title: Gas exchange detection of exercise-induced right-to-left shunt in patients with primary pulmonary hypertension.
abstract: BACKGROUND
  Because of high pulmonary vascular resistance in patients with primary pulmonary hypertension (PPH), right atrial pressure may exceed left atrial pressure during exercise, resulting in a right-to-left shunt via a patent foramen ovale (PFO). This shunting would disturb arterial PCO2 and H+ homeostasis if the pulmonary blood were not simultaneously hyperventilated to compensate for the high CO2 and H+ in the shunted blood. This article first hypothesizes and then describes unique changes in gas exchange when right-to-left exercise-induced shunting (EIS) occurs.
  
  
  RESULTS
  Retrospectively, the cardiopulmonary exercise tests of 71 PPH patients were studied. Criteria postulated to document hyperventilation of the pulmonary blood flow due to a right-to-left EIS were (1) an abrupt and sustained increase in end-tidal O2 with a simultaneous sustained decrease in end-tidal CO2; (2) an abrupt and sustained increase in the respiratory exchange ratio; and (3) usually, an associated decline in pulse oximetry saturation. Each patient was evaluated for a PFO with resting echocardiography. The investigators interpreting the gas exchange evidence of EIS were blinded to the echocardiographic readings. Forty-five percent of the patients had demonstrable EIS by gas exchange criteria. Almost all were also positive for a PFO by echocardiography. Using the resting echocardiograph as the reference, the sensitivity, specificity, positive and negative predictive values, and accuracy were all between 90% to 96%.
  
  
  CONCLUSIONS
  Exercise-induced right-to-left shunting can be detected by noninvasive, cardiopulmonary exercise testing in patients with PPH.
authors.affiliation: Department of Medicine, Harbor-UCLA Medical Center, Torrance, Calif 90509-2910, USA.
authors.forename: Xing-Guo
authors.initials: XG
authors.lastname: Sun
authors.forename: James E
authors.initials: JE
authors.lastname: Hansen
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Oudiz
authors.forename: Karlman
authors.initials: K
authors.lastname: Wasserman
mesh_terms: D000328:Adult; D001784:Blood Gas Analysis; D004452:Echocardiography / Q000379:methods; D005080:Exercise Test; D005260:Female; D006344:Heart Septal Defects, Atrial / Q000503:physiopathology*; D006801:Humans; D006976:Hypertension, Pulmonary / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012680:Sensitivity and Specificity