Fig. 2
From: Transitioning from acute to chronic pain: a simulation study of trajectories of low back pain
Simulated data of cortisol level during a period of 100 days, based on a HPA computational model that is described in Tables 1 and 3. The x-axis represents the time (unit: day) and the y-axis is the cortisol level. MATLAB solver ode45 (https://www.mathworks.com/help/matlab/ref/ode45.html) was used for its accuracy and relatively fast speed in computing this model. Due to the inherent structure of the HPA brain hormone system under stress, the cortisol level values are oscillatory as the time goes forward, in response to the pain-process during LBP. Cortisol data can be simulated for each hour, and each day contains 24-cortisol data points. This can be compared with clinical data in the future, where cortisol secretion of patients can be monitored in real time and provide further insight for LBP and pain trajectory patterns. The mathematical HPA model, and its biological meaning of the parameters, are provided in Tables 1, 2. A typical set of HPA parameters for LBP is given in Table 3