Introduction: At present, there is neither a laboratory test nor an imaging technique able to differentiate people with fibromyalgia (FM) from healthy controls. This lack of an objective biomarker has hampered FM recognition and research. Heart rate variability (HRV) analyses provide a quantitative marker of autonomic nervous system activity. Nighttime is a stable period in which most people are resting. Sleep is modulated by autonomic activity. Sleeping problems are prominent in FM. The objectives of this study are: 1) to explore different nocturnal HRV parameters as potential FM biomarkers and 2) to seek correlation between such HRV parameters and diverse FM symptoms. Methods: We studied 22 women suffering from FM and 22 age-matched controls. All participants filled out several questionnaires related to FM symptoms. All participants used a Holter monitor over 24 hours while undertaking their routine activities during the day and while sleeping at their homes at night. Time-domain HRV parameters analyzed from 0000 to 0600 hours included, among others: mean normal-normal interbeat intervals (mean NN), standard deviation of the NN intervals (SDNN), and standard deviation of the successive NN differences (SDSD). Results: Nocturnal SDNN of less than 114 ms had the greatest predictive value to set apart patients from controls with an odds ratio of 13.6 (95% confidence interval: 3.9 to 47.8). In patients, decreased nighttime HRV markers indicative of sympathetic predominance had significant correlations with several FM symptoms: SDSD was associated with pain intensity (r = - 0.65, P = 0.001). SDNN correlated with constipation (r = - 0.53, P = 0.001), and mean NN with depression (r = - 0.53, P = 0.001). Controls displayed an opposite behavior. For them, increased nighttime SDNN correlated with Fibromyalgia Impact Questionnaire scores (r = 0.69, P = 0.001) and with other FM symptoms. Conclusions: Nocturnal HRV indices indicative of sympathetic predominance are significantly different in FM women when compared to healthy individuals. In FM patients, these HRV parameters correlated with several symptoms including pain severity. Opposite associations were seen in controls. FM may not be just one end of a continuous spectrum of common symptoms. Nocturnal HRV analyses are potential FM biomarkers.

Depression and anxiety are highly prevalent psychological disorders in end-stage renal disease (ESRD) that have a negative clinical impact. The purpose of our study was to identify factors associated with the presence of depression and anxiety, in a sample of ESRD patients treated with hemodialysis. We included 187 patients from two dialysis facilities, age 18–65 years. Beck’s depression and anxiety inventories, KDQOL36 questionnaire, the cognitive distortion scale and the Mexican scale of resilience were used. Socio-demographic and clinical information was obtained from medical records. Depression was present in 143 (76.4%) patients. Patient with depression were older (33 (26–52) years vs. 30 (24.43) years, p = 0.025), had a lower education level (36% vs. 9%, p = 0.001), used more medications (67% vs. 36%, p = 0.001), had a comorbidity (75% vs. 41%, p = 0.001), and a higher proportion were waiting for a kidney transplant. Anxiety was present in 112 (59.8%) cases. By multivariate analysis, depression was independently associated with lower education, absence of previous kidney transplant, anxiety, higher cognitive distortion, lower psychological resilience, and lower quality of life scores. In conclusion, lower psychological resilience, lower education level, and higher cognitive distortions are factors associated with depression and anxiety in ESRD patients.