Physiology of Aging of Older Adults

Most oral health care providers encounter older adults in their practices and can play a critical role in supporting independence and quality of life for this aging cohort. Physiologic and structural oral cavity changes associated with normal aging may affect the presentation and oral health care of older adults. This article reviews the normative aging of dentition and oral structures and physiologic changes associated with normal aging, including cardiovascular, metabolic, and musculoskeletal changes, and how they may affect oral health. Oral health providers should be aware of normal aging processes when they plan care or schedule procedures for older adults.

Key points

  • There is greater physiologic heterogeneity in older adults than in younger cohorts, which makes clinical care more complex for the geriatric practitioner.

  • Normal physiologic changes associated with aging different from the disease process and warrant an in-depth understanding and application for patient-centered care.

  • Cardiovascular and pulmonary changes associated with normal aging can result in vital sign lability, reduced tolerance for prolonged procedures, and need for special considerations regarding patient positioning.

  • Metabolic changes related to liver or kidney function may require alternate drug selection or dose adjustments of commonly used medications, such as antibiotics.

  • Older adults may have multiple physiologic changes that combine, leading to increased risk for frailty and poorer oral health.

Introduction

As 2030 approaches, the decade all baby boomers will be over the age of 65, providers must be prepared to provide up-to-date comprehensive care for aging patients. 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 physiologic heterogeneity of this population. In simple terms, healthy older adults are more unlike each other than are equally healthy younger adults in most studies of physiologic function. Although less thoroughly studied, oral health changes over the life span appear to observe the same principles of normative physiologic aging as 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 have an impact on the oral cavity. Many of these physiologic changes contribute to the lower threshold for developing oral disease, nutritional and swallowing problems, taste and smell impairment, chronic pain, and psychological distress. As information and research on normative changes with aging have emerged, this material has been updated to confirm and reinforce what already is known with new information on normal aging and the clinical significance of normal aging of older adults. This article reviews the concepts of physiologic reserve; normative aging processes of the cardiovascular, metabolic, and musculoskeletal systems that are applicable to oral health; and age-related changes in the oral cavity and the clinical significance of those changes. This article is not meant to focus on diseases related to aging but rather to begin to explore the normal physiologic changes associated with aging dentition and systemic changes with age for a better understanding of the presentation of older adults and how it may change the approach to diagnosis and treatment.

Physiology of aging

First, when considering aging physiology, it is important to understand that the line between normative aging and disease is uncertain. Despite this, aging alone changes the physiologic threshold at which individuals can withstand physiologic challenges due to stressful occurrences, such as surgery, illness, injury, and severe environmental conditions. In older adults, physiologic reserve is reduced and the ability to maintain healthy physiologic balance is blunted. For example, an older adult given an intravenous salt load may lack the cardiac or renal reserve to adapt to sodium and volume shifts. Studies reveal that healthy older adults have stiffer hearts and, therefore, do not get as much ventricular stretch and Starling curve–induced increased cardiac output with this volume expansion. Changes in the autonomic nervous system also may lead to a loss of variation in heart rate response to stimuli. Even in the healthy older adult, the ability to increase heart rate is limited and impedes the cardiorenal system from filtering salt as rapidly or efficiently as younger adults. This lowered threshold for maintaining homeostasis, coined homeostenosis , results from a decreased ability of physiologic systems to modulate such deviations from physiologic baselines. In describing systemic physiologic changes, it becomes hard to isolate each system because of the interconnectedness needed to adapt and maintain normal functioning. Multiple systemic physiologic changes also can combine to contribute to frailty and functional decline. The next section more specifically explores 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, resulting in slower resting and maximum heart rates. As described by Cefalu and colleagues, normal aging increases stiffness of the left ventricle, resulting in a decrease in left ventricular compliance. Even with the addition of left ventricular filling that results with 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 decreased nitrous oxide vasodilator effects, raises systolic vascular resistance, further impeding forward flow, increasing myocardial oxygen demand and cardiac work. In addition to the aforementioned normative changes in left ventricular function, the aging heart experiences decreasing abilities to raise heart rate and has more muted responses to cholinergic and sympathomimetic stimulation. This limits the heart’s ability to respond to additional stress. This results in an increased risk of congestive heart failure 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 may have difficulty adapting under stressors, such as a dental appointment.

In the dental office, it is important to understand blood pressure changes found in older adults. With the normal aging heart, blood pressure tends to increase partially due to increased aortic and arterial stiffness. Systolic pressure has been known to rise continuously with age whereas diastolic pressure fluctuates with age, leading to an increase in pulse pressure. In adults over the age of 50, increased pulse pressure and systolic blood pressure greater than 140 mm Hg are more significant risk factors for heart disease than diastolic blood pressure. , Hypertension, a risk factor for cardiovascular disease and one of the most common medical conditions among adults older than 75, affects approximately two-thirds and three-fourths of men and women, respectively. Older adults with systolic blood pressure greater than 150 mm Hg merit referral for initiation or intensification of treatment. Additionally, because of blunted baroreceptors in the carotid arteries that do not modulate acute changes in blood pressure in normal aging, oral health providers also must 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 and alterations in connective tissue with reduced diaphragmatic and intercostal muscle strength, including early fatigue of the diaphragm, decreased perception of dyspnea, and reduced airway size and shallower alveolar cells and sacs, which result in decreased vital capacity and forced expiratory volume with an increase in residual volume and functional residual capacity. Although all these changes are considered normal, these physiologic changes 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 impacting oral health through an increase the risk of aspiration both in the dental chair during treatment and of plaque accumulation on teeth and dentures. Additionally, normative changes with age associated with decreased genioglossal reflex and an elongated soft palate increase the risk for obstructive sleep apnea and hypertension secondary to obstructive sleep apnea.

Liver

As the liver ages, it decreases in size by approximately 1% every year beginning at age 40 and, as the aging process continues, blood flow to the liver decreases by 40% to 45%. In vivo and in vitro studies also have 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 function, such as decreases in renal blood flow, glomerular and tubular mass, and glomerular filtration rate (GFR). By age 40, the GFR declines by a rate of 1% per year. Despite this, fluid homeostasis generally is maintained. For older adults with and without chronic kidney disease, renal excretion of medications takes longer than younger adults. , ,

The clinical importance in dentistry of renal physiologic changes due to aging are related primarily to prescribing. Classes of drugs commonly prescribed by dentists in which renal dose adjustment is important to prevent side effects include fluroquinolones (phototoxicity, hallucinations, delusions, seizures, and cognitive dysfunction), penicillins (seizures and cognitive dysfunction), fluconazole, and aminoglycoside antibiotics. , Additionally, some opioids, such as morphine and hydromorphone, have metabolites that are excreted in the kidneys and should be used with increased caution in older adults.

Musculoskeletal

In the normal aging process of the musculoskeletal system, there is a decline in bone mineralization and architectural strength of the bony matrices; microfractures accumulate and joints stiffen as a result of a decline in water content in the tendons, ligaments, cartilage, and synovial compartments. Additionally, both muscle mass and total body water decrease with an increase in total body fat. This decreases the volume of distribution of water-soluble medications, such as penicillin, effectively concentrating the dose in older adults compared with younger adults. Conversely, the distribution of lipid-soluble medications increases and drugs, such as diazepam and lidocaine, may reach lower serum concentrations but have a longer half-life due to distribution throughout adipose tissue.

Normal age-related functional changes also may include a greater loss of strength in the lower extremities compared with the upper extremities but with a reduction in hand grip strength. In healthy but frailer individuals, this could affect tooth brushing and flossing ability and efficiency. Adaptive devices and tooth brush modifications may need to be made to accommodate an individual’s ability. Gait speed and the ability to change position or tolerate positioning also may be impacted by normal musculoskeletal changes with aging, which may require modifications in the physical layout of the dental office and considerations in scheduling.

In summary, due to diminished physiologic reserve of the cardiopulmonary, metabolic, and musculoskeletal systems 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 older adult patients and prescribing for them.

Frailty and oral health

Frailty as a geriatric syndrome is characterized by the presence of weight loss, fatigue, weakness, and decreased physical activity. Although not considered part of normal aging, frailty is more prevalent as older adults age and increases the risk for disablement, hospitalization, and mortality. The risk for developing frailty is increased by the presence of functional decline and multiple comorbidities, and frailty can increase the risk for further functional decline. For example, an older adult with decreased cardiopulmonary and musculoskeletal reserve may become easily fatigued during meals, and basic hygiene tasks, contributing to weight loss, poorer oral hygiene, and a negative feedback loop that contributes to increased frailty.

In summary, due to diminished physiologic reserve of the cardiopulmonary, metabolic, and musculoskeletal systems 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 older adult patients and prescribing for them.

Oral/Pharyngeal Changes

The normal aging process of the oral cavity undergoes many physiologic changes; however, many of these changes are secondary due to chronic systemic disease and their treatment regiments (inflammatory response, medication, chemotherapy, and radiotherapy). This section focuses on the normative changes in the aging oral cavity and the clinical significance of those changes rather than pathologic changes associated with disease, trauma, and unnatural wear.

Dentition

Due to a variety of factors, older adults are retaining more of their natural teeth; however, tooth retention varies widely with socioeconomic status. Aging changes in tooth anatomy and histology depend on chemical and mechanical wear from mastication as well as factors, such as culture, diet, occupation, tooth composition, and resiliency and strength of teeth and the surrounding periodontal apparatus. There has not been a significant amount of research documenting changes in the dentition since the last publication; the clinical significance to normative age-related changes for the dental practitioner is highlighted.

Enamel

Enamel is composed of the highest percent of mineral content, making it the hardest tissue in the body. It has been observed that changes occur in both physical appearance and molecular composition in health aging adults, related mainly to the exchange of minerals in the oral environment with the enamel surface and mechanical wear over time.

The demineralization-remineralization process that occurs throughout life has an impact on the enamel hardness and subsequent tooth wear. Additional site-specific wear patterns and changes in enamel thickness have been observed in older adults compared with younger cohorts. , Fig. 1 illustrates the thickening and shortening of the enamel at the incisal edge of the tooth and the thinning of the enamel at the cervical third of the tooth at the cement-enamel junction. Signs of overall tooth wear are flattening, darkening, and smoother surfaces due to the loss of the outer enamel surface.

Mar 21, 2021 | Posted by in General Dentistry | Comments Off on Physiology of Aging of Older Adults
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