Chicago doctor weighs in after Damar Hamlin's terrifying incident

CHICAGO - There are candles and signs, and prayers, outside the Cincinnati hospital where Buffalo Bills player Damar Hamlin is being treated.

Inside, we’ve learned that Hamlin’s vital signs have improved, but he is still in the fight for his life.

It's being reported that Hamlin was originally on 100-percent oxygen, but that is now down to 50-percent — signs that he's improving.

At 5 minutes and 58 seconds in the first quarter, what seemed like a typical play turned out to be one of the most terrifying moments in NFL history.

Hamlin, 24, fell to the turf after a play. Medical experts believe the helmet to the chest impacted the heart’s rhythm, causing it to stop.

EXPLAINER: WHAT HAPPENED TO BUFFALO BILLS SAFETY DAMAR HAMLIN?

Over nine minutes of CPR was administered before his heart restarted. It's still unknown if any damage was done during the time that no blood was flowing to the brain.

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"Right at the exact time of the hit, his heart was beating in a certain way where it suddenly stopped. And he went into the dangerous heart rhythm call ventricular fibrillation, and at that point you need CPR and a defibrillator," said Dr. Marlon Everett, a cardiologist with Advocate Trinity Hospital.

Everett says the next 24 hours will be crucial to determine Hamlin’s condition.

"We often will perform something called a hypothermic protocol where we can actually lower the body's core temperature for a while, for about 24 hours, just to let the brain cells relax a little bit, and then evetnuyally warm the body back up so the brain cells can wake back up," Everett said.

The Buffalo Bills tweeted Tuesday afternoon saying Hamlin is in the Intensive Care Unit and remains in critical condition. He's sedated with a breathing tube, but his vital signs are back to normal.

"Hearing his vital signs are stable, I think that is encouraging," Everett said.