Hemodynamic and Oxygen Transport Characteristics of Common Ventilatory Modes: Measurements
Right heart catheterization was performed using a 7F Swan-Ganz catheter (Edwards Laboratories, Santa Ana, Calif) inserted percutaneously via an internal jugular or subclavian vein. All measurements were done while in supine position with the zero pressure taken as the atmospheric pressure at the midaxillary level. All values were recorded at end expiration. The CO was measured in triplicate with a computer (Hewlett Packard, Watham, Mass) by injecting 10 ml of 5 percent dextrose in water at room temperature. The injection time was less than 4 s. Pulmonary artery pressure (PAP) and pulmonary artery occlusion pressure (PAOP) were measured via a quartz transducer (Hewlett Packard). Systemic blood pressure (BP) was recorded with a radial artery catheter. Heart rate was taken from the ECG.
Mixed venous samples (2 ml) were drawn very slowly from the distal port of the pulmonary artery catheter with the balloon deflated and the first 4 to 5 ml of blood discarded. Then 2-ml samples of arterial blood were drawn from the arterial line. Both samples were handled anaerobically, placed on ice, and analyzed immediately for O2 and CO2 tensions, Sa02, and pH measurements (ABL-2 Blood Gas Systems, Radiometer of America, Westlake, Ohio).
Since Vt, f, and minute ventilation (Ve) change constantly during all three ventilatory modes, an average of a 1-min recording of the Vt and f were used during each experimental period as a representation of these measures on a given ventilatory mode. Peak and mean inspiratory airway pressures (PIP and MIP, respectively) were also recorded for 1 min and the average value was used for comparison among various ventilatory modes.
Data were corrected and standardized by dividing them to the calculated body surface area and were presented as indexes rather than as absolute numbers, using the standard formulas:
• Arterial oxygen content (СаОг)=(1.34 • SaC>2 • Hb)+ (Pa02- 0.003)
• Mixed venous oxygen content (Cv02)=(1.34 • Sv02 • Hb)+ (Pv02-0.003)
• T02I=Ca02-CI10
• Vo2I=(CaO2-CvO2)CM0
• Oxygen extraction ratio (02ЕВ)=Са02—Cv02:Ca02
Hemodynamic parameters including cardiac index (Cl), stroke volume index (SVI), systemic vascular resistance index (SVRI), and pulmonary vascular resistance index (PVR1) were computer-derived.