Limb oxygenation during the cold pressor test in spinal cord-injured humans

Abstract

Afferent activity coming from below the lesion due to cold stimuli would reflexively enhance sympathetic activity in both the arm and leg in individuals with cervical SCI but only in the leg in individuals with thoracic SCI. A decrease in tissue oxygenation might have been caused by sympathetic vasoconstriction. The reduction of tissue oxygenation in the arm was marked in individuals with cervical SCI, suggesting differential control of arm oxygenation and leg oxygenation in the region below SCI.

Cold pressor test in spinal cord injury—revisited

“…Eight studies have investigated the effect of hand CPT [8,10,12,13] and foot CPT [6,7,[9][10][11]13] on cardiovascular outcomes, such as BP and HR, in individuals with SCI. Furthermore, several studies also examined responses in cerebral blood flow velocity and cerebrovascular resistance [8,9], endocrine responses [7], calf vascular resistance [14], skin temperature [7], and tissue oxygenation [6] during CPT. For the purpose of this review we are, however, focusing only on BP and HR as they were the most common CPT outcomes across all CPT studies in individuals with SCI.…”

“…The increased BP during foot CPT in individuals with tetraplegia suggests that reflex sympathetic discharge to the peripheral vessels is likely activated through the isolated spinal cord, which is no longer influenced by supraspinal inhibitory pathways (see Fig. 3A, B) [6,7,9,10,13]. This is probably due to similar mechanism involved during AD and this hypothesis is reinforced by the fact that plasma norepinephrine, the neurotransmitter released at sympathetic postganglionic endings, is significantly increased during foot CPT [7].…”

“…During foot CPT a significant increase in MAP of 14-20 mmHg has been found in individuals with tetraplegia [6,7,9,10,13]. In individuals with sensorimotor complete (AIS A) tetraplegia the afferent stimuli from skin thermoreceptors do not reach the thalamus and consequently vasomotor center in the medulla cannot elicit a cold pressure response.…”

“…In terms of HR responses during foot CPT, studies report either no change in HR [7] or a decrease in HR [6,9] in individuals with tetraplegia. The decrease in HR was suggested to be due to stimulation of sinoaortic baroreceptors and increased vagal efferent activity, i.e., baroreflex-mediated bradycardia often seen during AD bouts [6,9]. This is in contrast to the rise in HR observed in able-bodied individuals and can be explained by the fact that individuals with high-level SCI have lost or diminished sympathetic supraspinal control over their heart, but intact paraysmpathetic cardiac control through the vagal nerve.…”

“…As an SCI can result in a disruption of neuronal pathways involved in the control of spinal sympathetic circuits, the outcome of a CPT in individuals with SCI might be altered. Several publications have investigated CPT responses in individuals with SCI [6][7][8][9][10][11][12][13]. Depending on the lesion level of an SCI and the location of cold application, the CPT responses can vary enormously.…”