Neurovascular Research Laboratory, School of Kinesiology, Western University, London, Ontario, Canada.
Department of Physiology and Pharmacology, Western University, London, Ontario, Canada.
J Appl Physiol (1985). 2022 Aug 1;133(2):349-360. doi: 10.1152/japplphysiol.00045.2022. Epub 2022 Jun 23.
We tested the hypotheses that spontaneous baroreflex control of integrated muscle sympathetic nerve activity (MSNA) burst occurrence and action potential (AP) subpopulations would be blunted in older compared with young adults and that sympathetic transduction will be blunted in older adults relative to young adults. Integrated muscle sympathetic nerve activity (MSNA) and the underlying sympathetic APs were obtained using microneurography and a continuous wavelet analysis approach, respectively, during 5 min of supine rest in 13 older (45-75 yr, 6 females) and 14 young (21-30 yr, 7 females) adults. Baroreflex threshold relationships were quantified as the slope of the linear regression between MSNA burst occurrence (%) and diastolic blood pressure (mmHg), or AP cluster firing probability (%) and diastolic blood pressure (mmHg). Integrated MSNA baroreflex threshold gain was greater in older compared with young adults (older: -5.7 ± 2.6%/mmHg vs. young: -2.7 ± 1.4%/mmHg, < 0.001). Similarly, the baroreflex threshold gain of AP clusters was modified by aging (group-by-cluster effect: < 0.001) such that older adults demonstrated greater baroreflex threshold gains of medium-sized AP clusters (e.g., , older: -8.2 ± 3.2%/mmHg vs. young: -3.6 ± 1.9%/mmHg, = 0.003) but not for the smallest-sized (, older: -1.6 ± 1.9%/mmHg vs. young: -1.0 ± 1.7%/mmHg, > 0.999) and largest-sized (, older: -0.5 ± 0.5%/mmHg vs. young: -0.2 ± 0.1%/mmHg, = 0.819) AP clusters compared with young adults. In contrast, the peak change in mean arterial pressure (MAP) following a spontaneous MSNA burst (i.e., sympathetic transduction) was impaired with aging (older: -0.7 ± 0.3 mmHg vs. young: 1.8 ± 1.2 mmHg, < 0.001). We conclude that aging is associated with elevated baroreflex control over high-probability AP content of sympathetic bursts that may compensate for impaired sympathetic neurovascular transduction. The present study demonstrates for the first time that the spontaneous baroreflex threshold gains of integrated muscle sympathetic nerve activity burst occurrence and medium-sized action potential clusters are greater in older compared with young adults. Since sympathetic transduction was blunted in older compared with young adults, we interpret the data to indicate that the central arc of the baroreflex is enhanced in older adults to compensate for impairments in the peripheral arc.
与年轻人相比，老年人自主压力反射对整体肌肉交感神经活动（MSNA）爆发发生和动作电位（AP）亚群的控制会减弱，并且相对于年轻人，交感神经传递会减弱。在 13 名老年人（45-75 岁，6 名女性）和 14 名年轻人（21-30 岁，7 名女性）平卧位休息 5 分钟期间，使用微神经记录法和连续小波分析方法分别获得整体肌肉交感神经活动（MSNA）和潜在的交感神经 AP。通过 MSNA 爆发发生率（%）与舒张压（mmHg）或 AP 簇发射概率（%）与舒张压（mmHg）之间的线性回归来量化压力反射阈值关系。与年轻人相比，老年人的整体 MSNA 压力反射阈值增益更高（老年人：-5.7±2.6%/mmHg 与年轻人：-2.7±1.4%/mmHg， < 0.001）。同样，AP 簇的压力反射阈值增益也会随年龄变化而改变（组-簇效应： < 0.001），老年人的中大小 AP 簇的压力反射阈值增益更高（例如，老年人：-8.2±3.2%/mmHg 与年轻人：-3.6±1.9%/mmHg， = 0.003），但最小大小（老年人：-1.6±1.9%/mmHg 与年轻人：-1.0±1.7%/mmHg， > 0.999）和最大大小（老年人：-0.5±0.5%/mmHg 与年轻人：-0.2±0.1%/mmHg， = 0.819）AP 簇的压力反射阈值增益则没有年轻人高。相比之下，自发性 MSNA 爆发后平均动脉压（MAP）的峰值变化（即交感神经传递）随年龄增长而受损（老年人：-0.7±0.3 mmHg 与年轻人：1.8±1.2 mmHg， < 0.001）。我们的结论是，衰老与交感神经爆发中高概率 AP 内容的自主压力反射控制增强有关，这可能是对交感神经血管传递受损的代偿。本研究首次证明，与年轻人相比，老年人的整体肌肉交感神经活动爆发发生和中大小动作电位簇的自发性压力反射阈值增益更高。由于老年人的交感神经传递比年轻人更差，我们可以解释为数据表明，压力反射的中枢弧在老年人中增强，以代偿外周弧的损伤。
