Background. Correct volume management is essential in patients with
respiratory failure. We investigated the ability of respiratory variations in noninvasive pulse pressure (ΔPP), photoplethysmographic waveform amplitude (ΔPOP), and pleth variability index (PVI) to reflect
hypovolemia during noninvasive
positive pressure ventilation by inducing
hypovolemia with progressive
lower body negative pressure (
LBNP). Methods. Fourteen volunteers underwent
LBNP of 0, -20, -40, -60, and -80 mmHg for 4.5 min at each level or until
presyncope. The procedure was repeated with noninvasive
positive pressure ventilation. We measured stroke volume (suprasternal Doppler), ΔPP (Finapres), ΔPOP, and PVI and assessed their association with
LBNP-level using linear mixed model regression analyses. Results. Stroke volume decreased with each pressure level (-11.2 mL, 95% CI -11.8, -9.6, P < 0.001), with an additional effect of noninvasive
positive pressure ventilation (-3.0 mL, 95% CI -8.5, -1.3, P = 0.009). ΔPP increased for each
LBNP-level (1.2%, 95% CI 0.5, 1.8, P < 0.001) and almost doubled during noninvasive
positive pressure ventilation (additional increase 1.0%, 95% CI 0.1, 1.9, P = 0.003). Neither ΔPOP nor PVI was significantly associated with
LBNP-level. Conclusions. During noninvasive
positive pressure ventilation, preload changes were reflected by ΔPP but not by ΔPOP or PVI. This implies that ΔPP may be used to assess volume status during noninvasive
positive pressure ventilation.