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Rapid ascent to high altitude (2500m or more) can result in the development in High Altitude Pulmonary Oedema (HAPE). Discuss the aetiology and the pathophysiology of HAPE.

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Introduction

Rapid ascent to high altitude (2500m or more) can result in the development in High Altitude Pulmonary Oedema (HAPE). Discuss the aetiology and the pathophysiology of HAPE.

In recent years mountain climbing and mounting trekking has grown in popularity, however there are certain dangers associated with high altitude (2500m or higher) pursuits. It has been known for centuries that there are risks of damaged health to humans by going to high altitudes; with the physiological effects of being at altitude being realised since the 19th century. It has also been known that these effects are as a result of inspiring less oxygen as there is a fall in barometric pressure with altitude (Sonna, 2002) (Figure 1).

(Figure 1). Shows the fall in barometric pressure and PO2 associated with a rise in  

                  altitude.

image00.png

(Lumb, 2000).

As seen from viewing figure 1, both the barometric pressure and inspired PO2 dramatically decrease with an increase in altitude. From sea level (0 m) to 3000m (the typical altitude HAPE develops at) there is a decrease from 760 mmHg to 520 mmHg for barometric pressure, a 140 mmHg / 18.5 % decrease. Inspired PO2 values decrease from 150 mmHg to 100 mmHg, a 50 mmHg / 33.3 % decrease. It is this decrease in oxygen inspiration that causes physiological problems associated with high altitudes.

There

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Middle

4.5

Rennie

Nepal

Maggiorini

Swiss Alps

3650

82

34

27

2.4

Basnyat

Gosaikkund

4300

228

68

-

4.8

Nepal

Cremona

Monte Rosa

4559

262

-

15

0.4

Italy

(Sonna, 2002).

As can be seen from figure 2 the number of people who contract AMS is high with a mean value of 49.5 % ± 14.6 %, however the number of people who then develop   HAPE is relatively low at 2.5 % ± 1.9 %.  

High altitude pulmonary oedema (HAPE) is a subject that has grown in interest in the past 15 years as more people are getting into situations where they may develop HAPE and better scientific techniques such radiographic images, which can specify between other pulmonary oedemas and HAPE (Gluecker et al., 1999) are allowing gradual understanding of the aetiology and pathophysiology of this condition.

The pulmonary circulation main function is to move a good supply of blood from the right ventricle to the alveolar capillaries (blood gas barrier) so gas exchange can occur (Cotes, 1993; West, 2000). This system is disrupted when HAPE occurs as the rise in pulmonary capillary pressure causing interstitial oedema, which disrupts the ventilatory perfusion ratio, the congestion caused by the oedema results in reduced lung compliance and maximum ventilation, hence many patients continually hyperventilate (Cotes, 1993; Maggiorini et al., 2001). Symptoms include those that are similar to AMS, dyspnea, chest congestion, nausea, tachycardia, fever, weakness, coughing, chest infections, sputum upbringing on coughing and

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Conclusion

Gluecker, T., Capasso, P., Schnyder, P., Gudinchet, F., Schaller, M., Revelly, J., Chiolero, R., Vock, P. and Wicky, S. (1999). Clinical and radiologic features of pulmonary edema. Radiographics, 19, 1507-1531. (Abstract).

Hultgren, H. N., Honigman, B., Theis, K. and  Nicholas, D. (1996). High-altitude pulmonary edema at a ski resort. Western Journal of Medicine, 164, 222-227.

Kumar, P. and Clark, M.  (1998). Clinical  Medicine 4th ed . London.: W. B. Saunders.

Lumb, A. B. (2000). Applied Respiratory Physiology 5th ed. Oxford.: Butterworth Heinemann.

Maggiorini, M., Mélot, C., Pierre, S., Pfeiffer, F., Greve, I., Sartori, C., Lepori, M., Hauser, M., Scherrer, U. and Naeije, R. (2001). High-altitude pulmonary edema is initially caused by an increase in capillary pressure. Circulation, 103, (16), 2078 - 2083.

McArdle, W. D., Katch, F. I., and Katch, V. L. (1996). Exercise Physiology: energy, nutrition and human performance 4th ed. Baltimore, MD.: London: Williams & Wilkins.

Roach, R. C., Houston, C. S., Honigman, B., Nicholas, R. A., Yaron, M., Grissom, C. K., Alexander, J. K. and Hultgren. (1995). How well do older people tolerate moderate altitude ? Western Journal of Medicine, 162, 32 - 36.

Scherrer, U., Vollenwider, L., Delabays, A., Savcic, M., Eichenberger, V. and Kleger, G-R. (1996). Inhaled nitric oxide for high altitude pulmonary edema. New England Journal of Medicine, 334, 624 – 629. (Abstract).

Sonna, L. A. (2002). Pulmonary oedema at moderately high altitudes. The Lancet, 359, (9303) 276 – 280.

Taylor, A. E., Rehder, K., Hyatt, R. E. and Parker, J. C. (1998). Clinical Respiratory Physiology. London.: W. B. Saunders.

West, J. B. (2000). Respiratory Physiology: The essentials 6th. Baltimore, MD.: London: Lippincott Williams & Wilkins.

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