Photoplethysmographic assessment of pulse wave reflection : Blunted response to endothelium-dependent beta2-adrenergic vasodilation in type II diabetes mellitus

OBJECTIVESWe sought to determine whether a simple index of pressure wave reflection may be derived from the digital volume pulse (DVP) and used to examine endothelium-dependent vasodilation in patients with type II diabetes mellitus.BACKGROUNDThe DVP exhibits a characteristic notch or inflection point that can be expressed as percent maximal DVP amplitude (IPDVP). Nitrates lower IPDVP, possibly by reducing pressure wave reflection. Response of IPDVPto endothelium-dependent vasodilators may provide a measure of endothelial function.METHODSThe DVP was recorded by photoplethysmography. Albuterol (salbutamol) and glyceryl trinitrate (GTN) were administered locally by brachial artery infusion or systemically. Aortic pulse wave transit time from the root of the subclavian artery to aortic bifurcation (TAo) was measured by simultaneous Doppler velocimetry.RESULTSBrachial artery infusion of drugs producing a greater than threefold increase in forearm blood flow within the infused limb was without effect on IPDVP, whereas systemic administration of albuterol and GTN produced dose-dependent reductions in IPDVP. The time between the first and second peak of the DVP correlated with TAo(r = 0.75, n = 20, p < 0.0001). The effects of albuterol but not GTN on IPDVPwere attenuated by NG-monomethyl-l-arginine. The IPDVPresponse to albuterol (400 μg by inhalation) was blunted in patients with type II diabetes mellitus as compared with control subjects (fall 5.9 ± 1.8% vs. 11.8 ± 1.8%, n = 20, p < 0.02), but that to GTN (500 μg sublingually) was preserved (fall 18.3 ± 1.2% vs. 18.6 ± 1.9%, p = 0.88).CONCLUSIONSThe IPDVPis influenced by pressure wave reflection. The effects of albuterol on IPDVPare mediated in part through the nitric oxide pathway and are impaired in patients with type II diabetes.