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Resting End-Tidal CO₂ and Negative Affectivity

Department of Psychology (I.V.D., S.V., I.C., S.D.P., S.D., O.V.d.B.) and Department of Respiratory Medicine, University Hospital Gasthuisberg (K.P.V.d.W.), University of Leuven, Belgium.

Address correspondence and reprint requests to Ilse Van Diest, Research Group for Stress, Health and Well-Being, Department of Psychology, University of Leuven, Tiensestraat 102, B-3000 Leuven, Belgium. E-mail: Ilse.Vandiest{at}psy.kuleuven.ac.be

OBJECTIVE: Dhokalia, Parsons, and Anderson (Psychosom Med 1998;60:33–37) found a positive correlation between a trait measure of negative affectivity (NA; neuroticism) and resting end-tidal fractional concentration of CO₂ (FetCO₂) (fractional-concentration of end-tidal carbon dioxide) in a nonclinical sample. This contrasts sharply with studies reporting a negative association of FetCO₂ with state measures of NA and with studies reporting no or a negative relationship between FetCO₂ and trait NA. In two studies we aimed to clarify this paradox.

MATERIALS AND METHODS: In the first study, 110 participants (83 women) completed the PANAS and a Checklist for Psychosomatic Symptoms in daily life. FetCO₂ was measured noninvasively during 5 minutes via a nose cannula connected to a capnograph. In the second study, FetCO₂ of high (N= 20, 10 men) and low (N= 20, 10 men) NA participants was sampled once with a nasal cannula and once while breathing through a mouthpiece for 6 minutes each during rest, completion of the NEO-PI-R questionnaire, and completion of a verbal knowledge test.

RESULTS: The first study found no association between trait NA and resting FetCO₂ after partialling out the effects of gender, menstrual phase, and use of oral contraceptives. The second study showed that FetCO₂ increased significantly in the high NA group only when the particpants filled out the questionnaires, regardless of its type.

CONCLUSIONS: Overall, no association between dispositional NA and cross-situational FetCO₂ was observed. Apparently inconsistent findings may be caused by lack of control for hormonal status and mental load during testing.

Key Words: negative affectivity, • neuroticism, • carbon dioxide pressure, • hyperventilation.

Abbreviations: NA = negative affectivity;; FetCO₂ = fractional concentration of end-tidal carbon dioxide;; PANAS = positive and negative affect scales;; CPS = checklist for psychosomatic symptoms;; ASI = anxiety sensitivity index;; STAI = trait version of the state-trait anxiety inventory;; NEO-PI-R = revised NEO personality inventory.

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