Is it normal to happen voice problem after heart bypass sergery?

my uncle was 56 years old and he is a heart patient. so he done bypass surgery 3 weeks before. but after the surgery he is fine but his voice changed completely. he can't able to speak well. when he trying to speak air only coming no sound comes. doctors says this is happen for some patients because of inserted tube through his throat during the surgery and he will get his voice soon. but still now no improvement in his voice. so my question is he recover soon or it necessary to go to doctor. is it normal?