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Specificity of Panic Response to CO2 Inhalation
in Panic Disorder: A Comparison With Major Depression
and Premenstrual Dysphoric Disorder
Researcher: Justine M. Kent, M.D.


Objective: The behavioral response to
CO2 inhalation has been used to differentiate
panic disorder patients from normal
subjects and other clinical populations.
This study extended examination of the
diagnostic specificity of CO2-induced anxiety
by testing panic disorder patients and
clinical populations with reported low
and high sensitivity to CO2 inhalation (patients
with major depression and patients
with premenstrual dysphoric disorder, respectively).
Method: The behavioral responses to inhalation
of 5% and 7% CO2, administered
by means of a respiratory canopy, were
studied in 50 patients with panic disorder,
21 with major depression, and 10 with
premenstrual dysphoric disorder and in
34 normal comparison subjects. Occurrence
of panic attacks was judged with
DSM-IV criteria by a blind rater. Subjects
were rated on three behavioral scales at
baseline and after each CO2 inhalation.
Results: Panic disorder patients had a
higher rate of CO2-induced panic attacks
than depressed patients and normal subjects,
whose panic rates were not distinguishable.
The panic rate for patients
with premenstrual dysphoric disorder
was similar to that for panic disorder patients
and higher than that for normal
subjects. Subjects with CO2-induced panic
attacks had similarly high ratings on the
behavioral scales, regardless of diagnosis,
including the small number of panicking
normal subjects. Seven percent CO2 was a
more robust panicogen than 5%, and response
to 7% CO2 better distinguished
panic disorder patients from normal subjects
than response to 5% CO2.
Conclusions: Patients with panic disorder
and patients with premenstrual dysphoric
disorder are highly susceptible to
CO2-induced panic attacks, and depressed
patients appear to be insensitive to CO2 inhalation.
The symptoms of CO2-induced
panic attacks have a similar intensity regardless
of the subject’s diagnosis.


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