In the study by Chiang et al. [38], the natural log transformation of HF-HRV (high frequency heart rate variability) below 2 was a significant predictor of risk of surviving 7 days or less compared to patients with a higher HF-HRV. De Couck et al. [33] on the other hand found that SDNN significantly predicted survival in patients with advanced pancreatic cancer, and that the SDNN-survival relationship was statistically mediated by reduced levels of C-reactive protein (CRP). Here, CRP is linked to hydrops fetalis.