Critical Care Research and Practice

Research Article

Respiratory Variations in Pulse Pressure Reflect Central Hypovolemia during Noninvasive Positive Pressure Ventilation

Table 2

Data from the generalized mixed model analyses showing effect estimates of LBNP and NPPV separately and in combination (LBNP * NPPV).


	ΔPP (%)		ΔPOP (%)		PVI (%)		PI (%)
	Estimate (95% CI)	value	Estimate (95% CI)	value	Estimate (95% CI)	value	Estimate (95% CI)	value

LBNP	1.2 (0.5, 1.8)	<0.001^#	0.7 (−0.3, 1.3)	0.233	1.0 (−0.5, 1.4)	0.337	−0.1 (−0.4, 0.0)	0.018^#
NPPV	−0.6 (−2.7, 1.5)	0.571	1.0 (−1.7, 3.9)	0.435	−1.0 (−4.0, 2.4)	0.609	0.4 (−0.2, 1.0)	0.196
LBNP * NPPV	1.0 (0.1, 1.9)	0.033^#	0.2 (−1.0, 1.4)	0.777	1.1 (−0.4, 2.3)	0.186	−0.1 (−0.4, 0.2)	0.504

	SV (mL)		HR (beats/min)		MAP (mm Hg)		PP (mm Hg)
	Estimate (95% CI)	value	Estimate (95% CI)	value	Estimate (95% CI)	value	Estimate (95% CI)	value

LBNP	−11.2 (−11.8, −9.6)	<0.001^#	7.3 (6.0, 8.6)	<0.001^#	−0.4 (−1.5, 0.6)	0.415	−3.5 (−4.5, −2.0)	<0.001^#
NPPV	−3.0 (−8.5, −1.3)	<0.009^#	0.3 (−4.1, 4.7)	0.898	0.4 (−3.1, 4.0)	0.822	1.7 (−3.2, 5.7)	0.586
LBNP * NPPV	−0.7 (−2.3, 0.7)	0.305	1.6 (−0.2, 3.5)	0.091	−0.7 (−2.2, 0.8)	0.347	−0.6 (−2.5, 1.3)	0.519

Estimates of LBNP-effects and LBNP * NPPV-effects are given as changes per 20 mmHg change in LBNP (−20, −40, −60, and −80 mmHg). Estimates of NPPV-effects are constant and independent of LBNP-level. There are separate statistically significant effects of both LBNP and NPPV on SV. This means that LBNP led to a decrease in SV both during spontaneous breathing and NPPV, and NPPV led to a decrease in SV both during normo- and hypovolemia. In contrast, the effect of NPPV on ΔPP is due to a significant interaction between LBNP and NPPV (LBNP * NPPV), which means that NPPV only affected ΔPP significantly during hypovolemia. PI is significantly affected by LBNP alone.
LBNP: lower body negative pressure; NPPV: noninvasive positive pressure ventilation; LBNP * NPPV: interaction between LBNP and NPPV; ΔPP: pulse pressure variation; ΔPOP: photoplethysmographic waveform amplitude variation; PVI: pleth variability index; PI: perfusion index; SV: stroke volume; HR: heart rate; MAP: mean arterial pressure; PP: pulse pressure; ^#: statistically significant.