Device: Pulse Volume Measurement
patients will wear a newly designed calf monitor that will be hooked up to a computer that will monitor leg peripheral pulse volumes which will then be correlated to pressures obtained with Swan Ganz monitoring. The calf monitor is gut two bands with sensors that are wrapped around the ankle and below the knww
Peripheral Pulse Volume (PPV) is the change in the volume of a limb that occurs when blood passes through the limb. The limb also acts as an electrical conductor whose electrical impedence changes with limb geometry and volume. Each time the heart beats, the volume of the limb segment changes, and therefore its electrical impedence changes. A plethysmograph can be used to measure volume changes of a part of the body by producing a plethysmographic waveform. Selectively capturing a number of these plethysmographic wave forms with acceptable noise levels and averaging them using the EKG as a reference-timing signal generate a highly reproducible pulse volume signal. Signal averaged pulse volume measurement will be obtained non-invasively from the lower extremities of patient volunteers. A disposal non-occluding electrical monitoring strap will be applied to the calf of each patient. Changes in the calf's size/volume caused by changes in the patient's cardiac output and calf blood flow will result in electrical impedance changes. These changes will be recorded by an analog admittance plethysmograph attached to the lower extremity strap. The analog plethysmograph is coupled to a digital computer for signal enhancement and measurement.