Study design: the present study is an observational, descriptive, cross-sectional design.

According to the altitude and accessibility to obtain the corresponding samples, the following localities of the Cajamarca Region, Peru, were considered.

Blood pressure was recorded according to Williams B. et al. [13] and Unger et al. [14] , using automatic and semi-automatic oscillometric devices, in accordance with the specifications of the Pan American Health Organization [15] .

The measurement of pulse oximetry was performed as described by Mejía Salas and Mejía Suarez [16] .

The procedure for obtaining the haematocrit and its corresponding reading was performed according to parameters described in the literature [17] - [20] .

Study population

A non-probabilistic and convenience sample was considered and its ages ranged from 1 to 70 years of age. Recruitment was carried out systematically in each of the nine pre-established locations for the study, achieving the participation of a total of 476 people.

Inclusion criteria were considered to be: subjects of both sexes, of the determined altitude, natives and non-natives with a stay of more than one year at the altitude measured, and who accepted to participate in the project and signed the Informed Consent Form, in this last aspect, if they were adults, and in the case of minors, their parents did so.

Exclusion criteria included: a history of cardiovascular, pulmonary or haematological disease, respiratory symptoms at the time of the test such as cough, expectoration or dyspnoea. Patients with a diagnosis of obesity and with a body mass index greater than 30 or who were regular smokers were also excluded.

Data analysis

The statistical software R Project was used to analyze the data. An initial assessment of the distribution of the data revealed that they did not follow a normal distribution. Given this situation, it was decided to use non-parametric statistical tests. Specifically, the Kruskal-Wallis test was applied to determine significant differences between proportions of continuous and categorical variables. The results were presented in tables using the R package gtsummary, which facilitates the creation of high-quality statistical tables.

Ethical considerations: Ethical considerations included requesting informed consent from participants, as well as discretion and confidentiality in the use of the information obtained.

In our study, we found higher average values for HR, HR and Hto in men than in women. In addition, typical responses to altitude, such as increased heart rate and respiratory rate, decreased oxygen saturation and increased haematocrit in the Cajamarca population were evident. Also, expected physiological patterns are observed, such as a higher heart and respiratory rate in childhood that decreases in adulthood, a progressive increase in systolic blood pressure and haematocrit with age, as responses to hypobaric hypoxia as altitude increases. Our results are consistent with the studies of Bardales Zuta et al. [21] . Healthy residents of Huamachuco were recruited for this cross-sectional convenience study. Arterial blood was drawn using standard procedures. People with obesity, diabetes, high levels of physical activity and a history of substance use were excluded. They concluded that in inhabitants of high Andean areas pO₂ and pCO₂ decreased and haematocrit increased.

Tremblay J. C. and Ainslie P. N. [22] , who in their research used a Geographic Information Systems (GIS) approach to quantify the human population at 500 m altitude intervals in each country. Presenting the population for 500 m intervals to provide a flexible interpretation of “high altitude”, as the threshold for high altitude eliciting a physiological response varies between individuals and populations. Concluding that research in countries with substantial high-altitude populations is needed to understand how the environmental (physiological and social) stresses of high altitude affect physiology, adaptation, health and disease. These conditioning factors are similar to the reality of the Peruvian highlands in our study.

On the other hand, Julian C. G. and Moore L. G. [23] , in their review study, analyse the types of evidence that have evaluated the widespread acceptance of the idea that genetic adaptation in high altitude Andean residents with respect to the physiological characteristics that distinguish them from acclimatised newcomers and the genomic or genetic factors potentially involved. Concluding that, there are several unique O₂ transport characteristics of the Andean resident compared to acclimatised residents or newcomers including lower alveolar ventilation, lower hypoxic pulmonary vasoconstrictor response, slightly larger lung volumes, higher uterine artery blood flow and possibly lower mean cerebral blood flow, lower peak exercise O₂ consumption due to altitude and higher cardiac efficiency. Taken together, these suggest greater efficiency in O₂ transfer and utilisation; in turn, such differences between acclimatised or permanent residents of high altitude support the existence of an Andean genetic adaptation to high altitude.

Sex differences in physiological parameters show significant differences between sexes in heart rate (76 vs 80 bpm, p = 0.012), respiratory rate (19.60 vs 20.71 breaths/min, p = 0.002) and haematocrit (46.4% vs 48.1%, p = 0.020). 020), being consistent with previous studies reporting sexual dimorphism in adaptations to altitude [24] . A recent study in Andean populations confirmed that men tend to have higher haematocrit values as a compensatory mechanism to chronic hypoxia [25] .

Regarding oxygen saturation, considered the fifth vital sign, it is an accurate and non-invasive measurement; alteration of vital signs occurs several hours before the occurrence of an adverse event; vital signs are the cheapest, simplest information; the measurement of SatO₂ trends added to respiratory rate provides a holistic view of respiratory function [26] . In our study, however, respiratory rate is not altered despite low saturations.

It is important to take into account the publication by Townsed [27] , where food insecurity, female sex and BMI were significantly and independently associated with increased systolic blood pressure, the peculiarity of this study is that participants were mailed a kit containing a blood pressure monitor, scales and a tape measure for each participant to measure themselves; in our study the measurement was direct and carried out by the research team. However, we have not considered dietary habits and physical activity in our data, which could be a point to be taken into account in future research.

The study published by Yook Chin Chia [28] considers weight and height self-reported by the participants, the accuracy of these data may vary, 2781 participants were considered, the majority 61.7% of the participants were overweight or obese, these measurements were then corroborated with the measurement of the team finding reliability in the measurements, in our study the measurement was directly by the research team.

Particularly notable is that no significant sex differences were found in oxygen saturation (93.3% vs 93.6%, p = 0.5) or systolic blood pressure (111 vs 109 mmHg, p = 0.10). This contrasts with the previous study by Santos-Martínez L. E. et al. [29] who reported minor differences in SpO₂ between sexes in Andean populations, suggesting that the Cajamarca populations may present a specific adaptive pattern.

Variations by altitude and sex reveal that all clinical characteristics studied show significant differences by sex and altitude (p < 0.001 for all variables). Haematocrit values show a progressive increase with altitude in both sexes, from 43.7% in women at 1294 m to 48.0% at 3502 m, and from 45.1% to 48.6% in men at the same altitudes. This pattern is consistent with the Nishimura T. et al. [30] study describing increased erythropoiesis as a primary response to hypobaric hypoxia.

Heart rate showed an interesting behaviour, with lower values at higher altitudes (71 - 74 bpm in women and 67-84 bpm in men at different altitudes), which may reflect chronic cardiovascular adaptation. Ortiz-Prado E. et al. [24] study in Peruvian high altitude populations has reported lower heart rates in chronic residents compared to seasonal visitors.

Findings of age group differences show significant differences in all variables by life course (p < 0.001). Haematocrit shows a progressive increase with age, from 44.4% in the 0 - 11 age group to 49.1% in the over 60 age group. This age pattern has been documented in the study by Santos-Martinez L. E. et al. [29] in Andean populations, where erythrocytes tend to increase with age as a result of prolonged chronic exposure.

Oxygen saturation showed a decrease with age (98.8% in children vs 91.7% in older adults), which is in agreement with the study by Bravo-Jaimes K. et al. [31] , reporting lower ventilatory efficiency in older populations living at high altitude.

The impact of altitude on physiological parameters confirms significant differences in all parameters by altitude (p < 0.001). Haemoglobin and haematocrit values increase progressively with altitude, while oxygen saturation shows a decreasing trend. These findings are consistent with the physiological profile typical of Andean populations described by Santos-Martínez L. E. et al. [29] , characterised by compensatory erythrocytosis and lower SpO₂ compared to Tibetan populations. These findings have clinical relevance for establishing specific reference values for high-altitude populations in the Peruvian context, considering the sex, age and altitude differences documented in the present study. The research contributes to the knowledge of Andean adaptive physiology and may guide differential diagnostic strategies in mid-altitude populations.