Although care was taken to study similar types of subjects undergoing comparable surgical stresses, marked variability in response among subjects occurred. This variation might be a reflection of differing intravascular volume status, as well as differing LV systolic and diastolic function. EDA as an estimate of LV filling volume varied from 3.4 to 26.4 cm2 in our patients, although most patients had an EDA around 9.8 cm2. Furthermore, we saw that subjects with a larger EDA had less variation in their LV area after a positive-pressure breath. Alteration in diastolic function can also occur after cardiac surgery. The average EDA and pulmonary artery occlusion pressure (Ppao) in our subjects before cardiopulmonary bypass were not significantly different before (EDA, 10.5 ± 5.9 cm2; Ppao, 14 ± 4 mm Hg) and after bypass (EDA, 8.6 ± 4.1 cm2; Ppao, 12 ± 5 mm Hg). yaz birth control
We studied similar patients with various levels of cardiac function. All of these patients had coronary artery disease and were undergoing the same type of surgery with open and closed chest conditions. Vasoactive medications were not changed during the protocol. IABP was used transiently in two patients, but it was turned off shortly prior to and during the positive-pressure breath because the arterial pressure waveform would not have been interpretable. Patients with severe left main disease have a prophylactic IABP inserted prior to the operation to prevent decompensation before the bypass, as in our patients. We deliberately chose to evaluate patients with nonhomogeneous cardiac functions because, as stated in the introduction, the goal of our study was to study the effect of positive-pressure ventilation on systolic arterial pressure over a spectrum of cardiac contractility.
Because our results seem to reflect a spectrum of responses in LV area to positive-pressure ventilation as opposed to a single mechanism, one could question the validity of our measurements, especially after considering that we accepted only 60% of the data for interpretation, based on our criteria.