Cold pressor test in tetraplegia and paraplegia suggests an independent role of the thoracic spinal cord in the hemodynamic responses to cold

Background: Cold application to the hand (CAH) is associated in healthy people with increase in heart rate (HR) and blood pressure (BP). Objective: To study hemodynamic responses to CAH in humans following spinal cord injuries of various levels, and examine the effect of spinal cord integrity on the cold pressor response. Design: An experimental controlled study. Setting: The spinal research laboratory, Loewenstein Hospital, Raanana, Israel. Subjects: Thirteen healthy subjects, 10 patients with traumatic T_4-6 paraplegia and 11 patients with traumatic C_4-7 tetraplegia. Main outcome measures: HR, BP, HR and BP spectral components (low frequency, LF; high frequency, HF; LF/HF), cerebral blood flow velocity (CBFV) and cerebrovascular resistance index (CVRi). Methods: The outcome measures of the three subject groups monitored for HR, BP and CBFV were compared from 5 min before to 5 min after 40-150 s of CAH. The recorded signals were digitized online and analyzed offline in both the time and frequency domains. Results: During CAH, HR and CVRi increased significantly in all subject groups (P<0.001), and BP in control subjects and in the tetraplegia group (P<0.01). BP increase was not statistically significant in paraplegia, and CBFV, HR LF, HR HF and BP LF did not change significantly during CAH in any group. Conclusions: The CAH effect in tetraplegia and the suppressed BP increase in paraplegia, supported by the other findings, suggest a contribution of an independent thoracic spinal mechanism to the cold pressor response.