What are two common early clinical signs of hypoxia in flight?

• A. Nausea and vomiting
• B. Blurred vision and dizziness
• C. Seizures
• D. Headache and tachycardia (often with tachypnea)

Answer: (D)

Early hypoxia signs come from the body's attempt to compensate for reduced arterial oxygen. The brain is particularly sensitive to low O2, so cerebral blood flow increases and can cause a headache. At the same time, the heart rate rises to boost oxygen delivery to tissues, and breathing generally speeds up to bring in more oxygen. Together, headache and tachycardia (often with tachypnea) are classic, reliable early indicators of hypoxia in flight. Other symptoms like nausea, blurred vision, dizziness, or seizures can occur but are less consistently early or indicate more advanced hypoxia.