That pulmonary airflow is required for human vocalization is a matter of everyday observation and fundamental physiological definition, requiring no formal citation.
The claim states that pulmonary airflow generated by exhalation or inhalation is required for human vocalization. This is a basic, universally understood physiological fact of human speech production (phonation requires airflow from the lungs to vibrate the vocal folds). It falls under common knowledge, so no citations are needed and index lists remain empty.