Aging and the Exercise Pressor Reflex in Humans

Abstract

Background-Blood flow limitation to exercising muscles engages the muscle reflex during exercise, evoking an increase in heart rate (HR), blood pressure (BP), and muscle sympathetic nerve activity (MSNA). Methods and Results-In the current study, we examined forearm flow and autonomic responses to ischemic handgrip in young and older subjects. We studied 6 younger subjects (mean age 23.5Ϯ2.2 years) and 7 older subjects (mean age 65.0Ϯ2.4 years). Subjects performed rhythmic handgrip (thirty 1-sec contractions/min) at 30% maximal voluntary contraction during six 1-minute stages: freely perfused exercise (E1) and exercise with forearm pressure of ϩ10, ϩ20, ϩ30, ϩ40, and ϩ50 mm Hg (E2 through E6). We measured HR, BP, MSNA, forearm flow velocity, forearm venous oxygen saturation, H ϩ , and lactate. Compared with E1, ischemic exercise (E2 through E6) increased HR, BP, and MSNA, reduced forearm velocity, lowered venous oxygen saturation, and raised venous lactate and H ϩ . Compared with the younger subjects, the older subjects had attenuated BP at E6, attenuated MSNA indices (%⌬bursts, bursts/100 heart beats and signal averaged MSNA), attenuated H ϩ at E6, a trend toward higher levels of oxygen saturation, and similar forearm velocity and HR responses. Key Words: aging Ⅲ exercise Ⅲ reflex Ⅲ blood flow D uring exercise, the sympathetic nervous system is activated. This helps redistribute blood flow to active muscle and aids in preventing blood pressure (BP) from falling. 1 Two neural systems contribute to sympathetic activation: central command, 2 a feed-forward process, and a muscle reflex termed the exercise pressor reflex. 3 The muscle reflex is engaged when mechanically or metabolically sensitive thin fiber afferents within contracting muscle increase their discharge. 4 During forearm exercise, the muscle reflex is engaged when the muscle fatigues and/or when a mismatch occurs between blood supply and metabolic demand. 5 In the present study, we examined the effects of aging on the exercise pressor reflex in humans. Despite the fact that this reflex is an important determinant of exercise flow regulation, little is known about the effects of aging on this reflex. The reflex is evoked by a muscle work/blood flow mismatch. Therefore, to engage the reflex, a paradigm was employed in which the level of work was kept constant as external impedance to muscle flow was progressively increased. We examined whether age affects the BP response to reflex engagement and if sympathetic nerve responses to reflex engagement is different in young and older subjects. The results of these studies support the concept that the muscle reflex becomes attenuated with age. Conclusions-Aging Methods SubjectsSix young (4 males, 2 females; mean age 23.5 years; mean body mass index 23.5) and 7 older subjects (4 males, 3 females; mean age 65.0; body mass index 26.2) were studied. All were normotensive non-smokers on no medications. Each signed an Institutional Review Board-approved consent. Forearm PressureSubjects performed handgrip in a sealed...

Muscle sympathetic nerve activity during cold stress and isometric exercise in healthy older adults

“…Studies of adults exercising in cold environments are few and generally limited to those using varied methodology exploring either the control of cutaneous blood flow during exercise (46) or the performancerelated effects of cold acclimation (17,57,61). At thermoneutral temperatures, older adults exhibit either similar (21,40,49) or blunted (26,33,48) increases in MSNA and BP during static HG compared with the increases demonstrated in young adults. Consistent with these previous studies, we report no agerelated differences in the sympathetic and pressor responses to static HG at baseline (i.e., mean T sk 34.0°C).…”

“…This effect may be mediated via impairments in the sympathetic control of the cardiovascular system and BP regulation during combined cold stress and isometric exercise. At thermoneutral temperatures (ϳ20 -22°C), the increases in MSNA during isometric handgrip (HG) in healthy older adults have been shown to be either similar to (21,40,49) or less than (26,33,48) the increases observed in young adults. Studies of both young and older subjects exercising in cold environments are surprisingly limited.…”

Attenuated Increases in Blood Pressure by Dynamic Resistance Exercise in Middle-Aged Men

“…However, we speculate that the mechanism may be as follows. In middle-aged men, the muscle sympathetic nerve activity is higher at rest than in young men (16), whereas during exercise it is lower in the former than the latter (16). This results in attenuation of the increases in cardiac output and peripheral vasoconstriction induced by sympathoexcitation during exercise with advancing age (34)(35)(36).…”

“…Understanding the pressor response during dynamic resistance exercise using large muscle groups is essential for exercise prescription. However, most previous studies have focused on static resistance exercise (11,12,16,33), and have provided little information regarding the cardiovascular response during dynamic resistance exercise (10), or the interaction between age and BP response to dynamic resistance exercise using large muscle groups. We found that pressor responses during dynamic resistance exercise at relative intensities were lower in middle-aged than in young men, suggesting that the BP response to dynamic resistance exercise may be attenuated with advancing age despite age-associated arterial stiffening.…”

“…Systolic and diastolic blood pressures (BPs) rise rapidly to extremely high values during heavy weight-lifting exercise (10), and BPs are extreme even when exercise is performed with a relatively small muscle mass (11,12). Most previous studies have focused on the BP responses to resistance exercise in young adults (13)(14)(15), and thus have provided little information regarding BP responses in middle-aged and older individuals (12,16). Furthermore, the interaction between age and BP response for dynamic resistance exercise using large muscle groups has not been reported in middle-aged men with stiffening arteries or young men with compliant arteries.…”