Air hunger, shortness of breath, breathlessness, or a feeling that you just can’t breathe is medically known as dyspnea. If you don’t have asthma, pneumonia, or chronic obstructive pulmonary disease (emphysema or chronic bronchitis) and recently changed your thyroid dose, you could be over or undermedicated, which is affecting your breathing.
Thyroid hormone impacts metabolism, and this affects the lungs. Respiratory rate, or the number of breaths taken per minute, is one indicator of thyroid levels. Someone who is truly hypothyroid may breathe so infrequently that they complain of “air hunger.” Here’s a case study [A Case of Myxedema Coma with Severe Hypoventilation] where severe hypothyroidism (myxedema coma) was causing insufficient breathing (hypoventilation). Hypothyroidism causes neuromuscular dysfunction in breathing, which leads to respiratory insufficiency.
Hyperthyroidism will cause similar feelings of breathlessness during exertion, for a different reason. The high levels of T3 and/or T4 are causing stress on the heart, which is unable to keep up with the increased demands during exertion. Palpitations, exercise intolerance, and dyspnea (breathlessness) on exertion are signs of thyrotoxicosis (severe hyperthyroid state). [Thyrotoxicosis and the cardiovascular system: subtle but serious effects.] Tachycardia (rapid heart rate), systolic hypertension (top number in blood pressure is high), and atrial fibrillation (abnormal heart rhythm) are other signs that the dose is too high. Long term, this can lead to heart failure, which is why treatment of hyperthyroid Graves’ patients is so aggressive.
If you feel like you can’t breathe, look at other signs and symptoms, like your BP, heart rate, and respiration rate to determine whether your dose is too high or too low. If the breathlessness shows up only during exertion, chances are you’re overmedicated, not undermedicated. This may not be reflected in your body temperature, so don’t always assume you need more thyroid hormone based on that one variable. There may be other factors keeping your body temperature low, but in the meantime, your heart may suffer if you take too much thyroid hormone. Each organ takes up different amounts of thyroid hormone, depending on supply and/or need. The heart is one of the most sensitive organs to thyroid hormone excess or deficiency, and the heart rate usually reflects that. Ironically, heart rate can be high when severely hypothyroid too, so factor in other signs like bowel movements, etc.