SIMULATION OF THE RELATIONSHIP BETWEEN EXERCISE AND CARDIOPULMONARY FUNCTION AT HIGH ALTITUDE

Introduction: Due to various uncertain and unexpected factors in life such as diseases, natural disasters, traffic accidents, and congenital disabilities, the number and proportion of lower limb amputations are still rising for many reasons, so the research on lower limb prostheses is particularly important. Objective: This work aimed to study the relationship between altitude exercise and cardiopulmonary function. Methods: A model of abnormal changes in cardiopulmonary function was established, and then 40 plateau exercisers were selected, all of whom arrived in Tibet in March 2017. The relationship between pulmonary circulation volume and internal pressure in the chest was observed and compared. The relationship between cardiopulmonary sensory reflex and exercise (high altitude) breathing and heart rate was analyzed. A comparison of the cardio-pulmonary function of subjects of different genders was implemented. Moreover, the influence of different altitudes on the subjects’ cardiopulmonary function and the subjects’ cardiopulmonary function changes before departure and during the first, second, and third week after departure were observed and compared. Results: I. As the pressure in the thoracic cavity increased, the subjects’ pulmonary circulation blood volume gradually decreased, and the decrease was most obvious in the stage of thoracic pressure -50 to 0. II. As the cardiorespiratory reflex coefficient increased, the subjects’ breathing and heart rate compensatory acceleration appeared. III. Tracking and monitoring of the subjects’ cardiopulmonary indicators revealed that with the increase in altitude, the subjects’ average arterial pressure, respiratory frequency, and heart rate all showed an upward trend, while the blood oxygen saturation value showed a downward trend. IV. No matter how high the altitude was, the average arterial pressure, respiratory rate, and heart rate monitored of the subjects under exercise were significantly superior to the indicator values under resting state. In contrast, the blood oxygen saturation value showed the opposite trend. V. The subjects’ average arterial pressure, respiration, and heart rate in the first week were higher than other periods, but the blood oxygen saturation was relatively lower. In the second and third weeks, the changes in cardiopulmonary function were relatively smooth (all P<0.05). VI. The changes in the index of the cardiopulmonary function of subjects of different genders were small (p>0.05). Conclusion: Through modeling, the results of the plateau environment on the cardiopulmonary function of the body were made clearer, and these research data provided theoretical references for the training of the sports field in the plateau area. Level of evidence II; Therapeutic studies - investigation of treatment results.


INTRODUCTION
Altitude exercise refers to exercise in areas above 500 meters above sea level.The plateau terrain is relatively flat, and there are large undulating areas.Due to its high altitude, low air pressure, and low oxygen content, this special environment is more conducive to improving people's physical strength and endurance quality, so as to help athletes maximize their inner potential. 1,2xercising in a plateau environment has the greatest impact on the exerciser's cardiopulmonary function, and the improvement of the athlete's physical fitness depends to a high degree on the improvement of the cardiopulmonary function.It can provide a reliable theoretical basis for exercisers by analyzing the relationship between the them. 3n previous studies, it was found that most researchers performed statistical analysis on the physiological response results of exercisers under altitude exercise without establishing a model, making the research results more limited.The emergence of an analysis model of abnormal interaction changes that can consider cardiopulmonary function parameters made this research enter a more specialized level. 4,5Therefore, an analysis model of abnormal changes in the interaction of cardiopulmonary function was established in this research, and 40 plateau exercisers were selected as the research object.A simulation study on the relationship between altitude exercise and cardiopulmonary function was carried out, aiming to provide a reference for the sports world or subsequent research.The following reports were made.

Principles of modeling the relationship between altitude exercise and cardiopulmonary function
The most important part of establishing the relationship model between altitude exercise and cardiopulmonary function was the setting of physiological parameters, which mainly referred to the parameters of cardiopulmonary function.Among the cardiopulmonary function parameters, the important indicators included cardiopulmonary oxygen uptake (Po 2 ), carbon dioxide emissions (Pco 2 ), and heart rate (HR).In addition, there are ventilation volume per unit time (Pa), oxygen pulse (O 2 P), etc.The calculation equations were as follows.Maximal oxygen uptake: Cardiopulmonary oxygen uptake: Oxygen pulse: MN represents the output of each pulse, and LT represents the difference in oxygen content between arteries and veins.Oxygen pulse can measure the athlete's ventricular function.Maximum heart rate: Studies believed that the person's age had the greatest impact on heart rate.Athlete's breathing entropy in altitude sports: Respiration entropy expresses the oxygen exchange rate of athletes during breathing.

Model of abnormal changes in cardiopulmonary function interaction
When athletes exercise in the plateau area, their heart and lung excitement is much higher than that in the plain area.Usually, the excitement of the heart and lung receptors will reduce the tension of the foot shaft, while the tension of vagus nerve of the heart will increase, reducing the heart rate and blood pressure.The relationship between intrathoracic pressure and cardiopulmonary receptors can be described by the following equation.

Research objects
40 plateau athletes were selected, all of which arrived in Tibet in March 2017.Among them, there were 21 males and 19 females; aged 27 to 36 years old, with an average of (31.32±1.93)years old; average body weight (62±7) kg.The occupations of the included persons were all ordinary employees, they had no history of plateau tourism in the past six months, and didn't perform strong physical labor.They had no previous history of cardiopulmonary diseases, no infectious diseases, neurological diseases, etc., The physical examination indicators before being included in the study were all normal.The exercise route of all research objects was Lhasa-Nyingchi area (2000m above sea level).

Research methods
Giving the difficulty of collecting specimens in plateau areas, not every subject adopted the method of non-invasive detection method.The monitored indicators included heart rate, blood pressure, respiration, and blood oxygen saturation.

Observation indicators
I. The relationship between pulmonary circulation volume and the internal pressure of the chest.II.The relationship between cardiopulmonary sensory reflex and exercise (high altitude) breathing and heart rate.III.Cardiopulmonary function comparison of subjects of different genders, including mean arterial pressure, respiration, pulse, and blood oxygen saturation.IV.The effects of different altitudes on the subjects' cardiopulmonary function, including mean arterial pressure, blood oxygen saturation, heart rate, and respiration.V.The subjects' cardiopulmonary function changes before departure and the first, second, and third weeks after departure.All were monitored at 8:00 in the morning.

Statistical methods
SPSS 21.0 version software was employed for data analysis, and P<0.05 was deemed as statistically significant.( s x ± ) was how measurement data were expressed, which were tested by t test.

The relationship between pulmonary circulation volume and intrathoracic pressure
Statistics showed that with the increase of intrathoracic pressure, the subjects' pulmonary circulation blood volume gradually decreased, and the decrease in thoracic pressure -50 to 0 was the most obvious, with considerable differences (p<0.05)(Figure 1).

The relationship between cardiorespiratory reflex and exercise (high altitude) breathing and heart rate
According to statistics, with the increase of the cardiorespiratory reflex coefficient, the subjects' respiration and heart rate compensatory acceleration appeared, the difference was statistically substantial (p<0.05)(Figure 2).

Cardiopulmonary function comparison of subjects of different genders
According to statistics, the changes in the indicators of cardiopulmonary function of subjects of different genders were small, and the difference wasn't obvious (p>0.05)(Figure 3).

The influence of different altitudes on the subjects' cardiopulmonary function
According to statistics, no matter how high the altitude was, the average arterial pressure, respiratory rate, and heart rate monitored of the subjects under exercise were notably higher than the indicator values under resting state, while the blood oxygen saturation value showed the opposite trend.With the increase in altitude, the subjects' average arterial pressure, respiratory rate, and heart rate all showed an increasing trend, while the blood oxygen saturation value showed a decreasing trend, with substantial differences (p<0.05)(Figure 4-6).
The subjects' cardiopulmonary function changes before departure and at first, second, and third week after departure According to statistics, the average arterial pressure, respiration, and heart rate of the subjects in the first week were higher than those of other time periods, but the blood oxygen saturation was relatively lower.The changes in cardiopulmonary function in the second and third weeks were relatively gentle, and all the differences were remarkable (p<0.05)(Figure 7).

DISCUSSION
After the athletes in the plain area enter the high-altitude area for a short time, the body will inevitably undergo a series of changes in order to adapt to the low oxygen environment. 6The human body's response to altitude hypoxia begins with changes in the respiratory and circulatory systems. 7In this research, the plateau area and the heart and lung changes were studied through modeling.The traditional cardiopulmonary parameter analysis model must require the parameters to be stable without abnormal changes.Once the parameters change irregularly, the modeling process can't be completed effectively. 8Therefore, a model of interactive abnormal changes in cardiopulmonary function was adopted in this work.The results showed that with the increase of intrathoracic pressure, the subjects' pulmonary circulation blood volume gradually decreased, and the decline was most obvious in the stage of thoracic pressure -50 to 0. As the cardiorespiratory reflex coefficient increased, the subjects' breathing and heart rate compensatory acceleration appeared.It reflected the relatively intuitive impact of the low-oxygen environment in the plateau area on subjects, which was similar to the results of related researchers. 9he hypoxic environment in the plateau area can directly trigger the compensatory excitatory response of the cardiopulmonary.Mean arterial pressure, respiratory rate, heart rate, and blood oxygen saturation are the first to undergo compensatory changes. 10According to the above research results, with the increase in altitude, the average arterial pressure, respiratory rate, and heart rate of the subjects all increased, while the blood oxygen saturation value decreased.It was caused by physiological changes in the arteries and blood vessels of the heart and lungs.In plateau areas, the human cardiopulmonary nerve receptors are stimulated by strong mechanical stimulation in the thoracic cavity.Moreover, as the altitude increases, respiratory exercise will cause changes in the blood volume and pressure of the heart and lungs, and the stimulation of the heart and lung receptors will increase, leading to increased heart rate variability.In addition, it was also found that the indicators of cardiopulmonary function of subjects of different genders changed little.

CONCLUSION
The model further analyzed the influence of exercise under the plateau environment on the body's heart and lung function.The simulation results showed that as the pressure in the chest cavity increased, the subjects' pulmonary circulation blood volume gradually decreased.The most obvious decrease in chest pressure was from -50 to 0. Moreover, as the cardiorespiratory reflex coefficient increased, the subjects' breathing and heart rate compensatory speeded up.The tracking and monitoring of the subjects' cardiopulmonary indicators found that with the increase in altitude, the subjects' average arterial pressure, respiratory rate, and heart rate all increased, while the blood oxygen saturation value decreased.
The author declare no potential conflict of interest related to this article

n 1
represents cardiopulmonary sensory reflex exercise, l 1 represents the coefficient of sensory transmission, and r represents the enhancement coefficient of sensory reflex, which is related to the breathing intensity during exercise.The baroreflex produced by lung breathing movement can be expressed by the following equation.W Wr 0.25* We = + (7) W represents the sensory pressure value, Wr represents the average carotid artery pulse pressure, and We represents the carotid artery pulse pressure.

Figure 1 .
Figure 1.The relationship between pulmonary circulation volume and intrathoracic pressure.

Figure 2 .
Figure 2. The relationship between cardiopulmonary sensory reflex and exercise (high altitude) breathing and heart rate.

Figure 3 .
Figure 3. Cardiopulmonary function comparison of subjects of different genders.

Figure 4 .
Figure 4. Mean arterial pressure of subjects at different altitudes.

Figure 5 .
Figure 5. Blood oxygen saturation of subjects at different altitudes.

Figure 6 .
Figure 6.Heart rate and respiration of subjects at different altitudes.

Figure 7 .
Figure 7. Changes in the cardiopulmonary function of subjects at different times.

(
A: before departure; B: first week after departure; C: second week after departure; D: third week after departure.)