Vertical lines are the beginning and end of hyperventilation. F, C, O, Td, Ts – SCP registration areas
It can be assumed that in a reaction of the “strong” type, intracranial processes are masked by a reaction of non-brain origin having the same orientation. Most likely, it is due to the vasomotor reaction of extracranial vessels. Unlike the brain, where the blood flow substantially depends on the local regulation of the extracranial vessels of the head to a greater extent vasomotor adrenergic fibers, it is carried out mainly by central mechanisms, which determines the generalized nature of the changes. However the reaction
blood circulation
tone
tonus
regulation is determined
which
The “strong” type, obviously, also implies significant changes in blood flow and CRC in the brain, since with such a reaction to hyperventilation, significant dynamics occur in the EEG. In healthy subjects, when the AMR reaction to “strong” type hyperventilation occurs in the EEG, there are significantly more pronounced changes in the form of a decrease in the relative spectral power of the alpha rhythm and an increase in the relative power of the theta and delta activity than in the “weak” type. Relatives of patients with DAT were more often observed reactions of the “strong” type of large amplitude. At the same time, discharges of synchronously theta and delta waves were recorded in the EEG, the generation of which is associated with the median structures of the brain (see Section 8.1). In relatives of patients with a “weak” reaction of AMR to hyperventilation, bilaterally synchronous activity on the EEG appears in about half of cases, whereas in the case of a “strong” type this phenomenon is almost always observed.
The origin of the weak reaction is more complex. In this case, shifts of the SCP and EEG are small in amplitude, and changes in the SCP and the spectral power of the EEG correlate with each other. Shifts in SCP during “weak” type reactions are asynchronous in different leads and often begin with a negative phase, indicating the development of alkalosis in the brain. Perhaps, due to the fact that extracranial vasoconstriction is less pronounced in “weak” type reactions, intracerebral changes in them are more noticeable than in “strong” type reactions.
Is it possible to exclude the influence of non-cerebral factors on SCP in hyperventilation in order to identify shifts of brain-derived SCP? In our opinion, this is possible if we study the SCP in bipolar registration or consider local SCP. Since the influence of the vascular extracerebral factor during hyperventilation is sufficiently generalized, the role of this factor significantly decreases with bipolar registration. Of course, this also eliminates the same shifts in the various leads of brain-derived SCP. Nevertheless, an SCP recorded in this way is more closely related to brain activity, which can be assessed by EEG characteristics. In particular, the difference in SCP between the symmetric temporal leads reliably correlated with the corresponding difference in the spectral power of the alpha rhythm in the same areas before and during hyperventilation ( r = 0.66, p = 0.026; r = 0.61, p = 0.044, respectively ) But the correlation coefficient was significantly higher ( r = 0.77, p = 0.006), when the corresponding shifts of SCP and EEG during hyperventilation were considered. An increase in the correlation coefficient in the study of shifts in SCP and EEG during hyperventilation is understandable, since this reduces the weight of extraneous factors affecting both of these indicators.
A review of the bipolar differences of the SCP revealed that, although changes in individual individuals can reach several millivolts, the sign of the shift of the SCP may be different. The averaged shifts of bipolar SCP in healthy subjects are not significantly different from zero. The absence of average trends indicates, in our opinion, the dependence of these reactions on the previous state of the brain tissue, which is confirmed by the high negative correlation between the shift in SCP during bipolar registration and the background level of the corresponding parameter of SCP. In addition, with bipolar abduction, those brain reactions that occur simultaneously and have the same amplitude in both areas of registration are not manifested. Since hyperventilation has a fairly generalized effect on the brain normally, it is clear that there are no changes in the average values of SCP in bipolar leads.
So, with hyperventilation due to hypocapnia, vasoconstriction of the brain and extracranial vessels of the head occurs. As a result, hypoxia of brain tissue develops, leading to
109 changes in both neuronal activity and cerebral
energy metabolism with the development of lactic acidosis. Under the influence of hyperventilation, regular changes are observed
SCP, which in most cases have a positive orientation, due to acidosis of the tissues of the head in relation to the arm.
Changes in SCP during hyperventilation reflect the reactivity of the nervous and vascular systems with respect to hypocapnia. Marked shifts in positive-focus SCP (3 mV or more) indicate high sensitivity to hypocapnia, powerful vasoconstriction of cerebral and extracerebral vessels, and brain hypoxia during hyperventilation. Such shifts are accompanied by significant dynamics of the EEG. Regular changes in SCP during hyperventilation can be used when conducting appropriate functional tests.