Comparison of Compensatory Reserve Index to Intravascular Volume Change and Stroke Volume
Condition: Hemorrhage
MeSH terms: Hemorrhage
Study type: Observational

Summary: 
      This study is designed to validate implementation of the CRI algorithm in the CypherOx CRI
      system.

      Healthy human subjects will undergo progressive reduction in central blood volume to the
      point of hemodynamic instability (defined by a precipitous fall in systolic blood pressure
      (SBP) below 70 mmHg and/or voluntary subject termination due to discomfort (such as sweating,
      nausea, or dizziness) to validate the following hypotheses:

      The CypherOx CRI system will A. Trend intravascular volume changes (hemorrhage) B. Trend
      stroke volume changes and C. The CRI trend value is not relative to an initial CRI reading,
      instead it is an actual CRI trend value that does not require calibration or being placed
      during normal physiological conditions.
    

Detailed description: 
      Hemorrhagic shock is a leading cause of death in both civilian and battlefield trauma.
      Currently available medical monitors provide the capabilities to measure standard vital signs
      that are often imprecise, subjective, intermittent and inconsistent. More importantly, the
      appearance of hypotension and other signs and symptoms of shock represent a point in time
      when it may be too late to apply effective lifesaving interventions. Understanding the
      physiological signals that provide the best indicators of blood volume loss and impending
      circulatory failure is critical to bridging the capability gap of identifying the need for
      early intervention. Under a previous BAMC IRB-approved protocol, we used lower body negative
      pressure (LBNP) as an experimental model of central hypovolemia to simulate progressive blood
      loss that results in hemodynamic instability (e.g., hypotension, tachycardia, presyncopal
      symptoms) in conscious, healthy human subjects. From data collected within this original
      protocol, we now understand that arterial waveforms (either blood pressure or pulse oximetry)
      are important variables associated with hypovolemia. Feature extraction and machine learning
      techniques were applied to these previously collected data and an algorithm was developed
      called Compensatory Reserve Index (CRI) which was designed to reflect progressive blood loss
      and decreasing stroke volume. This algorithm was installed in a pulse oximeter in which the
      photo-plethysmographic waveform (PPG) was used to calculate the CRI. Using this CRI Pulse
      oximeter, a pretrial study of 24 subjects indicated a high correlation in trending of blood
      volume loss (DOD study at Mayo Clinic) and a mean correlation of 0.96 when comparing CRI to
      stroke volume (LBNP at AISR Laboratory). The work proposed herein will validate those
      findings. During each experiment each test subject will wear 4 FDA cleared pulse oximeters
      which transmit PPG data to an off-the-shelf handheld tablet (meets military specs) which will
      calculate and display the CRI value. The subjects will also wear 2 FDA cleared Nexfin
      hemodynamic monitors that display stroke volume. LBNP will be used to produce progressive
      central hypovolemia in healthy human subjects until the point of hemodynamic decompensation
      (presyncope). This approach will validate the correlation of CRI to stroke volume.
    

Time perspective: Prospective
Sampling method: Non-Probability Sample
Study population: 
        Healthy non-pregnant volunteers with no cardiovascular disease or other health issues.
      
Keywords: Pulse Oximeter; Stroke Volume; Hemorrhagic shock; Compensatory Reserve Index