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Sleep Fragmentation Index - Validation Reference

Last Updated: Jul 26, 2016 06:01PM CDT

Preliminary explanation of the Sleep Fragmentation Index (SFI).

Sleep Fragmentation is an index of restlessness during the sleep period expressed as a percentage. [6] The higher the index, the more sleep is disrupted. [4]

The original fragmentation index (FI) was measured in PSG as the number of changes from deep sleep to sleep stage 1 (light sleep) divided by all sleep time (in hours) times 100, resulting in a percentage of total sleep time (TTS).   FI is usually accompanied by relatively fast movement lasting between 1 and 3 seconds, which are also called micro arousals. [5]

In relation to actigraphy, a Belgium study written in December of 1986 (revised 4/6/1987 [1] ) compared data from a device called Actometer[2] with PSG data to determine FI and the following indexes: a movement index (MI), a fragmentation index (FI), and a global index (MFI).

The movement index (MI) was”…obtained by dividing the number of minutes with one or more movements by TIB (time in bed) and multiplying that by 100.” [1]

The fragmentation index (FI) was determined to be “…the ratio of the number of phases of 1-min. immobility to the total number of immobility phases of all durations multiplied by 100.” [1]   Or “…the number of times that sleep was terminated after 1 minute expressed as a percentage of total estimated sleep time.” [4]

‘Phases’ from the paper correlate to epochs since they are using 1-min. as a reference time. 

“The global index (MFI) is obtained by adding MI and FI…”   This is the SFI , as it includes both restlessness and fragmentation of the sleep period. [3]

The Actiwear® software from Respironics® includes sleep fragmentation as: “((number of mobile epochs lasting four epochs + number of immobile epochs < 1 minute duration / number of immobile epochs > 1 minute duration) x 100)”3, with data recorded at 1-minute epochs. 

MI – total of scored awake minutes divided by Total time in bed in hours x 100                                                   

FI – total of 1 minute scored sleep bouts divided by the total number of sleep bouts of any length x 100

SFI – is the sum of MI and FI                

1 G. Aubert-Tulkens, et al, Ambulatory Evaluation of Sleep Disturbance and Therapeutic Effects in Sleep Apnea Syndrome by Wrist Activity Monitoring, AM REV RESPIR DIS 1987

2 Gueuning F, Eugene C., A long-term microprocessor-bases wrist-worn actimeter, (abstract) Padova: ISAM, 1985: 707-12 (Note: first know battery operated Actigraph).

3 Elizabeth J. Mezick, et al, Intra-Individual Variability in Sleep Duration and Fragmentation: Associations with Stress, 10.1016/psyneuen 2009.04.005

4 Andrea Loewen, et al, Sleep Distrution in Patients with Sleep Apnea and End-Stage Renal Disease, J Clin Sleep Med. 2009 August 15; 5(4): 324-329

5Mary J. Morrell, et al, Sleep Fragmentation, Awake Blood Pressure, and Sleep-Disordered Breathing in a Population-based Study, American Journal of Respiratory and Critical Care Medicine. Vol. 162, No.6 (2000), pp 2091-2026,

6Kristen L. Knutson, et al, Cross-Sectional Associations Between Measures of Sleep and Markers of Glucose Metabolism Among Subjects With and Without Diabetes, Diabetes Care 34:1171-1176, 2011.


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