Influence of age and sex on the pressor response following a spontaneous burst of muscle sympathetic nerve activity

Abstract

The sympathetic nervous system is critical for the beat-to-beat regulation of arterial blood pressure (BP). Although studies have examined age- and sex-related effects on BP control, findings are inconsistent and limited data are available in postmenopausal women. In addition, the majority of studies have focused on time-averaged responses without consideration for potential beat-to-beat alterations. Thus we examined whether the ability of muscle sympathetic nerve activity (MSNA) to modulate BP on a beat-to-beat basis is affected by age or sex. BP and MSNA were measured during supine rest in 40 young (20 men) and 40 older (20 men) healthy subjects. Beat-to-beat fluctuations in mean arterial pressure (MAP) were characterized for 15 cardiac cycles after each MSNA burst using signal averaging. The rise in MAP following an MSNA burst was similar between young men and women (+2.64 ± 0.3 vs. +2.57 ± 0.3 mmHg, respectively). However, the magnitude of the increase in MAP after an MSNA burst was reduced in older compared with young subjects (P < 0.05). Moreover, the attenuation of the pressor response was greater in older women (+1.20 ± 0.1 mmHg) compared with older men (+1.72 ± 0.2 mmHg; P < 0.05). Interestingly, in all groups, MAP consistently decreased after cardiac cycles without MSNA bursts (nonbursts) with the magnitude of fall greatest in older men. In summary, healthy aging is associated with an attenuated beat-to-beat increase in BP after a spontaneous MSNA burst, and this attenuation is more pronounced in postmenopausal women. Furthermore, our nonburst findings highlight the importance of sympathetic vasoconstrictor activity to maintain beat-to-beat BP, particularly in older men.

Spontaneous bursts of muscle sympathetic nerve activity decrease leg vascular conductance in resting humans

“…In this regard, Wallin and Nerhed (33) identified clear pressor responses following spontaneous MSNA bursts using a spike-triggered averaging approach to assess beat-by-beat changes in diastolic BP following individual MSNA bursts. We recently extended these findings to describe TVC decreases associated with the BP rise following MSNA bursts as well as clear blunting of these responses with advancing age (31). In the present study, we adapted the spike-triggered averaging method to include simultaneously acquired beat-by-beat femoral vascular conductance measures.…”

“…Accordingly, we used a spike-triggered averaging approach similar to that used by Wallin and Nerhed when they demonstrated for the first time that arterial blood pressure (BP) transiently increased following MSNA bursts (33). Our laboratory recently extended this work by showing that the BP responses following MSNA bursts are primarily mediated by decreases in total vascular conductance (TVC) and that the magnitude of the pressor response is positively related to the size of MSNA bursts (31). In the present study, we determined to what degree the skeletal muscle vasculature contributes to TVC decreases and arterial BP rises following spontaneous MSNA bursts.…”

Aging alters muscle reflex control of autonomic cardiovascular responses to rhythmic contractions in humans

“…The effects of aging on exercise-induced increases in blood pressure remain equivocal, with some studies revealing an exaggerated response in the elderly (17,18), whereas others have found no difference across age groups (24,30,32,56). Since the MAP response to both absolute and relative exercise intensities was similar in both groups (Fig.…”

Augmented pressor and sympathetic responses to skeletal muscle metaboreflex activation in type 2 diabetes patients

“…The changes in BP measured using the Finometer have been shown to provide an accurate estimate of directly measured intra-arterial BP (18,46). Also, an automated sphygmomanometer (Welch Allyn, Skaneateles Falls, NY) recorded resting BP by the auscultation of the brachial artery of the right arm for absolute values of BP and to validate BP measurements from the Finometer (7,54). Respiratory movements were monitored using a strain-gauge pneumograph placed around the abdomen (Pneumotrace, UFI, Morro Bay, CA) to avoid potential confound of large respiratory excursions on cardiovascular measurements during handgrip and PEI.…”

“…Multiunit postganglionic MSNA was recorded using standard microneurographic techniques, as previously described (13,36,53,54). Briefly, a tungsten microelectrode was placed into the peroneal nerve near the left fibular head, and a reference microelectrode was inserted 2-3 cm away.…”