The heart, beating twelve times per minute, was pumping blood that was carrying small amounts of oxygen to tissues whose demand for oxygen had been reduced by the cold to a fraction of their normal requirement.

The equation was deeply unbalanced — far less oxygen delivery than a healthy person needs, far less than any physician would want to see in a patient.

But the demand side of the equation had been reduced as well, and for six hours, the supply was just barely sufficient.

How close to failure did it come?

Nobody knows.

The monitoring of Jean Hilliard’s vital signs began when she arrived at the hospital — not during the six hours on the porch.

Whether her heart rhythm had been stable or had flickered close to fatal arrhythmia during those hours is not knowable.