IEEE Systems, Man and Cybernetics Magazine - April 2023 - 54

be optimized by mutual comparison
of the left and right legs [38].
Both venous emptying and the
venous emptying rate are key
parameters of LRR equipment and
are most associated with DVT. In an
experiment that happened in 1991,
77 patients were lying in bed at 120º
hip and knee angles to perform
10 ankle dorsiflexion activities over
15 s. This activity was repeated
three to five times. The results
showed that the specificity could be
improved to 89%, with a sensitivity
of 83%, when varying the threshold
to a slope less than 0.17 [39]. In 1993,
a study used a threshold adjusted to
0.35 and the same detection requirements.
The result showed a sensitivity of 96.4% and a specificity
of 82.9%. Both studies show that LRR equipment has
an important diagnostic ability and that the control of sensitivity
and specificity can be achieved with methods that
control thresholds [40].
The VRT is another effective parameter of the LRR
The marginal loss
associated with using
POCT equipment
for diagnosis is
much less than the
medical burden
and cost associated
with a referral
from a preliminary
diagnosis.
fewer than 21 s as the threshold
showed a PPG sensitivity of 100%
and specificity of 47%. The preceding
results indicate that VRT
parameters have an extremely
strong ability to exclude DVT [41].
In 2021, an experiment using
PPG to diagnose simulated DVT
had better results. Its best performance
had a sensitivity of 82% and
a specificity of 90%. The study
developed a DVT examination system
consisting of an LRR sensor
and a motion sensor. The LRR sensor
can compensate for the blood
displacement at optical skin densities
with different skin colors,
thicknesses, and soft tissue. It
method for detecting DVT. Venous emptying reaches a
peak with movement through the calf muscle pump. The
time is designated as the VRT when the blood reflex subsequently
progresses to the lower extremities, and corresponding
PPG light reflex values decline to plateau. In
1989, the investigators placed a PPG device 3 cm above the
medial malleolus and instructed patients to elevate their
ankle 10 times. With the examination of 82 patients, the
sensitivity could reach 69.7% and the specificity 81.6% compared
with venography, which had a significant ability to
exclude DVT [9]. In 1999, experiments using the VRT in
Table 5. Selected studies using PPG
in the diagnosis of DVT.
Feature
Shape
of PPG trace
Venous
emptying time
69 (41/28)
Venous refilling
time
Venous
emptying and
refilling time
476 (167/309)
36-79
82 (0/82)
103 (66/37)
-
448 (224/224)
96.4
69.7
100
53-82
Reference
method
Venography
Number of
subjects
92
allows quantitative assessment of vein location by the
quality of the LRR signal [12]. Subsequently, this research
team used machine learning algorithms to classify the
acquired signals in another study. Machine learning has
enabled the intelligence of equipment and enhanced its
ability to be used in nonmedical locations [42].
With the miniaturization of equipment and the application
of artificial intelligence, the method of PPG for evaluating
the venous blood flow of lower limbs is more
convenient and accurate. It is possible to use PPG for
long-term continuous monitoring. These factors together
promote the PPG method to become one of the POCT
diagnostic methods with great developmental potential.
(control/patient) Sensitivity (%) Specificity (%) Study
131 (61/70)
84
69 (45/24)
83-96
71-89
82.9
81.6
35-56
59-90
44-85
Discussion and Conclusion
This article discussed the approach for conventional DVT
diagnostic management and highlighted the potential of
POCT equipment in DVT diagnosis. In
current diagnosis management, DVT
diagnoses can be made only in the
hospital. D-dimer has a high capacity
for positive screening, and US has a
high sensitivity. However, D-dimer
depends on the lab, and US relies too
much on the experience of the user.
These disadvantages reduce the frequency
of diagnosis and delay the
diagnosis of patients with acute DVT.
There is ample evidence that POCT
equipment offers unmatched benefits
regarding early diagnosis and ongoing
follow-up. Ideally, the equipment
used to perform early DVT monitoring
should meet many requirements,
such as speed, low cost, miniaturization,
accuracy, ease of use, noninvasive
characteristics, and low power
consumption. Both POCUS and PPG
Thomas
1991 [37]
Mitrani
1991 [39]
Arora
1993 [40]
Ginsberg
1989 [9]
Tan
1999 [41]
Liu
2021 [12]
Liu
2022 [42]
54 IEEE SYSTEMS, MAN, & CYBERNETICS MAGAZINE April 2023
IEEE Systems, Man and Cybernetics Magazine - April 2023

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