AGING AS A PROCESS OF COMPLEXITY LOSS - Complex Systems Science in Biomedicine - page 621

Table 3 . Decreased complexity in disease

Disease (ref) Measure
Alzheimer's disease (25) EEG correlation dimension is reduced
Emphysema (26) Reduced 1/ f slope of size distribution
of terminal airspace clusters
Vent. fibrillation (27) Reduced HR fractal scaling (1/ f slope*)
and long-range correlations (DFA**)
Atrial fibrillation (28) Increased RR regularity (ApEn + ) and
decreased long-range correlations (DFA)
CHF (10) and CAD (29) Reduced HR fractal scaling (1/ f ) and
long-range correlations (DFA)
Aging and Huntington's Loss of stride interval long-range
disease (15) correlations (DFA)
Breast cancer (30) Fractal dimension of mammographic mass
*1/ f = the slope of the log-transformed power spectrum (see text). **DFA = detrended fluctuation analysis, a
technique that quantifies the fractal-like correlation properties of time-series data (see text). + ApEn = Ap-
proximate entropy, a measure of regularity in time series data (11). ApEn quantifies the (logarithmic) likeli-
hood that a series of data points that are a certain distance apart for a given number of observations remain
within the same distance on the next incremental comparisons. Reprinted with permission from (2).

Table 4 . Long-term consequences of complexity loss

Study Complex Complex Adverse
authors/ref. Subjects system measure outcome
Ho et al. 52 CHF pts.+ 52 RR interval DFA Mortality

Circ 1997 (31) matched controls (2( ECG) = 1.9 yr

Huikuri et al. 347 random Heart rate 1/ f slope Mortality

Circ 1998 (32) elders >65 yr (24( ECG) = 10 yr

Makikallio et al. Case-control, RR interval DFA Ventricular

AJC 1999 (27) post-MI +/- VF (24( ECG) 1/ f slope fibrillation

Huikuri et al. 446 MI pts w/ RR interval DFA Mortality

Circ 2000 (29) decreased LV fxn (24( ECG) = 1.9 yr

Makikallio et al. 499 CHF pts. RR interval DFA Mortality

AJC 2001 (33) w/ EF< 35% (24( ECG) = 1.8 yr

Colantonio et al. 87 elderly stroke Psycho- Social net- Fx'l loss,

J Geron 1993 (34) survivors social fxn. work index NH adm.

Fratiglioni et al. Popn. of 1203 Psycho- Social Dementia

Lancet 2000 (35) elders >75 yrs. social fxn. network

Reprinted with permission from (2).

5.

LOSS OF COMPLEXITY AS A PATHWAY TO FRAILTY
IN OLD AGE

These considerations have led to the theory that loss of complexity is the
physiologic basis of frailty in old age (2). This is illustrated in Figure 7. During
youth, a multitude of physiologic systems interact to produce a highly complex
output signal (such as heart rate), which is associated with a high level of physi-
cal function. With progressive aging, many of the physiologic inputs and their