Friday, 22 February 2019

Ageing and Health

Ageing and Health

Ageing and Health


Although there have been many theories advanced to account for ageing with none gaining wide acceptance, some generalizations are agreed upon by most investigators. The life span is represented by growth and development and then decline or senescence (normal ageing) over time. These are not static stages but represent the continuously changing processes of the life cycle. Senescence results from declines in actual numbers of active metabolic cells and cellular functions because of the accumulation of environmental exposures and behaviours coupled with genetic vulnerabilities over time (Jazwinski, 1996; Kirkwood, 1996).

However, individuals also have an innate and unique genetic or biological plasticity that is coupled with adaptive or coping strategies for the management of ageing-related somatic changes. Thus ageing also produces increasing heterogeneity between individuals as they age. Coupled with this heterogeneity and particular health behaviours can be seen differential rates of decline and change among cells, tissues and organ systems, so that individuals will age at different rates with some biologically ‘old’ at 45, while others can be vigorous and ‘young’ at 75. 

General ageing 
Generally, with senescence, there is a quantitative loss of tissue mass as well as functional decline. An example of functional changes can be seen in the timing of circadian rhythms that affect temperature control, sleep patterns and the secretion of hormones such as cortisol, as well as growth hormone, the gonadotropins,  thyrotrophin and melatonin. The significance of these latter changes is not yet well understood, yet it is interesting to speculate about them in the light of the reports from the MacArthur studies on successful ageing which showed that individuals with higher nocturnal secretion of cortisol and catecholamines, and higher systolic blood pressures were more likely to show greater declines in cognitive and physical function during the follow-up period of three years (Rowe & Kahn, 1998).

Of the organ systems, the normal kidney, lung and the skin age much more rapidly than the heart and liver in both sexes, while the musculoskeletal system and the gonads decline at different ages in males and females (Finch & Schneider, 1985; Kenney, 1989). There is an 80% decrease in overall muscle mass and an average of 35% increase as well as a significant redistribution of body fat. Fat deposition accumulates around and within the viscera while there is a loss of fat on the surface. Thus older people lose ‘insulation’ and are more sensitive to extremes of ambient temperature than are younger people.

Cardiovascular system
The age-related decline in the cardiovascular system may be critical for decreased tolerance for exercise and loss of conditioning, and the major factor contributing to feelings of agedness and overall decline in energy reserve. However, there is much more than heart and blood vessel deterioration in the loss of energy reserve. There is a gender-specific dependency as well, on the muscles and skeleton and the lungs. Changes occur in the heart chambers, and the blood vessels and valves. With time, the heart muscle thickens, the ventricular cavities become smaller and the amount of blood pumped per contraction decreases. Heart rate also slows with time as cells in the sinus node decline by up to 90%. The decrease in rate may be related to ‘down regulation’ or decreased responsiveness of adrenergic receptors on heart muscle even though synthesis and clearance of epinephrine does not change. Thus, the maximum heart rate in response to increased activity and responses to stress demands diminishes (Lakatta, 1987; Marin, 1995).

Blood vessels narrow and become more rigid contributing to the slow elevation in blood pressure with ageing in the absence of cardiovascular disease. Women appear to enjoy a slower rate of progression of cardiac disease before the menopause with a lower incidence of coronary artery disease in pre menopausal women. (Anderson et al., 1995). However, cardiovascular disease becomes
the major killer of older post-menopausal women, can present with atypical symptoms and can be more lethal than in men often with delay in seeking care because of stereotypic or lay perceptions of what heart disease and acute attacks should feel like (see ‘Symptom Perception’ and ‘Delay in Seeking Help’).

Respiratory system
There is an even more rapid rate of functional decline in all parts of the respiratory system. This includes lung tissue as well as the chest cavity, with its muscles and the ribs and vertebral column. There is less work capacity as all the types of muscles age in bronchi, the diaphragm and chest wall. There are clear gender differences in thoracic cage ageing. This may result from bone and muscle mass losses that are greater in females and cause diminished exercise capacity as well as a greater vulnerability of and a greater possibility for immobilization. Within the lung itself, the alveolar or air sac septae are the exchange sites for the gases, oxygen and carbon dioxide. Old lungs have scattered areas of scarring and damage to the septae that interfere with gaseous exchange. These manifestations
of ‘senile’ emphysema may limit the amount of exercise and energy that can be expended even more than functional changes in the cardiovascular system described previously (Rossi et al., 1996).

Moreover, it is difficult to determine how much of the respiratory functional decline that is observed is age-related and how much is environmentally and behaviourally induced since most individuals are exposed to some degree of air pollution and cigarettes or other inhaled substances abuse exaggerates the ageing changes. Smoking produces scarring or fibrosis, increased secretions and an increased rate of chronic infection. The cough is less vigorous and clearance of foreign particles is slower and bronchitis and emphysema result.

Musculo-skeletal system
Skeletal ageing probably generates most of the common symptoms responsible for limitations of recreational activities and functions of daily living as well as restrictions in job related activities; the joint and muscle aches and stiffness attributed to ‘getting old’. Bones thin at a rate of 0.8–1.0%/yr over the lifespan for both men and women, but there is acceleration in the rate for females around the menopause, of between 8–10%/yr. Thus post-menopausal women are more vulnerable than males of the same age to pathologically thin bones or to osteoporosis which can cause fractures of the vertebral spine. While both men and women are at risk for fractures of the long bones, women are fracture prone 10 years earlier than men of the same cohort. (Kenny, 2000; Raiz, 1997). Smoking changes these fracture risk odds for men and women because cigarette smoking is also toxic for bone growth cells and is a major cause of osteoporosis in both male and female smokers.

Liver
The liver has remarkable regenerative capacity but undergoes modest decreases in weight and size. Hepatic blood flow shows a 1.5% fall/yr so that there will be a 50% reduction in flow over the lifespan. All ingested drugs as well as metabolites absorbed from the small intestine and stomach, pass through the liver; some are unchanged while most undergo metabolic detoxification by microsomal enzymes into water-soluble substances for renal excretion. With decreases in liver mass, losses in this critical enzymatic function (primarily Cytochrome P-450) are seen and, along with a decrease in blood flow, there is a decrease in the rate of Phase I biotransformation, particularly in men. These functional changes result in a prolongation in the half-life of many of the metabolites and drugs that are inactivated by the liver. Conjugation or Phase II remains largely unchanged.

Kidney
All kidney functions deteriorate with age because of a steady loss of nephrons over time. Thus there are declines in filtration, active tubular secretion and re-absorption and passive tubular diffusion. This decline in renal function has serious implications for drug prescribing patterns (Kenney, 1989; Finch & Schneider, 1985) since the kidneys serve as the major excretion site for metabolites and drugs after transformation through the liver and renal insufficiency or functional loss prolongs the body’s exposure to drugs and toxic substances as well as digestive by-products.

Immune system
With increasing age, the total number of immune cells changes minimally, but the functional, or qualitative changes in immunity with age are much more notable than the quantitative ones. Investigators in the field of physiological psychology have described complex and direct links between the central nervous system and the immune system. The neurohumorally mediated effects of stress on the immune system have also been well demonstrated in carefully controlled experiments with rodents and primates (Borysenko & Borysenko, 1982; Rosenberg et al., 1982). Studies in humans have demonstrated similar effects, though it is impossible to achieve the same degree of control as in the animal studies. Health surveys have reported clusters of illness (from the common cold to cancer) occurring around the time of major life changes (Minter & Patterson-Kimball, 1978). Other studies have found strong correlations between loneliness and decreased proliferative responses of lymphocytes to mitogens, decreased natural killer cell activity and impaired DNA splicing and repair in lymphocytes (Glaser et al., 1985). Healthy adults over the age of 60 years with a strong social support system (i.e. a close confidant/e) have significantly greater total lymphocyte counts, and stronger stimulus-induced responses than those without such a relationship (Thomas et al., 1991). Persons experiencing the stress of care giving for a spouse with dementia have poorer antibody responses to influenza vaccination than matched control subjects, and their lymphocytes make less interleukin 1b and interleukin 2 when stimulated with virus in vitro (Kiecolt-Glaser et al., 1996). These caregivers also display delayed wound healing after punch biopsy of the skin compared to non-care giving, age-matched controls (Kiecolt-Glaser et al., 1995). The mechanisms that underlie such associations, and the modulating effects of age, are not fully understood but are clearly important for maintaining full independent function (see also ‘Psychoneuroimmunology’, ‘Stress and Health’ and
‘Social Support and Health’).

The nervous system
Given the complexity of the nervous system, it is to be expected that there will be significant variability in the functional changes that mirror anatomic changes of ageing. In general, these descriptions are based on cross-sectional studies and are thus open to criticism, but it appears that functions that change very minimally from ages 25 to 75 include: vocabulary, information accrual and comprehension and digit forward pass. There are subtle changes in hand two point discrimination, and minimal touch sensation loss in the fingers and toes. A greater than 20% decline is seen in ‘dexterity areas’ including hand- and foot-tapping and tandem stepping. Greater decrements are seen in the ability to rise from a chair; however, these tasks must reflect muscle as well as nervous system function and may be confounded by joint disease. Arthritic changes in the hands will produce difficulty in ‘dexterous’ activities such as cutting with a knife, zipping and buttoning. Thus, studies of function using ADL types of behaviour may significantly confound ageing with chronic illness.

Recent research has shown that there is much less neuronal loss than had previously been assumed, although brain weight declines significantly with age and blood flow is decreased by about 20% in the absence of vascular disease. In addition, decrements are seen in cerebral autoregulation. Cells disappear randomly throughout the cortex, but in other brain areas, there is clustered loss, i.e. the disproportionally greater loss of cells in the cerebellum, the locus ceruleus and the substantia nigra. The hypothalamus, pons and medulla have modest age-related losses (Anglade et al., 1997). These may be responsible for the altered sleep patterns characteristic of the elderly, and disturbances of gait and balance. The alterations in sleep patterns are a source of much concern for up to 50% of persons aged 60 and older with 12% of an epidemiological sample of persons over 65 reporting significant and chronic insomnia. Ageing individuals believe they sleep poorly and insist they are up all night long. Indeed they are frequently aroused, but the total amount of sleep that occurs during the night is essentially unchanged (see ‘Sleep and Health’). Careful inquiries reveal that such persons are usually refreshed and rarely sleepy when they awake, even though their sleep patterns have changed. Up to half of community-dwelling elderly persons use either over-the-counter or prescription sleeping medications. Most studies suggest a greater prevalence of subjective sleep abnormalities and greater use of hypnotics by older women, and those that have been studied have been shown to have sleep aberrations on monitoring. On the other hand, older women appear to have better preservation of slow wave sleep than older men. (Fukuda, 1999). The problem that confronts the clinician becomes the seeking of sleeping or hypnotic potions. The excessive prescribing of hypnotic medications is common for older patients. Hypnotic drugs cannot increase locus ceruleus cell number or reverse age related sleep cycle changes but can increase vulnerability to confusion and delirium as well as addiction. Thus it may be inappropriate to prescribe hypnotics, except under times of extreme stress or during hospitalization or sickness. Non-pharmacologic interventions to facilitate good ‘sleep hygiene’ need to be utilized to treat a maladaptive response to normal ageing.

Myelin decreases primarily in the white matter of the cortex. (Saunders et al., 1999; Mielke et al., 1998; Sjobeck et al., 1999). Apoptosis or programmed cell death may be responsible for brain neuron loss. (Sastry et al., 1997). Although there is cellular dropout, new synapses continue to form throughout the life span. (Aamodt & Constantine-Paton, 1999). The number of spinal cord motor neurons remains essentially unchanged until the seventh decade, after which losses occur in the anterior horn cells (Cruz-Sanchez et al., 1998). Vibratory and tactile thresholds decrease and the thermal threshold in the fingers goes up thereby decreasing sensory sensitivities.

In summary, there are significant organ and cell-specific biological changes that occur at different rates within and between ageing individuals. The ability to respond to stress becomes compromised, yet in the absence of significant chronic disease, functional independence can be maintained well into the ninth decade. Specific aspects of senescence are particularly relevant for the health psychologist who must appreciate the limited reserve of the older patients, the fragility of the immune response and the increased vulnerability to medications of all types and, in particular, to psychoactive drugs and yet appreciate the remarkable resiliency of the elderly ‘survivor’. See also ‘Psychological Care of the Elderly’.

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