Earliest symptom of acute mountain sickness is
The low paial pressure of oxygen at high altitude causes aeriolar dilatation and if cerebral autoregulation does not compensate, there is an increase in capillary pressure that ors increased transudation of fluid into brain tissue.Ref: Ganong's Review of Medical Physiology Kim E Barrett, Susan M Barman, Scott Boitano, Heddwen L Brooks 23rd edition page no - 619
Blurring of vision
Fever
Nausea and vomiting
Headache
Respiratory system