Department of Health and Kinesiology, University of Texas at San Antonio, San Antonio. TX 78249, USA.
J Appl Physiol (1985). 2011 Oct;111(4):1048-58. doi: 10.1152/japplphysiol.00231.2011. Epub 2011 Jul 28.
Higher oscillations of cerebral blood velocity and arterial pressure (AP) induced by breathing with inspiratory resistance are associated with delayed onset of symptoms and increased tolerance to central hypovolemia. We tested the hypothesis that subjects with high tolerance (HT) to central hypovolemia would display higher endogenous oscillations of cerebral blood velocity and AP at presyncope compared with subjects with low tolerance (LT). One-hundred thirty-five subjects were exposed to progressive lower body negative pressure (LBNP) until the presence of presyncopal symptoms. Subjects were classified as HT if they completed at least the -60-mmHg level of LBNP (93 subjects; LBNP time, 1,880 ± 259 s) and LT if they did not complete this level (42 subjects; LBNP time, 1,277 ± 199 s). Middle cerebral artery velocity (MCAv) was measured by transcranial Doppler, and AP was measured at the finger by photoplethysmography. Mean MCAv and mean arterial pressure (MAP) decreased progressively from baseline to presyncope for both LT and HT subjects (P < 0.001). However, low frequency (0.04-0.15 Hz) oscillations of mean MCAv and MAP were higher at presyncope in HT subjects compared with LT subjects (MCAv: HT, 7.2 ± 0.7 vs. LT, 5.3 ± 0.6 (cm/s)(2), P = 0.075; MAP: HT, 15.3 ± 1.4 vs. 7.9 ± 1.2 mmHg(2), P < 0.001). Consistent with our previous findings using inspiratory resistance, high oscillations of mean MCAv and MAP are associated with HT to central hypovolemia.
高呼吸阻抗诱导的脑血流速度和动脉压（AP）高频震荡与症状延迟出现和对中心性低血容量的耐受性增加有关。我们检验了这样一个假设，即对中心性低血容量具有高耐受性（HT）的受试者在即将出现晕厥前与低耐受性（LT）的受试者相比，脑血流速度和 AP 的内源性震荡会更高。135 名受试者接受了逐渐增加的下体负压（LBNP），直到出现晕厥前症状。如果受试者至少完成了 -60mmHg 水平的 LBNP（93 名受试者；LBNP 时间为 1880 ± 259s），则将其归类为 HT，如果他们没有完成这个水平（42 名受试者；LBNP 时间为 1277 ± 199s），则归类为 LT。通过经颅多普勒测量大脑中动脉速度（MCAv），通过光体积描记法测量手指动脉压（AP）。MCAv 和平均动脉压（MAP）从基线到 LT 和 HT 受试者的晕厥前均逐渐降低（P < 0.001）。然而，在 HT 受试者中，低频率（0.04-0.15Hz）的 MCAv 和 MAP 均值震荡在晕厥前更高，而在 LT 受试者中则较低（MCAv：HT，7.2 ± 0.7 vs. LT，5.3 ± 0.6（cm/s）（2），P = 0.075；MAP：HT，15.3 ± 1.4 vs. 7.9 ± 1.2mmHg（2），P < 0.001）。与我们之前使用吸气阻力的发现一致，MCAv 和 MAP 均值的高频震荡与对中心性低血容量的 HT 有关。
