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AMSGRA user manual

Introduction

Before using any of the VU-AMS programs that extract physiological parameters (like AMSRES and AMSIMP), it is important to first create a so-called label data file (default extension .lbl). Labeling divides the entire measurement period into separate smaller periods. For each period start and end times are given as well as a set of codes and text labels describing the state of subject during that period in terms of posture, activity, physical load, social situation, mood state, work load, etc.. To create these labeled periods you have to use the AMSGRA program in combination with the subject’s diary or your observation chart/video recording. In the label data file all descriptive information on the subject's activity you might want to use in future analyses should be present. Make sure you have labeled all periods that might be considered of interest. There seems to be no urgent need to also label periods that you consider to be "irrelevant" or that are expected to occur in only a few subjects. However, we advise to always label the entire 24 hour recording. For example if the labeled periods are 18 minutes on average, this adds up to 78 labels per subject. In term of time, that is at least 25 minutes per subject. The advantage is that it will give confidence in the results later on (When using ambulatory physiological data, you will always want to check the influence of posture, and this is only possible if you have detailed information on posture).

The aim of labeling is to classify all activities of your subjects into a fixed number of activity categories with a fixed number of levels.

We cannot give you any firm directions on what labels to use. It really depends on the population and the research question. Here are some examples:

Activity category Category levels
Type of activity Reading, attending a meeting, eating, dancing, PC work, conversing, watching TV, exercising, attending a musical, car driving, ironing, etc.
Posture Sitting, standing, lying, walking, etc.
Physical activity Heavy, moderate, light, none
Social situation Alone, with significant other, with friends, With colleagues, etc.
Location At home, at the office, travelling, restaurant, etc.
Time of day Work, leisure time, sleep
Mood state Angry, friendly/happy, sad, anxious, tired

The label configuration file ... and how to create one!

When you have decided on the type of categories and levels within categories you want to use during labeling you need to summarize these in a ‘label configuration file’ (label.cfg). 

You can create your own label configuration file in two ways:

  1. use the ‘Create configuration file’ option from the submenu of ‘Labels’ in AMSGRA or 
  2. use a previous made label.cfg. An example of the text in such a label configuration file is given below. 

Make sure you copied the label.cfg file into the same directory as the .ams files that you want to label!

Example of a VU-AMS label configuration file (label.cfg)


#posture
10 lying
11 sitting
12 standing
13 walking
14 lying sitting
15 sitting standing
16 sitting standing walking
17 standing walking
18 unknown

#physical exertion
20 light physical activity
21 moderate physical activity
22 heavy physical activity
23 very heavy physical activity
24 sleep

#type of activity
29 desk work
30 administrative work
31 household activities
32 recreational activities
33 transportation (active)
34 transportation (passive)
35 telephone/talking at work
36 telephone/talking private
37 reading, internet or other recreative PC use
38 eating/drinking
47 watching TV
39 sleep

#location
40 work
41 home
42 outside
43 friends house
44 on the road
45 public building
46 physicians, dentists, or therapists office
48 house of family

#social situation
50 alone
51 with SO
52 with own children
53 with friends
54 with colleagues
55 with others
56 unknown


It cannot be said often enough that the label file really is central to the VU-AMS!! All further processing is tailored to it. By looking at start and end times of the labels, all programs adding variables like PEP etc will automatically attach the label information from the label data files. Time stamps, your activity and posture codes as well as any textual label will be attached automatically to each single value of the parameters that are being scored. Although this may appear to be extreme overkill, it is very convenient once you bring your final data matrix into your statistical program!

How to label an AMS file in AMSGRA

Loading data

Use the ‘Open AMS file’ command from the ‘File’ menu to load a data file (.ams).

Upper and lower graphical displays

The total registration of the subject is now shown in the upper display of your screen. The grey graded box between the two vertical bars indicates which part of this total registration is shown in the lower display. By moving the two vertical bars with your mouse, the size of the graded box and thus which part of the total registration is displayed enlarged in the lower panel, can be changed (a double headed arrow is displayed when this option is available). You can also move the whole box to the left or the right with your mouse (a ‘hand’ is displayed when this option is available).

Signal properties

For the heart rate (HRA), motility (MOT) and root mean squared successive differences of the heart rate (MSSD) settings can be changed by clicking on the colored box of the activated variable. By ticking the option ‘visible’ on or off a choice can be made which signals are displayed in the graphical panels.

Labelling your .ams file

HR and MSSD signals are highly sensitive to posture and physical activity. To obtain information about a subject’s daily routine, all subjects have to keep a detailed diary during the ambulatory measurement day. This diary information about type of (changes in) posture and activity is used during the labelling procedure. The VU-AMS device also contained an accelerometer (Montoye et al., 1983) which is sensitive to changes in vertical acceleration (MOT signal). This motility signal can be used to confirm the activities and postures written down in the diary.

The actual labeling procedure is done in the lower graphical display. Use your left mouse button to select the start and end point of the new label you want to add. Releasing the mouse button shows which time period is covered by your new label. This label is still red chequered. Click on the appropriate Category and Code names for this time period to finish the label. The label is now red. Repeat this procedure until the whole .ams is labelled.

Further analyses

Close AMSGRA after you have labelled your .ams file. A label file (.lbl) will be saved. This .lbl file is an ASCII file. In the .lbl file an average HR, MSSD and MOT value is given for each labeled time period. Therefore, the .lbl file can be used for further statistical analyses in for example in SPSS. Click on the ‘example files’ item in the Menu to find an example of such a SPSS file (lable.sps).

The next step should be a rigorous control of your label data file(s). First make sure that the minimum and maximum values reported for HR and MSD remain within acceptable physiological values. HRs above 200 or below 30 should be distrusted always. MSSD normally does not exceed 200 msec, and periods where the standard deviation of HR (HRSD) is above 30 should also be distrusted. No adequate calibration of the vertical acceleration monitor has been implemented in the VU-AMS as yet. MOT scores always vary between 0 and 100%. For each registration AMSGRA looks for the maximum and minimum motility value in the raw data file and scores all further motility values as a percentage of these extremes. Therefore, motility should not be compared across subjects. MOT is heavily skewed because sensitivity of the sensor is kept very crude to be able to deal with excessive movements as during stair climbing.


Reference

Montoye HJ, Washburn R, Servais S, Ertl A, Webster JG, Nagle FJ. Estimation of energy expenditure by portable accelerometer. Med Sci Sports Exerc 1983;5:403-7.