
The effects of superimposed tilt and lower body negative pressure on anterior and posterior cerebral circulations
Author(s) -
Tymko Michael M.,
Rickards Caroline A.,
Skow Rachel J.,
IngramCotton Nathan C.,
Howatt Michael K.,
Day Trevor A.
Publication year - 2016
Publication title -
physiological reports
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.918
H-Index - 39
ISSN - 2051-817X
DOI - 10.14814/phy2.12957
Subject(s) - supine position , medicine , cerebral blood flow , blood volume , transcranial doppler , anterior cerebral artery , cerebral autoregulation , middle cerebral artery , blood pressure , blood flow , anesthesia , hemodynamics , cerebral circulation , head down tilt , posterior cerebral artery , cardiology , autoregulation , ischemia
Steady‐state tilt has no effect on cerebrovascular reactivity to increases in the partial pressure of end‐tidal carbon dioxide ( P ET CO 2 ). However, the anterior and posterior cerebral circulations may respond differently to a variety of stimuli that alter central blood volume, including lower body negative pressure ( LBNP ). Little is known about the superimposed effects of head‐up tilt ( HUT ; decreased central blood volume and intracranial pressure) and head‐down tilt ( HDT ; increased central blood volume and intracranial pressure), and LBNP on cerebral blood flow ( CBF ) responses. We hypothesized that (a) cerebral blood velocity ( CBV ; an index of CBF ) responses during LBNP would not change with HUT and HDT , and (b) CBV in the anterior cerebral circulation would decrease to a greater extent compared to posterior CBV during LBNP when controlling P ET CO 2 . In 13 male participants, we measured CBV in the anterior (middle cerebral artery, MCA v) and posterior (posterior cerebral artery, PCA v) cerebral circulations using transcranial Doppler ultrasound during LBNP stress (−50 mmHg) in three body positions (45° HUT , supine, 45° HDT ). P ET CO 2 was measured continuously and maintained at constant levels during LBNP through coached breathing. Our main findings were that (a) steady‐state tilt had no effect on CBV responses during LBNP in both the MCA ( P = 0.077) and PCA ( P = 0.583), and (b) despite controlling for P ET CO 2 , both the MCA v and PCA v decreased by the same magnitude during LBNP in HUT ( P = 0.348), supine ( P = 0.694), and HDT ( P = 0.407). Here, we demonstrate that there are no differences in anterior and posterior circulations in response to LBNP in different body positions.