Hemodynamic response to lower body negative pressure in children: a pilot study

Although head-up tilt and upright standing are common methods used to induce orthostatic stress, lower body negative pressure (LBNP) is another safe and easy technique that induces orthostatic stress independently of gravity. However, the use of LBNP in children has never been investigated. The purpose of this pilot study was to determine whether LBNP was capable of inducing hemodynamic adaptations in pre-pubertal boys. Ten healthy pre-pubertal boys (9+/-1 years) were recruited and randomly exposed to 3 levels of LBNP (15, 20 and 25 mm Hg). Heart rate, manual and beat-by-beat systolic (SBP), diastolic and mean arterial blood pressure were monitored continuously. Aortic diameter was measured at rest and peak aortic blood velocity was recorded continuously for at least 1 min during each condition. R-R interval (RRI), heart rate, stroke volume (SV), cardiac output (Q), total peripheral resistance (TPR), low frequency (LF) and high frequency (HF) baroreceptor sensitivity (BRS), as well as LF/HF RRI ratio were calculated. With increasing LBNP TPR increased while SBP decreased (P< or =0.05). As well, a trend towards a decrease in SV (P=0.054) and Q (P=0.06) was found. However, LF and HF BRS, and LF/HF RRI ratio did not significantly change from baseline to LBNP 15, 20 or 25 mm Hg. In conclusion, the results of this pilot study suggest that low levels of LBNP are capable of inducing hemodynamic adaptations in children that are to be expected when undergoing an orthostatic stress. As well, LBNP is a safe and effective method of inducing orthostatic stress in children.