Associations of biological stress markers in hurricane survivors: Heartrate variability, Interleukin-2 and Interleukin-6 in depression and PTSD.

OBJECTIVE: Inflammatory and immunologic cytokines and vagal activity have important roles in health and mental health, and may influence each other. The authors assessed relationships of representative biomarkers linked to disaster exposure-heart rate variability (HRV) with Interleukin-2 (IL-2, cell-medicated immunity) and Interleukin-6 (IL-6, pro-inflammatory and pro-immunologic), stratified by psychiatric diagnosis.

DESIGN: Participants were assessed for psychiatric diagnosis, IL-2, IL-6, HRV, and HR reactivity to trauma reminders.

SETTING: Outpatient university psychiatry clinics in Oklahoma City and Tulsa.

PARTICIPANTS: Relocated Katrina survivors and demographically matched controls, not on psychiatric, cardiovascular, or inflammatory medications.

MAIN OUTCOME MEASURES: SCID-IV, baseline serum IL-2 and IL-6, HRV through power spectral analysis.

RESULTS: Survivors had higher sympathetic and lower parasympathetic activity at baseline and lower parasympathetic HR reactivity than controls, with flattened parasympathetic reactivity in the presence of depression and of post-traumatic stress disorder (PTSD). Survivors' IL-2 and IL-6 did not differ from controls and did not differ in PTSD or depression. Depressed survivors' sympathetic reactivity correlated negatively with IL-2 and parasympathetic reactivity correlated positively with IL-2.

CONCLUSIONS: HRV differed after hurricane exposure and with survivors& depression and/or PTSD, more sensitively capturing somatic sequelae than assessed cytokines. Higher sympathetic HR reactivity associated with lower immuno-logic IL-2 may indicate a double biological "hit" in depressed disaster survivors, possibly rendering them more vulnerable to cardiovascular and immunologic illness as well as depression. Associations of HRV with IL-2 may support reciprocal influences of cytokines and vagal activity. Lack of significant correlations of IL-6 with HRV measures is consistent with its pleiotropic role.