Orthostatic increase of respiratory gas exchange inhyperventilation syndrome

摘要

BACKGROUND—Hyperventilation syndrome (HVS) is a common disorder which is difficult to diagnose because of somatic symptoms and its episodic nature. In previous studies respiratory alkalosis in arterial blood was often found during orthostatic tests in patients with HVS. The purpose of this study was to assess these orthostatic changes by non-invasive pulmonary gas exchange measurements and to evaluate whether these responses discriminate patients with HVS from healthy subjects.
METHODS—Respiratory gases were collected with a face mask and pulmonary gas exchange was measured after 10 minutes at rest and after eight minutes standing upright in 16 patients with HVS and 13healthy control subjects. In patients with HVS arterial blood samples were also drawn at rest and in the standing position.
RESULTS—At rest the variables of respiratory gas exchange did not differ significantly between the groups. As a response to standing, minute ventilation increased in both study groups but significantly more in the patients with HVS (mean difference 5.4 l/min (95% CI 1.1 to 9.6)). The changesin end tidal CO2 fraction (FETCO2) and in ventilatory equivalents for oxygen(V̇E/V̇O2) and forCO2 (V̇E/V̇CO2) during theorthostatic test were also significantly larger in patients with HVSthan in healthy controls. During standing FETCO2 was significantly lower (mean difference-1.1 kPa; 95% CI -1.5 to -0.6) andV̇E/V̇O2 (mean difference18.4; 95% CI 7.7to 29.0) andV̇E/V̇CO2 (meandifference 11.7; 95% CI 4.8 to 18.6) were significantly higher in HVSpatients than in healthy controls. By using the cut off level of 4%for FETCO2 the sensitivity and specificity ofthe test to discriminate HVS were 87% and 77%, respectively, and byusing the cut off level of 37 forV̇E/V̇O2 they were 93%and 100%, respectively. In the HVS patients arterial PCO2 and FETCO2 wereclosely correlated during the orthostatic test(r = 0.93, p<0.0001).
CONCLUSIONS—As aresponse to change in body position from supine to standing, patientswith HVS have an accentuated increase in ventilation whichdistinguishes them from healthy subjects. These findings suggest thatnon-invasive measurements of pulmonary gas exchange during orthostatictests are useful in the clinical evaluation of patients withhyperventilation disorders.