Exercise tolerance evaluated by respiratory gas analysis during treadmill exercise test in panic disorder patients

Exercise intolerance is commonly complained by panic disorder patients. In the present study, exercise capacity was evaluated in panic disorder patients by the anaerobic threshold (AT) which can be measured at submaximum workload and is hardly influenced by subjects' motivation. The subjects were ten (8 male and 2 female) panic disorder patients and seventeen male sedentary control subjects. Each of them underwent a respiratory gas analysis during a treadmill exercise test. Each of oxygen uptake (V̇O₂), heart rate (HR) and ventilatory equivalent for oxygen uptake (V̇E/V̇O₂) at rest. At AT and at peak workload were obtained. Covariance analyses in which age was used as a covariate were utilized for some of the indices because they correlated with age and patients were generally younger than controls (31.0±9.0 vs. 55.8±8.2; mean±SD), and the comparison was made only in male subjects. We also examined the presence of mitral valve prolapse (MVP) because it had been reported that MVP was related to impaired working capacity in anxiety disorder patients. In addition, we measured the level of experienced anxiety during exercise to clarify the relationship between subjective anxiety and exercise intolerance. Oxygen uptake at AT (V̇O₂-AT; F(1.21) - 0.12, p=0.7359) as well as at peak oxygen uptake (V̇O₂-peak; F(1.21) - 0.52, p=0.4771) were very similar in the two groups, but patients showed significantly higher HR at rest (t(23) = 2.60, p=0.0162) and at AT (t(22)=4.65, p=0.001). Patients without MVP experienced the highest anxiety before starting exercise (p=0.0351). Thus, objective exercise intolerance was not present in view of normal V̇O₂-AT and V̇O₂-peak, but hyperresponsiveness of HR and/or anticipatory anxiety against exercise could be related to subjective exercise intolerance in panic disorder patients. This study was only preliminary, and larger numbers of panic disorder patients and age and sex matched sedentary control subjects should be included in future studies.