Each cell has certain voltage across the cell wall for the sodium potassium pump.
The resting membrane potential
Imagine taking two electrodes and placing one on the outside and the other on the inside of the plasma membrane of a living cell. If you did this, you would measure an electrical potential difference, or voltage, between the electrodes. This electrical potential difference is called the membrane potential.
To understand more about the cell voltage please refer to the Khan Academy article.
Oxygen is also needed for a cell to function normally.
If oxygen is low then voltage of that cell also drops due to stress/inflammation/toxins/heavy metals etc.
If voltage is low then oxygen level also drop in a cell due to stress/inflammation/toxins/heavy metals etc.