Frequently Asked Questions
In this FAQ, we’ve defined key scientific terms, explained the fundamentals of our algorithm, and clarified what our technology is—and what it isn’t.
This is not an exhaustive technical overview, but a brief, high-level guide to some of the most common questions we encounter when introducing Avalyra to clinicians, academics, and investors.
Our goal is to provide clear, thoughtful context for understanding what makes our approach distinct.
In Vivo vs. In Vitro
In Vivo means “in the body.” It refers to tests, measurements, or observations made directly inside a living organism.
In Vitro means “in glass.” These are lab tests done outside the body—typically in a test tube or petri dish.
Why it matters: Avalyra’s technology works in vivo—in real time, on real people—not just in a lab.
Non-Invasive
Non-invasive means no needles, no cuts, no surgery.
It refers to techniques that can collect health data from the surface of the body—like through the skin or fingertip—without breaking it.
Why it matters: Avalyra’s device gathers critical blood and fluid information without drawing blood.
Biophotonics
Biophotonics is the science of using light to understand or interact with biological tissues.
It combines biology and optics to “read” what’s happening inside the body using safe, targeted light.
Why it matters: Avalyra uses biophotonics to extract deep physiological insight from a simple finger sensor.
Laser vs. LED
LEDs are the kind of light you find in lamps or electronics—broad, less focused.
Lasers are more powerful, precise, and concentrated. They can target specific molecules or tissues.
Why it matters: Avalyra uses laser-based sensing for highly accurate, real-time monitoring. Avalyra is on path with research and development to incorporate next-generation, more powerful and more focused LEDs into future generations of devices as well.
Bioanalytics / Blood Analytes
Bioanalytics is the measurement and analysis of substances in the body.
Blood analytes are the specific components of blood we measure—like hemoglobin, hematocrit, or plasma volume.
Why it matters: Avalyra analyzes these markers continuously and non-invasively, helping clinicians make smarter, faster decisions.
Hemodynamics
Hemodynamics is the study of how blood flows through the body.
It includes blood pressure, heart rate, vascular volume, and how well organs are being perfused (getting enough blood).
Why it matters: Avalyra tracks these signals in real time to help detect internal bleeding, fluid shifts, and cardiac strain.
Raman Spectroscopy
Raman spectroscopy is a technique that uses light to identify molecules based on how they scatter that light.
Think of it as shining a laser into the body and getting a fingerprint of what's inside—based on how the light bounces back.
Why it matters: It’s part of the core science behind Avalyra’s ability to “see inside” without ever breaking the skin.
FRD-PVOH
What it stands for:
Fluid Removed Determination – Plasma Volume, Oxygenation, Hematocrit is an algorithm, originating in Avalyra’s patents, where it was first discovered, defined, and published.
Lay explanation:
FRD-PVOH is the name of the discovery behind Avalyra’s non-invasive technology platform. It uses a wearable finger probe to shine a laser into the skin and collect light that tells us what’s happening with your blood in real time—without drawing a drop of it.
Why it matters:
This technology helps clinicians see how much fluid has been removed during dialysis or whether a patient may be bleeding internally—all with a fast, painless scan. (We call it “Freddy-PeeVo”)
Autonomic Compensation
Lay explanation:
When the body senses blood loss or fluid imbalance, it reacts automatically—tightening or relaxing blood vessels, adjusting heart rate, or shifting blood around. This is called autonomic compensation.
Why it matters:
Unlike other devices, Avalyra’s sensor can pick up these subtle signs, helping caregivers understand whether the body is under stress before things get worse.
Hematocrit (Hct)
Lay explanation:
Hematocrit is the percentage of your blood that’s made up of red blood cells. It’s a vital sign doctors use to track bleeding, dehydration, and response to dialysis.
Why it matters:
Traditional hematocrit tests require a needle. Avalyra reads changes in hematocrit continuously and non-invasively, helping avoid complications.
Raman Spectroscopy and the FRD-PVOH Algorithm
Lay explanation:
Avalyra uses a special kind of laser-based light analysis called Raman spectroscopy to see inside the blood without touching it. Think of it like using light to “listen” for signals in the bloodstream.
Why it matters:
It’s part of how we detect shifts in plasma and red blood cells with precision—enabling insights that were once only available through invasive blood tests.
The “Plasma Moves First” Insight
Lay explanation:
When something happens in your body—like blood loss—the plasma (the clear part of your blood) changes faster than the red blood cells. Avalyra’s sensor can detect that shift in real time.
Why it matters:
This early signal helps doctors know when to intervene—before things spiral into a crisis, and long before the current medical model is able to “see” the impact of these changes.
FAQ
Origin of the name “FRD-PVOH”?
“Fluid Removed Determination-Plasma Volume Oxygen Hematocrit”
The name of the algorithm changed as we learned more about the measurement process and the information it provides. Initially, the algorithm was called “PVH” because that was what was measured, plasma volume hematocrit. About a year later, the name was extended to “PV[O]H” because we discovered that the measurement was also sensitive to the amount of oxygenated hemoglobin, like an oximeter. Within months we tired of typing the extra square brackets and shortened the name to “PVOH”. After publishing papers using PVOH, we discovered that Googling “PVOH” produced literally millions of hits involving “polyvinyl alcohol”, a material in many, many products, before hitting our product. At about that time, while exploring the possibility of calibrating our then prototype device based on the fluid removed during dialysis, we decided to add the prefix “FRD”, finally giving “FRD-PVOH”. We intend not to change the name going forward, if at all possible.
What’s the difference between the FRD-PVOH and a pulse oximeter?
To the patient, because they are both completely painless, they both use a finger clip or other location, and they both shoot light into the skin, they are similar. But pulse oximetry has been in existence since the 1970’s and FRD-PVOH is a completely new technology. To function, the pulse oximeter shoots in 2 colors of light, the FRD-PVOH only one. At any given time and location of the finger clip, not all hemoglobin molecules in blood are carrying oxygen to and from the lungs. The pulse oximeter measures the percent of total hemoglobin carrying oxygen. The FRD-PVOH simultaneously 1) measures the current amount of plasma in your blood vessels as a percentage of the amount present when monitoring began, and the same for red blood cells, and 2) is sensitive to the difference between the percent of hemoglobin carrying oxygen and the percent without oxygen. The two devices give different information, i.e., vital signs that medically trained people can interpret to diagnose and treat different conditions.
The oximeter reflects lung and heart function and helps save many lives every day world-wide. The FRD-PVOH gives blood composition and total amounts of plasma and red blood cells, which relate directly to, e.g., the effects of internal bleeding, with or without external injury. It also relates to the variations in systemic blood composition induced during dialysis.
Do FRD-PVOH and pulse oximeter devices use the same kind of light source?
FRD-PVOH requires a laser, but pulse oximeters use an LED like current light bulbs. Laser light can be more tightly focused leading to more back-scattered, i.e., signal light that can be detected and analyzed.
Is FRD-PVOH like photoplethysmography?
Plethysmography involves a medical device that uses a “cuff” like a conventional blood pressure device. Photoplethysmography replaces the cuff with a clip that shoots light into the fine blood vessels in fingertip skin and detects the light reflected by the red blood cells. This provides the blip on a monitor seen in almost every hospital room, the source of the term “flat line”, and a convenient inexpensive way to measure pulse rate and to some extent quantify pressure and content.