Loss of 'complexity' and aging. Potential applications of fractals and chaos theory to senescence

The concept of "complexity," derived from the field of nonlinear dynamics, can be adapted to measure the output of physiologic processes that generate highly variable fluctuations resembling "chaos." We review data suggesting that physiologic aging is associated with a generalized loss of such complexity in the dynamics of healthy organ system function and hypothesize that such loss of complexity leads to an impaired ability to adapt to physiologic stress. This hypothesis is supported by observations showing an age-related loss of complex variability in multiple physiologic processes including cardiovascular control, pulsatile hormone release, and electroencephalographic potentials. If further research supports this hypothesis, measures of complexity based on chaos theory and the related geometric concept of fractals may provide new ways to monitor senescence and test the efficacy of specific interventions to modify the age-related decline in adaptive capacity.

Leg extensor power and functional performance in very old men and women

1. Residents of a chronic care hospital (13 men of mean age 88.5 +/- 6 SD years and 13 women of mean age 86.5 +/- 6 SD years) who had multiple pathologies were assessed for leg extensor capability in several ways. 2. A custom-built rig was used to assess leg extensor power, that is, maximal power output over less than 1 s in a single extension of one leg. Performance measures were obtained by timing chair rises (from a standard chair 0.43 m high), stair climbing (four risers, total height 0.635 m) and a walk (6.1 m). For each measurement the best of several trials were recorded as definitive. 3. Leg extensor power was significantly correlated with all performance measures, but the performance measures were not related to each other except for chair rising and walking speed. 4. Women had significantly less extensor power than men, but their power explained more of the variance in performance, e.g. power accounted for 86% of the variance in walking speed. 5. There was no relation within the group between age and any of the variables measured. 6. Measurement of leg extensor power in frail elderly people may prove useful in focusing effective rehabilitation programmes.

Risk factors for delirium in hospitalized elderly

OBJECTIVE

To determine risk factors for delirium in elderly hospitalized patients.

DESIGN

Cohort analytic study. Using a reliable and valid instrument for detection of delirium, we prospectively followed up a cohort of elderly patients admitted to an acute care hospital. Using standardized criteria, we collected risk factor data from patient medical records.

SETTING

General medical and surgical wards of a tertiary-care hospital.

PATIENTS

Patients (n = 325) were 65 years of age or older, from either a geographically defined community or a long-term-care institution. We studied those patients (n = 291) not delirious on first evaluation. Fifty-seven patients or their families refused participation.

MAIN OUTCOME MEASURES

Incidence of delirium and risk factors calculated as adjusted odds ratios (ORs).

MAIN RESULTS

Delirium developed in 91 patients. By stepwise logistic regression, the independent risk factors for in-hospital delirium included prior cognitive impairment (OR, 8.97; 95% confidence interval [CI], 3.99 to 20.14), age over 80 years (OR, 5.22; 95% CI, 2.60 to 10.46), fracture on admission (OR, 6.57; 95% CI, 2.23 to 19.33), symptomatic infection (OR, 2.96; 95% CI, 1.42 to 6.15), and male sex (OR, 2.40; 95% CI, 1.19 to 4.84). Among medication groups, only neuroleptic use (OR, 4.48; 95% CI, 1.82 to 10.45) and narcotic use (OR, 2.54; 95% CI, 1.24 to 5.18) were independently associated with delirium. Anticholinergic use was not associated with delirium.

CONCLUSIONS

Delirium in hospitalized patients is most closely associated with factors already present on admission such as prior cognitive impairment, advanced age, and fracture. In the hospital, use of neuroleptics and narcotics and the presence of infection are less strongly associated with this syndrome.

Delirium. The occurrence and persistence of symptoms among elderly hospitalized patients

We evaluated the occurrence and persistence of delirium in 325 elderly patients admitted to a teaching hospital from either a defined community or a long-term care facility. Of the study participants, 34 (10.5%) had Diagnostic and Statistical Manual of Mental Disorders, Third Edition--defined delirium at initial evaluation; of the remaining patients, 91 (31.3%) developed new-onset delirium. An additional 110 patients also experienced individual symptoms of delirium without meeting full criteria. Preexisting cognitive impairment and advanced age were associated with increased risk of incident delirium in the community sample but not the institutional one. Delirium was not associated with an increased risk of mortality, but it was associated with a prolonged hospital stay and an increased risk of institutional placement among community-dwelling elderly. Only five patients (4%) experienced resolution of all new symptoms of delirium before hospital discharge, and only 20.8% and 17.7%, respectively, had resolution of all new symptoms by 3 and 6 months after hospital discharge. These data suggest that delirium is a common disorder that may be substantially less transient than currently believed and that incomplete manifestations of the syndrome may be frequent.

Spectral analysis of heart rate dynamics in elderly persons with postprandial hypotension

Prior studies suggest that postprandial hypotension in elderly persons may be due to defective sympathetic nervous system activation. We examined autonomic control of heart rate (HR) after a meal using spectral analysis of HR data in 13 old (89 +/- 6 years) and 7 young (24 +/- 4 years) subjects. Total spectral power, an index of overall HR variability, was calculated for the frequency band between 0.01 and 0.40 Hz. Relatively low-frequency power, associated with sympathetic nervous system and baroreflex activation, was calculated for the 0.01 to 0.15 Hz band. High-frequency power, representing parasympathetic influences on HR, was calculated for the 0.15 to 0.40 Hz band. Mean arterial blood pressure declined 27 +/- 8 mm Hg by 60 minutes after the meal in elderly subjects, compared with 9 +/- 8 mm Hg in young subjects (p less than or equal to 0.0001, young vs old). The mean change in low-frequency HR power from 30 to 50 minutes after the meal was +19.4 +/- 25.3 U in young subjects versus -0.1 +/- 1.5 U in old subjects (p less than or equal to 0.02). Mean change in total power was also greater in young (19.0 +/- 26.6 U) subjects compared with old subjects (0.0 +/- 1.6 U, p greater than or equal to 0.02). Mean ratio of low:high-frequency power increased 3.1 +/- 3.3 U in young subjects vs 0.5 +/- 2.7 U in old subjects (p less than or equal to 0.01). The increase in low-frequency HR power and in the low:high frequency band ratio in young subjects is consistent with sympathetic activation in the postprandial period.(ABSTRACT TRUNCATED AT 250 WORDS)

Postural change in blood pressure associated with age and systolic blood pressure. The National Health and Nutrition Examination Survey II

The prevalence of postural change in blood pressure and its association with age and systolic blood pressure were examined in data from 8,574 White nondiabetic persons aged 25-74 who participated in the second National Health and Nutrition Examination Survey (1976-1980). Postural change in blood pressure was defined as a drop of 20 mm Hg or more on change from supine to seated position. In subjects on no antihypertensive medications (n = 7,316), the prevalence of postural change in blood pressure increased with older age and with higher blood pressure levels, regardless of age. However, systolic blood pressure levels also increased with age. In logistic regression models, level of supine systolic blood pressure was strongly related to postural change in blood pressure (Relative odds (RO) = 1.59, 95% confidence interval (CI) = 1.49, 1.70 for a 10 mm Hg increase in systolic blood pressure) whereas age was not related to postural change in blood pressure (RO for age = 1.07, Cl = .89, 1.19 for a 10-year increase in age). Results were similar for those medicated for hypertension. All results were unchanged by addition of health status indicators, including reports of hospitalization and number of medical conditions, to the model. These data suggest that the age-related increase in the prevalence of postural hypotension previously reported may be partially explained by age-associated increases in systolic blood pressure.

Causes and correlates of recurrent falls in ambulatory frail elderly

To determine causes and clinical correlates of recurrent falls in ambulatory frail elderly people, we evaluated 70 recurrent fallers and 56 nonfallers (mean age = 87 years) from two long-term care facilities. Evaluations included a detailed history, physical examination, performance-oriented mobility assessment, and laboratory studies. Primary causes including stroke, parkinsonism, blindness, drug-related hypotension, and arthritis were established for the most recent fall in 51 (73%) fallers. Eighteen fallers (26%) had multiple conditions that could not be prioritized for their contribution to the fall. Fallers were more often women, were functionally more impaired, and were taking more medications than nonfallers. Specific diseases did not distinguish fallers from nonfallers. Fallers of both sexes took more steps to turn 360 degrees, could not stand up from a chair without pushing off, had a higher prevalence of antidepressant use, and had impaired position sensation. These easily obtained clinical variables characterized nearly three-quarters of ambulatory elderly nursing home residents with a history of recurrent falls.

Aging and the complexity of cardiovascular dynamics

Biomedical signals often vary in a complex and irregular manner. Analysis of variability in such signals generally does not address directly their complexity, and so may miss potentially useful information. We analyze the complexity of heart rate and beat-to-beat blood pressure using two methods motivated by nonlinear dynamics (chaos theory). A comparison of a group of healthy elderly subjects with healthy young adults indicates that the complexity of cardiovascular dynamics is reduced with aging. This suggests that complexity of variability may be a useful physiological marker.

Forearm blood flow response to posture change in the very old: non-invasive measurement by venous occlusion plethysmography

Little is known about the peripheral vascular response to posture change in very elderly people who are vulnerable to the development of orthostatic hypotension. This is due, in part, to the risks of currently utilized invasive vascular monitoring techniques in the elderly population. We studied the forearm vascular response to active standing in 18 healthy young, 10 healthy old, and 19 impaired elderly subjects, using the non-invasive technique of venous occlusion plethysmography. In six subjects this technique was compared to duplex doppler ultrasonography for the measurement of postural changes in forearm blood flow. Forearm blood flow changes determined by venous occlusion plethysmography were 11% larger than doppler measurements, but the two methods strongly correlated (r = 0.90, P less than .001). Mean forearm vascular resistance increased to a significantly greater extent at 1 minute of standing in young subjects than in both groups of old, although the response was quite variable in all groups. Two healthy elderly (20%) and eight impaired elderly (40%) subjects had unexpected forearm vasodilatation at 1 minute of standing. By 3 minutes, forearm vascular resistance had increased by similar amounts in all three groups of subjects. Five impaired elderly and no healthy young or healthy old subjects had orthostatic hypotension, defined as greater than or equal to 10 mm Hg decline in mean arterial blood pressure at 1 or 3 minutes of standing. Forearm vascular resistance changes did not correlate with blood pressure response to standing. Thus, forearm vascular response to 1 minute of active standing is attenuated in many elderly subjects. This abnormality may impair adaptation to orthostatic stress in advanced age.

The epidemiology and natural history of pressure ulcers in elderly nursing home residents

We analyzed prospective data from 19,889 elderly residents of 51 nursing homes from 1984 to 1985 to determine the prevalence, incidence, and natural history of pressure ulcers. Among all residents admitted to nursing homes, 11.3% possessed a stage II through stage IV pressure ulcer. For those residents admitted to the nursing home without pressure ulcers during the study period, the 1-year incidence was 13.2%. This increased to 21.6% by 2 years of nursing home stay. People already residing in a nursing home at the start of the study had a 1-year incidence of 9.5%, which increased to 20.4% by 2 years. Pressure ulcers were associated with an increased rate of mortality, but not hospitalization. Longitudinal follow-up of residents with pressure ulcers demonstrated that a majority of their lesions were healed by 1 year. Most of the improvement occurred early in a person's nursing home stay. Although nursing home residents with pressure ulcers have a higher mortality, with good medical care pressure ulcers can be expected to heal.

Nonsteroidal anti-inflammatory drug-associated azotemia in the very old

We conducted a prospective study in 114 elderly patients to determine the renal effects of short-term therapy with nonsteroidal anti-inflammatory drugs (NSAIDs) in the very old. Study subjects were patients in a long-term care facility (mean age, 87 years) newly begun on a regimen of NSAID therapy. For the study group as a whole, the serum urea nitrogen level rose 1.7 mmol/L 5 to 7 days after initiation of therapy, with no significant changes in serum creatinine or potassium levels. In a comparison group of 45 patients not receiving NSAID therapy, no significant change in the serum urea nitrogen level was noted during a similar period. A subgroup of 15 patients (13%) experienced a greater than 50% increase in the serum urea nitrogen level during NSAID therapy, with a mean increase of 89% (8.6 mmol/L). A return to the baseline level occurred within 14 days after discontinuation of NSAID therapy. Two factors were significantly predictors of a greater than 50% increase in the serum urea nitrogen level: concurrent loop diuretic therapy (odds ratio, 2.2) and high NSAID dose (odds ratio, 2.0). These findings suggest that reversible azotemia develops in a sizable proportion of the very old who are treated with short-term NSAID therapy.

Hypotensive responses to common daily activities in institutionalized elderly. A potential risk for recurrent falls

Transient hypotension may be one of many factors contributing to the high prevalence of falls among elderly people. To determine the frequency and magnitude of hypotensive responses to common daily activities, and their potential relationship to falls in the elderly, we examined blood pressure (BP) and heart rate during a standardized series of activities in 38 institutionalized recurrent fallers (age, 87 +/- 6 years), 20 institutionalized nonfallers (age, 85 +/- 5 years), and 10 healthy young control subjects (age, 24 +/- 3 years). The coefficient of variation for systolic BP during all activities was higher in elderly subjects (fallers, 14% +/- 5%; nonfallers, 12% +/- 3%) than in young control subjects (8% +/- 1%). In contrast, the coefficient of variation for heart rate during all activities was higher in young subjects than in the elderly subjects. Elderly subjects had marked BP reduction following meals and nitroglycerin, which was significantly greater in fallers than in nonfallers, independent of the cause of the fall. Thus, institutionalized elderly have marked BP variability and hypotensive responses to meals and nitroglycerin. A decline in BP during common preload-reducing stresses may predispose some elderly people to falls.

Spectral characteristics of heart rate variability before and during postural tilt. Relations to aging and risk of syncope

Fourier analysis of heart rate (HR) may be used to characterize overall HR variability as well as low- and high-frequency components attributable to sympathetic and vagal influences, respectively. We analyzed HR spectral characteristics of 12 healthy young (18-35 years) and 10 healthy old (71-94 years) subjects before and during 60 degrees head-up tilt. Total spectral power in the 0.01-0.40-Hz frequency range and low-frequency (0.06-0.10 Hz) and high-frequency (0.15-0.40 Hz) components of the HR power spectrum were significantly lower in old than in young subjects in supine and upright positions. To characterize and compare overall HR variability in young and old subjects, we computed the regression lines relating the log amplitude to the log frequency of the supine HR spectra (l/fx plots). The regression lines for old subjects were lower and steeper (mean slope, -0.78 [5%, 95% confidence limits (CL), -0.73, -0.83]) than in young (mean slope, -0.67 [CL, -0.62, -0.72]), indicating not only reduced overall spectral amplitude but also relatively greater attenuation of high-frequency HR components in the old subjects. This finding illustrates a novel way to quantify the loss of autonomic influences on HR regulation as a function of age. During postural tilt, HR variability was unchanged in the old subjects. For the entire group of young subjects, total HR variability increased during tilt. Six young subjects developed vasovagal syncope during tilt, enabling us to examine differences in the HR spectra of these subjects while they were asymptomatic before syncope.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced supine cardiac volumes and diastolic filling rates in elderly patients with chronic medical conditions. Implications for postural blood pressure homeostasis

Very elderly individuals with multiple chronic illnesses are at high risk of orthostatic hypotension, falls, and associated morbidity and mortality. Alterations in cardiac volumes and filling characteristics may contribute in part to an increased prevalence of orthostatic hypotension and falls in these people. In this study cardiac function was evaluated with gated radionuclide ventriculography in eight healthy young subjects (19-38 years) and 25 elderly persons with stable chronic illnesses (73-96 years), 14 of whom had a history of recurrent falls. Blood pressure was measured supine during the radionuclide ventriculography, then after one minute of standing. Supine stroke volume index, end diastolic volume index, cardiac index, and peak filling rates were significantly lower in elderly subjects compared to young, and ejection fraction and end systolic volume index (measures of systolic function) were the same in young and old. Compared to the young, elderly subjects had a reduction in ventricular filling during the first third of diastole, but an augmentation in the last third, during atrial contraction. Within the group of elderly subjects, the directional change in systolic blood pressure during orthostasis was significantly correlated with basal supine systolic blood pressure (R = 0.81, P less than .0001) and supine cardiac index (R = 0.66, P = .002). Thus, very old people representative of those seen in clinical practice have reduced cardiac volumes and impaired early diastolic filling, a result possibly related to elevations in systolic blood pressure. These changes in cardiac structure and function may contribute, in part, to orthostatic hypotension in advanced age.

Reduced susceptibility to syncope during postural tilt in old age. Is beta-blockade protective?

Clinical studies of syncope suggest a decreased prevalence of vasovagal syncope in old age. To examine this possibility and its pathophysiologic implications, we report the results of two studies. The first evaluated responses to head-up tilt in young and old subjects. Presyncopal vasovagal symptoms occurred in 4 of 9 young subjects and only 1 of 22 old subjects. The second study asked whether decreased beta-adrenergic responsiveness protected the old during tilt via unopposed alpha-adrenergic-mediated vasoconstriction. Blood pressure, heart rate, and forearm vascular resistance responses to tilt in 11 healthy young subjects randomized to receive intravenous propranolol hydrochloride or saline were compared with those of 10 healthy elderly. Propranolol attenuated heart rate and forearm vascular resistance responses. Vasovagal symptoms occurred in 4 young and no old subjects; 2 were symptomatic during propranolol administration. Thus, presyncopal vasovagal symptoms are less common during tilt in old age. Propranolol did not prevent the vasovagal reaction or enhance forearm vasoconstriction. Propranolol's attenuation of vasoconstriction may be due to decreased activation of cardiopulmonary baroreceptors during beta-blockade.

Altered blood pressure homeostasis in advanced age: clinical and research implications

Aging and associated increases in systolic blood pressure may cumulatively produce alterations in many blood pressure regulatory mechanisms that impair an older person's ability to adapt to hypotensive stress. Both age and hypertension impair baroreflex sensitivity and decrease compliance of the heart and vasculature. These changes increase the risk of hypotensive responses to activities that reduce cardiac preload and to conditions that produce tachycardia or eliminate atrial contraction. Common clinical examples include orthostatic and postprandial hypotension, nitrate intolerance, and atrial fibrillation. The increased intra- and interindividual variability in blood pressure, resulting from impaired homeostatic capacity, challenges established diagnostic criteria for hyper- and hypotensive syndromes and necessitates new multivariate approaches to research data analysis. Gerontologic investigations utilizing blood pressure measurements should examine individual as well as group responses, and stratify subjects by level of basal blood pressure to isolate the effect of aging from the effects of blood pressure elevation.

Impaired heart rate responses to cough and deep breathing in elderly patients with unexplained syncope

To test the hypothesis that elderly patients with unexplained syncope have impaired autonomic control of heart rate, chronotropic responses to deep breathing and cough were studied in 12 elderly patients (85 +/- 4 years), 14 elderly control subjects (82 +/- 7 years) and 10 young subjects (26 +/- 5 years). There was no difference in resting RR interval between elderly patients with syncope and control subjects. However, the ratio of the maximum RR/minimum RR (an index of heart rate variability) during deep breathing was significantly lower in patients than in control subjects (p less than 0.005). In the minute following cough, there was no difference in initial reflex tachycardia, but subsequent rebound bradycardia was blunted in the elderly patients with syncope. The predominant impairment in elderly patients with unexplained syncope was the bradycardia component of the responses to deep breathing and cough, suggesting that these patients may have impaired parasympathetic modulation of heart rate. Although not likely to be the cause of syncope in these patients, these findings may reflect an underlying autonomic defect.

Biomedical research in the nursing home: methodological issues and subject recruitment results

Although nursing homes are potentially important sites for geriatric research, previous reports have identified impediments to subject recruitment in this setting. We are conducting five simultaneous clinical studies in a 725-bed nursing home. Utilizing a systematic subject recruitment methodology designed to minimize patient and staff burden, we have recruited over 100 subjects. The average recruitment rate over two years from nursing home residents meeting study entry criteria was 43%. The rate was highest (81%) for a study of urinary incontinence offering direct benefit to participants, and lowest (28% and 14% respectively) for physiologic studies of vasopressin regulation and dermal vitamin D production, offering no direct benefit. Studies of syncope and dementia which benefitted groups affected by these problems but not controls, had intermediate recruitment rates (46 and 44%, respectively, P less than .002 compared to incontinence). Thus, clinically relevant projects, sensitive to the needs of the patient and institution, can recruit subjects from the nursing home.

The prevalence and prognosis of minimally elevated creatine kinase-myocardial band activity in elderly patients with syncope

Syncope in elderly patients is often the initial manifestation of myocardial infarction (MI). Small elevations in creatine kinase-myocardial band (CK-MB) activity following syncope may represent MI, transient myocardial hypoperfusion, or insignificant background activity. To determine the prevalence and prognostic significance of minimal CK-MB elevations in elderly patients with syncope, serial serum CK-MB activities and subsequent survival experiences were determined for elderly syncope patients with and without MI, and for age-matched nonsyncopal controls. While all syncope patients with MI by specific clinical criteria had one or more abnormal CK-MB levels (greater than 5 U/L) and died within 31 months, 10% of syncope patients without MI and 10% of controls had abnormal CK-MB with no impact on mortality. Using standard clinical laboratory techniques, minimal elevation in CK-MB was found in 10% of elderly subjects with and without syncope and probably had no prognostic significance.