Changes in cerebral oxygenation and blood flow during LBNP in spinal cord-injured individuals

Abstract

Spinal cord-injured (SCI) individuals, having a sympathetic nervous system lesion, experience hypotension during sitting and standing. Surprisingly, they experience few syncopal events. This suggests adaptations in cerebrovascular regulation. Therefore, changes in systemic circulation, cerebral blood flow, and oxygenation in eight SCI individuals were compared with eight able-bodied (AB) individuals. Systemic circulation was manipulated by lower body negative pressure at several levels down to -60 mmHg. At each level, we measured steady-state blood pressure, changes in cerebral blood velocity with transcranial Doppler, and cerebral oxygenation using near-infrared spectroscopy. We found that mean arterial pressure decreased significantly in SCI but not in AB individuals, in accordance with the sympathetic impairment in the SCI group. Cerebral blood flow velocity decreased during orthostatic stress in both groups, but this decrease was significantly greater in SCI individuals. Cerebral oxygenation decreased in both groups, with a tendency to a greater decrease in SCI individuals. Thus present data do not support an advantageous mechanism during orthostatic stress in the cerebrovascular regulation of SCI individuals.

Orthostatic hypotension following spinal cord injury: understanding clinical pathophysiology

“…In support of this, another study by the same group found that both able-bodied controls and SCI individuals had similar reductions in cerebral oxygenation to simulated standing using supine lower body suction, despite the SCI subjects having larger decreases in systemic blood pressure. 82 Similarly, they also noted that the SCI group had larger falls in cerebral blood flow during the orthostatic stress. The greater decline in cerebral blood flow seems contrary to the other studies, and the control of cerebral blood flow in SCI requires further examination.…”

“…The crucial factor in determining consciousness, however, is not specifically cerebral blood flow, but rather cerebral oxygenation. 82 SCI patients, although demonstrating a much larger fall in blood pressure upon orthostasis than able-bodied controls, show a similar reduction in cerebral oxygenation when upright. 83 Thus, although the systemic circulation is compromised in SCI patients, cerebral oxygenation is maintained as well as in able-bodied controls.…”

“…17 This is important because during orthostasis the carotid baroreceptors lie above heart level, and as such are activated by the relative fall in pressure due to the hydrostatic effects of gravity, 80 and normally bring about the coordinated reflex responses to orthostasis. In SCI, the baroreceptor pathways may be impaired, 64 and in addition there may, 82 or may not, 81,83 be a disruption of cerebral blood flow during standing.…”

Effect of hypotensive challenge on systemic hemodynamics and cerebral blood flow in persons with tetraplegia

“…There have been several reports on the effects of orthostatic maneuvers on CBF and MAP in persons with tetraplegia; the results are somewhat conflicting and none has identified a lower limit of MAP below which CBF is compromised [10][11][12]23]. One study examined group differences for the change in MAP and CBF during a graded HUT maneuver among symptomatic and asymptomatic individuals with tetraplegia [10].…”

A cerebral blood flow evaluation during cognitive tasks following a cervical spinal cord injury: a case study using transcranial Doppler recordings

“…The majority of previous studies have examined a link between SCIs and CBFV in patients with a high level of SCI, i.e. above the sixth thoracic segment (Phillips et al 2013;Catz et al 2007;Houtman et al 2001). These contributions showed that SCI can lead to other health disorders: cardiovascular and broncho-pulmonary diseases, musculoskeletal, gastro-intestinal, renal and immune dysfunctions in addition to incomplete/complete tetraplegia/paraplegia and dysfunctions (Phillips et al 2013;Scott et al 2011).…”