Inspiration Expiration (I:E) Ratio
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The Flow Rate graph is a visual record of each and every breath you took while using the machine. You are inhaling when the Flow Rate is positive and you are exhaling when the Flow Rate is negative. Stronger inhalations result in higher (positive) peaks and stronger exhalations result in lower (more negative) valleys in the Flow Rate graph. The events from the Event Table are superimposed on the Flow Rate graph with vertical lines of different colors.
The Flow rate graph can be enhanced by showing a dotted line at zero flow by right-clicking on the left margin of the Flow Rate Graph and using the context menu to set a Dotted Line at Zero. Everything above that line is inspiration (I) and everything below is expiration (E). This is a good example of normal I:E where in inspiration time is shorter than expiration. Normal breathing in this case, the inspiration quickly gains in flow rate (volume in mL/sec) and reaches a peak at which time the flow rapidly slows to zero, then expiration seamlessly beings. The expiration cycle is passive, meaning your chest simply relaxes and gravity does most of the work of collapsing the chest and causing air in the lungs to flow out. Expiration results in a fast flow rate at first which gradually slows to near zero resulting in the flattened line near zero flow. This is not holding your breath, but is the result of a relaxed normal exhale, as compared to a forced exhale. Take a look at your figure with the transitions from I to E marked. We can look at the transitions in the time scale (x-axis) and see that inspiration is approximately one breath every 5-seconds (12 BPM) with inspiration being about 2.2 seconds and expiration being 2.8 seconds. Notice the green line bisecting the graph during expiration below and showing -3.43 mL/sec flow. This shows the exact place where your cursor was located is indeed in expiration and there is expiratory flow. This would be textbook normal.
Inspiration Expiration Ratio (I:E Ratio)
The usual way of expressing the I:E ratio is to compare inspiration time to expiration time. The best statistic to use for calculating the I:E Ratio is the median inspiration and expiration times. For example median values from your data, assume your inspiratory time is 1.54 and expiratory time is 2.88. 2.88/1.54=1.87, or a ratio of 1 to 1.87 (Also expressed as 1:1.87). In this case, the expiration is nearly twice as long as inspiration which is normal. In general, the I:E ratio will range from 1:1 to 1:3, meaning normal exhale can be in a range of equal to 3 times the time of inhale.
We often see an I:E ratio of less than 1 suggesting a longer inspiration time than expiration. This inverse I:E ratio can occur, but most of the time it is an error in the respiration timing by the CPAP machine. In most cases, the machine will count part of expiration as inhale, resulting in an incorrect I:E time or ratio. An I:E ratio must be greater than zero and generally greater than 1:0.5 (one to one-half seconds), and will usually be less than 1:3 (one to three-seconds). Please note that Sleepyhead and OSCAR currently show incorrect I:E times on all Philips CPAP and BiPAP machines because inspiration starts when flow returns to zero from expiration. Work is in progress to correct this error by changing the inspiration signal to a positive flow rate. Resmed machines generate the I:E data and it can be considered reliable.
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