Background: Recently, we provided first evidence for altered autonomic nervous system (ANS) function indexed by reduced heart rate variability (HRV) in the presence of of pain in apparently healthy subjects. Self-medication with analgesics is common among individuals that experience pain. Such reports might therefore provide further information on the severity of reported pain symptoms and individual coping strategies. Within the present analysis we aimed to investigate the relation of analgesic self medication and HRV.
Methods: Pain symptoms were assessed using the 4 pain related items from the symptom checklist (SCL-90r). Participants were asked to rate the frequency of analgesic self medication for all available pain killers on four categories: never (0), once (1), sometimes (2), or on a regular base (3). For further analysis a dichotomized variable for each medication (no to barely and sometimes to regular intake) was generated and subjects were stratified to groups. HRV was measured for 5 minutes in a supine position using a portable device to record inter-beat-intervals at a sampling frequency of 1000 Hz. The root mean square of successive differences (RMSSD) – a vagally mediated measure of HRV – was derived and log transformed for further analysis. Multiple linear regression analysis adjusting for age, sex, body weight and height was used to assess the relation of analgesic intake to HRV.
Results: A total of 58 participants completed the trial. Time to time intake was reported most frequently for Ibuprofen (44.8%), Aspirin (31.0%), and Voltaren (24.1%). The frequency of Ibuprofen intake was associated with the presence of headaches (r = .460, p < .001). The log transformed population average of RMSSD was 3.99±0.69 ms. Subjects that frequently used Ibuprofen had significantly lower log RMSSD (F(1;51) = 13.136, p < .001) compared to subjects that did not or barely use it. Linear regression results indicate a significant decrease in log RMSSD in participants indicating to use Ibuprofen sometimes or regularly. All other variables were not associated with RMSSD. Explained variance was 23%
This is the first study to show that subjects that frequently use Ibuprofen for analgesic self medication have lower vagal activity. These findings are likely moderated by the presence of pain, since self-medication correlated with the presence of headaches. However, in line with our previous reports on reduced HRV in subjects with pain, we provide further evidence using a different methodological approach. Future studies should investigate the impact of coping style on this association.