Wanna see my dawn phenomenon?

The dawn phenomenon (anyone have a better link for this?) is a powerful beast. One of my reasons for wanting a CGMS was that I was waking up high in the morning, and because of my hypoglycemia unawareness I often didn't know if the high fasting sugars were due to the dawn phenomenon or rebound from a nighttime low.

In July I posted a very nice example of the latter, when I stupidly ignored the Dexcom warning that my blood sugar was dropping, tanked into the 40's, and rebounded.

This morning, I woke up to a high threshold alert (> 140 mg/dL) at about 4:30 am. I fell back asleep (whoops), but I woke up again about an hour later and the receiver showed my blood glucose a little over 200 mg/dL.


The Dexcom Seven manual says never to correct for high or low blood glucose without a confirmatory finger stick. Most people with half a brain* will, over time, learn when they do and don't need the finger stick. I know that when my sugar is trending up, I can usually correct for a high blood sugar based only on the Dexcom reading. So I corrected, my sugar came down, and I didn't hang out for hours with excessive glucose in my blood. Hurray for Comrade Dex. Anyway, I just thought I'd post this so you can see what the Dexcom Seven does for people who wake up high. It is helping me catch nighttime lows, and it is helping me realize right away when I need to ratchet up my early a.m. basal rates.



*This footnote is to acknowledge that some Dexcom users, with whole and functioning brains, will find that they do need finger sticks to confirm every Dexcom reading before making a correction.

Stupid User Experience: Rebound high

About a week ago I had a Stupid User Experience (SUE). See the screenshot of the Glucose Trend graph. Note that this is an example of enlarging a selected time frame for closer scrutiny.

I was especially exhausted this night, and I had gone to bed without bringing some source of sugar for a nighttime low, like I usually do.

A little before 11:00 pm, I got the buzz alerting me to a breach of the low threshold. I was tired and really didn't want to get out of bed to find some juice. I'm embarassed to admit it, but all I did was turn off my basal delivery for an hour and a half, hoping that would counter the insulin on board, and I would magically sleep through the night without going low. Well, you can see the result. Around 1:30 am, I got the buzz telling me I was headed up. I think the high peaked at about 240.

Why am I sharing this? Two points. One, this is a great example of the Dexcom doing its job. One of my motivations for buying this thing was the increasing number of mornings I woke up over 200. Without this monitor, I probably would have slept through the whole rollercoaster ride. I would have gone low without realizing it, and I would have rebounded without realizing it, waking up hours later with a high blood sugar and no idea what had happened. Without the high threshold I would not have taken a correction insulin dose at 1:30, and might have peaked even higher, certainly for much longer, before I woke up.

Dexcom also did its job alerting me in plenty of time to avoid the low in the first place, which brings me to the second point. One big problem about diabetes that is probably common to many chronic conditions: it's easy to get complacent, and having the CGMS doesn't magically protect me from extreme blood sugar swings. I feel silly needing these occasional reminders, these SUEs, that simply being alerted to a low isn't enough - I still have to be in charge, even when I'm too tired. I don't know if non-diabetics can understand, and I hope I'm not the only one out there who does things like this.

I also hope after posting this that no one shows up at my door and revokes my license to practice intensive insulin management. Turning off my basal delivery - what was I thinking? Next thing you know it will be Regular and NPH for me, just like in the dark ages. Nooooooo!

The main point is: thanks Comrade Dex for doing what you're supposed to. I dropped the ball. Nice textbook example of a rebound hyperglycemia though.

Dexcom Seven Software: Exporting Data

Apparently the really exciting thing the Seven software provides is the ability to export data for your own manipulative enjoyment. I find it hard to believe they didn't make this possible with the three-day system, but at least they got it right for the Seven.

Exporting the data is easy. From the main Dexcom Software menu, select Tools --> Export Sensor / Meter Data:

You can export all readings, or choose a subset. You can select sensor or meter readings (you have to export them separately and merge if you want them in the same file). You can choose an XML file, or tab-delimited TXT file. Defaults are all readings from the sensor in an XML file. Here is the dialog box for exporting data:

Here is an excerpt of the XML file containing my sensor readings:

Here is an excerpt of the TXT file containing my meter readings:












These files require some sophistication to manipulate, but it's easy to import them into Excel or another software program once you get the hang of it.

Dexcom Seven Software: Daily Statistics

Daily statistics gives you just that – lots of descriptive statistics broken down by day. You can display any number and combination of days that you choose. The statistics include a pie chart similar to those in the Glucose Distribution output, and a row of statistics similar to the first column of the Hourly Statistics table.

Here is my Daily Statistics output for 5 days, starting when I initiated my second sensor:












Here is a close-up showing how you can select certain groups of days to view:











Nothing really new to discuss here.

Dexcom Seven Software: Glucose distribution graph

The glucose distribution graph presents selected glucose values by time of day and categorized glucose level. Here I have selected one day of readings:

The colors indicate percent of sugars in the low range (blue, default definition is less than 80 mg/dL), percent in the target range (green, default 80 mg/dL - 130 mg/dL), and high (red, default is greater than 130 mg/dL). This target range is at odds with the 80-140 default target range in the hourly statistics graph, but perhaps I am mistaken in one or the other. You can customize the target range.

The pie charts break the readings down by time of day in the following categories: All day totals, early morning, before breakfast, after breakfast, before lunch, after lunch, before dinner, after dinner, and late evening. You can customize the hours for each of these categories. Categories can overlap. You can also create new categories. For instance, I was able to create a category called "Pre-dawn phenomenon" and define it as the hours from 11:00 pm - 4:00 am.

The bar chart on the right shows the percent of total readings for the specified time period by glucose category. Default categories are less than 40-55, 56-70, 71-100, 101-130, and so on. I don't think these categories can be changed.

You can choose to display statistics for any number of consecutive days, or types of days, for instance weekeneds or Mondays. You can even select groups of days, like "Tuesdays and Thursdays".

Dexcom Seven software: Hourly statistics graph

Hourly statistics give you a deluge of information and some cool looking boxplots. You can customize many details, and it's too confusing to summarize here. Read on.

Here is the hourly statistics window, covering all my blood sugar readings for the past 8+ days:
I don't know how clear the picture is if you click on it, but it is showing data from all days, all hours, all glucose readings. Nothing held back, nothing filtered.

As you can see, I am having some issues in the late afternoon.

This funny chart at the bottom gives lots of statistics broken down by hour of the day. The first row gives the number of 5-minute averages used to calculate the numbers for each hour. The next row gives the average glucose reading for that hour. For those of you who are into the rest of the stats, the table also gives minimum, quartiles (25, 50, 75), maximum, standard deviation, estimated standard deviation (highest and lowest 25% classified as "outliers" and removed), standard error of the mean, and percentage coefficient of variation. I'm not going into what all that means here, but I am a biostatistician, and if you ever want an explanation about a certain type of statistic, contact me and I'm happy to enlighten you.

The cool thing about the hourly statistics is that you have a lot of control over how things are categorized, and then you can display the information according to category. For instance, here are the default definitions of hypoglycemia, low blood sugar, target range, high blood sugar, and hyperglycemia:








These definitions don't quite work for me, so I can customize them to my personal goals:



The rows in blue indicate categories that I edited.




Now I can filter my graph to only show readings that are categorized as hyperglycemia:


You can see some hyperglycemia after breakfast, some after lunch, and most of it after dinner. Now I get to target my dinner boluses to reduce the highs. Maybe in a month I can use this chart to show progress.

Dexcom Seven Software: Installation and Glucose Trend graph

I hear the software released with the 3-day system really sucks. I have been playing with the 7-day system software this morning. Here are my thoughts in no particular order. I will clean up this post as time goes on.

INSTALLATION AND DATA UPLOAD

1. Software takes a long time to install, but it's easy. Also easy to upload. Plug in receiver, plug into USB port on computer. People who don't know much about computers should be able to figure it out.

2. If you have more than one family member using a Dexcom, you can maintain more than one person's data on the software. This is probably geared towards health care professionals (Dexcom sent a copy of the software to my endocrinologist).

Here is the screen that pops up when you launch the software:









3. Easy to upload data. Just select the patient from the menu and click the upload button. It takes a few minutes to upload the information from the receiver. The information is still on the receiver after it transmits to the computer.

DEFAULT GRAPHS

There are four graph types generated by the software: Glucose Trend, Hourly Statistics, Glucose Distribution, Daily Statistics.

Glucose Trend graphs are just what you'd think. They show the glucose values from the Dexcom and the One Touch Ultra over time. You can choose the day and time to start the graph, and you can display values for up to 7 days from the start time. Here is my first day of readings:

The blue dots are the 5-minute averages from the Dexcom sensor. The red diamonds are the calibration readings from my One Touch Ultra meter. The yellow bars represent signal gaps when the receiver failed to receive one or more 5-minute averages from the transmitter. The dashed lines are the high and low blood sugar alert thresholds as they were set when I uploaded the data. The green shaded area is my specified target glucose range. I can change this interactively using the software.

The second and third diamonds on the left are my initial calibration finger sticks. The first diamond shows that when I tested I was pretty low, so I treated that and waited before calibrating the meter. The blue circles start a few minutes after the initial calibration.

As you can see from the first day, the calibration finger sticks were pretty close to the Dexcom readings.

Here is a chart showing three days:









Finally, you can select a small segment for a close-up view:

Here you see some problems with gaps and accuracy. I am still learning how best to live with Comrade Dex, but I am getting better. One day soon I'll do a post on accuracy.