Wearable- and Catheter-Based Cardiovascular Signals during Progressive Exsanguination in a Porcine Model of Hemorrhage

Experimental Protocol

This protocol included 6 Yorkshire swine (3 castrated male, 3 female, Age: 114–-150 days, Weight: 51.5-–71.4 kg), each of which passed a health assessment examination but were not subject to other exclusion criteria. Anesthesia was induced in the animal with xylazine and telazol and maintained with inhaled isoflurane during mechanical ventilation. Intravenous heparin was administered as needed to prevent coagulation of blood during the protocol. Before the induction of hypovolemia, a blood sample was taken to assess baseline plasma absorption. Following this baseline sample, Evans Blue dye was administered for blood volume estimation. After waiting several minutes to allow for even distribution of the dye, a second blood sample was taken to measure plasma volume. In this method, plasma volume is used along with hematocrit to estimate total blood volume. For one animal in the protocol (Pig 4), atropine was administered to raise the starting heart rate and blood pressure due to critically low values.

Hypovolemia was induced by draining blood through an arterial line at four levels of blood volume loss (7%, 14%, 21%, and 28%) as determined by the estimated total blood volume from the Evans Blue dye protocol. After draining passively through the arterial line, the blood was stored in a sterile container. Following each level of blood loss, exsanguination was paused for approximately 5-10 minutes to allow the cardiovascular system to stabilize. If cardiovascular collapse occurred once a level was reached, as defined by a 20% drop in mean aortic pressure from baseline after stabilization, exsanguination was terminated. Note that cardiovascular collapse was reached at different blood volume levels for each animal: Pigs 1, 3, and 4 reached 21% blood volume loss; Pigs 2 and 6 reached 28% blood volume loss; and Pig 5 reached 14% blood volume loss before the experimental protocol was terminated.

Signals from wearable sensors were continuously recorded using a BIOPAC MP160 data acquisition system (BIOPAC Systems, Inc., Goleta, California, USA) with a sampling frequency of 2 kHz. Electrocardiogram (ECG) signals were captured using a three-lead system of adhesive-backed Ag/AgCl electrodes placed in Einthoven Lead II configuration, which interfaced with a BIOPAC ECG100C amplifier. Reflectance-mode photoplethysmogram (PPG) was captured with a BIOPAC TSD270A transreflectance transducer, which interfaced with a BIOPAC OXY200 veterinary pulse oximeter. The transducer was placed over the femoral artery on either the right or left caudal limb, contralateral to inducer placement. Seismocardiogram (SCG) signals were captured using an ADXL354 accelerometer (Analog Devices, Inc., Norwood, Massachusetts, USA) placed on the mid-sternum, interfacing with a BIOPAC HLT100C transducer interface module.

Aortic root pressure was captured by inserting a fluid-filled catheter through a vascular introducer in the right carotid artery, fed through to the aortic root. Femoral artery pressure was obtained directly from an introducer placed on either the left or right femoral artery depending on accessibility. Right and left atrial pressures were captured with a Swan-Ganz catheter with proximal and distal monitoring ports inserted in either the right or left femoral vein. Left atrial pressure was inferred via PCWP captured using an Edwards 131F7 Swan-Ganz catheter (Edwards Lifesciences Corp, Irvine, California, USA). The vascular introducers were connected via pressure monitoring lines to ADInstruments MLT0670 pressure transducers (ADInstruments Inc., Colorado Springs, Colorado, USA). Data from the catheters were continuously recorded with an ADInstruments Powerlab 8/35 acquisition system sampling at 2 kHz.

Signal Pre-Processing

All signals were filtered with finite impulse response band-pass filters with Kaiser window, both in the forward and reverse directions to offset phase shift. Cutoff frequencies were 0.5–-40Hz for ECG and 1-40Hz for SCG. Only the dorso-ventral component of the SCG acceleration signal was used in this study. PPG signals, along with all four catheter-based pressure signals, were filtered with cutoffs at 0.5-10Hz. After filtering, data from all signals were heartbeat-separated using ECG R-peaks. The signal segments were then abbreviated to a length of 1,000 samples (500 ms) to enable more uniform analysis; however, due to the long left ventricular ejection time of Pig 3, a length of 1,500 samples (750 ms) is provided for this subject.

Using the Dataset

This dataset contains a separate .mat file for each of the 6 animal subjects in the protocol. The variables "scg" and "ppg" contain R-peak-separated signals from the SCG and PPG respectively during the protocol. The variables "aortic", "femoral", "rightAtrium", and "wedge" contain the R-peak-separated pressure waveforms from the catheters placed in the aortic root, femoral artery, right atrium, and left atrium (wedge pressure) respectivley. Each of these variables is a struct, with each of its fields representing a different level of blood volume loss. The field "B1" corresponds to the baseline level (pre-exsanguination); "L1", "L2", "L3", and "L4" correspond to the 7%, 14%, 21%, and 28% drop in blood volume respectively. Thus, the data in each field represents the heartbeat-separated signals collected during each blood volume level. The data has been selected such that periods of active draining of blood have been removed, such that the provided data reflects the heartbeat-separated signals during the resting period between blood-draws. The data is formatted in columnwise matrices, with the columns arranged in sequention order such that the first column is the first heartbeat and the last row is the last heartbeat.

The indices of ECG R-peaks are provided as a vector as well during each blood volume level, such that each element in the vector corresponds to its respective column in the provided column matrices. The unit of these values is in miliseconds, staring from t = 0 (onset of baseline recording).