Zavhorodnia V. Individual features of haemodynamic functioning in respiratory hypocapnia in men

The dissertation presents a study of the current problem of physiology, namely, the individual features of changes in central and cerebral haemodynamics, heart rate variability in respiratory hypocapnia. It is found that breathing at a rate of 30 cycles per minute for 10 minutes leads to a significant decrease in the level of carbon (IV) oxide in the alveolar air on average from 40.12 ± 0.361 mm Hg up to 18.59 ± 0.542 mm Hg with no complete recovery for 40 minutes. The reactivity of PetCO2 under the influence and during the recovery period has a wide range of individual manifestations. The latter is due to the baseline level of this indicator, which is an individual-typological characteristic of the human body. During 10-minute hyperventilation with a frequency of 30 cycles per minute, there is a decrease in the duration of R-R intervals and total peripheral vascular resistance, and an increase in cardiac index. During the recovery period, only an increase in the duration of R-R intervals to a maximum of 20 minutes was reliable. It is confirmed that the initial tone of the autonomic nervous system modulates changes in human haemodynamics in respiratory hypocapnia and affects the features of long-term changes after cessation of such influence: vagotonics and normotonics are characterized by optimal haemodynamic parameters, since the increase in heart rate during hypocapnia is accompanied by higher rates of shock and cardiac indices, along with a lower index of myocardial tension. Vagotonics are found to have higher level of PetCO2 than other the subjects. The reactivity of haemodynamics depends on the initial stress of carbon (IV) oxide in the alveolar air: the subjects with its medium and high levels have higher reactivity than in the group with low baseline PetCO2. The subjects with a medium baseline PetCO2 level have more effective haemodynamic changes, as hypocapnia has increased cardiac output due to the increased volumetric ejection velocity and stroke index, along with a decrease in stress period and myocardial stress index. The indicators of time analysis and spectrum power of R-R interval duration with hyperventilation is reliably decreased. Higher values compared to the baseline are observed in 40 minutes of recovery. Among the subjects with different baseline level of PetCO2, at rest and with hypocapnia, higher values of heart rate variability are found in the subjects with its high and medium level compared to the men with low level of PetCO2. There are differences in the changes of heart rate variability and their wave structure with respiratory hypocapnia and after it depending on the baseline level of autonomous tone. Vagotonics are found to be characterized with the highest reaction variability and the lowest stress of regulatory systems during hypocapnia. Under the influence of respiratory hypocapnia, on average, there is an increase in the tone of arterial vessels and a decrease in the blood supply of the carotid artery of the brain; there is an interhemispheric asymmetry, especially, of the artery tone. These reactions have significant individual differences. The subjects with high baseline of PetCO2, normotonics and vagotonics level have higher level of the blood supply and lower level of cerebral arteries during hypocapnia. The conducted research does not cover all the aspects of the considered problem and opens new opportunities for its study. Prospects for further study of the effects of hypocapnia on the state of the cardiovascular system are seen in the elucidation of the genetic mechanisms of the obtained patterns.