Vasomotor properties of the M2 segment of the middle cerebral artery

Abstract

Vasomotor response can be tested by means of transcranial Doppler sonography. It is assumed that flow changes during hyperventilation or breath-holding are due to altered resistance caused by changes in the diameter of vessels distal to the M1 segment of the middle cerebral artery. Evaluating velocities of the M2 and M1 segments together may help elucidate the vasomotor properties of distal segments. We simultaneously evaluated the vasomotor properties of the M1 and M2 segments of the middle cerebral artery in ten healthy volunteers (mean age 21.6 +/- 0.9 years) with breath-holding and hyperventilation. The radius index (RI), defined as the ratio of the M1-M2 segment radii, was estimated after 20 s and after the maximum duration of breath-holding, as well as at the first, second, and third minute of hyperventilation, in relation to velocity ratios. RI values in the resting state were compared with the values after activation procedures. The RI estimated with basal velocities ranged from 0.72 to 0.97 (mean 0.81 +/- 0.07). The RI ranged from 0.73 to 0.97 (mean 0.82 +/- 0.07) after 20 s and 0.75 to 0.90 (mean 0.82 +/- 0.06) after the maximum duration of breath-holding. The RI was 0.72-1.02 (mean 0.85 +/- 0.11), 0.71-1.03 (mean 0.86 +/- 0.12), and 0.71-1.14 (mean 0.88 +/- 0.15) at the first, second, and third minute of hyperventilation, respectively. The differences between RI values in the resting state and during each activation procedure were not statistically significant. These results suggest that the diameter ratio of the M1-M2 segments did not change after vasomotor activation, indicating that the two segments have similar vasomotor properties.

Cerebral vasomotor reactivity in epilepsy patients

“…Using sex-matched groups of patients and healthy controls would have eliminated confounding due to sex differences and would have been more representative. We limited the study groups to males, as in our previous study, because sex differences could influence TCD results [4,8].…”

“…The BHI is obtained by dividing the percentage of increase in mean flow velocity that occurs during breath-holding by the length of time (30 s was standardized in this study) subjects held their breath after normal inspiration (mean flow velocity at the end of breath-holding -mean flow velocity at rest/mean flow velocity at rest 9 100/seconds of breath holding) [4,9].…”

“…It is particularly useful for monitoring instant changes. It is assumed that flow changes during breath-holding are due to altered resistance caused by changes in diameter of the small vessels distal to the M1 segment and even distal to the M2 segment of the middle cerebral artery (MCA), and that the large vessels primarily serve as conductance channels without a diameter change [3][4][5]. These observed changes in the flow are indicative of cerebrovascular reserve of the cerebral vasculature in response to hypoxia [6].…”

Vasomotor reactivity in the ophthalmic artery

“…It is assumed that the velocity changes during breathholding are caused by varying resistance secondary to diameter changes in small vessels distal to the M2 segment of the middle cerebral artery (MCA). These changes observed in the velocity are considered to be indicative of the cerebro-vascular reserve of cerebral vascular structures formed in response to hypoxia (1).…”

Abnormal Vasomotor System Function in Idiopathic Generalized Epileptic Patients

“…Vasomotor response can be tested using transcranial Doppler sonography. It is assumed that flow changes during hyperventilation or breath-holding are due to altered resistance caused by changes in the diameter of vessels distal to the M1 segment of the middle cerebral artery (13). One study have investigated the effects of repetitive transcranial magnetic stimulation delivered as theta burst stimulation on cerebrovascular hemodynamics during simultaneous transcranial Doppler monitoring (14).…”