VENDYS®
Frequently Asked Questions
Q. What does VENDYS measure?
A. In simple terms, VENDYS measures vascular reactivity.
Q. What is “vascular reactivity”?
A. Vascular reactivity is a vital component of vascular function
that enables the circulatory system to respond to physiologic and pharmacologic stimuli that require adjustments
of blood flow and alterations of vessel tone and diameter. Vascular reactivity occurs in two forms –
vasoconstrictive and vasodilative – and can be exhibited at both the macrovascular and microvascular levels.
Q. How reproducible are VENDYS results? (Intra-individual and
inter-observer variability)
A. Our intra-individual repeatability studies (24-hour interval) in
apparently healthy individuals have shown that VENDYS parameters, TR (temperature rebound) and AUC (Area Under Curve),
are reproducible when performed under the recommended standard test conditions (see below). The coefficient of
variation (CV) was 5.7% for temperature rebound (TR), 8.7% for mean arterial pressure (MAP), and 11.4% for heart rate
(HR). These data indicate that TR reproducibility fits within the accepted reproducibility range for methods that have
been widely adopted in clinical practice, namely MAP and HR.
Q. How long does the VENDYS test take to complete?
A. The entire test procedure can usually be completed in 15 minutes. Details
are provided in the VENDYS Operating Manual.
Q. How long is cuff occlusion?
A. Traditionally, reactive hyperemia tests have been performed using a
5-minute protocol because flow-mediated dilatation of the brachial artery has been found to plateau after 5 minutes
cuff occlusion. However, our preliminary studies have shown that fingertip temperature rebound after a shorter period
of cuff occlusion (as short as 2 minutes) can distinguish individuals with increased cardiovascular risk (higher
Framingham Risk Score, higher coronary calcium score, abnormal myocardial perfusion, and obstructive coronary artery
disease). Note that observed temperature rebound values will be higher with 2 minute cuff occlusion than with 5
minute occlusion, simply because the fingertip temperature will fall further during a longer period of cuff occlusion.
It is recommended that VENDYS users choose and utilize a consistent duration of cuff occlusion if they wish to compare
TR values.
Q. Does 5-minute cuff occlusion pose any risk to the subject?
A. Numerous studies have used 5-minute cuff occlusion and reported no
significant problems. However, it is recommended that VENDYS testing be aborted if the subject complains of excessive
pain or discomfort. In our studies involving over 1500 subjects, only one subject experienced this problem. In some
subjects, mild skin bruising occurs at the cuff site.
Q. What is “hot finger,” and how does diurnal variation in
fingertip temperature affect VENDYS test results?
A. Studies have shown that resting fingertip temperature usually ranges
from 27°C to 33°C (average 30°C) and is primarily affected by mental stress, physical activity, and thermoregulatory
mechanisms (in response to ambient temperature and metabolic activity). It is well known that fingertip temperature
varies with the status of autonomic nervous system activity in such a way that the higher the sympathetic activity,
the lower the fingertip temperature. Also, temperature rebound (TR) appears to be inversely correlated with the
starting fingertip temperature. As the starting temperature increases above 33°C (and approaches core body
temperature, 37°C), the magnitude of temperature rebound appears to be artificially reduced in such a way that the
higher the starting temperature, the lower the TR (possibly resulting in a negative TR). This effect occurs because
maximum fingertip temperature usually does not exceed core body temperature. To address this issue, Advanced VENDYS
Analysis Software provides normalized TR and other VENDYS indices, such as area under the curve (AUC), slope of
temperature recovery (SLP), and bioheat vascular reactivity index. However, in our initial clinical studies, we chose
TR because it was the simplest index of thermal reactivity. Despite the apparent “dampening effect” of high starting
temperatures on temperature rebound, unadjusted TR has demonstrated strong predictive value in multiple clinical
studies, as shown in the Clinical Findings section. (See VENDYS Operating Manual for additional information.)
Q. What is “cold finger,” and what should be done about it?
A. We define “cold finger” as a baseline fingertip temperature below
27°C. This situation is usually indicative of heightened, sympathetic nervous system activity (from mental stress,
anxiety, pain, etc.), although it may also result from vasospasm (e.g., Raynaud’s phenomenon) or cold ambient
temperature. As stated in the International Brachial Artery Reactivity Task Force guidelines, these situations are
sub-optimal for vascular function measurement and must be addressed by reducing mental stress, warming the subject’s
hands (preferably with dry heat), and increasing the room temperature. If all attempts to relax the subject and increase
the fingertip temperature fail, it is recommended that VENDYS testing be rescheduled.
Q. What are the recommended test conditions?
A. The optimum conditions for VENDYS testing are similar to optimum
conditions for measuring blood pressure and other vascular function and reactivity tests. A comprehensive list of
such conditions has been outlined by the International Brachial Artery Reactivity Task Force and is included in the
VENDYS Operating Manual.
Q. How often can VENDYS tests be performed?
A. The answer is not quite clear. However, research studies have suggested
that 5 minute cuff occlusion creates a “vascular memory” effect that may require 30 minutes, or more, to reset.
Therefore, cuff reactive hyperemia studies, such as the VENDYS test, should be performed at least 30 minutes apart.
Q. What is the second temperature probe used for?
A. The second probe monitors fingertip temperature changes on the
contralateral, non-occluded hand. Temperature data from the second probe were originally intended to serve as a
relatively stable, reference curve. However, recent studies have revealed that temperature changes in the
non-occluded hand may provide additional insight into the subject’s vascular function. It is hypothesized that
increased fingertip temperature in the contralateral hand is a physiologic, neurally-mediated, systemic response to
the ischemic stimulus. It is further hypothesized that this response would be vasodilatory in healthy individuals and
hampered in individuals with cardiovascular risk factors and sympathetic overactivity.
Q. In what format are VENDYS data files stored? Can the data be
exported to data analysis software?
A. In addition to showing a real-time, graphical display and saving the
test results in the VENDYS database (SQL), the raw data can be exported in .CSV and .XML formats to other databases.
Q. What does Advanced VENDYS Analysis Software provide?
A. The software performs an extensive analysis of temperature data obtained
from both fingers and generates a detailed report of multiple parameters, including temperature rebound (TR), area under
the curve (AUC), slope of temperature fall and recovery, and parameters obtained using advanced bioheat algorithms.
Also included are adjusted values for TR and AUC, based on various starting fingertip temperatures.
Q. What is adjusted Temperature Rebound (aTR), and what is the unit
of measurement, "Celsius" or "Fahrenheit?"
A. The VENDYS software utilizes a proprietary method to calculate what the
fingertip temperature rebound curve would look like if no vascular reactivity were present, taking into account the
starting fingertip temperature and the amount of temperature fall during cuff occlusion. The difference between this
“zero reactivity curve” and the actual observed temperature curve is used to determine the adjusted temperature rebound
(aTR) presented in the VENDYS test report. Consequently, aTR is a dimensionless number whose magnitude directly
correlates with the extent of the subject’s vascular reactivity. The higher the aTR, the higher the vascular reactivity,
the better the vascular function.
Q. What is the definition of “macrovascular” and “microvascular”?
A. “Macrovascular” pertains to large, conduit arteries with an internal
diameter greater than 100 microns. “Microvascular” refers to small, resistance vessels (pre-capillary arterioles)
with an internal diameter of less than 100 microns. It is estimated that the microvasculature accounts for over 95%
of the total body vasculature.
Q. What is the relationship between “vascular reactivity” and
“endothelial function”?
A. Microvascular reactivity (vasodilative reactivity) causes reactive
hyperemia (increased blood flow in response to ischemia or similar pharmacologic stimuli), whereas macrovascular
reactivity (flow mediated dilatation, or FMD) results from reactive hyperemia. Both macro- and micro-vascular
reactivity are governed by multiple physiologic (endothelium-dependent and –independent) regulatory mechanisms and
are mediated by a number of biochemical agents, such as nitric oxide (NO), prostaglandins, adenosine, bradykinin,
histamine, and other vasoactive substances. It is believed that macrovascular reactivity is predominantly mediated
by endothelium-derived NO, whereas microvascular reactivity is only partially mediated by NO. Traditionally,
assessment of macrovascular reactivity (FMD) at the brachial artery level by high resolution ultrasound imaging has
been described as an endothelial function test. However, some key opinion leaders believe that “endothelial function”
is a misnomer because endothelial cells have numerous functions. Moreover, endothelial cells exist in all vascular
beds and play critical roles at both macro- and microvascular levels.
Q. How does VENDYS measure vascular reactivity?
A. VENDYS monitors, records, and analyzes fingertip temperature, which
serves as a surrogate marker of blood flow changes that result from vascular reactivity. The VENDYS test begins with
an automated blood pressure measurement in the left arm, followed by a period of suprasystolic cuff occlusion of the
right arm (usually 5 minutes). During the cuff occlusion, fingertip temperature in the right hand falls because of
the absence of warm circulating blood. The occlusion of blood flow elicits a vasodilatory response in the ischemic
area. Once the cuff is released, blood flow rushes into the forearm and hand, causing a temperature rebound (TR) in
the fingertip which is directly proportional to the reactive hyperemia response. The higher the temperature rebound,
the better the vascular reactivity.
Q. Does VENDYS temperature rebound (TR) change in the presence of
nitric oxide (NO) inhibitors?
A. Studies have shown that cutaneous microvascular reactivity, measured
by laser doppler flowmetry (LDF, the current, standard method of measuring skin blood flow), is blunted by NO
synthase inhibitors. Similar studies using VENDYS are underway. These studies not only investigate the effect of an
eNOS (endothelial NO synthase) inhibitor on fingertip temperature reactivity in the occluded arm, but also aim to test
the hypothesis that increased temperature in the contralateral finger during cuff occlusion is partly effected by eNOS
and nNOS (neuronal NO synthase).
Q. How does the VENDYS method compare to laser Doppler flowmetry
(LDF)?
A. Several studies have shown that skin temperature correlates strongly
with skin blood flow measured by LDF. However, unlike LDF, which is sensitive to red blood cell motion only at the
skin level (1-2 mm depth), VENDYS temperature signals can reflect blood flow changes in both skin and subcutaneous
tissues simply because the heat from the inrush of warm blood travels from deep tissues to the skin surface. Also,
LDF is markedly sensitive to any movement at the measurement site, whereas VENDYS is not affected by finger motion.
Q. How does the VENDYS method compare to Doppler ultrasound flow
velocity measurement?
A. Our studies have demonstrated a direct relationship between VENDYS
parameters and flow velocity changes in the radial and ulnar arteries at the wrist level. In most circumstances,
fingertip temperature changes appeared to reflect changes in Doppler blood flow velocities, but with dampened
amplitudes as well as lower noise. Unlike Doppler ultrasound, which is reliant on proper probe placement and
handling by the operator, VENDYS temperature recording is automated and does not require probe handling. Our studies
have also shown a disparity between Doppler velocity measurements and VENDYS parameters when the fingertip
temperature approaches (>35°C) body core temperature (37°C).
Q. What is the correlation between VENDYS and other vascular
function tests?
A. VENDYS has been studied in relation to FMD-BAUS (flow mediated
dilatation-brachial artery ultrasound), Doppler flow velocity, LDF (laser Doppler flowmetry), and PAT (peripheral
arterial tonometry-EndoPAT). In summary, VENDYS exhibited modest correlations with these methods. We believe that
VENDYS, by reflecting both cutaneous and deep tissue vascular reactivity, introduces a new angle to vascular
function assessment and does not equate with any of the above techniques; in fact, based on our preliminary studies,
VENDYS is a very sensitive marker of vascular (and neurovascular) reactivity and may prove to be the most useful and
cost effective clinical tool for monitoring vascular function.
Q. How does the VENDYS method compare to EndoPATTM peripheral
artery tonometry?
A. Although both EndoPATTM and VENDYS measure vascular reactivity at the
fingertip and employ a similar cuff-induced reactive hyperemia procedure, the EndoPATTM probe includes a fingertip
cuff that obstructs microvasculature at the point of measurement; therefore, EndoPATTM may not be able to accurately
evaluate microvascular reactivity at the fingertip. Studies have shown a modest correlation (r=0.29, p=0.01) between
EndoPATTM reactive hyperemia index (RHI) and VENDYS temperature rebound (TR).
Q. How well does VENDYS correlate with conventional cardiovascular
risk factors (Framingham Risk Score), subclinical atherosclerosis (coronary calcium score), and obstructive
coronary artery disease (coronary angiography and myocardial perfusion)?
A. Our studies have clearly demonstrated that lower VENDYS fingertip
temperature rebound (TR) is associated with increased Framingham Risk Score (FRS) and higher coronary calcium score
(CAC). More importantly, TR has been shown to significantly improve the predictive value of FRS in the detection of
high-risk, subclinical atherosclerosis (CAC>100) in asymptomatic population. Similarly, we have also found that a
combination of TR and FRS has shown a higher predictive power in the identification of obstructive coronary artery
disease (diagnosed by coronary angiography and myocardial perfusion imaging) in vaguely symptomatic patients. These
data suggest a potential clinical utility for VENDYS as a complementary, non-invasive, non-imaging, inexpensive test
for cardiovascular risk assessment in asymptomatic and vaguely symptomatic populations. For more information, please
see the Clinical Findings Section.