Physiological Effects of Altitude on Respiratory System
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This presentation discusses the physiological effects of altitude on the respiratory system. It covers the partial pressure of oxygen, haemoglobin saturation, and the pathophysiological mechanism of HAPE. It also provides information on the prevention and treatment of HAPE.
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PHYSIOLOGICAL EFFECTS OF ALTITUDE ON RESPIRATORY SYSTEM Name of the Student Name of the University Author Note
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Introduction •Everest Base Camp is located at an altitude of 5364m or 17,600ft above sea level. •The atmospheric pressure at this altitude is 401 mmHg. •The physiological fluctuations, taking place in the body while high- altitude trekking is known as acclimatisation (Smith et al., 2017).
Partial Pressure of Oxygen •With an increase in vertical height, a non-linear decrease in barometric pressure can be observed. •The percentage of oxygen present in that altitude is same, i.e. 21%. However, with the decrease in barometric pressure, which is 401mmHg, the oxygen level decrease and it becomes 53% of the availability at sea level. •PATO2=(PAtm– PH2O) FiO2– PaCO2/ RQ Where PATO2= Partial Pressure of Oxygen in the Alveoli PAtm= Atmospheric Pressure PH2O= Partial Pressure of water FiO2= Fraction of Inspired Oxygen PaCO2= Partial Pressure of Carbon Dioxide in the alveoli RQ = Respiratory Quotient
Figure 1 Source: (Grocott et al., 2013) Calculations •The following formula can calculate the oxygen content of arteria or CaO2. CaO2= (SaO2 x 1.34 x Hb x 0.01) + (0.023 x PaO2 in kPa) Where, SaO2 = Arterial oxygen saturation (%) 1.34 = Huffner’s constant (milliliters of oxygen carried by 1 g of Hb in vivo) 0.023 = solubility coefficient of oxygen
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Partial Pressure and Haemoglobin Saturation •The mean partial arterial pressure of O2at the altitude of 5300m is 50±3 mmHg. •Haemoglobin saturation (SPO2) at this arterial pO2is over 80% (Grocott et al., 2013). •A central alkaline environment is produced when CO2is washed out due to delivery of cerebral oxygen in case of arterial hypoxemia, stimulated by increased cerebral blood flow (Sarkar, Niranjan & Banyal., 2017). Figure 2: Oxy–hemoglobin dissociation curve Source: (Baumstarket al.,2019)
Physiological Response To Changes & HAPE •The individuals need to allow sufficient time to let their bodies acclimatised or otherwise would suffer from acute high-altitude illness (Casey et al., 2019). •Faster breathing is quite normal when the ascent is quick, however, breathlessness while resting mean that the lungs are incapable of providing sufficient oxygen to the blood and indicates the development of High Altitude Pulmonary Edema (HAPE).
Factors Causing HAPE •HAPE is a severe high-altitude sickness that can get fatal. HAPE is thought to occur secondary to hypoxia and is a type of non-cardiogenic pulmonary edema (Jensen & Vincent., 2018). •Following are the few factors causing HAPE: a)Stress failure and leaks in capillary walls b)Elevated pulmonary artery pressure c)Elevated hypoxic pulmonary vasoconstriction
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Pathophysiological Mechanism of HAPE •Two major pathophysiological mechanisms are accounting for pulmonary hypertension. •First is regional over perfusion of capillaries in zones of low arterial vasoconstriction caused by inhomogeneous pulmonary vasoconstriction. •Second is pulmonary vein level hypoxic constriction, which increases the resistance downstream of fluid filtration region (Griva et al., 2017). •Excessive hypoxic pulmonary vasoconstriction of small veins and arteries leads to distension of vessel walls, which then opens up cellular junctions and causes stress failure of alveolo-capillary membrane (Dunham-Snary et al., 2017)
Signs of HAPE •While travelling to high altitude, the body will first experience minute ventilation, which results in respiratory alkalosis. •After TBC 2,3-DPG levels start increasing, the Hgb-O2dissociation curve shifts to the right (decreased O2affinity by hemoglobin) (Baumstark et al., 2019). This allows the stressed tissues (due to trekking) to get more oxygen. •The various signs that the trekkers should look out for are shortness of breath while at rest, dyspnea, clammy skin, blue-tinged lips, a blood-tinged cough that has frothy sputum and palpitations.
Prevention & Treatment •When signs of HAPE are recognized, one should stop their ascend uphill to give appropriate time to body for acclimization. •Supplement oxygenation and treatment with 20mg nifedipine, if medications are available. •The foremost priority should be a rapid descent.
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Conclusion •Partial pressure of oxygen (pO2) decreases with the increase in height. •At the altitude of 5300m, where the Everest Base camp is situated, only 53% of oxygen is present, compared to that in sea level. •If the ability to acclimatize fails, severe disorders like HAPE (High Altitude Pulmonary Edema) can occur. •Dyspnea, cyanosis and rales can develop if HAPE is left untreated. •To prevent HAPE, one has to gradually ascend and give proper time to the body to acclimatize. •Once the signs of HAPE are confirmed, one should stop ascend.
References Baumstark, A., Pleus, S., Jendrike, N., Liebing, C., Hinzmann, R., Haug, C., & Freckmann, G. (2019). Proof of Concept Study to Assess the Influence of Oxygen Partial Pressure in Capillary Blood on SMBG Measurements.Journal Of Diabetes Science And Technology, 193229681983336. doi: 10.1177/1932296819833369 Breitnauer, N., Bush, D., Stillwell, P. C., & Carpenter, T. (2016). A Case Of Pulmonary Edema At Moderate Altitude: Extending The Spectrum Of Hape?. InC62. PEDIATRIC CASES I(pp. A5627-A5627). American Thoracic Society. Casey, J., Janz, D., Russell, D., Vonderhaar, D., Joffe, A., & Dischert, K. (2019). Bag-Mask Ventilation during Tracheal Intubation of Critically Ill Adults.New England Journal Of Medicine,380(9), 811-821. doi: 10.1056/nejmoa1812405 Dunham-Snary, K. J., Wu, D., Sykes, E. A., Thakrar, A., Parlow, L. R., Mewburn, J. D., ... & Archer, S. L. (2017). Hypoxic pulmonary vasoconstriction: from molecular mechanisms to medicine.Chest,151(1), 181-192.
Griva, K., Stygall, J., Wilson, M. H., Martin, D., Levett, D., Mitchell, K., & Edsell, M. (2017). Caudwell Xtreme Everest: A prospective study of the effects of environmental hypoxia on cognitive functioning.PloS one,12(3), e0174277. Grocott, M., Martin, D., Levett, D., McMorrow, R., Windsor, J., & Montgomery, H. (2013). Arterial Blood Gases and Oxygen Content in Climbers on Mount Everest.New England Journal Of Medicine,360(2), 140-149. doi: 10.1056/nejmoa0801581 Jensen, J. D., & Vincent, A. L. (2018). High Altitude Pulmonary Edema (HAPE). InStatPearls [Internet]. StatPearls Publishing. Sarkar, M., Niranjan, N., & Banyal, P. K. (2017). Mechanisms of hypoxemia. Lung India: official organ of Indian Chest Society, 34(1), 47. Smith, Z. M., Krizay, E., Sá, R. C., Li, E. T., Scadeng, M., Powell Jr, F. L., & Dubowitz, D. J. (2017). Evidence from high-altitude acclimatization for an integrated cerebrovascular and ventilatory hypercapnic response but different responses to hypoxia.Journal of Applied Physiology,123(6), 1477-1486.