Yet humans are rarely attacked by a shark, while millions of sharks are killed by humans. Some populations of shark species, such as the shortspine spurdog, may have dropped by 95 percent. The sharksâ population decline has a ripple effect â throwing entire marine ecosystems out of balance.
Quick Answer. A normal blood oxygen level during sleep is approximately 94 to 98 percent, according to Sleep Apnea Guide. Levels below 90 percent oxygen saturation are dangerous to the human body. The human brain can only survive four minutes without oxygen before cell death occurs.
Normal Blood Oxygen Levels. Healthy people have a normal range of oxygen saturation from 95% â 100%, although levels down to 90% are common and not usually cause for alarm.During exercise, the increased oxygen consumption may reduce blood saturation, but the increased breathing rate and blood flow compensate for this.xygen saturation is measured by a pulse oximeter, a device placed on the finger that uses light absorption to indicate the level of saturated hemoglobin, the protein on the red blood cell that stores oxygen during transport.