"The volume of an ordinary breath is approximately 400 to 600 mL. When each breath is inhaled, air first fills the upper airway, trachea, and bronchi; speech is generated here, but no gas exchange takes place in this anatomical dead space. Only air that exceeds the volume of this dead space is conducted to the alveoli for gas exchange. Normal speech only requires approximately 50 mL of gas per syllable—thus, stating “I can't breathe” would require 150 mL of gas (5). Anatomical dead space is typically one third the volume of an ordinary breath. George Floyd could have uttered those syllables repeatedly with small breaths that filled only the trachea and bronchi but brought no air to the alveoli, where actual gas exchange happens.
Phonation can occur with exhalation alone in the complete absence of inhalation by using the expiratory reserve volume that remains after a normal tidal breath is exhaled. In contrast, adequate gas exchange to support life requires inhalation, as well. A 70-kg adult requires 4 to 5 L of air per minute (at rest) to reach the alveoli, where oxygen and carbon dioxide are exchanged with the blood; light muscular activity requires double that, and a person in extremis may require more than 100 L of air per minute (6). If less air reaches the alveoli, there may be devastating cardiopulmonary consequences, including death."
Phonation can occur with exhalation alone in the complete absence of inhalation by using the expiratory reserve volume that remains after a normal tidal breath is exhaled. In contrast, adequate gas exchange to support life requires inhalation, as well. A 70-kg adult requires 4 to 5 L of air per minute (at rest) to reach the alveoli, where oxygen and carbon dioxide are exchanged with the blood; light muscular activity requires double that, and a person in extremis may require more than 100 L of air per minute (6). If less air reaches the alveoli, there may be devastating cardiopulmonary consequences, including death."