Physiology of Aging of Older Adults

This article reviews the concepts of physiologic reserve, the principles of the normative aging process as exemplified by the cardiovascular, neurologic, and musculoskeletal systems. How these principles apply to oral health, and age-related changes in the oral cavity itself, is reviewed and suggests how they may affect disease management by oral health care providers. It does not focus on diseases related to aging, but rather aims to explore the normal physiologic changes associated with aging dentition and systemic changes related to age, thus enabling clinicians to obtain a better understanding of the presentation of older adults and how it may change their approach to diagnosis and treatment.

Key points

  • Oral health plays a vital role in several functions that contribute to life quality, longevity, and functional independence.

  • The oral cavity, when functioning properly, provides and contributes to the enjoyment of taste and smell; the appropriate steps needed for deglutition and nutrition; maintenance of facial anatomy; and self-esteem.

  • Older adults differ more from one another physiologically than do younger adults, which makes geriatric care a greater challenge for the clinician.

Introduction

Much has been written about the nature and extent of the demographic shift taking place in the United States. By 2030 the baby-boomer generation will reconstruct the population pyramid into a population rectangle, with the fastest growing segment of that polygon being the oldest of the old (>85 years). As the population ages it becomes more heterogeneous, with a wider distribution of physiologic reserve for each individual. Cognitive status, chronic multiple diseases, and medications add to the heterogeneity of this physiologically diverse population segment. Normative aging studies demonstrate a wider distribution around the mean in most physiologic measures. In simpler terms, healthy older adults are more unlike each other than equally healthy younger adults in most studies of physiologic function. Though less thoroughly studied, changes in oral health over the life span seem to observe the same principles of normative physiologic aging that apply to other organ systems and physiologic processes. “Oral aging” is as relevant as any other health care challenge facing an aging society. Many well-studied physiologic functions of the older adult population affect the oral cavity. Many of these physiologic changes contribute to the lower threshold for the development of oral disease, nutritional and swallowing problems, taste and smell impairment, chronic pain, and psychological distress. This article reviews the concepts of physiologic reserve, the normative aging processes of the cardiovascular, neurologic, and musculoskeletal systems that are applicable to oral health, and age-related changes in the oral cavity itself, and reflects on how they may contribute to disease management by oral health care providers. The article is not intended to focus on disease related to aging but rather aims to explore the normal physiologic changes associated with aging dentition and systemic changes related to age, thus enabling clinicians to obtain a better understanding of the presentation of older adults and how it may change their approach to diagnosis and treatment.

Introduction

Much has been written about the nature and extent of the demographic shift taking place in the United States. By 2030 the baby-boomer generation will reconstruct the population pyramid into a population rectangle, with the fastest growing segment of that polygon being the oldest of the old (>85 years). As the population ages it becomes more heterogeneous, with a wider distribution of physiologic reserve for each individual. Cognitive status, chronic multiple diseases, and medications add to the heterogeneity of this physiologically diverse population segment. Normative aging studies demonstrate a wider distribution around the mean in most physiologic measures. In simpler terms, healthy older adults are more unlike each other than equally healthy younger adults in most studies of physiologic function. Though less thoroughly studied, changes in oral health over the life span seem to observe the same principles of normative physiologic aging that apply to other organ systems and physiologic processes. “Oral aging” is as relevant as any other health care challenge facing an aging society. Many well-studied physiologic functions of the older adult population affect the oral cavity. Many of these physiologic changes contribute to the lower threshold for the development of oral disease, nutritional and swallowing problems, taste and smell impairment, chronic pain, and psychological distress. This article reviews the concepts of physiologic reserve, the normative aging processes of the cardiovascular, neurologic, and musculoskeletal systems that are applicable to oral health, and age-related changes in the oral cavity itself, and reflects on how they may contribute to disease management by oral health care providers. The article is not intended to focus on disease related to aging but rather aims to explore the normal physiologic changes associated with aging dentition and systemic changes related to age, thus enabling clinicians to obtain a better understanding of the presentation of older adults and how it may change their approach to diagnosis and treatment.

Physiology of aging

When considering aging physiology, it is first important to understand that we are unsure of where aging ends and disease begins. Wherever that line divides normative physiologic changes of aging and disease, it is clear that aging alone changes the physiologic threshold for any individual to withstand physiologic challenges, whether brought on by medications, stressful interventions such as surgery, severe environmental conditions, or other illness. What we do know is that, in the elderly, physiologic reserve is reduced and the ability to maintain the physiology within the healthy is blunted. Take, for example, elderly patients and the ability to adapt to a salt load delivered by dietary means or the health care system. This process primarily involves both cardiac and renal adaptation. Studies reveal that healthy older adults have “stiffer” hearts and, therefore, do not achieve as much increased cardiac output induced by ventricular stretch and Starling curve with this volume expansion. Just as important, even in healthy older kidneys, salt excretion occurs less efficiently and takes longer. This lowered threshold for maintaining homeostasis, coined homeostenosis, results from a decreased ability of the systems built to interact with and modulate such deviations from physiologic normal. Another example of this involves changes in the autonomic nervous system. Changes in receptor sensitivity and feedback-loop automaticity result in a loss of variation in heart-rate response to stimuli. In the salt-load example, even in the normal healthy older adult, the ability to increase heart rate is limited and impedes the cardiorenal system from filtering salt as rapidly as in younger adults. One can discern from these examples that in describing systemic physiologic changes it becomes difficult to isolate each system or organ, because of how they work together and respond to one another while adjusting and adapting to carry out daily functions. The next section explores more specifically the relationship between known normative age-related changes in physiology and their impact on oral health.

Systemic changes associated with oral health

Cardiovascular

Normal cardiovascular changes with age are both structural and functional. There is an overall decreased cardiovascular reserve with a loss of and hypertrophy of myocytes; 90% of pacemaker cells in the sinus node are lost by the age of 75 years, resulting in slower resting and maximum heart rates. As described by Cefalu, normal aging increases stiffness of the left ventricle, resulting in a decrease in left ventricular compliance. Even with the addition of left ventricular filling resulting in atrial contraction, the normal aged left ventricle creates a higher left ventricular end-diastolic pressure, a more robust Starling curve position point, and a higher stroke volume as the ventricle moves from diastole to systole. Arterial stiffness, the result of age-related calcification and collagen deposition in place of elastin, coupled with vasodilatory effects of decreased nitrous oxide, raises systolic vascular resistance, further impeding forward flow, increasing myocardial oxygen demand, and increasing cardiac work. In addition to the aforementioned normative changes in left ventricular function, the aging heart experiences decreasing abilities to raise the heart rate and has more muted responses to cholinergic and sympathomimetic stimulation, thus limiting the heart’s ability to respond to additional stress including, but not limited to, exercise. This process results in an increased risk of congestive heart failure or heart block in the presence of chronic disease processes such as diabetes, hypertension, and coronary heart disease. Despite these changes the cardiovascular system compensates to maintain function, but finds it is difficult to adapt during stress or a medical intervention such as a dental appointment.

In the dental office, this can translate clinically to understanding the changes in blood pressure found in older adults. With the normal aging heart blood pressure tends to increase, partially because of decreased compliance of the aorta and flexibility in the arteries. Systolic pressure has been known to continuously increase with age whereas diastolic pressure fluctuates with age, leading to an increase in pulse pressure. In adults older than 50 years, increased pulse pressure and systolic blood pressure greater than 140 mm Hg is a more significant risk factor for heart disease than diastolic blood pressure. Hypertension, a risk factor for cardiovascular disease and one of the most common medical conditions among older adults, affects approximately two-thirds and three-fourths of men and women, respectively, older than 75 years. As a result of aforementioned physiologic changes with aging, clinicians are now more concerned about hypertension defined as systolic blood pressure greater than 160 mm Hg than with the conventional definition of hypertension, blood pressure greater than 140/90 mm Hg. In addition, because of blunted baroreceptors in the carotid arteries that do not modulate acute changes in blood pressure in normal aging, oral health providers must also be aware of postural hypotension likely to occur in normal individuals on standing from a sitting or lying position in the dental chair.

Pulmonary

Normal structural changes with age in the respiratory system include: stiffening of the rib cage; reduced diaphragmatic and intercostal muscle strength, including early fatigue of the diaphragm; decreased chemoreceptive response (reducing the perception of dyspnea); alterations in connective tissue; reduced airway size and shallower alveolar cells and sacs; and decreased vital capacity and forced expiratory volume, with an increase in residual volume and functional residual capacity. Although all of these physiologic changes are considered normal and continue to maintain respiration, they lower the threshold for adaptive ability, increase the risk of disease, and have an effect on oral health.

Many of these changes contribute to a decreased cough reflex and defective mucus clearance, directly affecting oral health through an increase the risk of aspiration both in the dental chair during treatment and through plaque accumulation on teeth and dentures. In addition, normative changes with age associated with decreased genioglossal reflex and an elongated soft palate increase the risk for obstructive sleep apnea (OSA) and hypertension secondary to OSA.

Musculoskeletal

In the normal aging process of the musculoskeletal system, there is a decline in bone mineralization and architectural strength of the boney matrices. Microfractures accumulate and joints stiffen as a result of a decline in water content in the tendons, ligaments, cartilage, and synovial compartment. In addition, both muscle mass and total body water decrease with an increase in total body fat. This process increases the distribution of water-soluble medications such as acetaminophen, effectively concentrating the dose in older adults in comparison with younger adults. Conversely, the distribution of lipid-soluble medications decreases, and drugs such as diazepam and lidocaine (commonly administered by dentists) have a longer half-life owing to their distribution throughout adipose tissue.

Normal age-related functional changes may also include reduction in hand-grip strength, with a greater loss in the lower extremities than in the upper extremities. In healthy but frailer individuals, this could affect tooth brushing and flossing efficiency. Toothbrush modifications may need to be made to accommodate an individual’s ability.

Liver

As the liver ages it decreases in size by approximately 1% every year beginning at age 40 years, and as the aging process continues blood flow to the liver decreases by 40% to 45%. In vivo and in vitro studies have also shown a decrease in hepatic metabolic activity, further reducing liver function with age. These changes affect hepatic drug metabolism and clearance, and should be taken into consideration when prescribing medications.

Kidney

The normal aging kidney undergoes structural and physiologic changes that may compromise functional reserve, such as a decrease in glomerular and tubular mass, a decrease in glomerular filtration rate (GFR; a measurement of renal function), and decreased renal blood flow. By age 40 years, the GFR declines by a rate of 1% per year. Even with these changes, the healthy kidney maintains homeostasis of body fluids. In older adults with and without chronic kidney disease, renal excretion of medications takes longer than in younger adults.

The clinical importance in dentistry of such age-related physiologic changes is linked with prescribing medication and scheduling of appointments. Classes of drugs commonly prescribed by dentists for which changes in dosed medication are important to prevent side effects include fluoroquinolones (phototoxicity, hallucinations, delusions, seizures, cognitive dysfunction), penicillins (seizures, cognitive dysfunction), fluconazole, and aminoglycoside antibiotics.

Owing to the diminished physiologic reserve of both the liver and the kidney associated with the aging process and possible comorbidities, the body’s ability to respond to external stress decreases. To decrease potential external stress, it is important to take into consideration appointment time, duration, and procedure type when scheduling elderly patients.

Only gold members can continue reading. Log In or Register to continue

Stay updated, free dental videos. Join our Telegram channel

Oct 29, 2016 | Posted by in General Dentistry | Comments Off on Physiology of Aging of Older Adults

VIDEdental - Online dental courses

Get VIDEdental app for watching clinical videos