Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada.
Centre for Heart, Lung, and Vascular Health, School of Health and Exercise Sciences, University of British Columbia, Kelowna, British Columbia, Canada.
Am J Physiol Heart Circ Physiol. 2020 Jul 1;319(1):H213-H221. doi: 10.1152/ajpheart.00296.2020. Epub 2020 Jun 5.
Muscle sympathetic nerve activity (MSNA) exhibits well-described within-breath respiratory modulation, but the interactive contributions of the arterial baroreflex remain unclear. The present study assessed ) within-breath modulation of sympathetic baroreflex sensitivity (BRS) and ) the effect of acute intermittent hypercapnic hypoxia (IHH) on within-breath sympathetic BRS and respiratory-sympathetic entrainment. Seventeen men (24 ± 4 yr) underwent an 8- to 10-min spontaneously breathing baseline while continuous measures of blood pressure (BP), heart rate, MSNA, ventilation, and end-tidal gases were collected. A subset of 12 participants subsequently underwent a 40-min IHH exposure composed of 40 consecutive 1-min breathing cycles: 40 s of hypercapnic hypoxia and 20 s of normoxia. Data were compared between inspiration and expiration and low and high lung volume (calculated from the integral of spirometry-derived flow). Sympathetic BRS was determined by the slope of the weighted linear regression between diastolic BP and MSNA burst incidence. Respiratory-sympathetic entrainment was quantified as percentage of MSNA bursts during each respiratory epoch relative to the total burst count. Sympathetic BRS was similar between inspiration and expiration (-3.9 ± 2.0 vs. -3.6 ± 1.8 bursts·100 heartbeats·mmHg; = 0.61) but greater during low versus high lung volumes (-4.6 ± 2.3 vs. -2.1 ± 1.6 bursts·100 heartbeats·mmHg; < 0.01). High ( = -0.64; < 0.01)- but not low ( = -0.24; = 0.35)-lung volume sympathetic BRS was associated with resting MSNA. IHH increased resting MSNA burst frequency (15 ± 7 vs. 20 ± 7 bursts/min; < 0.01) and diastolic BP (68 ± 5 vs. 77 ± 9 mmHg; = 0.02), without altering resting or within-breath sympathetic BRS or respiratory-sympathetic entrainment (all > 0.05). These findings provide novel insight into the mechanisms controlling within-breath modulation of sympathetic outflow in humans. In resting spontaneously breathing men, the present study observed that sympathetic baroreflex sensitivity (BRS) was higher during low versus high lung volumes but not different between inspiration and expiration. High- but not low-lung volume BRS was negatively associated with resting muscle sympathetic nerve activity (MSNA). Acute intermittent hypercapnic hypoxia increased resting MSNA and diastolic blood pressure, without altering within-breath BRS. These findings provide novel insight into mechanisms controlling within-breath modulation of MSNA in humans.
肌肉交感神经活动 (MSNA) 表现出描述良好的呼吸内调制，但动脉压力反射的相互作用仍不清楚。本研究评估了呼吸内交感神经反射敏感性 (BRS) 的调制和急性间歇性高碳酸缺氧 (IHH) 对呼吸内交感神经 BRS 和呼吸-交感神经同步的影响。17 名男性（24±4 岁）进行了 8-10 分钟的自主呼吸基线测量，同时连续测量血压 (BP)、心率、MSNA、通气和呼气末气体。其中一部分 12 名参与者随后接受了 40 分钟的 IHH 暴露，由 40 个连续的 1 分钟呼吸周期组成：40 秒高碳酸缺氧和 20 秒正常氧。数据在吸气和呼气以及低和高肺容积（根据肺活量计衍生的流量积分计算）之间进行比较。交感神经 BRS 通过舒张压与 MSNA 爆发发生率之间的加权线性回归斜率来确定。呼吸-交感神经同步性被量化为每个呼吸周期内 MSNA 爆发的百分比相对于总爆发计数。交感神经 BRS 在低肺容积时大于高肺容积（-4.6±2.3 对-2.1±1.6 个·100 次心跳·mmHg； = 0.61），但在吸气和呼气时相似（-3.9±2.0 对-3.6±1.8 个·100 次心跳·mmHg； = 0.61）。高（ = -0.64； < 0.01）但不是低（ = -0.24； = 0.35）肺容积的交感神经 BRS 与休息时的 MSNA 相关。IHH 增加了休息时 MSNA 爆发频率（15±7 对 20±7 次/分钟； < 0.01）和舒张压（68±5 对 77±9 mmHg； = 0.02），但不改变休息时或呼吸内交感神经 BRS 或呼吸-交感神经同步性（均 > 0.05）。这些发现为控制人类呼吸内传出交感神经活动的机制提供了新的见解。在休息时自主呼吸的男性中，本研究观察到，在低肺容积时，交感神经反射敏感性 (BRS) 高于高肺容积，但在吸气和呼气时没有差异。高但不是低肺容积 BRS 与休息时的肌肉交感神经活动 (MSNA) 呈负相关。急性间歇性高碳酸缺氧增加了休息时的 MSNA 和舒张压，而不改变呼吸内 BRS。这些发现为控制人类 MSNA 呼吸内调制的机制提供了新的见解。
