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.
(This is the most commonly asked question) Oxygen levels are commonly measured by two techniques. The first is a blood gas in which a blood sample is taken directly from an artery. This is the most accurate assessment of oxygen. The normal oxygen level using this technique is 80-100 (mmHg). The second technique is bloodless and is called pulse oximetry. The result here is not a direct measurement of oxygen but rather represents the percentage of hemoglobin that is saturated with oxygen.