Received November 9, 2007
Revised January 2, 2008
Accepted after revision February 18, 2008

¹ University of Turku
² Tampere University Hospital
³ Turku University Central Hospital

^* To whom correspondence should be addressed. E-mail: jemato{at}utu.fi.

	Abstract

While there are a number of studies demonstrating association between arterial oxyhemoglobin saturation events during sleep and markers of vascular impairment, the contribution of peripheral carbon dioxide to the development of atherosclerosis is poorly understood. We used ultrasound imaging to measure carotid artery intima-media thickness (IMT) as well as flow-mediated dilatation (FMD) and nitroglycerin-mediated dilatation (NMD) of brachial artery in 103 generally healthy 46-year-old (± 2 years) women. Characteristic event patterns were extracted from their overnight recordings of arterial oxyhemoglobin saturation (SaO2), end-tidal carbon dioxide (EtCO2) and transcutaneous carbon dioxide (TcCO2). Importance of the event patterns was evaluated through predictive modeling of classes of the ultrasound measurements while controlling for potential confounders. Prediction accuracy was assessed with cross-validation and reported as the area under the receiver operating characteristic curve (AUC). Overnight TcCO2 patterns predicted each of the ultrasound measurements with high accuracy (IMT: AUC=0.70, FMD: AUC=0.75, and NMD: AUC=0.81, all with p<0.001). Adding the SaO2 or EtCO2 patterns into the models did not significantly increase their predictive powers (AUC=0.72, AUC=0.77, and AUC=0.83, respectively). The most important patterns reflected overnight variability in TcCO2. These results suggest a novel link between overnight carbon dioxide events and early signs of vascular impairment in middle-aged women. Non-invasive TcCO2 measurements combined with non-linear modeling techniques could be used to reveal potential markers of vascular impairment already in relatively healthy subjects.

Key Words: Carbon dioxide, Cardiovascular, Sleep