yourself. The moment you slow your breath, you’re sending a signal to your brain that you’re safe. That one choice can change your day.

5. Use gentle movement paired with breath awareness (like yoga or swimming) — If you're ready to go further, try pairing gentle exercise with conscious breath control and activities that can help you reprogram your breathing patterns. "Breathing exercises via yoga could help, or gentle physical conditioning where breath control is important, as with swimming," Natelson said.⁹

The key is to focus on breath mechanics while you move. Are you holding your breath while climbing stairs? Are you gasping after small tasks? These moments are your training ground. Use the movement to teach your breath how to stay calm and steady — low, slow, and nose-based.

Let your breath act as your guide. If you feel calmer, more energized, or notice less dizziness or air hunger after training, you're on the right path.