“…Briggs et al (1993) demonstrated that patients with the respiratory subtype of panic suffer more spontaneous PAs than patients with the residual subtype and that they respond better to imipramine than to alprazolam. The respiratory subtype has been shown to be associated with increased familial risk of PD (Horwath et al, 1997;Nardi et al, 2003Nardi et al, , 2006a, to be more common among heavy smokers, to have a longer duration and major severity of illness (Biber and Alkin, 1999), and to have a lower resting end-tidal pCO 2 (Moynihan and Gevirtz, 2001) and a higher sensitivity to CO 2 inhalation (Biber and Alkin, 1999;Valenca et al, 2002;Abrams et al, 2006;Nardi et al, 2006a, b). Other clinical features displayed by PD patients with the respiratory subtype include a later onset of the disease and a faster response to nortriptyline (Nardi et al, 2003(Nardi et al, , 2006a, more past traumatic suffocation experiences and respiratory diseases (Bouwer and Stein, 1997;Verburg et al, 1995), higher levels of anxiety sensitivity, and more panic-agoraphobic spectrum symptoms (Onur et al, 2006).…”