Vagal tone declines markedly with age (Tanaka et al., 2001). Basal (resting) cardiac vagal modulation (or ‘tone’) of the R–R interval (the time between two successive R waves on the QRS interval of an electrocardiogram) is how it can be interpreted on a heart monitor. Regular aerobic exercise modulates selective age-associated impairments of the autonomic nervous system’s physiological function. Tonic vagal modulation of the cardiac period (R–R interval) decreases with age and in more sedentary adults (50% more) than in those who habitually exercise (Tanaka et al., 2001). Those who regularly walk more than 8,000 steps a day are significantly less likely to die from cardiovascular disease than those that take 4,000 steps a day (Saint- Maurice et al., 2020). Heart rate Aging also leads to a progressive infiltration of fat into the heart muscle as well as an increase in collagen and connective tissue found in the extracellular space around the heart cells (Chester & Rudolph, 2011). The fatty accumulation in the heart can be found in particular around the sinoatrial (SA) node, which sometimes creates a partial or complete separation of the node from the surrounding heart tissue and eventually changes the heart’s electrical conduction. This fatty and connective tissue may also contribute to the increased thickness of the left ventricle that is seen with aging. In addition to the fatty infiltrations’ influence on the heart’s electrical conduction, there is a pronounced decrease in the number of pacemaker cells with aging. By age 70, fewer than 10% of the pacemaker cells typically seen in younger adults remain (Strait & Lakatta, 2012). The fatty and connective tissue infiltration and the decrease in the number of pacemaker cells contribute to changes in electrical conduction through the heart and to changes in heart rate that occur with aging. Even in healthy individuals, the maximal heart rate decreases with aging. Numerous changes occur that alter the autonomic signaling of the heart in older adults, contributing to the alterations and decreases in maximal heart rate seen with aging. A decrease in the sensitivity of sympathetic receptors in the body also occurs (Paneni et al., 2017), and the combination of changes in the electrical conduction of the heart and changes to the autonomic response ultimately leads to a Maximal heart rate (HR max ) can be estimated in older adults using the following Gelish formula (Liguori & American College of Sports Medicine, 2020): 207 – (0.7 × age) This newer formula for HR max has replaced the older formula (220 – age) as a better predictor of maximal heart rate in older adults. Specialized regression equations for calculating HR max may be superior to the equation of 220 – age because this equation can under- or overestimate measured HR max , as found by Tanaka et al. They proposed a similar formula (208 – [0.7 × age]) after conducting an extremely large meta-analysis of formulae (2001). Older adults, as a result of both conduction and sympathetic changes, not only have a lower HR max , but they also have a decreased ability to alter (increase or decrease) their heart rate as functional demands dictate, resulting in a decrease in heart rate variability (Paneni et al., 2017). This leads to a decreased ability to respond to any additional demands placed on the body, and in extreme circumstances, such as after surgery or during illness, this may lead to an inability to meet the body’s demands for oxygen, resulting in death (Struthers et al., 2008). Numerous cardiovascular changes occur outside of the heart and lead to further systemic changes. decrease in maximal heart rate. Calculating Maximal Heart Rate
to a standing position. A decrease of more than 20 mm Hg in systolic pressure or 10 mm Hg in diastolic pressure is diagnostic of orthostatic hypotension (MedlinePlus, 2022). Hypotension affects an estimated 6% of Americans, including between 10% and 30% of older adults (MedlinePlus, 2022). Perhaps even more troubling than orthostatic hypotension is the systemic rise in blood pressure that is also related to the decreased compliance of the arteries. An increase in blood pressure increases the pressure against which the heart must pump, which results in additional left ventricular hypertrophy (North & Sinclair, 2012). Many older adults experience an increase in systolic blood pressure with aging that may be partially attributed to increased stiffness of the arteries (Chester & Rudolph, 2011; North & Sinclair, 2012). However, while systolic blood pressure increases, after age 50, diastolic blood pressure typically decreases (Strait & Lakatta, 2012). This leads to progressively larger differences between systolic and diastolic pressures. The difference between systolic blood pressure and diastolic blood pressure, known as the pressure product, is an important indicator of arterial health in older adults. An increase in the pressure product, resulting from larger differences between systolic and diastolic pressure, indicates the decreased ability of the arteries to adapt to changes in blood flow. A pressure product of greater than 60 mm Hg is indicative of less compliant, thicker arterial walls and has been associated with an increased risk of cardiovascular disease, stroke, and heart attack in older adults (Strait & Aging also leads to numerous functional changes that take place within the cardiovascular system. Many of these functional changes result from the previously mentioned structural changes that take place in the heart and arteries. In a body at rest, the cardiac output, measured as the amount of blood pumped through the heart each minute, averages four to six liters—regardless of age—in the absence of disease. However, with vigorous activity, the older adult’s heart is no match for that of a young adult. With exercise or extreme stress, the older adult’s heart is unable to keep pace with a young adult’s heart, and large differences are seen between young and old individuals’ ability to perform vigorous exercise. Heart failure with preserved ejection fraction (HFpEF) is common in older adults, especially women, with the risk skyrocketing with age (Paneni et al., 2017). Maximal cardiac output, or the maximal amount of blood the heart can pump in one minute, decreases with age by as much as 25%. Maximal oxygen uptake, VO 2max , decreases by 50% between the ages of 20 and 80 (Strait & Lakatta, 2012). VO 2max is a measure of an individual's cardiovascular fitness, and decreased rates indicate lower physical fitness. While even master athletes experience declines in VO 2max with age, inactivity can accelerate the loss, and sedentary individuals may experience decreases in VO 2max by as much as 10% per decade after age 25 (Strait & Lakatta, 2012). Cardiovascular system changes are numerous and take place throughout the entire body. While it is clear that we do not fully understand the age-related changes that occur in the cardiovascular system, we do know that exercise intervention can delay and even reverse some of these changes (Booth et al., 2011; Booth & Zwetsloot, 2010). Pulse Lakatta, 2012). Cardiac output There is a connection between heart rate and pulse, but they are not the same. Your heart rate is how fast your heart is beating, and your pulse is how you can feel your heart rate.
Page 82
EliteLearning.com/Physical-Therapy
Powered by FlippingBook