Effect of tidal volume, intrathoracic pressure, and cardiac contractility on variations in pulse pressure, stroke volume, and intrathoracic blood volume

摘要

© Springer-Verlag Berlin Heidelberg 2006, 2009, 2012. Purpose: We evaluated the impact of increasing tidal volume (V t ), decreased chest wall compliance, and left ventricular (LV) contractility during intermittent positive pressure ventilation (IPPV) on the relation between pulse pressure (PP) and LV stroke volume (SV LV ) variation (PPV and SVV, respectively), and intrathoracic blood volume (ITBV) changes. Methods: Sixteen pentobarbitalanesthetized thoracotomized mongrel dogs were studied both before and after propranolol-induced acute ventricular failure (AVF) (n = 4), with and without chest and abdominal pneumatic binders to decrease chest wall compliance (n = 6), and during Vt of 5, 10, 15, and 25 ml/kg (n = 6). Svlv and right ventricular stroke volume (SV RV ) were derived from electromagnetic flow probes around aortic and pulmonary artery roots. Arterial pressure was measured in the aorta using a fluid-filled catheter. Arterial PPV and SVV were calculated over three breaths as (max - min)/[(max + min)/2]. Itbv changes during ventilation were inferred from the beat-to-beat volume differences between SV RV and SV LV . Results: Arterial PP and SV LV were tightly correlated during IPPV under all conditions (r 2 = 0.85). Both PPV and SVV increased progressively as V t increased and with thoraco-abdominal binding, and tended to decrease during AVF. Sv RV phasically decreased during inspiration, whereas SVLV phasically decreased 2-3 beats later, such that ITBV decreased during inspiration and returned to apneic values during expiration. Itbv decrements increased with increasing Vt or with thoraco-abdominal binding, and decreased during AVF owing to variations in SV RV , such that both PPV and SVV tightly correlated with inspiration-associated changes in SVRV and ITBV. Conclusion: Arterial PP and SV LV are tightly correlated during IPPV and their relation is not altered by selective changes in LV contractility, intrathoracic pressure, or V t . However, contractility, intrathoracic pressure, and V t directly alter the magnitude of PPV and SVV primarily by altering the inspiration-associated decreases in SV RV and ITBV.