The neural interaction between the arterial baroreflex and muscle metaboreflex is preserved in older men

Abstract

New Findings r What is the central question of this study?Sympathetic baroreflex sensitivity increases during isolated skeletal muscle metaboreflex activation in young adults, but whether this neural interaction between the arterial baroreflex and the muscle metaboreflex is altered in healthy ageing remains unclear. r What is the main finding and its importance?The collective findings indicate that the neural interaction between the arterial baroreflex and the skeletal muscle metaboreflex in the regulation of muscle sympathetic nerve activity is preserved in healthy ageing. This has potential implications for the regulation of blood pressure during exercise in older adults.Sympathetic baroreflex sensitivity is increased during selective activation of the skeletal muscle metaboreflex with postexercise ischaemia (PEI) in young adults. However, to date, there are no data demonstrating this neural interaction between the arterial baroreflex and the muscle metaboreflex in healthy older adults. Therefore, the goal of the present study was to examine the influence of healthy ageing on the metabolic component of the exercise pressor reflex and its interaction with the arterial baroreflex in the control of sympathetic outflow. Postexercise ischaemia following static hand grip performed at 30% maximal voluntary contraction was used to isolate muscle metaboreflex activation in young [n = 10; 24 ± 1 years old; resting blood pressure (BP) 116 ± 3/64 ± 3 mmHg] and older men (n = 9; 59 ± 2 years old; resting BP 120 ± 2/77 ± 2 mmHg). Arterial BP (Finometer) and muscle sympathetic nerve activity (MSNA) were measured continuously. Weighted linear regression analysis between MSNA and diastolic BP was used to estimate arterial baroreflex MSNA gain. There were no age-related differences in the increase in mean BP (young, 14 ± 3 mmHg versus older, 15 ± 2 mmHg; P > 0.05) or MSNA burst frequency (young, 11 ± 2 bursts min −1 versus older, 9 ± 1 bursts min −1 ; P > 0.05) during PEI. Likewise, the gain of arterial baroreflex control of total MSNA increased to a similar extent in both groups during PEI (young, −4.2 ± 0.9 baseline versus −6.3 ± 1.1 PEI a.u. beat −1 mmHg −1 ; and older, −3.7 ± 1.1 baseline versus −6.7 ± 1.4 PEI a.u. beat −1 mmHg −1 ; P < 0.05 for both). Collectively, these findings indicate that the neural interaction between the arterial baroreflex and the skeletal muscle metaboreflex in the regulation of MSNA is preserved in healthy ageing.

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

“…Pressure bins containing zero values for MSNA were included in the linear regression analysis to maintain consistency between conditions and groups. A minimal r value of 0.5 was used as criterion for accepting slopes, which is consistent with previous literature using this analysis technique (21,42,43). One young subject and two older subjects did not fit this criterion and were excluded from the analysis.…”

“…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).…”

“…The slope of the relation between MSNA variables and diastolic BP was identified using weighted linear regression analysis. To account for the number of cardiac cycles within each pressure bin, all data were weighted to remove bias due to bins containing fewer cardiac cycles (21,42). Pressure bins containing zero values for MSNA were included in the linear regression analysis to maintain consistency between conditions and groups.…”

“…Multiunit postganglionic MSNA was recorded using standard microneurographic techniques, as previously described (20,21,56). Briefly, a unipolar tungsten microelectrode was inserted percutaneously into muscle fascicles of the peroneal nerve near the fibular head of the left leg.…”

“…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.…”