Challenging patients in the laboratory has been a widely used tool in the study of panic disorder (PD). There is now ample evidence demonstrating that compared to normal controls, PD patients display heightened physiologic activation, marked rise in fear, and increased probability of panic in response to voluntary hyperventilation (Beck & Scott, 1988; Gorman et al., 1984, 1988, 1994; Holt & Andrews (1989a) and Holt & Andrews (1989b); Nardi, Valenca, Nascimento, Mezzasalma, & Zin (1999) and Nardi, Valenca, Nascimento, Mezzasalma, & Zin (2001); Papp et al., 1997), inhalation of 5% CO2 (Gorman et al. (1984), Gorman et al. (1988) and Gorman et al. (1994); Papp et al., 1997; Woods, Charney, Goodman, & Heninger, 1988), 7% CO2 (Gorman et al., 1994; Papp et al., 1997), and 35% CO2 (Gorman et al., 1990; Griez, Lousberg, van den Hout, & van der Molen, 1987; Papp et al., 1993; Perna, Bertani, Arancio, Ronchi, & Bellodi (1995) and Perna, Bussi, Allevi, & Bellodi (1999); Perna, Gabriele, Caldirola, & Bellodi, 1995). Moreover, PD sufferers show greater sensitivity to 5% and 35% CO2 than patients with obsessive compulsive disorder (Griez, de Loof, Pols, Zandbergen, & Lousberg, 1990; Perna, Bertani, Arancio, Ronchi, & Bellodi, 1995), generalized anxiety disorder (Perna, Bussi, Allevi, & Bellodi, 1999; Verburg, Griez, Meijer, & Pols, 1995) or depression (Kent et al., 2001; Perna, Barbini, Cocchi, Bertani, & Gasperini, 1995) and greater sensitivity to hyperventilation challenges compared to those with generalized anxiety disorder, or social phobia (Holt & Andrews, 1989b; Rapee, Brown, Antony, & Barlow, 1992). Based on these findings, it has been suggested that respiratory abnormalities play a central role in the pathogenesis of panic disorder (Klein, 1993).
Despite the plethora of respiratory challenge studies, none to our knowledge have examined differential emotional responding to hyperventilation among panic patients with and without extensive agoraphobic avoidance. When present in panic disorder, agoraphobia is associated with markedly greater disruption in quality of life (de Jong & Bouman, 1995), significantly higher rates of comorbid depression (Goisman et al., 1994), substance abuse (Rapee & Medoro, 1994), and a less favorable response to both pharmacologic and cognitive-behavioral treatment (Goisman et al., 1994; Keller et al., 1994). Although panic patients with and without agoraphobia do not differ on panic attack frequency (Cox, Endler, & Swinson, 1995; Craske & Barlow, 1988; Rapee & Murrell, 1988; Telch, Brouillard, Telch, Agras, & Taylor, 1989), there are some data suggesting that panic patients with agoraphobia may display more intense respiratory distress such as faintness or dizziness during their panic attacks (de Jong & Bouman, 1995; Noyes, Clancy, Garvey, & Anderson, 1987; Telch et al., 1989).
The overall aim of the present investigation was to examine the role of respiratory sensitivity in panic disorder and agoraphobia by comparing emotional responding to voluntary hyperventilation challenge among three panic groups: non-patients with current panic attacks (non-clinical panickers (NP)), patients with PD but minimal or no agoraphobia, and patients with PD plus moderate to severe agoraphobia. Several specific questions were addressed: (a) Do patients with PD (with or without agoraphobia) display greater anxious responding to a respiratory challenge compared to NP? (b) Do patients with PD with significant agoraphobia display heightened emotional responding relative to PD patients with minimal or no agoraphobia? and (c) Do measures of emotional sensitivity to hyperventilation challenge predict patients’ clinical status after controlling for clinical and demographic differences. Similarly, do indices of respiratory sensitivity predict agoraphobia status, even after controlling for differences in demographic and clinical characteristics?
