High Altitude - Effects on Respiration and Mountain Sickness - Essay Example

Running head: EFFECTS OF HIGH ALTITUDE High altitude: effects on respiration and mountain sickness Highaltitude: effects on respiration and mountain sickness Before understanding the effects of high altitude on respiration and mountain sickness, it is essential to first understand what high altitude means. "Altitude is defined on the following scale High (8,000 - 12,000 feet [2,438 - 3,658 meters]), Very High (12,000 - 18,000 feet [3,658 - 5,487 meters]), and Extremely High (18,000+ feet [5,500+ meters])" (Curtis, 1995). As a person goes up a higher altitude, both barometric pressure and the partial pressure of oxygen decrease. According to Ward et al (1995), barometric pressure falls to approximately as low as 65 mmHg while oxygen pressure falls to approximately as low as 55% at an altitude of 9000m. The normal barometric pressure is much higher! This means that at a higher altitude, your body must adjust to the lower barometric and oxygen pressure. Other conditions that the body needs to adjust to at high altitude are low air temperature, low humidity and high solar radiation intensity. Failure of the body to adjust to all these can cause fluid accumulation in the lungs and brain and if not treated immediately, this can lead to serious consequences (Curtis, 1995). "For any given energy expenditure, the ventilation (VEBTPS; lmin-1) increases proportionately with altitude. Since barometric pressure decreases, there is less oxygen per volume of gas than at sea level" (Schoene, 2001). As the body receives lesser oxygen as you move higher and higher, the breathing rate must increase. This produces the extra oxygen content required and helps the body adjust to lower volumes of oxygen molecules. This inflow of oxygen by the lungs from the atmosphere and the corresponding outflow of oxygen into the atmosphere is referred to as pulmonary ventilation and hence, it tends to increase with altitude. If pulmonary ventilation is not increased in response to a decrease in the barometric and oxygen pressure, severe repercussions can result on human health. While pulmonary ventilation needs to increase, pulmonary diffusion is not greatly affected at altitude. It is mainly only affected with an increase in workload. As people move to higher altitudes, they may develop a condition called Acute Mountain Sickness. AMS can affect any person, of any gender or age and is promoted by a number of causes but Erba et al. (2004) states that hypoxia seems to a play a major role and can impair the pulmonary gas exchange. This can worsen AMS because effective pulmonary gas exchange is essential at high altitude because of the inadequate oxygen supply available. However, there is still confusion as to whether hypoxia is the major factor for AMS. Therefore, a study was conducted in which "the evolution of breathing patterns and oxygenation over two successive nights at 3,560 m and 4,559 m, respectively, in mountaineers ascending from lowlands to 4,559 m within v24 h were studied. Clinical and physiological observations were compared among mountaineers developing AMS (AMS-group) and those remaining well (controls)" (Erba et al., 2004). These observations were based on measurements such as cycle time of periodic breathing, heart rate, rest time, estimated sleep efficiency, number of oxygen saturation dips, etc. The study was successful in proving the hypothesis that hypoxia is indeed a major factor in the promotion of AMS. The study revealed that compared to the controls group, the AMS group depicted a lower sleeping efficiency, higher number of oxygen saturation dips and higher heart rate when ascending to a higher altitude. Therefore, Erba et al. (2004) concluded that "nocturnal hypoxemia unrelated to hypoventilation but likely due to impaired pulmonary gas exchange is the major determinant of AMS." The maximal oxygen uptake also decreases as altitude increases. According to McArdle et al, (2001) “VO2max decrease linearly at a rate of approximately 10% per 1,000-m increase in altitude.” VO2max is basically the point at which the oxygen consumption stops increasing with an increase in exercise or any other exhaustive activity. Once this point is achieved, VO2max may remain stable or start falling. As high altitude is reached, VO2max starts falling. This is because as you travel higher and higher, a point arrives where your heart rate reaches a maximum and cannot rise any further, thereby causing the oxygen consumption to decline too as less and less oxygen is delivered by the blood to the muscles. While there are respiratory responses to altitude, there are also cardiovascular responses. As high altitude is reached, an initial decrease in plasma volume is experienced. A decrease in plasma volume indicates lesser red blood cells per unit. In fact, Pugh (1964) found a 21% reduction in blood plasma after 18 weeks at altitude above 4000m in four members. Initially as a person goes up a high altitude, heart rate increases to be able to adjust the body for the lesser supply of oxygen available but as the person goes up even higher and higher, heart rate begins to decrease which limits oxygen delivery and uptake, resulting in hazardous consequences if not treated properly and immediately. Since less oxygen supply is available at higher altitudes because of the decrease in oxygen molecules as a person travels higher and higher, people will not be able to achieve their maxVO2 level and hence, endurance activities will tend to be affected at high altitude. In fact, "Above 1600 m Vo2 max decreases approximately 11% for every 1000 m" " (Wilmore, Costill, 1994). Therefore, athletes performing exhaustive and endurance activities may experience an impaired sports performance at high altitude. However, such people can perform training to allow a boost in their performance at high altitude. These training sessions are aimed at boosting the VO2max level. According to Smith (2005), "The theory behind High Altitude Training (HAT) is that if you can adjust your body to perform at competitive levels with less oxygen in your blood and muscles, then when you travel to sea level to compete you should have a higher level of endurance." These training sessions begin at high altitude and weeks prior to the actual game and comprise repeated practice sessions aimed at the athletes getting used to lower levels of oxygen (Smith 2005). Although endurance activities are significantly affected at high altitude, anaerobic activities that last less than 2 minutes are not significantly affected. This is because "The thinner air at altitude provides less aerodynamic resistance and less gravitational pull, thus potentially improving sprinting, jumping, and throwing events" (Wilmore, Costill, 1994). According to Hannon et al (1968), at altitude, plasma volume decreases, resulting in more blood cells and thus more hemoglobin for a given volume of blood which increases the viscosity and oxygen carrying capacity of blood. Also, according to Wilmore and Costill (1994), "Within the first few hours of arrival at altitude, a persons plasma volume begins to progressively decrease and it plateaus by the end of the first few weeks." It can go on to decrease up to as much as 25% but if the person is provided with appropriate fluids then the plasma volume can return to normal (Wilmore, Costill, 1994). However, as more and more days are spent at altitude, the hemoglobin and hematocrit content in blood reach their peaks and eventually start declining. Some of the common mountain sicknesses that may result from high altitude are Acute Mountain Sickness (AMS), High Altitude Pulmonary Edema (HAPE) and High Altitude Cerebral Edema (HACE). The most common of them is the AMS. Symptoms do not start immediately after reaching a high altitude but a few hours after it. In fact, King & Robinson (1972) stated that development of AMS was associated with a failure to increase ventilation during the first 6 hours at altitude of 4267m. If the symptoms of AMS are prolonged, acute or mild AMS may transform into severe AMS where excessive fluid builds up into the lungs and the person may experience difficulty in carrying out the normal activities of life. Severe AMS can only be treated by immediately moving from a high to a low altitude. However, even severe AMS is not so severe when compared to HAPE and HACE. HAPE is a disease that requires immediate medical attention. In cases where adequate medical attention is not provided, this disease can lead to disastrous effects on human health, ultimately leading to respiratory problems and in some cases, even death. This disease generally occurs when fluid accumulates in the lungs, causing breathing difficulties. Treatment of HAPE also requires that the affected person be brought to a lower altitude as soon as possible. Unlike AMS and HAPE, HACE does not result from spending a few hours at high altitude, but after several days. Therefore, it is the most severe form of mountain sickness, evident from the fact that it results when the tissues in a human brain swell due to continuous leakage of the fluid. Although medication can reduce the severity of the symptoms, proper medical attention and descending to a lower altitude are necessary. To sum up, effects of high altitude on respiration and mountain sickness can be hazardous and can even lead to death. Therefore, immediate medical attention is compulsory. References 1. Curtis, (1995). Outdoor Action Guide to High Altitude: Acclimatization and Illnesses. Princeton University Outdoor Action. 2. Erba, P., Anastas, S., Senn, O., Maggiorini, M., & Bloch, K.E. (2004). Acute mountain sickness is related to nocturnal hypoxemia but not to hypoventilation. European Respiratory Journal. 24, 303-308. 3. Hannon et al (1968) 4. King, AB., Robinson, SM.,(1972).Ventilation response to hypoxia and acute mountain sickness 5. McArdle, D., Katch, I., Katch, L., (2001). Exercise physiology: energy, nutrition and human performance. Philadelphia ; London : Lippincott Williams & Wilkins 6. Pugh, L. (1964).Blood volume and hemoglobin concentration at altitude above 18000ft. J.physio L. 70,344-45 7. Schoene, B. (2001).Limits of human lung function at high altitude. The Journal of Experimental Biology. 204, 3121-3127. 8. Smith, Stew (2005). High Altitude Training. Military.com 9. Ward, P., Milledge, S., & West, B. (1995). High altitude medicine and physiology. London: Chapman and Hall Medical. 10. Wilmore, H., Costill, L., (1994). Physiology of sport and exercise. Champaign, Ill. : Human Kinetics Publishers Read More