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.