Physiology of Aging
Understanding the physiology of aging is crucial, especially considering the ambiguous distinction between normal aging and disease. Aging inherently alters the physiological threshold for coping with stressful events, such as surgeries, illnesses, injuries, or harsh environmental conditions (Cefalu 2011). The reduced physiological reserve in the elderly limits their ability to maintain equilibrium in health. Research indicates that elderly individuals typically have fewer elastic hearts, leading to limited ventricular stretching and a reduced increase in cardiac output from volume expansion. Additionally, changes in the autonomic nervous system may reduce heart rate variability in response to different stimuli. Older adults often have a diminished capacity to accelerate their heart rates, affecting the efficiency of the cardiorenal system in processing salt compared to younger individuals. This reduced ability to maintain homeostasis, termed homeostenosis, stems from the decreased adaptability of physiological systems to deviations from their baseline states. The systemic physiological changes are challenging to isolate due to the interconnectedness required for normal function, and they collectively contribute to frailty and functional decline.
Cardiovascular
Age-related cardiovascular changes are both structural and functional. There is a general decrease in cardiovascular reserve marked by loss and hypertrophy of myocytes. By age 75, up to 90% of pacemaker cells in the sinus node are lost, resulting in slower resting and maximum heart rates (Cefalu 2011). As noted by Cefalu and colleagues, normal aging leads to increased stiffness in the left ventricle, reducing its compliance. Even with enhanced filling from atrial contraction, the aging left ventricle generates higher end-diastolic pressure, a more pronounced Starling curve position, and increased stroke volume transitioning from diastole to systole. Arterial stiffness, caused by age-related calcification and collagen replacement of elastin, along with reduced nitric oxide vasodilatory effects, increases systolic vascular resistance, thereby elevating myocardial oxygen demand and cardiac workload. The aging heart also exhibits diminished capabilities to increase heart rate and muted responses to cholinergic and sympathomimetic stimulation, limiting its stress response. This results in a heightened risk of congestive heart failure, especially in the presence of chronic diseases like diabetes, hypertension, and coronary artery disease (Cefalu 2011). While the cardiovascular system compensates to maintain functionality, it may struggle under stressors, including dental appointments (Bergman et al, 2006).
In the dental setting, it's vital to recognize changes in blood pressure commonly seen in older adults. Normal aging often causes a rise in blood pressure, partly due to increased aortic and arterial stiffness. Systolic pressure tends to increase continuously with age, while diastolic pressure varies, leading to a higher pulse pressure. For individuals over 50, elevated pulse pressure and systolic blood pressure above 140 mm Hg are more significant heart disease risk factors than diastolic pressure (Glick 2004; Pinto 2007). Hypertension, prevalent in about two-thirds to three-fourths of older men and women, poses a significant cardiovascular risk (Lipsitz 2013. Older adults with systolic blood pressure over 150 mm Hg should be referred for treatment evaluation or intensification (Qaseem et al, 2017). Furthermore, due to diminished sensitivity of baroreceptors in the carotid arteries in normal aging, dental practitioners should be aware of the likelihood of postural hypotension in elderly patients when moving from sitting or lying positions in the dental chair (Cefalu 2011).