Noninvasive Point of Care Device for Assessing Cardiac Response to Acute Volume Changes

Abstract

Purpose

The change in the amplitude of a peripheral pulse in response to a Valsalva maneuver has diagnostic utility for assessing volume status at the bedside. We have developed a device to automatically quantify the Valsalva pulse response (VPR) to a standardized Valsalva maneuver that the device guides a user to perform. In this study, we sought to determine whether VPR by the device, Indicor, is sensitive enough to detect the acute increase in central pressure and volume load that occurs with a passive leg raise (PLR) in healthy volunteers.

Methods

Healthy volunteers were tested semirecumbently at 45 degrees, then again after being leaned back on a pivoted wedge with legs raised at 45 degrees and torso and head flat, and then again in the semirecumbent position. The device recorded a finger photoplethysmography (PPG) signal during a 10-second expiratory effort of 20 mmHg as guided by the device. VPR was automatically calculated as the ratio of the end-Valsalva pulse amplitude to the baseline pulse amplitude.

Results

In the 30 participants who completed testing, VPR increased from baseline to PLR in every participant, from 0.34 ± 0.13 to 0.60 ± 0.14 (p < 0.0001). Back upright, VPR decreased back to 0.33 ± 0.10 (p < 0.0001 versus PLR; NS versus baseline position).

Conclusion

In this proof-of-concept study of healthy participants, the Indicor device, a noninvasive, convenient device that automatically calculates VPR from a finger photoplethysmography signal during a standardized Valsalva maneuver, was sensitive enough to detect the increase in VPR that occurred with an acute central volume load from a PLR. Future studies should examine whether VPR responds differently to a PLR in heart failure patients with abnormal cardiac performance and/or congestion.

Plain Language Summary

It is often important clinically to determine whether there has been a change in the volume of fluid in the heart and chest (known as central volume). We have developed a noninvasive technique for assessing changes in central volume. The technique involves measuring the change in blood volume in a fingertip while a person blows into a closed tube for 10 seconds. An index is calculated from the change in fingertip blood volume. In this study, we measured this index before and after a central volume change in healthy participants. We produced an increase in central volume in the participants by changing their position from legs flat and head elevated, to legs elevated and head flat. Thirty participants successfully completed testing. In all participants, the index increased when they changed position to legs up and head down. Thus, this technique can detect an acute increase in central volume. Future studies should examine whether the index can detect longer-term changes in central volume in patients with abnormal heart conditions such as heart failure.

Keywords:

• Valsalva maneuver
• photoplethysmography
• filling pressure
• fluid volume
• passive leg raise
• fluid load
• pulse amplitude

Acknowledgment

The authors gratefully acknowledge Benjamin Verschoore and Jonathan Woodward for their assistance in the performance of this study. This work was supported by Vixiar Medical, Inc.

Disclosure

Dr. Silber is the inventor of the technology, has been a paid consultant to Vixiar Medical, and owns shares. In addition, Dr. Silber has patents in the US and in Europe with royalties paid to Johns Hopkins University. Dr. Miller was formerly employed by Vixiar Medical and owns shares. In addition, Dr. Miller has a patent “SYSTEMS AND METHODS FOR AUTOMATICALLY INTERPRETING PHOTOPLETHYSMOGRAPHY(PPG) SIGNALS DURING PHYSIOLOGIC PERTURBATIONS” pending to Vixiar Medical. The authors report no other conflicts of interest in this work.