Using a Masimo Might Sat Pulse Oximeter for Acclimating to Altitude
The effects of high altitude on humans are considerable; many changes in the body are occurring simultaneously. The key elements in acclimating to altitude aim at securing the proper amount of oxygen to tissues and organs. A body deprived of an adequate supply of oxygen can develop a condition known as generalized hypoxia. This may or may not be a good thing depending on the training goal. If you are trying to acclimatize to high altitudes, then periods of hypoxia are good and your body will adapt. But if you are hypoxic any other time, this may represent something bad called tissue hypoxia. Fortunately, it is now possible to easily monitor heart rate and blood oxygen saturation levels with affordable finger pulse oximeters.
In acute exposure to high altitude, your blood oxygen levels will drop because there is less oxygen in the air. For example, if you go up to 10,000 feet (3000 m), the concentration of oxygen in the air is about 15%. A pulse oximeter will show a range of SpO2 from 88 to 92% in most people. Also, there will be an increase in the respiratory and heart rates; and the volume of blood ejected from the heart is reduced (stroke volume). In addition, plasma volume is reduced over 24–48h to improve the oxygen carrying capacity of the blood, and is further improved during a prolonged exposure at altitude through an enhanced erythropoiesis and larger hemoglobin mass, allowing for a partial or full restoration of the blood volume and arterial oxygen content. Most of these adaptations are observed from quite low altitudes, even 3500 feet (1000 m) above sea level. The effects become very prominent at 6000 feet (2000 m). At these higher altitudes, additional adaptations occur, one being a reduction in the maximal heart rate response and consequently a lower peak cardiac output. Thus, despite a normalization of the arterial oxygen content after 4 or more weeks at altitude, the peak oxygen uptake reached after a long acclimatization period is essentially unaltered compared with acute exposure. What is gained is a more complete oxygenation of the blood in the lungs, i.e. the saturation of arterial oxygen is increased.
What to look for in the Masimo Mighty Sat while at Altitude
The first couple of days you want to see a lower SpO2 and an elevated heart and respiratory rate. Increasing the respiratory rate is how you naturally avoid the complications of altitude exposure. This lower level of oxygen stimulates the body to adapt as described above. A SpO2 of 88 to 92% is usually a good number to start off with. Anything higher than that means you are not at a high enough altitude or the pulse oximeter is not functioning. After 2 to 3 days, you can probably go to a higher altitude and the SpO2 may drop even more. This is fine as long as you do not have any symptoms of Acute Mountain Sickness (AMS). With prolonged stays at altitude, most people’s SpO2 stay about the same or increase slightly, it is the heart and respiratory rates that normalize, as well as the person’s ability to perform exercise at altitude.
Pleth Variability Index (PVI)
Using a pulse oximeter that has PVI in high altitude situations can be important for many reasons. You want to know that your body is responding appropriately to lower oxygen levels. Another common problem at high altitudes is dehydration. The Mighty Sat has a parameter called PVI or Pleth Variability Index. It is a complicated measurement, but know that it is a measure of your body’s hydration status. Using the PVI, you can better know if your body is hydrated. For most people, if the PVI is 25 or above, it is safe to say that you should drink more. If it is below 20, you are probably fine.
Respiratory Rate (RR)
Using the RR function of the Mighty Sat, you can better gauge your recovery after higher intensity workouts. At altitude, your RR is going to be elevated anyway as your body demands more oxygen. Knowing your RR after certain workouts can be valuable. For example, if you compare the time it takes your RR to come back to base line after performing a 5 minute interval at sea level and compare this to the same workout at 6000 feet, you will see that your RR takes longer to recover. As you acclimate to higher altitudes, you should be able to observe the time of the recovery of RR drift back towards your baseline if you are adapting appropriately. If you find that you are not adapting at all after a couple of weeks, you may need to take a closer look at what is happening your body. Several things could be going on that is beyond the scope of this article, but inadequate iron intake, underlying sickness, overtraining are all possibilities that should be considered.
There is considerable inter-individual variation in the heart rate response at moderate altitude. The practical importance is that the athletes may train at intensities that are too high if they are guided by solely by heart rate that is not adjusted for the possible change in maximal heart rate. This is reinforced by the fact that the submaximal exercise heart rate response is elevated at low to high altitudes. The reduction in maximal heart rate at more severe levels of hypoxia has been explained by a reductions in the ability of the heart to pump blood to the body.
Johnathan Edwards is a medical doctor with 30 years of sport medicine experience. A former professional athlete in the sport of motocross and a Category 1 bicycle racer, Johnathan understands human performance. He obtained a complete Physiology degree from UC Davis, medical school in Norfolk, VA, Internal medicine in Las Vegas, Sports medicine in Utah, and Anesthesiology in Florida. Today he is a performance coach, clinical instructor, team doctor for many cycling teams, UFC, motocross and Olympic athletes. Husband and father, he aspires to live part time in France and the United States, and riding his bike. Full Disclosure – Johnathan is a consultant for Masimo and the Mighty Sat.