As I arrived in Denver (5280′), and ultimately Frisco, CO (9000′), the first physical symptom I noticed from the high-altitude environment was dyspnea on exertion. On flat ground I didn’t feel any different than at home in New Jersey, but as soon as I began to climb stairs or hike the beautiful trails in the area, I quickly became winded. I had already read about the common symptoms of high-altitude acclimation and knew this was normal and was on the lookout for headache, nausea, or dizziness. I noticed my resting heart rate was elevated and told myself this was also normal because the low-oxygen environment required my heart to work harder to keep my pulse oxygen levels up. I already owned a pulse oximeter that I had bought during my time working with COVID patients in the Emergency Room on a previous rotation. I checked that within my first week and was initially disappointed that it was averaging around 91%, but soon found out this was also normal, especially since I was still acclimating. My Apple watch trended data over time on my heart rate and I noticed a tremendous difference in my resting HR compared to home.

I landed on May 2^nd, 2021 and I think the graphs above make that quite evident. My walking HR was even more noticeably elevated. “The initial cardiovascular response to altitude is characterized by an increase in cardiac output with tachycardia … after a few days of acclimatization, cardiac output returns to normal, but heart rate remains increased”¹

My persistently elevated heart rate caused me to feel anxious when hiking or doing other physical activity, and that anxiety in turn raised my heart rate even more. I had experienced PVC’s in the past which occurred only a few times a month, nowhere near the threshold for treatment, and had been reassured they were totally benign. On a hike during my first week in Colorado I experienced a few of these “skipped beats” followed by rapid heart rate and had to talk myself down from the anxiety it caused. This is what prompted me to research the effect of altitude on anxiety. “Adrenergic centers in the medulla are activated in acute hypoxia and augment the adrenergic drive to the organs.”² It seems as though the body’s compensatory mechanisms to physiological changes can be accompanied by unwanted mental health disturbances. This is especially true for people in the early stages of shifting from low altitude to high altitude. During the adjustment period individuals are most susceptible to new-onset anxiety disorders, but even those living long-term at high altitude are at increased risk of psychiatric ailments.⁴ In fact, living in high-altitude environments has been associated with serious mental health implications not limited to anxiety disorders, including depression and increased suicidality.⁴ This has been evidenced by statistically significant changes in PHQ-9 Total Score, PHQ-9 suicidal ideation, and GAD-7 Total Score.⁴

Sleep disturbances have often been faulted for these increases in anxiety and depression at high altitude, and although I didn’t have any formal sleep studies done while in Colorado, I felt well-rested and didn’t notice a change in my sleep at altitude.³ One hypothesis that could explain these findings and my personal experience, is that hypoxia has an inverse relationship with serotonin.⁴ Because oxygen is a requirement for the creation of serotonin, living somewhere with decreased oxygen could lead to deficiency. Serotonin has an expansive role in the human body, playing a role in cognition, sleep, mood, digestion and other crucial aspects of life. Low levels of this neurotransmitter have been implicated as a cause for depression and accordingly many of our best antidepressant medications like SSRI’s and SNRI’s work on these pathways. There is also a “chicken or the egg?” argument to be made. Is the anxiety brought on due to hypoxia which in turn causes somatic symptoms like palpitations, shortness of breath, and presyncope; or do these symptoms caused by hypoxia come first, resulting in anxiety and panic attacks? For example, hyperventilation, a well-known provocative factor of panic attacks, is also a response to altitude changes. Hypoxia leads to hypocapnia, which can ultimately lead to respiratory alkalosis.⁵ Although there are multiple hypotheses for these mental health changes, there does seem to be an agreement in the literature that they do exist.

Luckily, in my experience, my body adjusted over the span of a few weeks. My HR began to trend down towards my normal resting rate in the 70’s and my anxiety levels also dropped. I started doing more challenging hikes, traveling and enjoying the many natural wonders Colorado has to offer. Just being in amazing places like Rocky Mountain National Park and the San Isabel National Forest had a profound impact on my mood as I soaked in the scenery. I took pictures, breathed fresh mountain air and spotted wildlife, which all served to distract me from my worries. The mood-altering benefits of exercise also likely played a role in my increasing happiness. I grew to love the state and as soon as I felt fully adjusted, it was time to go back to New Jersey. Back to sea-level, outrageous humidity and hotter weather.

References:

1. Naeije R. Physiological adaptation of the cardiovascular system to high altitude. Prog Cardiovasc Dis. 2010 May-Jun;52(6):456-66. doi: 10.1016/j.pcad.2010.03.004. PMID: 20417339.
2. Richalet JP. Physiological and Clinical Implications of Adrenergic Pathways at High Altitude. Adv Exp Med Biol. 2016;903:343-56. doi: 10.1007/978-1-4899-7678-9_23. PMID: 27343107.
3. Bian SZ, Zhang L, Jin J, Zhang JH, Li QN, Yu J, Chen JF, Yu SY, Zhao XH, Qin J, Huang L. The onset of sleep disturbances and their associations with anxiety after acute high-altitude exposure at 3700 m. Transl Psychiatry. 2019 Jul 22;9(1):175. doi: 10.1038/s41398-019-0510-x. PMID: 31332159; PMCID: PMC6646382.
4. Kious BM, Bakian A, Zhao J, Mickey B, Guille C, Renshaw P, Sen S. Altitude and risk of depression and anxiety: findings from the intern health study. Int Rev Psychiatry. 2019 Nov-Dec;31(7-8):637-645. doi: 10.1080/09540261.2019.1586324. Epub 2019 May 14. PMID: 31084447.
5. Roth WT, Gomolla A, Meuret AE, Alpers GW, Handke EM, Wilhelm FH. High altitudes, anxiety, and panic attacks: is there a relationship? Depress Anxiety. 2002;16(2):51-8. doi: 10.1002/da.10059. PMID: 12219335.

Joseph Albanese is a second-year physician associate (PA) student attending Drexel University in Philadelphia, Pennsylvania. He grew up in Hillsborough, NJ. He got his BA from The Pennsylvania State University as a double major in Psychology and Film Studies. Prior to PA school he worked as a mental health associate in an inpatient psychiatry setting with actively suicidal and homicidal patients. The acuity of the unit he worked on made him appreciate the benefits of talk-therapy, but also the crucial role of medicine in many cases. This led him to apply to PA school. In his free time Joe loves to travel (favorite places include Japan, Iceland, Glacier National Park, and now Colorado). He also enjoys photography, playing sports, and eating new foods.