Pulse Waveform Analysis of the Ocular Blood Flow Using Laser Speckle Flowgraphy before and after Glaucoma Treatment

Figure 2

Definition and calculation of pulse waveform parameters. (a) Fluctuation is a parameter indicating instability of the blood flow. It is proportional to the mean fluctuation in the mean blur rate (MBR) divided by the average MBR in a waveform. Fluctuation = constant of promotion × mean of fluctuation/MBRaverage. (b) The blowout score (BOS) indicates the amount of the blood flow volume in one heartbeat and is calculated from the difference of the maximum and minimum MBR as well as the average waveform distribution. BOS = 100 × {2 − (MBRmax − MBRmin)/MBRavergae}/2. A high BOS is an indicator of high constancy of blood flow during the cardiac cycle. (c) The acceleration time index (ATI) is defined as the ratio of the time before the pulse wave peak value is reached in a heartbeat. ATI = 100 × length to peak/length of a heartbeat. A smaller ATI indicates a more rapid increase in the MBR to the peak. (d) Blowout time (BOT) is defined as the ratio of the half width (i.e., the time that the waveform is higher than half of the mean of the minimum and maximum signals) in a heartbeat. BOT = 100 × half width/width of a heartbeat. A higher BOT indicates that a high level of MBR is maintained for a larger proportion of a single heartbeat. (e) Skew represents asymmetry of the MBR waveform in the waveform distribution. If the waveform is completely symmetrical, the skew is zero. When the peak of the pulse wave comes faster than that of the symmetrical waveform, the skew increases, and when the peak comes slower, the skew decreases.

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