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→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 machinesbecause inspiration starts when flow returns to zero from expiration. Work is in progress to correct this errorby changing the inspiration signal to a positive flow rate. Resmed machines generate the I:E data and it can be considered reliable.
===Robysue's Flow Rate Interpretation from Forum Posts===
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