Cyclic changes in arterial pulse during respiratory support.

In 13 patients on respiratory support we combined two-dimensional echocardiography with hemodynamic monitoring to determine the mechanism of cyclic changes in arterial pulse, defined as an inspiratory rise in radial artery pulse pressure.Beat-to-beat evaluation of cardiac performance was obtained during the following three distinct consecutive phases of the controlled respiratory cycle: exhalation (phase I), preinspiratory pause (phase LI), and lung inflation (phase III).Airway pressure, left ventricular filling pressure (i.e., pulmonary capillary wedge minus esophageal pressure), and pulmonary artery and radial artery pressures were simultaneously recorded during mechanical ventila- 'tion along with beat-to-beat two-dimensional echocardiographic left ventricular end-systolic and end- diastolic dimensions.From a reference value for pulmonary artery and radial artery pulse contour obtained during a brief period of imposed apnea, beat-to-beat measurements of left and right ventricular stroke output were also performed during the controlled respiratory cycle with the pulse contour method.Cyclic changes in arterial pulse appeared to result directly from a transitory increase in left ventricular stroke output during lung inflation (41.4 + 14.6 ml/m2), whereas right ventricular stroke output exhibited a steep fall (31.7 ± 12.4 ml/m2) at this time.An opposite variation was also observed during exhalation, during which a fall in left ventricular stroke output (31.9 ± 11.2 mI/i2) was accompanied by a rise in right ventricular stroke output (38.6 11.9 ml/m2).Both stroke outputs reached an identical level during preinspiratory pause (37.4 + 14. 1 ml/m2 for left ventricle and 39.1 ±- 13.8 ml/m2 for right ventricle).Such an inspiratory increase in left ventricular stroke output during lung inflation was no doubt largely due to a transient improvement in left ventricular preload and this is supported by our finding of a concomitant increase in left ventricular filling pressure and end-diastolic dimensions during the inspiratory phase.Circulation 68, No. 2, 266-274, 1983.IN CRITICALLY ILL PATIENTS, continuous moni- toring consistently demonstrates an inspiratory rise in arterial pressure when respiratory support with me- chanically controlled ventilation is used.Often noted in the past,' this inspiratory increase in arterial pulse during positive pressure lung inflation has been called "reversed pulsus paradoxus,'2 in contrast with the inspiratory decline in arterial pulse (paradoxical pulse) sometimes observed during spontaneous breathing in cardiac tamponade3 or status asthmaticus.4Such an inspiratory increase in arterial pulse during positive- pressure breathing is quite unexpected since positive- pressure lung inflation, by increasing pleural pressure and lung volume, should act to decrease aortic flow,