Modified cold pressor test by cold application to the foot after spinal cord injury: Suggestion of hemodynamic control by the spinal cord

OBJECTIVE: Study hemodynamic responses to cold application to the foot (CAF) to explore the autonomic cardiovascular control by the spinal cord. DESIGN: Controlled experimental study. Hemodynamic variables were measured or calculated for 13 healthy subjects, 10 patients with traumatic T4-T6 paraplegia, and 11 patients with traumatic C4-C7 tetraplegia. Subjects were continuously monitored for heart rate (HR), blood pressure (BP), and cerebral blood-flow velocity (CBFV) from 5 mins before to 5 mins after 40-120 secs of CAF by ice water foot immersion. The recorded signals were digitized online and analyzed offline in the time and frequency domains. RESULTS: During CAF, HR increased in the control group but decreased in patients (P < 0.001). BP increased significantly in the control and tetraplegia groups (P < 0.001) and nonsignificantly in the paraplegia group. HR and BP spectral components (LF, HF, LF/HF) did not change significantly. CBFV increased significantly in the patient groups (P < 0.05) but not in the control subjects. The cerebrovascular resistance increased significantly in the control and tetraplegia groups (P < 0.001), but not in the paraplegia group. CONCLUSIONS: The findings support the presence of hemodynamic autonomic control by the spinal cord and show that responses to CAF can be used to assess its integrity.