Ludwig D A, Krock L P, Doerr D A, Convertino V A
Department of Mathematical Sciences, Univ. of North Carolina, Greensboro 27412-5001, USA.
Aviat Space Environ Med. 1998 Jul;69(7):630-8.
Research attempting to establish a relationship between human response to lower body negative pressure (LBNP) and +Gz acceleration has in general, disregarded the moderating effects of negative pressure and +Gz onset rates. Many of the past studies designed to examine the relationship between lower body decompression and +Gz acceleration tolerances have also ignored the problem of differences in body position typically encountered during LBNP and +Gz testing (supine LBNP vs. seated +Gz).
There were 17 male subjects (24-34 yr) who were tested in a seated LBNP chamber and received 3 pressure onset rates of 0.067, 0.33, and 2.0 mm Hg x s(-1). Relaxed acceleration tolerance was assessed on a 6.1 -m centrifuge using three gradual onset rates of 0.01, 0.05, and 0.2 +Gz x s(-1). LBNP and +Gz tolerances were subjected to principle components (factor) analysis, and the resulting factors correlated with variables derived from autonomic reflex control tests (Valsalva and carotid-cardiac baroreflex responsiveness) and height.
The factor model suggested a two-dimensional solution consisting of an acceleration factor and an orthostatic factor. The general pattern of the factor loadings indicates the relationship between tolerances of the two forms of orthostatic stress (acceleration and LBNP) is a function of how fast each stress is delivered. The correlation between LBNP tolerance and acceleration tolerance increases as LBNP onset rate is increased, or +Gz onset rate is decreased. Height was highly correlated (-0.71) and carotid-cardiac baroreflex responsiveness moderately correlated (0.54) with general orthostatic tolerance. Valsalva measures of autonomic reflex control had low correlations with general orthostatic tolerance (<0.30).
Although both LBNP and +Gz exposure can lead to eventual loss of consciousness, syncopal events associated with intolerance to either stress are a function of somewhat different cardiovascular mechanisms. There are however, specific situations where LBNP may constitute a viable substitute for +Gz.
试图建立人体对下体负压（LBNP）的反应与+Gz加速度之间关系的研究，总体上忽略了负压和+Gz起始速率的调节作用。过去许多旨在研究下体减压与+Gz加速度耐受性之间关系的研究，也忽略了在LBNP和+Gz测试中通常遇到的身体姿势差异问题（仰卧位LBNP与坐位+Gz）。
17名男性受试者（24 - 34岁）在坐位LBNP舱中接受测试，分别采用0.067、0.33和2.0 mmHg×s⁻¹三种压力起始速率。使用0.01、0.05和0.2 +Gz×s⁻¹三种逐渐增加的起始速率，在6.1米离心机上评估放松状态下的加速度耐受性。对LBNP和+Gz耐受性进行主成分（因子）分析，并将所得因子与自主反射控制测试（瓦尔萨尔瓦动作和颈动脉 - 心脏压力反射反应性）及身高得出的变量进行相关分析。
因子模型显示出一个二维解决方案，由一个加速度因子和一个直立位因子组成。因子载荷的总体模式表明，两种形式的直立位应激（加速度和LBNP）耐受性之间的关系，是每种应激施加速度的函数。随着LBNP起始速率增加或+Gz起始速率降低，LBNP耐受性与加速度耐受性之间的相关性增加。身高与总体直立位耐受性高度相关（-0.71），颈动脉 - 心脏压力反射反应性与总体直立位耐受性中度相关（0.54）。自主反射控制的瓦尔萨尔瓦动作测量值与总体直立位耐受性相关性较低（<0.30）。
虽然LBNP和+Gz暴露最终都可能导致意识丧失，但与对任何一种应激不耐受相关的晕厥事件，是由 somewhat 不同的心血管机制引起的。然而，在特定情况下，LBNP可能是+Gz的可行替代方案。 （注：“somewhat”在原文语境中语义不太明确，可能存在表述问题，但按照要求准确翻译）
