Tachycardia is caused by hypoxia due to
Reflexly through peripheral chemoreceptors
Diffuse vasodilation
Through central chemoreceptor
Secondarily after by hyperventilation
Tachycardia and vasodilation occur secondary to hyperventilation in cases of hypoxia. Central chemoreceptors do not have a role in hypoxia. Activation of peripheral chemoreceptors excites medullary vagal centre and causes Bradycardia.