Hyperventilation

We normally breathe in proportion to our body's needs, breathing out carbon dioxide (CO2) along the way. Hyperventilation occurs when the amount you breathe exceeds your body's needs, causing the carbon dioxide level in your blood to fall below normal.

Feeling breathless and unable to get enough air can easily make you think you are short of oxygen. In hyperventilation, however, the key issue is that too much carbon dioxide has been breathed out. Carbon dioxide is not just a useless gas: it is also an important signal that helps regulate blood vessel diameter and breathing rate.

When carbon dioxide levels fall suddenly, the following changes occur in the body.

• Small blood vessels supplying the brain narrow, reducing blood flow to the brain. This can make you feel foggy-headed or dizzy.
• It becomes harder for the blood to release oxygen to the tissues. This is because hemoglobin holds on to oxygen more tightly when carbon dioxide levels are lower. This is called the Bohr effect.
• Changes in blood chemistry can cause prickling or tingling in the fingertips, toes, and around the mouth. You can read more about these sensations under Paresthesia.
• You may feel your heart pounding, tightness in your chest, and increasing anxiety. A cycle can develop in which anxiety makes you breathe faster, and faster breathing makes you more anxious.

Low carbon dioxide (hypocapnia) is a state in which excessive breathing lowers the carbon dioxide level in arterial blood below normal. This hypocapnia is the physiological basis for the symptoms of hyperventilation.

Carbon dioxide helps widen blood vessels. When its level falls rapidly, the small arteries in the brain constrict, reducing cerebral blood flow. Reports suggest that cerebral blood flow decreases by about 2.5–4% for every 1mmHg decrease in the partial pressure of carbon dioxide in arterial blood. At the same time, the oxygen dissociation curve shifts toward hemoglobin holding on to oxygen more tightly. In other words, even if the blood carries enough oxygen, it becomes harder to deliver that oxygen to the tissues. When these two changes occur together, dizziness, tingling in the hands and feet, and a prickling sensation around the mouth can occur together.

Carbon dioxide levels rise again when you slow your breathing. As breathing settles, the symptoms usually settle too.

• During situations involving intense tension, such as presentations, exams, or a sudden fright
• During or immediately after vigorous exercise
• After suddenly ascending to a high altitude
• When you habitually take shallow, rapid breaths using only your upper chest, or sigh frequently

Besides a single acute episode of heavy, rapid breathing, some people have persistently shallow, rapid breathing in everyday life. In respiratory rehabilitation and physical therapy, this pattern is examined under the term Breathing pattern disorder. Breathing patterns and tension influence each other: tension makes breathing shallower, and shallow breathing makes it easier for the body to become more tense. Tension and the body's responses are linked to the Autonomic nervous system.

If you think you are starting to hyperventilate, try the following.

1. Sit down somewhere safe. Since you may feel dizzy, sit in a comfortable position rather than standing. 2. Focus on breathing out. Breathe in gently through your nose, then lightly purse your lips and breathe out in a slow, narrow stream. Aim to spend longer breathing out than breathing in. For example, breathe in for 4 seconds and out for 6 seconds. 3. Do not take in a lot of air at once. Let go of the urge to take deep breaths, and continue slowly with small breaths. 4. Place a hand on your abdomen. Feeling your abdomen move slightly can help settle breathing that has been confined to the upper chest. 5. Continue for a few minutes. As your breathing slows, you may notice the tingling and dizziness gradually easing too.

Practicing slow breathing in everyday life can make it easier to use when you need it urgently. You can find detailed instructions under Slow breathing with prolonged exhalation and Breathing retraining. Another approach to breathing is the Buteyko method.

If this is your first episode of hyperventilation, it is safer to distinguish it from other conditions with similar symptoms. If you have persistent crushing chest pain, difficulty breathing with wheezing, pain spreading to an arm or the jaw, or weakness in the limbs on one side with slurred speech, do not dismiss it as just a breathing problem; have your condition assessed right away. It is also worth looking into the cause if your symptoms do not settle after your breathing settles, or if they recur frequently.