PLASTICITY OF HUMAN BODY TO EXTREME CONDITIONS

IS THERE A HUMAN BODY PLASTICITY? WHAT ARE ITS LIMITS?

According to 2 notes written in LaRecherche, a little more than 15 French scientists led by Samuel Vergès (Hypoxia Physiopathology Laboratory of Grenoble, INSERM, University Grenoble Alpes), are  studying now  in La Rinconada-Peru (5100-5300 masl: meters above sea level, city of 50 000 inhabitants, dedicated to mining activity), the effects of hypoxia on sleep, physical exercise, genetics, hematological field and cardiovascular adaptation of this population as well as certain chronic health problems that affect 25% of permanent residents of  La Rinconada. It is known that in Mount Blanc (4807 masl), the oxygen content of the inspired air is scarcely 50% of the existing at sea level, while in the summit of the Everest this gas is barely 28%. It is also known that after a few weeks of adaptation to the environment, most newcomers to hypoxic environments increase their production of red blood cells to better transport oxygen, especially muscle and brain tissue, which are very sensitive to hypoxia. Thanks to these adaptations, more than 250 million people in the world live above 2,500 masl, thousands of permanent residents inhabit cities above 4000 masl in South America, Tibet and the Himalayas, while hundreds of hikers ascend every year up to 4000-5000 masl, without cylinders of oxygen. To adapt to hypoxia, the human body has chemoreceptors (nerve cells), sensitive to changes in blood oxygenation in different body parts, which in case of hypoxia, induce the respiratory and cardiovascular systems to increase their respiratory and cardiac rates, partially compensating for low oxygen pressure, improving arterial oxygenation and increasing blood flow to various organs. 1) So, does the human body in toto dispose of the capacity to adapt to any extreme environment? There are reports of remarkable corporal changes in environments with prolonged weightlessness. 2) What will happen when we will inhabit during several generations: Mars, Ganymede, the Moon, etc. Will we suffer bodily adaptations or genetic adjustments (Bigham A.W. 2018)? 50% of inhabitants who live at sea level and who travel to hypoxic environments of more than 4000 masl and ascend quickly, suffer from acute mountain sickness: headaches, nausea, fatigue, tinnitus that can be disabling and  which however,  can resolve spontaneously or with rest, although in some cases these effects can induce pulmonary or cerebral edema, which could lead to death. There are, however, some differences: some ascend Everest without oxygen cylinders, while others develop pulmonary edema at only 3500 masl. It is argued that some Sherpas and Tibetans would have developed genetic modifications to adapt to hypoxia and that 5 to 20% of permanent residents of high altitude (above 3500 masl), suffer from chronic mountain sickness or, Monge's disease (exacerbated production of red blood cells, promoter of an  increase in blood viscosity, which increases cardiac overload causing serious cardiovascular events, persistent headaches, neurological disorders and alterations in blood flow). With these new studies, Samuel Vergès hopes to answer: 3) why do some and not all residents of high altitude suffer from chronic mountain sickness? To answer this question, Vergès now has an excellent methodological design, advanced techniques, new ideas and an excellent spirit. 4) How does the human body adapt to high-altitude hypoxia? According to Vergès, outlining answers to this question will allow developing strategies to develop better performances in elite athletes, better understand certain extreme lung diseases and even prolong life. There will not be a single answer because it will depend in part on the interindividual peculiarities of   each inhabitant of the Rinconada. According to Vergès although it is considered impossible to live beyond 5000 masl, the residents of La Rinconada have developed physiological adaptations that allow them to tolerate hypoxia, in a more or less acceptable way. For Vergès, high-altitude hypoxia is a challenge for humans, both for residents from sea level, who arrive for the first time at great altitude, and for permanent residents, who have developed adaptations during generations. Preliminary studies of the French scientific team conducted on 800 residents of La Rinconada have identified 25% suffering from chronic mountain sickness. 5) Residents under study, have been divided into 2 groups: a) those who suffer from the effects of chronic mountain sickness with a symptom’score greater than 10 and b) others with few symptoms with different safety profiles at height. 6)  50 residents divided in 2 groups of 25, to whom samples have been taken for genetic, epigenetic, biological and hematological studies. Their states have been evaluated: vascular, cardiac, respiratory and cerebral, including a sleep assessment by means of polygraphy and a stress test. Most of those with chronic mountain sickness show hematocrit values: greater than 80%, being their blood very viscous. 7) With these findings Vergès fears that classical hypothesis (what suggests a direct link between excessively high hematocrit and symptoms of chronic mountain disease), be outdated. First results obtained with ultrasound of many of these inhabitants show a large dilation of  brain and arms arteries, in order to maintain an adequate blood flow in spite of the high blood viscosity, although this adaptation in the long run, may alter the ability of these blood vessels to dilate more, if necessary in some organs (due to the need for oxygen and nutrients). To this respect at the moment it is thought that these arterial dilatations allow to tolerate very high hematocrits and that great dilation of blood vessels could be responsible for the symptoms of chronic mountain disease (without the hematocrit being so important), causing the deterioration of affected people to tolerate certain health problems. The development of sleep apnea induced by hypoxia during sleep could favor the development of pulmonary arterial hypertension. This study  could help to improve blood viscosity, reduce the deleterious effects of the cardiovascular consequences of chronic hypoxia, make recommendations for transient decrease at a lower height, determine the relationship between genetic, epigenetic and physiological specificities by comparing bodily parameters  of Peruvians living at sea  level  ​​with  Peruvians living at different altitudes including those of  La Rinconada with and without high altitude intolerance.