his carbon dioxide levels rise from 5 percent to 6 percent. They keep rising. A minute later, Olsson’s levels are 25 percent higher than they were just a few minutes ago, taking him from an unhealthy hypocapnic zone to squarely within a medically normal range. All the while, his blood pressure drops about five points and heart rate sinks to the mid-60s. What hasn’t changed is his oxygen. From start to finish, even though he’s been breathing at a third of the rate considered normal, his oxygen hasn’t wavered: it stayed at 97 percent.
