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Physiologic Responses to Sudden, Loud Tones in Monozygotic Twins Discordant for Combat Exposure
Association With Posttraumatic Stress Disorder
Scott P. Orr, PhD;
Linda J. Metzger, PhD;
Natasha B. Lasko, PhD;
Michael L. Macklin;
Frank B. Hu, MD, PhD;
Arieh Y. Shalev, MD;
Roger K. Pitman, MD;
for the Harvard/Veterans Affairs Post-traumatic Stress Disorder Twin Study Investigators
Arch Gen Psychiatry. 2003;60:283-288.
Background Larger heart rate responses to sudden, loud (startling) tones represent one of the best-replicated psychophysiologic markers for posttraumatic stress disorder (PTSD). This abnormality may be a pretrauma vulnerability factor, ie, it may have been present prior to the event's occurrence and increased the individual's likelihood of developing PTSD on traumatic exposure. Alternately, it may be an acquired PTSD sign, ie, it may have developed after the traumatic exposure, along with the PTSD. Studying identical twins discordant for traumatic exposure offers an opportunity to resolve these competing origins.
Methods Subjects included pairs of Vietnam combat veterans and their noncombat-exposed, monozygotic twins. Combat veterans were diagnosed as having current PTSD (n = 50) or non-PTSD (ie, never had) (n = 53). All subjects listened to a series of 15 sudden, loud tone presentations while heart rate, skin conductance, and orbicularis oculi electromyogram responses were measured.
Results Consistent with previous reports, averaged heart rate responses to the tones were larger in Vietnam combat veterans with PTSD. These larger responses were not shared by their noncombat-exposed co-twins, whose responses were similar to those of the non-PTSD combat veterans and their noncombat-exposed co-twins. This result remained significant after adjusting for a number of potentially confounding factors.
Conclusions The results suggest that larger heart rate responses to sudden, loud tones represent an acquired sign of PTSD rather than a familial vulnerability factor.
From the Department of Psychiatry, Massachusetts General Hospital and Harvard Medical School, Boston, Mass, and Research Service, Veterans Affairs (VA) Medical Center, Manchester, NH (Drs Orr, Metzger, Lasko, and Pitman and Mr Macklin); the Department of Nutrition, Harvard School of Public Health, Boston (Dr Hu); the Department of Psychiatry, Hadassah University Hospital, Jerusalem, Israel (Dr Shalev); and the Vietnam Era Twin Registry, VA Medical Center, Hines, Ill.
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