Energy metabolism and oxygen consumption are closely related. The higher the oxygen consumption, the more intense is the energy metabolism. It would seem that with increased ventilation of the lungs and, correspondingly, a greater supply of oxygen with inhaled air, the energy exchange also increases. However, it is not. With hyperventilation – increased breathing, significantly exceeding the needs of the body, carbon dioxide is washed out from the blood, which leads to spasm of the vessels of the heart, brain, skin and other tissues and a decrease in the flow of oxygen to these organs. In peripheral vessels, on the contrary, there is vasodilation followed by the development of hypotension and . Under the influence of these causes, changes in homeostasis develop, and, in particular, CRR in the blood, brain tissue and other organs. Among many diseases accompanied by impaired functions of external respiration, a significant place is occupied by diseases, in the pathogenesis of which hyperventilation plays an important role (bronchial asthma, coronary heart disease, etc.). In healthy people, involuntary hyperventilation that occurs when the gas composition of the air changes or during stress can be accompanied by the development of serious pathological conditions. Hyperventilation causes the release of adrenocorticotropic hormone (ACTH), which triggers stress reactions. Arbitrary dosed hyperventilation is a convenient model for studying processes that are accompanied by increased ventilation of the lungs and lead to impaired homeostasis in healthy and sick people. That is why voluntary hyperventilation is one of the common tests used in functional diagnostics to detect pathological activity of the brain and heart.
Hyperventilation test consists in the fact that the subject breathes deeply and rhythmically, as a rule, within three minutes. Changes in biochemical and physiological processes in the body are quite diverse and not fully understood. Above we gave a conceptual diagram of the development of such changes. For us, the processes that occur in the brain are of most interest. At present, the dynamics of EEG with a hyperventilation test has been well studied. EEG changes in healthy people are characterized by an increase in amplitude and a slight increase in the slow-wave theta and delta activity. In cases of pathology, hyperventilation contributes to the manifestation of latent EEG disorders. Thus, in people with brain stem dysfunction, hyperventilation may cause flashes of bilaterally-synchronous high-amplitude slow waves of theta and delta ranges to appear or intensify . The main reason for all these changes is hypoxia due to cerebral vasoconstriction, under the influence of which a depolarization shift of the membrane potentials of neurons occurs with a subsequent change in EEG activity. EEG is also affected by alkalosis developing in the initial stage of hyperventilation in the nervous tissue.
It is shown that the metabolic factor is leading in the regulation of cerebral blood supply during hyperventilation. With strong arbitrary hyperventilation, a decrease in the partial pressure of carbon dioxide in arterial blood leads to a decrease in the concentration of hydrogen ions in the blood and brain tissue. An increase in pH causes an increase in the tone of regional pericapillary and pial vessels and, as a result, a decrease in cerebral blood flow . In addition, it is possible that reflex mechanisms play a role in cerebral spasm during hyperventilation . Derrow back in 1944, it was suggested that the cholinergic activity of cerebrovascular nerves decreases under the influence of hyperventilation, which is accompanied by a local vasoconstrictor effect. Further research revealed that a certain role in the change in cerebral circulation during hyperventilation is played by reflexes from the vagus nerve. Vascular spasm is adaptive in nature: it prevents the leaching of carbon dioxide and promotes the restoration of ASR. Due to the fact that brain SCP is an informative indicator of cerebral pH shifts, studying the dynamics of SCP in hyperventilation is of particular interest. We examined 3 groups of people: 31 healthy subjects aged 44 to 73 years old, patients with Alzheimer’s type dementia – DAT (21 people aged 65 to 76 years) and their first-degree relatives – 15 subjects aged 35 to 55 years . The parameters of SCP in the background and in the process of hyperventilation were evaluated. All subjects underwent neurological and EEG examination. Patients with DAT, in addition, underwent a psychiatric and CTG examination. The diagnosis was made by the staff of the Department of Late Mental Pathology NCPP RAMS – N.D. Selezneva, Ya.B. Kal yun . EEG data in healthy subjects were normal. Significant diffuse changes in EEG were revealed in DAT patients. Relatives of DAT patients were clinically healthy, but in the EEG they had signs of dysfunction of the median structures of the brain, and in some cases a decrease in the convulsive readiness threshold.
In healthy subjects, in most monopolar leads, except for the left temporal, under the influence of hyperventilation, there was a steady shift in the positive-focus SCP with an average amplitude of 2.2 + 0.9 mV with variations from -3 to 9 mV (Fig. 6.2). The mean values of bipolar and local SCP were not significantly changed. In contrast to other monopolar leads in the left temporal region, where no significant shifts of SCP were recorded, there was a negative correlation ( r = -0.51, p <0.004) between the initial SCP and its shift during hyperventilation. A negative correlation indicates that the nature of the SCP changes depends on its background level and is aimed at maintaining a stable SCP value. It is possible that in the left temporal region, the mechanism of regulation of CRR manifests itself more actively than in other regions.
SCP of the brain before and after hyperventilation in healthy subjects. * – significantly different from zero ( p <0.05) shifts of SCP under the influence of hyperventilation. F, C, O, Td, Ts – softener lead areas
The revealed patterns, with some nuances, are also characteristic of patients with DAT. Shifts in SCP of positive polarity were observed in monopolar leads. The magnitude of the average shift in SCP was less than in healthy ones, and amounted to 1.7 + 0.6 mV. In relatives of DAT patients, the shift of positive polarity SCP in monopolar leads was more pronounced and amounted to 3.1 + 1.2 mV.
To understand why there are deviations in SCP with positive polarity during hyperventilation, consider the possible mechanisms of these changes. With hyperventilation due to spasm of cerebral vessels, brain hypoxia develops. Therefore, there is a transition to anaerobic metabolism, and the synthesis of lactic acid is intensified, leading after a certain time to acidification of the nervous tissue, which can cause an increase in SCP. With hyperventilation, vasoconstriction of the skin vessels of the head also occurs, which is accompanied by a decrease in extracranial pH, and this can cause an increase in SCP. In addition, alkalosis develops in the peripheral vessels of the extremities under the action of hyperventilation, as a result of which a negative potential displacement may be observed in the arm region where the reference electrode is located. Due to this, the potential difference between the head and hand should increase.
Two additional experiments were performed to understand the nature of these reactions and explain the effects of each of these factors.
Shifts of peripheral-derived SCP were studied during hyperventilation. At the time of hyperventilation, the duration of which was 1.5 min, the blood flow was stopped through the main vessels of the right hand, on the wrist of which there was a reference electrode. For this, a tonometric cuff was put on the right shoulder region, the pressure in which was set higher than systolic (150 – 170 mm Hg). Due to this, alkalosis in the blood of the right hand did not develop during hyperventilation , which stabilized the potential in the region of the reference electrode. The active electrode was located on the wrist of the left hand, where the great vessels were not pinched. Pinching the right hand in itself does not cause a shift in the soft starter millivolt range.
A different picture is observed with hyperventilation: alkalosis develops in the tissues of an uncontrolled hand, which leads to a decrease in SCP by 2–3 millivolts.