Fifth part
CARDIOVASCULAR EFFECTS OF STAY AND TRAINING IN HEALTH
In addition to the strictly physiological aspects concerning athletic performance, an interesting aspect for the sports cardiologist is that concerning the possible cardiovascular effects of stay and training at height . The regular practice of physical exercise reduces morbidity and mortality due to cardiovascular diseases depending on the type, frequency, duration and intensity of physical activity, and it is reasonable to suppose that also the environmental conditions in which it is usually performed can play a significant role.
To summarize these concepts, we can say that hypoxia, however induced, is an effective erythropoietic stimulus, although the individual response appears variable. The hematological, muscular and respiratory adaptations resulting from this stimulus allow the athlete to increase his ability to transport oxygen and use it in the periphery. The ideal beneficiary of these practices is the endurance athlete, in whom the increase in aerobic power is followed by the improvement of the competition performance. On the other hand, the values of Hb and Hct reached are not very high, and in any case not such as to suggest a thrombotic risk. Physical activity at high altitudes would seem to be able to further reduce the risk of cardiovascular disease compared to physical exercise alone (but these data, extremely favorable for mountain people and mountain tourism and for us poor sailors, must be confirmed).
PHYSIOLOGY OF ALTITUDE
As the altitude increases, the air that reaches the alveoli contains less oxygen. Carbon dioxide partial pressures do not change much in absolute terms as this gas is only a small component of air.
As the alveolar P o2 decreases with altitude, the arterial P co2 decreases in turn, resulting in a condition known as hypoxemia. With low levels of oxygen in the blood, less oxygen is available to the tissues, resulting in hypoxia (decreased oxygen in the tissues). The degree of hypoxia depends on the altitude and how long the person has remained.
Initially hypoxemia gives rise to compensatory responses in an attempt to restore arterial P o2 . If P o2 falls below 60 mmHg, peripheral chemoreceptors are activated and the respiratory center increases ventilation. However, if the ventilation increases too much compared to the metabolic request, both the arterial P co2 and the concentration of hydrogen ions in the blood will decrease, causing a decrease in the activation of both peripheral and central chemoreceptors and thus counteracting the effects of the low concentration of oxygen. A state of respiratory alkalosis is then established . With a decrease in the acidity of the blood, there is a shift to the left of the hemoglobin dissociation curve (increased affinity). An increase in affinity means that less oxygen is released into the tissues, but it also means that more oxygen is linked to hemoglobin in the lungs.
If the stay at high altitudes lasts for a few days, the body starts to acclimatize. The kidneys help maintain the acid-base balance by producing bicarbonate to compensate for the loss of hydrogen ions that accompanies the reduction of arterial PCo2. If the stay lasts a long time, other acclimatization phenomena occur. In response to hypoxia, the kidneys secrete the hormone erythropoietin, which stimulates the synthesis of erythrocytes, resulting in an increase of up to 60% of the hematocrit, a condition indicated with the term polycythemia. With the increase in the number of erythrocytes there is an increase in the concentration of hemoglobin in the blood, therefore an increase in the oxygen carrying capacity of the blood.
Following exposure to low oxygen levels, oxyhemoglobin levels decrease, causing an increase in erythrocyte production of 2.3 DPG. The 2, 3DPG decreases the affinity of hemoglobin for oxygen, increasing the release of oxygen to the tissues and counteracting the effects of alkalosis.
Sometimes, staying at high altitudes is not tolerated by the body and the so-called chronic mountain sickness can develop . Initial symptoms include headache, dizziness, tiredness and shortness of breath. This pathology can worsen to cause disorientation and heart attacks. The symptoms of altitude sickness are mainly caused by hypoxia and polycythemia. Pulmonary vasoconstriction can also occur, forcing the right side of the heart to work more because of greater resistance.
Precautions and contraindications of altitude training
The heart patient may be at risk if exposed to high altitude due to the inability of the heart to adjust its performance in response to the stimulus generated by the reduced availability of oxygen. But from the experience reported by the various authors it can be stated that cardiac patients can resume attending the mountain at altitudes lower than 3000 meters, provided that certain rules are respected. First of all, an accurate clinical evaluation is recommended which establishes, through specific instrumental examinations, the patient's state of health, the conditions of function of his heart and the adequacy of the therapy. It is also advisable to limit physical activity during the first days of stay at altitude during the acclimatization process; reduce the amount of effort and avoid physical activity in unfavorable weather conditions (very cold, windy or very hot and humid days); pay attention to any problems that may arise during exertion or immediately afterwards (angina, dyspnoea, dizziness, excessive fatigue); not doing physical activity alone, not suspending the therapy in progress, avoiding the aspects of physical activity that involve a strong muscular commitment and an intense emotional stimulus. For lovers of alpine skiing it is advisable to avoid the rapid ascent at high altitude with the cable car and the rapid descent several times a day. It is better to give up a day in the mountains rather than having to then regret it.
Before starting a training period in altitude it is good to restore the Iron deposits, especially in those athletes with reduced blood values. In fact, athletes with Fe ++ deficiency are unable to increase red blood cells in response to altitude.
MOISTURE
Maintaining a normal altitude hydration is a very positive element for high-altitude sports performance: in fact it helps eliminate the risks associated with dehydration without affecting the transport of oxygen to the tissues.
TRAINING AND LIFE IN ALTITUDE
Controlled studies on subjects who spent a long period in altitude living and training at moderate altitudes have never been able to demonstrate an effective improvement in sea level performance. This method is valid if the training is done at high altitude.
DO NOT TAKE THE ATHLETE TO THE MOUNTAINS, BUT TAKE THE MOUNTAIN TO THE ATHLETE
Recently, an alternative method has been developed, able to provide a hypoxic stimulus "at home": the so - called hypoxic-hypobaric tents. These are closed structures in which the athlete stays for a few hours a day (usually night ones) breathing air in which the partial pressure of oxygen has been artificially reduced. This method is certainly cheaper than the traditional one and easier to use, but there are currently considerable discussions about its lawfulness.
Short hypoxic exposures (1.5-2.0 hours) are sufficient to stimulate the release of EPO, therefore to increase red blood cells.
LIVE IN QUOTE AND TRAINING AT THE LEVEL OF THE SEA
This strategy combines acclimatization at a moderate altitude (2500m) with training at a lower altitude (1200m) and has proven to be able to improve sea level performance for 8-20 minutes.
TYPES OF EXPOSURE: 3 GROUPS
1. It lives at 2500m, it trains at 1250m (High-Low)
2. Lives at 2500m, trains at 2500m (High-High)
Both groups living at 2500m show an increase in EPO, erythrocyte volume and Vo2max. Although the VO2 max has increased in both groups living at 2500m, only the group that performed the low-level training sessions has improved the time on the 5000m by 1.5%.
3. Lives and trains at sea level on a similar terrain type. (Low-Low)
The High-Low subjects are able to maintain both the training speed and the peripheral oxygen flow during intense training sessions (= 1000m of running at 110% of speed compared to the 5000m race speed) which are fundamental for the performance of athletes competing in running races.
The High-High subjects during intense training sessions ran at lower speeds, with lower oxygen consumption, a lower heart rate and a lower lactate peak.
While High-Low athletes are able to maintain the buffer capacity of their muscles, this does not happen in High-High athletes.
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Edited by: Lorenzo Boscariol
