Surgery for sinus problems or sleep apnoea has the potential to alter voice characteristics. One solution for sleep apnoea - a disorder where breathing stops many times during the night - is to remodel the nasal and throat cavity through surgery. Often the problem is that the uvula - a flap of tissue at the top of the throat obstructs night-time breathing.
If the uvula is trimmed - in an operation called uvulopalatopharyngoplasty (UPPP) - the shape of the throat and nose cavity is altered. Since the way your voice sounds depends on the way vibrations from the larynx resonate in this cavity, you might expect UPPP to affect the voice.
Researchers at a number of centres in the US looked at the voice characteristics of patients undergoing surgery. They found that vowels were unaltered, as were most consonants save for 'm' and 'n' which became less 'nasal'. The subjects themselves felt their voice was unchanged. But you don't hear your own voice as others do.
Friends and relatives thought that surgery had significantly improved the subjects' voices. A similar effect was seen in patients having surgery to treat sinus and tonsil problems.