Table 3. Studies assessing PA rates in RS and NRS subjects after a CO2 challenge test.
| Study | RS | NRS | CO2 challenge test | PA criteria | PA rates in RS, n (%) | PA rates in NRS, n (%) | p-value | Other outcomes |
|---|---|---|---|---|---|---|---|---|
| Biber54 | 28 | 23 | Single breath of 35% CO2 and 65% O2/breath holding for 5 seconds | Sensation of fear or panicAt least four DSM-III-R PA symptomsAt least one cognitive symptom | 22 (79) | 11 (48) | < 0.05 | Higher PAS scores and cigarette smoking in RS |
| Nardi69 | 11 | 9 | Double-breath 35% CO2 inhalation, breath holding for 8 seconds; test repeated after 2 weeks | Four or more DSM-IV PA symptomsAt least one DSM-IV cognitive symptom (fear of dying or fear of going crazy)Sensation of panic or fear resembling real-life PAAgreement of two medical doctors to confirm clinical PA | 7 (63.3)(1st test)9 (81.8)(2nd test) | 3 (33.3)3 (33.3) | 0.0240.011 | |
| Valença55 | 16 | 11 | Double-breath 35% CO2 inhalation, breath holding for 8 seconds; test repeated after 2 weeks | As in Nardi69 | 15 (93.7)(1st breath)14 (87.5)(2nd breath) | 5 (43.4)5 (43.4) | 0.0090.033 | |
| Abrams70 | 10 | 23 | 5% CO2 rebreathing challenge for 5 minutes or end-tidal CO2 pressure > 70 mmHg | At least four DSM-IV PA symptomsAt least one cognitive symptom | 4 (40) | 5 (23) | No statistical difference | Subjective suffocation, respiratory rate, and voluntary termination higher in RS |
| Freire25 | 66 | 51 | Double-breath 35% CO2 | As in Nardi69 | 53 (80.3) | 6 (11.8) | < 0.001 |
All studies used the Briggs et al. criteria29 to define the respiratory subtype of panic disorder.
NRS = non-respiratory subtype; PA = panic attack; PAS = Panic and Agoraphobia Scale; RS = respiratory subtype.