THORACOCARDIOGRAPHY - NONINVASIVE MONITORING OF LEFT-VENTRICULAR STROKE VOLUME

Purpose: Thoracocardiography noninvasively monitors global stroke volu me by inductive plethysmographic recording of ventricular volume curve s as previously validated by thermodilution. Our purpose was to invest igate the potential of thoracocardiography to individually assess stro ke volume of the left ventricle. We hypothesized that curves predomina ntly reflecting left ventricular volume could be obtained by recording waveforms from thoracocardiographic transducers placed at various lev els around the chest, and by identifying their origin as the left vent ricle if mean expiratory exceeded mean inspiratory stroke volumes duri ng spontaneous breathing. Materials and Methods: Stroke volumes obtain ed by thoracocardiography in normal subjects were compared beat by bea t with estimates derived from simultaneous measurements of left ventri cular cavity stroke area by echocardiography with automatic boundary d etection. Changes in respiratory variations of stroke volumes were ana lyzed during spontaneous breathing at fixed rate and tidal volume, dur ing mechanical ventilation, and resistive loaded breathing. Results: I n 170 comparisons of beat-by-beat stroke volumes, 89% of thoracocardio graphic fell within +/- 20% of echocardiographic estimates. Changes in tidal volume, resistive loaded breathing, and mechanical ventilation induced respiratory variations of thoracocardiographic derived stroke volumes consistent with the known effect of respiratory changes in int rapleural pressure on left ventricular stroke volumes. Conclusions: Th e results suggest that thoracocardiography noninvasively tracks change s in left ventricular stroke volumes. Their absolute value may also be monitored if an initial calibration by an independent technique, such as echocardiography, is performed. Copyright (C) 1998 by W.B. Saunder s Company.