In addition see more to HRV, therefore, respiration rate (RR) may be interesting as a measure

of autonomic nervous system functioning in people with prolonged fatigue. Before HRV and RR can be used in a clinical population of fatigued subjects, it is of great importance to assess the reproducibility of such measurements in a population with prolonged fatigue. Should these measurements remain stable over time and under similar conditions, they would be ideal for tracking modifications in clinical state when treatment plans are started. In this case, changes in the variables would have a high probability of truly representing PF477736 either alterations in the clinical state or the effects of the experimental condition (Stein et al. 1995). Sandercock et al. (2005a, b) recently reviewed the current literature on the reliability of short-term HRV measurements. They emphasized the need for further studies to assess the reliability of HRV, particularly in clinical populations. The present study has two goals. The primary goal is to evaluate the reproducibility of HRV and RR (measured with a device that is easy to use in practice) in participants with prolonged fatigue complaints during rest and light physical activity. Because previous research (Guijt et al. 2007) with the same

device has yielded reproducible measurements in healthy subjects, good reproducibility can be expected. Should measurements of HRV and respiration appear reproducible, the second goal of the study is to assess the concurrent validity of HRV and RR measurements as indicators of the degree of fatigue. 3-mercaptopyruvate sulfurtransferase Good concurrent validity can be expected for HRV, selleckchem as earlier studies have shown diminished HRV in subjects with chronic fatigue (Pagani et al. 1994; Stewart 2000). No expectations were expressed for RR, as no data were found on the effects of chronic stressors on RR, even

though increased RR is associated with situational perceived stressors (Grossman 1983). Methods Participants All participants were recruited from among the clients of two outpatient clinics for rehabilitation and medical fitness in the Netherlands. The parameters were evaluated within a heterogenous convenience sample of participants who had subjectively reported prolonged fatigue, which had resulted in functional impairments in their daily lives. A power analysis using nQuery Advisor (Elashoff 2000) was performed in advance. Results of this analysis showed that 23 participants were needed in order to find intra-class correlations with a 95% confidence interval between 0.80 and 0.95, a power of 0.80 and an α of 0.05. With respect to concurrent validity, 19 subjects were needed in order to find a correlation of 0.75 with a one-sided 95% confidence interval with a lower bound of 0.50, a power of 0.80 and an α of 0.05. Twenty-seven patients in the age of 18–65 years were asked to participate in this study. Prior to participation, all participants were informed.