Analysis of the facilitation of excitatory transmitter release at the crayfish neuromuscular junction

This pilot descriptive study investigated the effects of a nursing procedure on selected cardiovascular hemodynamic variables. The nursing procedure consisted of turning and positioning the patients from a (1) supine to right lateral, (2) right lateral to supine, and (3) supine to left lateral position. Stroke volume, cardiac output, heart rate, peripheral resistance, systolic pressure and diastolic pressure were recorded during and at selected intervals after the nursing procedure. The computer-monitoring system measured these variables by obtaining measurements through a stiff Teflon catheter inserted into the aortic arch. The validity of this method has been previously established. Six consecutive adult patients with an aortic valve prosthesis were utilized from the patients brought to the Thoracic and cardiovascular Intensive Care Unit at the Latter-day Saints Hospital in Salt Lake City, Utah. Systolic and diastolic pressure demonstrated the widest changes and also the most frequent changes. Heart rate did not appear to directly influence cardiac output except in one patient. Decreases in arterial pressure appeared to be due to inadequate compensation in peripheral vascular resistance. Positioning the patient within 12 hours after surgery in the right lateral position appeared to affect the cardiovascular hemodynamic variables more than did positioning in the supine or left lateral position. The smallest clinically significant changes occurred when the patients were positioned in supine position which might suggest that if a patient were experiencing physiological instability, this would be the position of choice. The alterations of greatest significance in the cardiovascular hemodynamic variables occurred during the turning procedure. This would suggest the close observations of the patient for signs of impending shock such as changes in respiration, faintness and alterations in skin color and moisture, should be made during the turning and positioning procedure and not at a later time. Return of the variables toward the initial base line readings was almost instantaneous although complete restoration to the original readings varied with each patient. Limitations inherent in this study were the clinical setting, small sample, technical difficulties with the computer, and possible psychological effects of anxiety and fear. Even though the results are based a small sample, they are based on valid observations. If replication of this study supports the conclusion presented her, that systolic and diastolic pressure are altered significantly when positioned in the right lateral position, the nursing profession would be well advised to examine its policies regarding lateral positioning in the immediate post-operative period in patients with aortic valve replacements.