My visit to Zion National Park in May included a not to be missed up to Angels Landing, a 4 hour round trip hike that would make a vertical climb of 1500 feet. Using controlled breathing techniques (pursed lip breathing) improved my stamina and overall enjoyment.
Making an ascent to higher altitudes imposes a strain on breathing due to lower barometric pressure. The fractional concentration of oxygen is the same whether one in San Francisco (sea level) or in Denver, (about 21% in ambient air). It is the weight of atmospheric pressure at sea level (760mmHg) that makes it easy for O2 to get from the surrounding air to the lungs where O2 diffuses into the bloodstream.
The higher a person ascends, especially of it is a quick trip, the more likely it is that person will experience the effects of altitude. The degree and severity depend on the person's baseline level of health and fitness and of of course the feet above sea level. One may notice fatigue, rapid heart rate, headache, sleep disturbances, nausea and if at extremely high altitudes, dangerous signs of pulmonary edema can occur. These symptoms can be ameliorated by descent and/or administration of supplemental O2.
So how is it that great explorers can make the trek atop Everest (alt. 29,000 ft.) . How do people survive in the Andes? And what can the average person do to improve their exercise tolerance while vacationing at Lake Tahoe? It would take a long journey into cardiopulmonary physiology to explain these mysteries. The most valuable thing to understand, I think, is how to use paced and pursed lip breathing. Pursed lip breathing works by slowing down the respiratory rate and allowing a greater efficiency of gas exchange and air volume to take place throughout the respiratory cycle. Also the narrower opening at the mouth creates a back pressure that is transmitted to the lungs leading to longer air distribution times, lessening of airway collapse and increasing oxygen levels in the blood.
The technique is simple: just purse the lips as if to whistle and blow out gently at regular expiratory volume. You will notice it takes a bit longer to exhale. Get the sense of pacing the breath by using a counting ratio for inhale/exhale. For example: inhale for 2 , exhale for 4.
During extreme exertion one may need to open the mouth for inspiration and use a 1:1 ratio. Inhaling through the mouth decreases resistance to inspired air, but offers no opportunity for humidification. So in addition to perspiration, and the exposure to dry air often at high altitudes, this makes it important to maintain good hydration.
I would love to discuss more at some point in the future. Don't hesitate to contact me with questions. Remember, if you are planning travel to high places this summer, bring lots of water and focus on your breathing.