A pulse oximeter is a unique device that measures oxygen saturation in the blood and the pulse rate. An accurate reading can be provided in seconds, or it can be worn continuously. Oxygen saturation (SpO2) and pulse provide a quick measure of cardio-respiratory function at a glance, which can be extremely useful for athletes, people living at high altitude, hikers, and those with respiratory illnesses. Pulse oximeters are machines that measure a complex physiological process, therefore it is good to have an understanding of how they work, and what exactly the oxygen saturation in your arteries can tell you. Scientia potentia est – knowledge is power, so arm yourself here.
Human beings need oxygen to live. All organs and tissue require oxygen for metabolism, but the brain and the heart are most vulnerable to– and the first to be affected by – a lack of oxygen. Hypoxia is the clinical name for a lack of oxygen. Severe shortages of oxygen can be rapidly fatal, but even mildly lowered levels of oxygen in the blood can have negative effects. If you’re not getting enough oxygen, you may experience difficulty concentrating, fatigue, irritability and an array of other subtle indications. Cognitive performance is generally degraded. If you want to perform physically and mentally at your best, you want to have blood fully saturated with oxygen.
Take a deep breath. You just inhaled a mix of air that contains oxygen into your lungs. The oxygen in your lungs is now picked up by your red blood cells. Red blood cells contain hemoglobin, the protein which binds with oxygen in the lungs and distributes it around your whole body through your arteries, before returning to the lungs through your veins to repeat the cycle.
Pulse Oximeters were first designed and developed in the early 1970s to be a noninvasive tool that could easily determine oxygen saturation in the arteries. The principle behind them is simple: hemoglobin that is saturated with oxygen absorbs light at a different frequency than hemoglobin not saturated with oxygen. This property of hemoglobin can be exploited to determine the total oxygen saturation of the blood by passing those two frequencies of light through (for example) your finger, and measuring how much of each frequency was absorbed and how much was not absorbed. The relative absorption of each frequency can then be used to determine the percentage of hemoglobin in your blood carrying oxygen. This is more or less how a pulse oximeter works – it’s placed over a finger, and shines a light through your fingernail from one side and measures how much light passes through.
Pulse oximetry is a reasonably accurate process, but it can be affected by a few important variables. The ones you should know are having a clean device – a dirty photo sensor on the inside of the device or crusted blood will reduce accuracy. Wearing nail polish can also affect the accuracy, and has been heavily studied. The colors blue, black, green, and purple most seriously affect the accuracy of these devices – so if you get a reading that is very low, don’t worry – think about these factors before concluding you’re dying. People with low blood pressure, those who smoke, and those who are anemic may also experience anomalous readings. Smoke contains carbon monoxide, which competes with oxygen to be able to bind to hemoglobin (and can bind ~250x stronger) so if you’ve just smoked you may not be getting a representative oxygen saturation reading.
Monitoring pulse and oxygen saturation by using a pulse oximeter can be a great tool for athletes during strenuous workouts - there is an optimum range of oxygen levels in the body, and monitoring this range to ensure that you stay inside the effective oxygen range can improve overall workout performance and increase endurance, speed, efficiency. Athletes can use a pulse oximeter to monitor oxygen levels during a workout to make on-the-fly adjustments to get proper oxygen flow during workouts. There is often a tendency to hold the breath or breath shallowly (chest breathing) during exercise or any kind of stress. This leads to less oxygen being available for your muscle tissue and brain precisely at the time it is most needed, reducing strength, speed, and above all, stamina. Further, it can be insidious and difficult to notice that you’re not breathing effectively and have lowered oxygen levels in the blood, because your ability to think clearly and quickly is compromised. It can therefore be useful to wear a pulse oximeter either continuously while performing aerobic exercise, or during rest periods as check to see if they recovered from their last exercise set – that they’ve “caught their breath” before going on to the next set.
Interpretation of Pulse Oximetry Readings – Different levels of Oxygen Saturation
It can be extra important to monitor oxygen levels if you're (new to) exercising at high altitude - e.g. you're a hiker or you just moved to Denver or somewhere at high altitude - wearing this device will help you avoid hypoxia - a state of too little oxygen in body, where performance is degraded. Hypoxia can be difficult to notice without a device like this, as it slows down mental awareness as well as physical performance so you're less likely to realize that you don't feel 100%. Athletes new to high altitude training can use it to see how well they are adapting to lower oxygen levels in the air. After about two weeks of being at a higher altitude, the body will have compensated by increasing the amount of oxygen it is capable of carrying in a given amount of blood.
People with respiratory illnesses like asthma or emphysema also benefit - exercise can improve their condition, but also risk causing shortness of breath - a pulse oximeter provides early warning of coming respiratory attack [by indicating dropping oxygen levels] so you can avoid it by taking a break/using inhaler before danger comes.
If you get a low oxygen level reading during exercise, you can decide take action to remedy it- e.g. proper breathing, with pursed lips increases the oxygen saturation level. A pulse oximeter is helpful because it can teach the athlete to recognize that they are holding their breath during activity, or that they need to change position to breath properly to maximize performance. Pulse oximetry can help to quantify rest periods - a period of time taken in between "sets" of exercises, where the athlete rests before resuming exercise - now athletes can know that they rested completely by watching their oxygen sat increase back to normal before resuming activity.
Dotsia Bausch, 2012 Olympic Silver medalist in women's cycling says,
"I began using a pulse oximeter as part of my Olympic training and recovery regimen back in 2010,....by tracking my oxygenation and pulse rate – along with numerous other biophysical and behavioral metrics – I use data to measure and improve my athletic performance and gauge my recovery.”
To summarize: monitoring oxygen levels is useful for athletes, those with respiratory illnesses, and those living at high altitude. There is an optimal range of oxygen saturation levels in the body, 96-99%, at which physical and mental performance is maximized. Oxygen levels below that can indicate that you need to rest and breath properly or risk degraded performance. A pulse oximeter is a tool that allows quick and easy monitoring of oxygen levels so that athletes can maximize their training performance and quantify their recovery.
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