**3.2.2 Peritraumatic risk factors**

In relation to the risk factors related directly to the traumatic event, sex differences have been widely reported in primary appraisal, and it has been suggested that the higher risk for stress-related disorders in females may be due to such differences. The A2 criterion of the DSM-IV PTSD diagnosis states that in order for an event to be considered traumatic, the person must have experienced intense fear, horror, or helplessness (American Psychiatric Association, 2000). Females have generally been found to be more likely than males to report such feelings in response to a PTE (Irish et al., 2011; Norris et al., 2002). Another common peritraumatic experience is dissociation, which is defined as a disruption in the usually integrated functions of consciousness, memory, identity, and perception (American Psychiatric Association, 2000). Dissociative reactions during or following a traumatic event have been found to be important risk factors for PTSD (Ehring et al., 2006; Ozer et al., 2003). Although there do not appear to be major sex differences in the prevalence of dissociative reactions in the general population (Spitzer et al., 2003), several studies have reported higher levels of trauma-related dissociation in females compared to males (Bryant & Harvey, 2003; Irish et al., 2011). It is thus possible that sex differences in such peritraumatic rections may account for sex differences in PTSD prevalence.

It has been suggested that the professional training of police officers, which is in accordance with a traditionally masculine minimisation of emotional reactivity, can account for the previously mentioned lack of reported sex differences in PTSD prevalence in police samples (Pratchett et al., 2010), which appears to be caused by a lower degree of traumatisation in female police officers compared to female civilians. Lilly et al. (2009) compared female police officers to female civilians and found that despite a higher degree of traumatic exposure, female police officers reported lower levels of PTSD. This could be accounted for by lower levels of peritraumatic emotional distress in the police officers. However, although female police officers also reported lower levels of peritraumatic dissociation, this did not

it was suggested that such differences were due to the masculine socialisation of police officers (Lilly et al., 2009). However, it could be argued that the women who choose to become police officers already differ from women who do not on a number of variables relevant to the development of PTSD. Such differences (which may be accounted for either by prior socialisation processes or differences in hormone levels and other physiological factors) may account for the similar PTSD prevalence found in male and female police

In sum, sex differences in the risk factors associated with PTSD may account for at least part of the increased prevalence of PTSD in females, and several studies have shown that when included in hierarchical regression models, sex often becomes non-significant after other variables are controlled for. This has led many researchers to conclude that the role of sex in PTSD research is not as important as has previously been assumed (e.g. Ozer et al., 2003). However, other studies have found that sex remains a significant predictor of PTSD severity even after risk factors, which are more prevalent in females have been controlled for (e.g. Ehlers et al., 1998, O'Conner & Elklit, 2008). In order to fully test the mediation hypothesis, specific mediation studies need to be conducted, which make an effort to include all risk factors known to be more prevalent in females. However, research on sex differences in PTSD is still in its childhood, and viewing sex simply as a risk factor or as a control variable may be too simplistic. We believe that sex differences in PTSD go much deeper than simple mediation effects. In addition to sex differences in the prevalence of PTSD, sex differences may also exist in the physiological response to trauma and in how such reactions may shape symptom development. The latter part of this chapter will focus on these less studied sex

It is generally accepted, that confrontation with a stressor results in immediate activation of the sympathetic nervous system (SNS) and release of the catecholamines epinephrine and norepinephrine, which encourage either fighting or fleeing behaviour. The activation of the SNS further stimulates the slower stress response of the hypothalamic-pituitary-adrenal (HPA) axis. This triggers the release of corticotropin releasing hormone (CRH), adrenocorticotropin hormone (ACTH), and glucocorticoids, particularly cortisol. However, the physiological stress response in males has been much more extensively studied than is the case for females (Peirce et al., 2002). Furthermore, both-sex studies are often based on small samples without sufficient power to detect sex differences. This is highly problematic because important sex differences have been reported in the HPA response to stress

Arginine vasopressin (AVP) and oxytocin are two peptide hormones induced by the HPA axis. Even though AVP and oxytocin are structurally similar and differ from each other by only two amino acids (Klein & Corwin, 2002), the two hormones differ widely in the roles they play in response to stress. Whereas AVP stimulates the fight-or-flight response and HPA axis activation (Klein & Corwin, 2002), oxytocin appears to suppress the HPA response to stress and be regulated by the parasympathetic nervous system (PNS; Klein & Corwin, 2002; Neumann, 2008; Neumann et al., 2000). AVP levels are higher in males than in females and may be regulated by testosterone (Rasmusson et al., 2002). In contrast, oxytocin levels are higher in females, and the bio-behavioural effects of oxytocin are enhanced by oestrogen (Klein & Corwin, 2002). Furthermore, there is preliminary evidence that the two female sex

officers better than any police-specific socialisation processes.

**4. Sex differences in initial trauma response** 

differences in PTSD.

(Kirschbaum et al., 1999).

account for any additional difference in PTSD levels. In contrast, Irish et al. (2011) found that perceived life threat could not account for sex differences in PTSD severity after an MVA, but that peritraumatic dissociation served as a partial mediator of 6 week and 6 month PTSD severity. Finally, Spindler et al. (2010) found that sex was no longer significantly associated with PTSD status in a logistic regression analysis after perceived life threat was controlled for, whereas two other studies have found that neither peritraumatic dissociation or perceived threat (Ehlers et al., 1998) nor peritraumatic helplessness or horror (O'Connor & Elklit, 2008) could eliminate sex as a risk factor for PTSD. Thus, contradictory findings have been reported on whether sex differences in peritraumatic reactions can account for sex differences in PTSD.
