Don't just do something, stand there! Reflections on the counterintuitive behavior of complex systems, seen through the eyes of System Dynamics, Systems Thinking and simulation.
In my last thyroid post, I described a classic case of overshoot due to failure to account for delays. I forgot to mention the trigger for this episode. At point B above, there was a low TSH measurement, at .05 well below the recommended floor of .4. That was taken as a signal for a … Continue reading “Thyroid Dynamics: Hyper Resurgence”
In my last two posts about thyroid dynamics, I described two key features of the information environment that set up a perfect storm for dose management: The primary indicator of the system state for a hypothyroid patient is TSH, which has a nonlinear (exponential) response to T3 and T4. This means you need to think … Continue reading “Thyroid Dynamics: Dose Management Challenges”
I just ran across a funny instance of TSH nonlinearity. Check out the axis on this chart: It’s actually not as bad as you’d think: the irregular axis is actually a decent approximation of a log-linear scale: My main gripe is that the perceptual midpoint of the ATA range bar on the chart is roughly … Continue reading “Thyroid Dynamics: Chartjunk”
A couple weeks ago I wrote about the perceptual challenges of managing thyroid stimulating hormone (TSH), which has an exponential response to the circulating thyroid hormones (T3 & T4) you’d actually like to control. Another facet of the thyroid control problem is noise. Generally, uncertainty in measurements is not made available to users. For example, … Continue reading “Thyroid Dynamics: Noise”
I’ve been working on thyroid dynamics, tracking a friend’s data and seeking some understanding with models. With only one patient to go on, it’s impossible to generalize about thyroid behavior from one time series (though there are some interesting features I’ll report on later). On the other hand, our sample size of doctors is now … Continue reading “Thyroid Dynamics: Misperceptions of Nonlinearity”
Quite a while back, I posted about the dynamics of the thyroid and its interactions with other systems. That was a conceptual model; this is a mathematical model. This is a Vensim replication of: Marisa Eisenberg, Mary Samuels, and Joseph J. DiStefano III Extensions, Validation, and Clinical Applications of a Feedback Control System Simulator of … Continue reading “Thyroid Dynamics”
A while back I reviewed an interesting model of hormone interactions triggered by stress. The bottom line: I think there might be a lot of interesting policy implications lurking in this model, waiting for an intrepid explorer with more subject matter expertise than I have. I think the crucial point here is that the structure … Continue reading “Biological Dynamics of Stress: the Outer Loops”
OK, I’ve stolen another title, this time from a favorite kids’ book. This post is really about the thyroid, which is a little less catchy than the spleen. Your hormones are exciting! They stir your body up. They’re made by glands (called endocrine) and give your body pluck. Allan Wolf & Greg Clarke, The Blood-Hungry … Continue reading “The Blood-Hungry Spleen”