[Exercise test in young steers at 2800 M above sea level].

Among its different activities the Mexican Health Ministry (SSA) promotes: 1) the specification of biological standards for the Mexican population; 2) mechanisms for early detection of physiopathological changes and 3) development of the appropriate technology as a basis for primary health care. As part of this program we studied a random sample of students at the "Colegio de Bachilleres" of Cuajimalpa a suburban area of Mexico City, situated at 2800 m above sea level, part of the equipment used was produced at the Center for Development and Technological Applications (CE-DAT), an agency of SSA. Height, weight, heart rate (HR), systolic and diastolic blood pressures (SBP/DBP) were measured at rest in sitting position, standing up and walking on a treadmill. The results show a population with similar physical characteristics to those described for other populations in Mexico, with HR values within a homogeneous distribution, except for three subjects with rates larger than 2 standard deviations (SD). At standing up, women showed an orthostatic reflex of 27 beats/min and men of 22 beats/min. At the beginning of the exercise, the HR curve becomes more homogeneous, showing a discrete ascending slope with a low correlation coefficient, suggesting low physical capacity of the studied population. As exercise continued, some subjects showed a low increment of HR, giving values differing by 2 SD. Five women and three men had resting SBP values lying 2 SD out of the mean values of the sample. During exercise, SBP increases 28 mmHg as average. Notwithstanding the low cardiac response, the time spent on the treadmill lies within the levels considered as good and, even, excellent, on the table of the National Institute of Cardiology. We discuss new procedures to analyze instantaneously the HR and the pressoreceptor reflex as well as their functional significance.