Isocapnic intermittent hypoxia and endothelial dysfunction

Subjects will be infused with L-N monomethyl arginine (LNMMA) and saline (placebo) in a single blinded randomized design on two separate days to assess the effect of nitric oxide synthase inhibition on arterial stiffness. Initially there will be a 10 minute baseline period. Then the LNMMA or saline will be infused over 5 minutes, after which there will be another 5 minute baseline period. Following this there will be the 20 minute period of hypoxia and then a 10 minute recovery period. During this the subjects will breathe through a mouthpiece connected to special equipment which delivers different gas mixtures and enables the delivery of the hypoxic exposure. Heart rate blood pressure, arterial stiffness ( via pulse wave analysis), and peripheral vasoconstriction (via peripheral arterial tonometry PAT) will be measured.