Morphological and functional changes in the cardiovascular system in postnatal ontogenesis are primarily associated with growth processes at the pre-definitive stage and subsequent structural, functional, and nosological transformations at the definitive and post-definitive stages of organism development. However, it should be emphasized that this results not only from the parallel growth of organs and the functional formation of the CVS, but also from the hemodynamic support of the growth process as a whole, and in the future of an individual, the vital activity of the body in all forms of manifestations of the somatic state and in the full functional range of “health–illness–pre-illness–disease.”
In the context of age-related dynamics of the formation and function of the CVS, the “ontogenetic model” of the CVS should be considered as a system of basic growth support, physical development, and vital activity of the organism. However, the completeness of such a model should be determined considering the specific features of human biology. The biological quality determines the direction of the stage-by-stage processes of growth and physical development and the specific features of ontogenetic adaptations of the organism. Such an evolutionary conditioned, ontogenetically formed, and fixed quality for a human is being erect. This primarily determines the features of all of the main components of anthropogenesis (morphology, physiology, and psychology) [1,2,3,4, 12,13,14, 28, 29, 32, 43, 49,50,51]. There is reason to believe that erectness also determines the nosology of a human, determining the specific features of morphological, functional and pathological transformations (pathological anthropology) of the somatic state of the organism during growth, physical development, and life activity in postnatal ontogenesis. This means that the “anthropogenics” in humans also permeates the “ontogenetic,” defining the features of all processes in postnatal ontogenesis.
Therefore, the “anthropogenic model” is considered not only as a step-by-step ontogenetic formation of upright walking, which is the main postural and motor form of human activity as an upright being, but also as a permanent organizational adaptation to Earth’s gravity in all of its physiological and pathological manifestations [3, 4, 6, 8, 29, 37, 49, 52,53,54].
This adaptation takes place continually throughout the entire organism growth period (increase in linear dimensions and changes in body proportions) [29, 55, 56], and especially with the gradual transition to erect walking during the first year of life (Fig. 9). As noted above, the hydrostatic column of blood also increases in line with the increase in total length of the body (height—h) and body mass (m). The relevance of this for blood circulation is enhanced by the formation of the vertical posture and the transition to life in an upright posture (sitting, standing, walking). In Fig. 9, a permanent increase in the height of the hydrostatic blood column is shown by a bar chart (darkened part) next to the body figures. The increase in body weight is accompanied by an increase in blood volume and mass, which increases the weight component of the hydrostatic blood column. In this case, the conditional value of the hydrostatic effect (g × m × h, [RU]) of blood circulation increases by several orders of magnitude (Fig. 9) [57].
On the graph, the rate of change in the value of the hydrostatic effect (Fig. 9) shows that its value (in percentage per year) increases throughout the definitive period of postnatal ontogenesis, up to end of the organism growth. Moreover, the first peak of the rate of “g × m × h” increase is marked by the end of the first year, when the child independently gets on its feet, and the hydrostatic conditions of blood circulation changes fundamentally. Then, for 2–3 years, the rate of increase in “g × m × h” slows down, after which it progressively increases until 12–13 years of age. It remains at a consistently high level until 17–18 years of age, and during the last period of overall growth (21–22 years of age) it progressively decreases to zero.
Thus, the most dynamic periods of the formation of the hydrostatic circulatory effects in a human is the first year of life (transition to upright walking), and then from 4–5 years of age to 12–13 years of age (to the beginning of puberty). This means that in these periods, the most pronounced instability of anti-gravity stress of blood circulation manifests. The regulation of blood circulation according to the hydrostatic effect in the period of puberty (12–18 years of age) remains in a state of stable tension. At the completion of physical development and the end of the growth stage (by 21–22 years of age), the hydrostatic situation of blood circulation and its regulatory support is stabilized at a final formed level, in accordance with the constitution and final dimensions of the body.
However, in the future life of an individual, during the reproductive and socially active period, anti-gravity tension increases relatively, especially during the first reproductive stage (22–35 years of age), due to an increase in the amount of time of the body being in an upright position (sitting, standing, walking). This is due to a violation of the daily rhythm with an increase in the time spent in a vertical position with a shortening of the lying period, including violations of the natural synchronization of the “day-night” biorhythm. The abovementioned factors result in an increase in the body’s tension in the anti-gravity mode [1,2,3,4, 6, 29, 32, 35, 39, 49, 51, 58], which actually leads to the development of fatigue syndrome. Several studies have demonstrated an association between chronic fatigue syndrome and orthostatic intolerance, predominantly postural orthostatic tachycardia syndrome [7, 59, 60].
During the reproductive age of women, it is particularly important to note the intensity of the cardiovascular system functioning and load for the influence of gravity (hydrostatic effect) on blood circulation during pregnancy, which is synergistically enhanced by the emerging physical conditions in connection with the process of placentation, growth of the uterus and fetus. At the same time, it is necessary to take into account the changes in the woman’s organism as a form of preparation for long-term pregnancy with a large fetus and, unlike other animals, mainly in an upright position of the body [36, 41, 61,62,63]. Hence, increased anti-gravity stress, vasoconstrictor regulation in this position of the body can become the basis of preeclampsia and the formation of arterial hypertension in pregnant women [17, 41], all the more that preeclampsia was observed primarily and predominantly in human beings [64]. Predictor of this variant of pregnancy course is a clear increase in the type III of dynamic organization of blood circulation (Fig. 10), especially in arterial hypertension and hemodynamically identifiable heart failure by perfusion type [26,27,28,29,30, 37] or in the pathology of pregnancy [41, 61,62,63].
Finally, the increase in anti-gravity stress of the cardiovascular system is realized on the background of increasing morbidity during the second reproductive age (over 35 years). Other possibilities of adaptation to the gravitational load when walking upright are determined in humans in the post-reproductive age. It is quite natural that against the background of aging, the ability to maintain the level of anti-gravity stress of the body is significantly weakened. By this time, in addition to painful conditions, a solid “baggage” of the depreciation of tissues and organs, which provided long-term adaptation of the body to gravity, has already accumulated. This explains why more and more people as they get older prefer to be at rest, especially in the supine position.
In this regard, the main non-communicable diseases typical of the human nosological profile are subject to special discussion. These are, first of all, cardiovascular diseases, such as arterial hypertension and hypotension, ischemic heart disease, disorders of cerebral circulation, and insufficiency of arterial and venous blood circulation of the lower extremities. In addition, there also are degenerative diseases of the spine and large joints, primarily the pelvic girdle and lower extremities, stomach and duodenal ulcer, diabetes and a number of other diseases.
On the one hand, against the background of any disease, the tension of the body’s systems in the anti-gravity support mode is further increased. Therefore, a widely practiced medical recommendation for people who are ill is to expand the routine use of bed rest. On the other hand, human diseases are a manifestation of a special (nosological) form of adaptation to the relatively increased influence of the Earth’s gravity [1,2,3,4, 29], which leads to disadaptation. This vital anti-gravity stress of the body throughout postnatal ontogenesis, interacting with the so-called risk factors (environmental and organizational origin), determines the anthropogenic basis of the aging process, including the main non-infectious diseases as well as the quality and duration of human life.
It therefore seems appropriate to revise the archaic definition of the term “pathological anthropology,” based on the idea that the development of disease in humans “is not limited to a local process, but affects the entire body” [1, 2, 12, 29]. When considering the intensively developing research in the field of evolutionary medicine, there are quite reasonable arguments to link the definition of “pathological anthropology” with the outstanding biological quality of a human—erect walking [3, 4, 11, 12, 17, 24, 39,40,41, 50, 57, 58].
Figure 11 illustrates the stages of the relative changes in the influence of the Earth’s gravity on the tension of organism adaptation during the process of growth, physical development and human life:
0—prenatal development (from fertilization to birth)
1—the formation of premontane (from birth to 1 year of age)
2—the formation of basic forms of locomotor bipedalism (to 5 years of age)
3—the ability to maintain the body in terms of premontane and bipedalism (to 7 years of age)
4—sexual consolidation of erectness and the formation of semi-differentiated forms of adaptation of the body of women and men to gravity (by 20–21 years of age)
5—reproductive age, including pregnancy in women, and nosological forms of adaptation during the first and second adulthood (from 20 to 21 years of age before menopause in women and up to 60 years of age in men); and 6—aging and amortization forms of adaptation to gravity (after menopause in women and over 60 years of age in men and until the end of life)
In addition to the age limits of the main stages in Fig. 11, the phrases on the age scale indicate the dividing date within specific stages: in stage 4—the phrase “14–15 years” corresponds to entry into puberty; in stage 5—the phrase “35 years” separates the periods of the first and second stages of reproductive age; in stage 6—the phrase “70 years” separates the phase of post-reproductive age before and after changes in the conditional life expectancy. The latter is taken as the conditional average life expectancy at birth of the total population according to WHO (World Health Organization) [53, 65].
The proposed “anthropogenic model” (periodization) of adaptation to the Earth’s gravity in the process of formation in the womb and during human life in specific conditions of bipedalism [6, 11, 12, 32] is projected into all three stages of postnatal human development (pre-definitive, definitive, and post-definitive) and are well-synchronized with the accepted periodization of human physical development.