Understanding Oxygen and the Apple Watch 6: A Primer on Oxygen Saturation 101

The tech world has had a hold on the imagination and pocketbook of Americans for decades, improving our day to day communication, entertainment and educational options, all contained in the device we hold in our hands. More recently, tech companies have entered the multi-billion dollar health and wellness market, claiming a roseate outlook on life quality by revealing a wealth of “health” data populated on our iPhone or Android phones for us to peruse. For those that majored in business, art, political science or philosophy in college, watched “Keeping Up with the Kardashians” instead of “Mr. Wizard” reruns and did not take a physiology or human biology course, these numbers may be bewildering. It is time to let some “air into this room” and provide a background for understanding tech and health devices.  After 4 decades around EKG’s and pulse oximeters attached to humans and a user of Apple products for almost as long, I will provide the introductory course on the latest Apple foray into health: oxygen saturation and the pulse oximeter.

Oxygen is a key to human health. Before it’s atmospheric debut, we had bacteria for a billion years with few tech inventions during this period, save for the flagella, a whip like structure that could take you a few inches across a scum filled pond. Queue the plants (algae and other photo-synthesizers) and oxygen enters the atmosphere allowing for multicellular organisms and ultimately us (now is the time to hug your house plant out of gratitude). What did oxygen do for us? It unlocked the ability to generate much more energy from food sources that allowed us to dig a ditch, launch a satellite or use your TV remote. As any biochemistry or medical  student knows, ATP, the powerhouse chemical we use to store and release energy, is manufactured 16 fold in the presence of oxygen (for the curious, see oxidative phosphorylation and electron transport chain for more details).

The engineering dilemma that evolution was faced with for us multicellular beings was a supply and distribution problem. How to get oxygen from the air to each of our cells?  To move a substance, you need a pressure gradient to drive the work and the atmosphere pressurizes oxygen to move from high to low pressure zones. But this does not get the prized element to deeper tissues. For that obstacle, we evolved the lungs, blood vessels, blood and heart to circulate oxygenated blood to tissues to bypass this problem. 

Yes, blood, that substance thicker than water. Oxygen can dissolve in blood but at very low concentrations. To improve on the quantity of oxygen, we inherited the red blood cell and its key constituent, hemoglobin. Hemoglobin is the main oxygen carrier in the blood and allows pick up and delivery of 02 to the tissues. Oxygenated blood is bright red (usually arterial) and less oxygenated blood (usually venous) is blue. We can exploit this light absorbing property to determine how much oxygen is bound to hemoglobin at a particular moment by shining a frequency of light at a blood vessel and checking how much is absorbed and reflected at one time in the heart beat cycle.  The ratio of oxygenated to  de-oxygenated hemoglobin is measured, and reported as  oxygen saturation.

Do you need a device that warns you of oxygen shortage? Shouldn’t you feel short of breath, breathe faster and get yourself into an emergency room in time? Not always, as your brain, highly dependent on oxygen, can go haywire with  confusion, lethargy and poor judgement as a consequence. This is why the flight attendant always directs you to put your oxygen mask on first before your children. What about turning blue (cyanosis) from low oxygen? Unfortunately, this is a late occurring sign which occurs when fully ⅓ of the hemoglobin is devoid of oxygen.

Is there an early warning device to warn us of oxygen deprivation?Cue the pulse oximeter:  oxygen saturation can be measured by a pulse oximeter, or more recently with tech watches that have similar technology. Healthy lungs at sea level usually allow for oxygen saturation over 95%. As with all technologies, certain pitfalls apply. If your hemoglobin is abnormal it may not be measured properly. Carbon monoxide poisoning, for instance, renders hemoglobin incapable of binding to oxygen but is not registered by the pulse oximeter. Yes, you can asphyxiate with a normal pulse oximeter reading. The sensors must be close to the skin and not moving or else a faulty reading could result. Even expensive devices can be subject to error. Many a time in the surgery center, a reading of 60% could appear in an awake, non sedated patient. Repositioning the sensor, recalibrating the device or wheeling a new machine into the OR solved the false reading.

So what can you glean from the result? High altitude can lower oxygen saturation due to lower oxygen pressures. Altitude sickness can result with headaches, shortness of breath and in extreme circumstances, flooding of the lungs with fluid. Severe pneumonia can lower oxygen saturation and in the case of COVID 19, may not result in air hunger which would normally warn you of severe lung infection. Severe asthma could also cause a drop in oxygen saturation. Apple has started a research trial examining the usefulness of the Apple Watch 6 in this circumstance.

 The most important use of this technology may be in screening for obstructive sleep apnea. This condition is quite common in the U.S with a prevalence up to 30% of males and 15% of females).  Celebrities such as Rosie O’Donnell, Shaquille O’Neal,  William Shatner, (aka Captain Kirk of Star Trek fame), Quincy Jones, Randy Jackson (of American Idol fame) are afflicted. Luminaries whose death may have been influenced by sleep apnea include William Howard Taft (former 27th President), Jerry Garcia (of the Greatful Dead), Justice Antonin Scalia, Carrie Fisher (of Star Wars fame) and James Gandolfini (of Sopranos fame). Sleep apnea has severe health consequences and has acceptable, effective therapy. With the increase in risk factors such as adult obesity and sedentary nature of the population, obstructive sleep apnea is becoming epidemic, resulting in upper airway obstruction at night with snoring, interruption of breathing and dangerous reduction in oxygen saturation. This condition often results in headaches, daytime fatigue, hypertension, acceleration of cardiac disease and premature death. A continuous positive pressure mask can ameliorate this condition. A convenient, readily available screening tool such as a reliable pulse oximeter for nighttime use could potentially save multiple lives by directing those into the office of sleep specialists for definitive diagnosis and treatment.

So should you climb on board the day and night pulse oximetry tech train?  With certain caveats (a device that has reproducible results and matched to gold standard testing, FDA approval and  that works for night-time monitoring) this metric may benefit you when hitting the ski slopes and when your significant other has had it with your snoring and asks you to “do something about it.” Take a deep breath and ponder that.