Pulse oximetry pulse indicator

DETAILED DESCRIPTION FIG.
1 illustrates the standard plethysmograph waveform 100, which can be derived from a pulse oximeter.
The waveform 100 is a display of blood volume, shown along the y-axis 110, over time, shown along the x-axis 120.
The shape of the plethysmograph waveform 100 is a function of physiological conditions including heart stroke volume, pressure gradient, arterial elasticity and peripheral resistance.
The ideal waveform 100 displays a broad peripheral flow curve, with a short, steep inflow phase 130 followed by a 3 to 4 times longer outflow phase 140.
The inflow phase 130 is the result of tissue distention by the rapid blood volume inflow during ventricular systole.
During the outflow phase 140, blood flow continues into the vascular bed during diastole.
The end diastolic baseline 150 indicates the minimum basal tissue perfusion.
During the outflow phase 140 is a dicrotic notch 160, the nature of which is disputed.
Classically, the dicrotic notch 160 is attributed to closure of the aortic valve at the end of ventricular systole.
However, it may also be the result of reflection from the periphery of an initial, fast propagating, pressure pulse that occurs upon the opening of the aortic valve and that precedes the arterial flow wave.
A double dicrotic notch can sometimes be observed, although its explanation is obscure, possibly the result of reflections reaching the sensor at different times.
FIGS.
2-3B illustrate plethysmograph waveforms 200, 310, 360 that display various anomalies.
In FIG.
2, the waveform 200 displays two arrhythmias 210, 220.
In FIG.
3A, the waveform 310 illustrates distortion corrupting a conventional plethysmograph 100 (FIG.
1).
FIG.
3B shows a filtered waveform 360 after distortion has been removed through adaptive filtering, such as described in U.
S.
Pat.
No.
5,632,272 cited above.
FIG.
3B illustrates that, although the waveform 360 is filtered, the resulting pulses 362 have shapes that are distorted in comparison to the pulses illustrated in FIG