1 Using PPG Morphology to Detect Blood Sequestration Stephen Linder Suzanne Wendelken Susan McGrath

2 Motivation Is it possible to monitor the behavior of the cardiovascular system with a pulse oximeter? Many studies have been done on the frequency characteristics of the pulse oximeter waveform, but not the spatial characteristics. The morphology of the pulse oximeter waveform has not been thoroughly studied under conditions of orthostatic stress. Pulse oximeters are cheap, easy to use and available off-the shelf. Numerous applications have been developed in clinical or remote monitoring and assessment.

3 Background The photoplethysmogram (PPG) measures the temporal variation in blood volume of peripheral tissue, and thus blood flow Used to detect Apnea and possibly airway obstructions PPG has been used in mechanically ventilated patients to  Ascertain breathing status from the Respiratory Sinus Arrhythmia  Blood Volume

4 Methods Sensor: 3 FDA approved Nonin ® pulse oximeters - Ear, finger, forehead Supine-Standing experiment  We monitored 11 healthy subjects 4 women, 7 men, ages trials each  One minute lying down followed by one minute standing up. Repeat. Grad student Beth Knorr with the Nonin pulse oximeter probes

5 Methodology Data segmented by feature extractor Pulses characterized by features:  Instantaneous Hear Rate  Pulse Height  Normalized Peak Width Wilcoxon Rank Sum test for equal means to detect changes in features real-time Normalized Peak Width (NPW) is the ratio of PW to CP.

6 Results Significant changes were found during standing for the following parameters:  Heart rate  Normalized Pulse Width  Pulse Height from the ear probe  Full Width Half max

7 Results Pulse amplitude decreases significantly for the ear probe, but not as much for the finger probe Interesting differences in the pulse envelope

8 Results Peak stays the same even as heart rate increases The troughs between peaks narrow Supine Just after Standing Standing

9 Change in Heart Rate As expected heart rate goes up for most subjects Stand up Lay down Normalized Heart Rate

10 Change in PPG Amplitude Ear PPG amplitude pinches Stand up Lay down Normalized Ear PPG Amplitude

11 Change in Normalized Pulse Width Pulse become a large percentage of cardiac cycle Stand up Lay down Normalized Pulse Width

12 Results NPW leads increase in heart rate which leads pinch in ear PPG amplitude Standing Reclining

13 Results Output of the feature detector  HR increase detected in all subjects  NPW increase detected in 31/33 trials  Pulse height (ear probe) decrease detected in 9/11 subjects – no false alarms  One false alarm (Subject 5) NPW Increased before HR increased.  21of the 33 trials the NPW begins to rise before the heart rate  Prompt to stand causes a statistically significant change in NPW – why? Prompt to stand

14 Future Work Lower body negative pressure studies  Sequesters approx. 3 Liters blood volume (60%) in the lower body (-90 mm Hg). Studies to compare supine- standing results to those from clinical tilt table tests  Additional monitors: ECG with Respiration tracing  Develop low cost cardiac assessments Subject in LBNP device. ISR, Brooks Army Medical Center

15 Acknowledgements Thanks to  Dr. Kirk Shelly for his valuable input  All the volunteers who stood up for us so many times Collaboration? Contact: Disclaimer This project was supported under Award No DT-CX- K001 from the Office for Domestic Preparedness, U.S. Department of Homeland Security. Points of view in this document are those of the author(s) and do not necessarily represent the official position of the U.S. Department of Homeland Security.

16 Pulse Oximetry Overview Uses the different light absorption properties of HbO 2 and Hb to measure heart rate, oxygen saturation (S p O 2 ) and pleth waveform Two LED’s of different wavelength  Red 660 nm  Infrared 940 nm HbO 2 absorbs less red and more infrared than HB. Hb absorbs less infrared and more red than HbO 2. Two equations, two unknowns… we can solve for S p O 2 The pleth waveform consist of the IR tracing. Indirect measurement of blood volume under the sensor