Thank you for your question. This dull pain you are experiencing on deep inhalation could be caused by several different etiologies. The first possible cause of this pain could be due to a muscle strain in the are of the shoulder. These muscles this could occur during any sudden movement of the shoulder which would lead to a sudden stretching and inflammation of the muscle.
Another possible cause of this pain could be related to the thoracic cavity in which your lungs are contained. There could be irritation of the pleura, which is a protective layer of tissue lining the thoracic cavity. This could cause such pain when you inhale.
Last but not least, you could be experiencing a condition known as atelectasis. Atelectasis is a condition is when a particular area of the lung collapses resulting in the inability to inflate when inhalation occurs. This would result in similar pain to which you are experiencing. The only way to be certain of what is occurring here is to have a thorough examination of your shoulder and lungs conducted by your doctor. Once the exact cause of this pain is elucidated, the appropriate treatment will be prescribed to you. If this is indeed a muscle strain, then simple rest, and analgesic medication will help. If you have atelectasis or an infection of the pleura then more complex treatment options will be required to alleviate your pain.
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