Table 2 Evidence for altered patterns of variability in illness states
From: Complex systems and the technology of variability analysis
Variability analysis | Cardiac | Respiratory | Neurological | Miscellaneous | Critical care |
|---|---|---|---|---|---|
Time domain | ?HRV ??mortality risk in elderly, CAD, post-MI, CHF and dilated cardiomyopathy [14–24] | Altered frequency distribution of airway impedance in asthma [5] Altered respiratory variability (?kurtosis) in sleep apnoea [148] |  |  |  |
Frequency domain | Altered spectral HRV analysis?illness severity in cardiac disease (CHF [50–52], hypertension [53,54], CAD [55,56], angina [57], MI [58]) and noncardiac disease (hypovolaemia [49], chronic renal failure [59], diabetes mellitus [60], anaesthesia [61]) |  |  |  | ?Total HRV, ?LF and ?LF/HF HRV following trauma [149], sepsis and septic shock in the ICU [62,64,68,150,151] and in ER patients [63] |
Power law analysis | Altered HRV power law (?HRV left shift and steeper slope) with age [84], CAD [85] and post-MI [86] | ?Respiratory variability (right shift) in patients with asthma [7] ?Variability of foetal breathing with maternal alcohol intake [152] | Altered variability in gait analysis [153–155] and postural control [156] with ageing and neurological disease Altered variability of mood?psychiatric illness [157–159] | Haematological: altered leucocyte dynamics [160,161] observed in haematological disorders (e.g. cyclic neutropenia) | Altered HRV power law (?HRV left shift)??mortality risk in paediatric ICU patients [33] |
DFA | Altered DFA scaling exponent?age [92], heart disease [93–96], post-ACBP [100], prearrhythmias [97], patients with sleep apnoea [98], and ?mortality risk post-MI [99] | Altered respiratory variability (?DFA scaling exponent)?age[101] |  | Temperature: altered temperature measurements?age[103] | ?Heart rate DFA scaling exponent?septic shock[162] and procedures[61] in paediatric ICU patients |
Entropy | ?HR ApEn?age [118], ventricular dysfunction [123], occurs prior to arrhythmias [119–121] | Greater respiratory irregularity in patients with panic disorder [136] | Altered EEG entropy with anaesthesia[132,163,164] | Endocrine: ?ApEn of GH [125,126], insulin [127,128], ACTH, GH, PRL [129,130], PTH [131]?age and/or illness | ?HR ApEn?healthy individuals infused with endotoxin [124] ?TV ApEn in respiratory failure [135] |