What makes a person able to speak in a low register when their normal speaking voice is hoarse, and in fact nearly gone?
ALWAYS one must see a doctor when the voice is hoarse to determine if there is a medical problem affecting the voice, such as allergies or acid reflux. It is also essential to determine whether or not the cords are healthy enough to continue speaking. Only once you are certain that using the voice will not cause any damage should you work with a voice therapist or teacher. You might need to rest the voice for a time until the hoarseness is gone before you can begin working.
The biggest mistake people make when trying to overcome hoarseness is increasing pressure on the voice, working harder. In fact, the only way to get a tone is to be extremely gentle. Using as little air as possible and vibrating only the finest edge of the vocal folds is the best way to produce a clear tone on any pitch. Whispering is not good for the voice. However, speaking very quietly and cleanly with the best resonance you can access will begin to restore vocal tone. The specialist you choose to work with will be able to help you with this. If there is no one in your community you can also work via Internet or telephone with someone.