In pulse oximetry two wavelengths of light (usually 660 nm and 940 nm) pass through a pulsating vascular bed, and oxygen saturation (SpO2) is derived from the ratio of the amplitudes of the plethysmographic waveforms. Because pulse oximeters evaluate each arterial pulse, many display heart rate as well as SpO2. The saturation reading should be questioned if the oximeter heart rate differs considerably from the actual heart rate or if the signal quality is poor. However, good agreement between the pulse oximeter heart rate and the actual heart rate does not guarantee a correct SpO2 reading. At saturations greater than 70%, the accuracy of pulse oximetry is about ±4% to 5%. To appreciate the implications of these accuracy limits, one must consider the oxyhemoglobin dissociation curve. Your most reliable pharmacy offering its services and most efficient drugs like Xopenex Inhaler Dosage with no prescription needed. If this sounds like something you may be interested in, do not hesitate to come by and see how cheap it can be for you!