What parameters does the device measure exactly?
Kaniusas: Essentially, five physical parameters are recorded. One of them, for example, is how long the patient has held their breath. If someone can hold their breath for more than 60 seconds, we assume that regulatory fitness is present - because the body can apparently cope well with apneas, i.e., internal imbalance. However, in most patients, this tends not to be the case. To measure this more accurately, we look at peripheral water constriction, the extent to which the vessels in the periphery were constricted during the apnea. If this constriction is strong enough, it means that the so-called diving reflex or regulatory fitness to compensate for the lack of oxygen to the central organs is present.
Furthermore, we measure the arterial oxygen saturation: If during apnea the oxygen level does not drop too much, fitness is also present. From the oxygen saturation we notice if the body can handle the situation.
Then there is the heart rate variation: when you hold your breath, bradycardia usually occurs, that is, the heart rate drops to reduce oxygen consumption in the heart; if this drop is prominent enough, that is another point for fitness.
Finally, we measure the change in blood pressure. From these four parameters plus the stopped air, we then calculate a kind of weighted index. This not only switches a traffic light indicator (green-yellow-red), but also gives a numerical value from zero to one hundred – according to which the anesthesiologist can determine whether the patient is at risk.
What risks are minimized by these findings?
Kaniusas: It's primarily about cardiovascular and pulmonary risks, because regulatory fitness relates to exactly that. If a patient loses blood during surgery, for example, the cardiovascular system naturally has to compensate for that loss by readjusting. We capture this ability to compensate before surgery by means of this mild stress of arrested breathing.
I like to compare this with a nuclear power plant: To test a nuclear power plant, you don't let it explode or stop, but you destabilize it very mildly. And then you see how well the power plant returns to normal. We do something similar here with humans by briefly throwing them off balance.