Ventricular interaction during mechanical ventilation in closed-chest anesthetized dogs.
The cardiac effects of positive pressure ventilation and positive end-expiratory pressure are incompletely understood. External constraint due to increased intrathoracic pressure decreases left ventricular end-diastolic volume; the effects on venous return and ventricular interaction are less clear. Phasic changes in inferior vena caval flow, end-diastolic ventricular dimensions and output were measured in seven anesthetized, ventilated normal dogs. During inspiration, caval flow, right ventricular diameter and output decreased; end-diastolic transseptal pressure gradient, septum-to-left ventricular free wall diameter, left ventricular area (ie, left ventricular volume index) and output increased despite the decreased sum of the septum-to-free wall diameters. The reverse occurred during expiration. Increased positive end-expiratory pressure decreased the left ventricular area, but the end-expiratory right ventricular diameter was unchanged. At given airway pressures, right ventricular diameter was greater at higher positive end-expiratory pressures, suggesting that a leftward septal shift (direct ventricular interaction) added to the effect of external constraint on left ventricular end-diastolic volume. In conclusion, positive pressure ventilation reduced right ventricular end-diastolic volume during inspiration and increased the transseptal pressure gradient, which shifted the septum rightward, increasing left ventricular end-diastolic volume and output. The reverse occurred during expiration. Positive end-expiratory pressure constrained left ventricular filling and decreased left ventricular end-diastolic volume further by a leftward septal shift.
Mitchell
Jamie R
JR
Department of Physiology and Biophysics, University of Calgary, Alberta.
Sas
Rozsa
R
Zuege
Daniel J
DJ
Doig
Christopher J
CJ
Smith
Eldon R
ER
Whitelaw
William A
WA
Tyberg
John V
JV
Belenkie
Israel
I
D000758:Anesthesia; D000818:Animals; D004285:Dogs; D005260:Female; D006334:Heart Function Tests; D006439:Hemodynamics / Q000502:physiology*; D008297:Male; D023421:Models, Animal; D015999:Multivariate Analysis; D011175:Positive-Pressure Respiration / Q000379:methods*; D011336:Probability; D011652:Pulmonary Circulation / Q000502:physiology*; D012044:Regression Analysis; D012121:Respiration, Artificial; D018570:Risk Assessment; D014655:Vascular Resistance / Q000502:physiology*; D016277:Ventricular Function, Left / Q000502:physiology*