According to this NASA page someone was killed when his space suit was ripped during a test of the ejection system.
Korolyovs [Korolevs] reaction to Dolgov's death was to take a number
of urgent and clever measures. First he had the exit hatch made
larger. Secondly, he increased to two seconds the interval between
shooting off the hatch and the operation of the ejector mechanism.
But blowing off the hatch and ejecting the seat with the cosmonaut was not all.
The Vostok capsule was pressurized with nitrogen and oxygen to about 1 bar. The air pressure at 7000 m height is about 0.41 bar. To avoid injuries caused by the explosive decompression, a pressurized suit with closed helmet and gloves were worn. There is too little oxygen at 7000 m for a human without altitude adaption. When ejecting the seat, the suit was disconnected from the life support system of the capsule and sealed to retain pressure.
Cables for medical telemetry and for voice communication (microphone and earphones) were disconnected too.
The pressure difference from inside the suit to outside at 7000 m was about 0.59 bar, the suit was not very flexible but only for few minutes. The air inside the suit was breathable for the short time of fast descent from 7000 m to about 2500 m without oxygen supply or carbon dioxide removal.
At a height of 2500 m and an air pressure of about 0.75 bar, the cosmonaut could open his helmet to breathe fresh air with an oxygen partial pressure of 0.16 bar. The pressurized cabins of passenger airplanes are operated at about 0.75 bar.