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					           Effect of Sleep on Heart Rate                                                                Overview
                     Variability
                                                                                                           Objectives
                                                                                                           Heart Rate
                                                                                                           Sleep: Significance of this study
                                                            -Payel Ghosh                                   Data
                                                                                                           Methodology
                                                                                                           Results
                                                                                                           Conclusion
                                                                Statistical Signal Processing-Fall 05




Objectives                                                                                              Heart Rate


     Objective: This study is aimed at finding how sleep
     affects the body, in terms of what is already
     understood about the heart rate PSD.
     The causes of heart rate variability have been
     researched a lot and co-related with the activity of                                                  Measured with the Electrocardiogram (ECG).
     the autonomic nervous system that affects blood                                                       Definition: Times per minute that the heart contracts.
     pressure, respiration etc.                                                                            RR (Inter beat interval) to HR (heart rate time series)
     Studied and compared the differences in heart rate                                                    conversion.
     PSDs of 7 subjects in awake and asleep states.
                                                                                                         * Image taken from http://ecg.mit.edu/time-series/fs3.gif




Heart Rate PSD                                                                                          Sleep: Significance of this study

                                                                Autonomous nervous                         Definition: Dynamic state of consciousness
                                                                system
                                                                                                           characterized by rapid fluctuations in
                                                                Parasympathetic activity
                                                                 –   Conservation of energy
                                                                                                           autonomic activity.
                                                                     (reduction in HR, BP etc.)            Gaps in our current knowledge
                                                                Sympathetic Activity                          –     Relatively new area of research (~50 years)
                                                                 –   Prepares the body for fear
                                                                     and flight. (increase in heart
                                                                                                              –     Understanding of autonomic activity during sleep
                                                                     rate, respiration, BP)                         is not clearly understood.
                                                                                                              –     Autonomic activity understanding-based on
                                                                                                                    observations of the heart rate and blood pressure.

* Image taken from http://ecg.mit.edu/time-series/fs3.gif




                                                                                                                                                                         1
Data                                                                                                                   Data Preprocessing

 Heart rate time series: 30-60 minute data.
 Awake state (posture: sitting)
 Asleep state (posture: lying down)
 Non-uniformly sampled at 1 Hz (approx.).
 5 minute durations used for analysis.
 Local stationarity assumption.
  –     Mechanisms responsible for heart rate variation are
        assumed to remain unchanged in this time period.




                                                                                                                                   Uniformly re-sampled at 2 Hz




Methodology
Blackman-Tukey Periodogram                                                                                             Methodology Continued

                                          0              Signal Data Record   N-1                                       Very low frequency components <0.02 Hz removed.
                                                                                                                        Length of lag window: 75 points
                                                                                                                        40s Parzen window
                       Periodogram: R x (e jω )
                                    ˆ                                         Autocorrelation:                          Confidence interval: 90%
                                                                                             L −1
                                                                                ˆ
                                                                               {rx (l )}     −( L −1)                   Low frequency power: Area under the PSD curve
                                 Convolution:
                                                                          Windowing:                                    (0.04-0.15 Hz)
                             R x ( e jω ) ⊗ W a ( e jω )
                             ˆ                                                                   L −1
                                                                           ˆ
                                                                          {rx (l )wa (l )}       − L −1
                                                                                                                        High frequency power: Area under the PSD curve
                                      R x PS ) (e jω )
                                      ˆ(                                                                                (0.15-0.5 Hz).
                                                                              DFT using FFT



 * Taken from SSP textbook                                                          R x( PS ) ( e jω )
                                                                                    ˆ                           2π
                                                                                                          w−
                                                                                                               N FFT




Results                                                                                                                Results Continued




                                                           Subject 1                                                                             Subject 2




                                                                                                                                                                          2
Results Continued         Results Continued




              Subject 3                                  Subject 4




Results Continued         Results Continued




              Subject 5                                  Subject 6




Results Continued         Results: Table

                              Asleep (msec2x103/Hz)             Awake (msec2x103/Hz)
                               LFP     HFP     LFP/HFP            LFP     HFP    LFP/HFP


                          1    15.99   4.98      3.21       1     24.18   7.81    3.09
                          2    14.23   4.17      3.41       2     31.71   9.54    3.32
                          3    12.18   10.07     2.10       3     27.29   9.71    2.81
                          4    20.81   6.41      3.24       4     25.46   9.34    2.72
                          5    13.43   5.39      2.48       5     19.54   6.49    3.01
                          6    17.81   6.85      2.60       6     22.46   8.14    2.75
                          7    19.48   8.03      2.42       7     23.33   8.02    2.91

              Subject 7       Average           2.78                              2.94




                                                                                           3
Conclusion                                              Thanks!

 The balance of sypathetic/para-sympathic activity of    Dr. James McNames.
 the heart for awake and asleep states of the 7
 subjects was comparable. This was expected
                                                         Reviewers for valuable feedback on my
 because the subjects were in resting state.             paper.
 Experiments with more number of subjects (in
 various other postures) should be performed before
 correlating physiological processes (that affect the
 shapes of the heart rate PSD) with sleep.                  Questions?




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posted:11/28/2011
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