Pulmonary "Capillary" Pressure and Its Relation To Left Auricular and Pulmonary Artery Pressure in Mitral Stenosis

We studied the effects of changes in pulmonary capillary wedge pressure (PCWP) on the slope (incremental resistance) and the extrapolated pressure intercept (PI) of the mean pulmonary artery pressure (PAP)-cardiac output (CO) relationship. Multipoint plots of PAP against CO were obtained in intact anesthetized dogs. Group 1 consisted of six dogs entirely in West zone 3 and group 2 of four dogs with mixed West zone 2-3. The four conditions studied were the following: 1) fixed low PCWP, 2) fixed high PCWP, 3) variable PCWP, and 4) time-control repeat of condition 1. The PI significantly exceeded PCWP at fixed low PCWP (group 1, 9.3 vs. 11.1 mmHg, group 2, 6.6 vs. 3.9 mmHg). PI became identical to PCWP only at fixed high PCWP in group 1 (19 +/- 2.0 vs. 19 +/- 1.1 mmHg). Thus PCWP reflects the effective vascular outflow pressure when PCWP is fixed and high. For both groups of dogs in condition 3, when PCWP was varied with CO, the slope of the resulting PAP-CO plot was significantly greater than when PCWP was constant. Also in 9 of 10 dogs, PI was less than PCWP when PCWP was varied. These findings demonstrate that when changes in PCWP are allowed to occur during the generation of a pulmonary artery pressure-flow plot, the resulting slope and intercept, as defined by a Starling resistor model, do not accurately represent the incremental resistance and outflow pressure of the pulmonary vasculature.

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Reliability of measurements of pulmonary artery pressure obtained with patients in the 60 degrees lateral position

American Journal of Critical Care ◽

10.4037/ajcc2000.9.1.43 ◽

2000 ◽

Vol 9 (1) ◽

pp. 43-51 ◽

Cited By ~ 5

Author(s):

LM Aitken

Keyword(s):

Pulmonary Artery ◽

Pulmonary Capillary Wedge Pressure ◽

Pulmonary Artery Pressure ◽

General Medicine ◽

Lateral Position ◽

Artery Pressure ◽

Pulmonary Capillary ◽

Quasi Experimental ◽

The Right ◽

Wedge Pressure

BACKGROUND: Monitoring of pulmonary artery pressure is an essential component of the care of critically ill patients. The conditions under which reliable measurements can be obtained must be clarified. OBJECTIVES: To determine (1) whether reliable measurements of pulmonary artery pressure can be obtained with patients in the right or left 60 degrees lateral position and (2) which characteristics of patients preclude obtaining reliable measurements. METHODS: One hundred five patients (65 cardiac surgery, 40 general medicine) with pulmonary artery catheters were enrolled in a prospective, stratified, quasi-experimental study. Subjects were repositioned from supine (head of bed elevated < 30 degrees with 1 pillow) to the left and right 60 degrees lateral positions. Systolic, diastolic, and mean pulmonary artery pressures and pulmonary capillary wedge pressure were measured before and 5, 10, and 20 minutes after lateral repositioning. The zero reference was the phlebostatic axis when patients were supine and the dependent midclavicular line at the level of the fourth intercostal space when patients were in the lateral positions. RESULTS: In most patients, measurements obtained with patients in the lateral position differed significantly from measurements obtained with patients supine. None of the variables examined were reliable predictors of which patients would have these differences. More than 11% of the patients had clinically significant differences in addition to the statistically significant differences. CONCLUSION: Reliable measurements of pulmonary artery pressure and pulmonary capillary wedge pressure cannot be obtained with patients in the 60 degrees lateral position.

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