FACE MASKS: "An N95 FFR user is always going to experience some level of difficulty breathing, or breathing resistance, even though these devices are designed to minimize breathing resistance as much as possible."
https://blogs.cdc.gov/niosh-science-blog/2020/06/10/ppe-burden/?s=09

FACE MASKS: "Enough breathing resistance could result in a reduction in the frequency and depth of breathing, known as hypoventilation (the opposite of hyperventilation)."

FACE MASKS: "Some of the known physiological effects of increased concentrations of CO2 include:

Headache;

Increased pressure inside the skull;

Nervous system changes (e.g., increased pain threshold, reduction in cognition – altered judgement, decreased situational awareness

FACE MASKS: "difficulty coordinating sensory or cognitive, abilities and motor activity, decreased visual acuity, widespread activation of the sympathetic nervous system that can oppose the direct effects of CO2 on the heart and blood vessels)"

FACE MASKS: "Increased breathing frequency;

Increased “work of breathing”, which is result of breathing through a filter medium;

Cardiovascular effects (e.g., diminished cardiac contractility, vasodilation of peripheral blood vessels);

Reduced tolerance to lighter workloads"

FACE MASKS: "To fix the problem of breathing too much CO2 that has built up within the respirator facepiece, a worker can simply remove the respirator."