LBNP Tolerance Analyzed Retrospectively Using a Structural Equation Model

Abstract

It would be useful to be able to predict tolerance to lower body negative pressure (LBNP) because of the association of low LBNP tolerance to low orthostatic tolerance. To determine how well tolerance to LBNP can be modeled using laboratory variables assessed noninvasively. There were 125 male and female college age and older (> 60 yr) subjects who underwent graded LBNP to presyncope. Tolerance was quantified by the LBNP tolerance index (LTI). Noninvasive variables assessed at rest and at presyncope were used to predict LTI via structural equation modeling (SEM). SEM can better address the correlation and variable interaction effects inherent in assessing orthostatic tolerance, e.g., multicollinearity, compared to traditional regression techniques. With SEM, the manifest variables of gender, % body fat, maximal change in heart rate from rest to presyncope (delta HR), and resting total peripheral conductance (TPC) explained 40% of the variance in LTI. All the variables had direct significant influences on LTI; in addition, % body fat mediated the influence of gender and age while AHR mediated the effects of TPC. An exaggerated HR response to LBNP was associated with an increased LBNP tolerance (beta = -0.396). About 40% of the variability in LBNP tolerance can be predicted using easily measured variables. Male gender, a potentiated HR response to LBNP, higher resting TPC, older age, and lower body fat are associated with an increased LBNP tolerance.