5 Peripheral Venous Dynamics, Venous Oxygen Saturation …
99
5.6 Extended Multi-Wavelength Venous Muscle Pump Test
for the Assessment of the Venous Blood Oxygen
Saturation Level
As already mentioned, the term “oxygen saturation“ means the ratio of oxygen
present in the blood to the maximum oxygen carrying capacity of the blood. In
the normal case, the arterial saturation is around 98% and the peripheral venous
saturation is around 73% to 75%.
Local disturbances in the human oxygen consumption chain are naturally
extremely important because, without oxygen, the cells can not assimilate nutrients and hence, cannot survive. Thus, without our cells burning oxygen, there is no
energy infused into the cells and thus no healthy metabolism. Usually, by puncturing
a central artery and vein and performing invasive blood gas analysis on the samples
collected from the vein and the artery, both arterial saturation and global (central)
venous saturation can be measured.
The non-invasive arterial pulse oximetry evaluates the local arterial oxygen saturation utilizing the heart synchronous pulsation in the arterial blood by analyzing
dual wavelength PPG signal from that local site. However, a pulse oximeter does
not provide information about the local hypoxia in terms of oxygen consumption,
because the method of oxygen saturation estimation used in a pulse oximeter can
not be used to detect the venous saturation and thus the local oxygen consumption
(the difference between the arterial and venous oxygen saturations) can not be ascertained with a pulse oximeter. The difference between the arterial and venous oxygen
saturations determines the metabolism “on-site” and thus diagnostically very important especially in patients with peripheral vascular disease. Such conditions are quite
normal in patients with diabetes, patients suffering from peripheral arterial disease
or patients with difficult to heal wounds (ulcers).
In this case, the arterial oxygen saturation is determined from the arterial pulsation,
and in addition, by applying an embossed leg exercise, the local venous oxygen
saturation can be assessed (from the resulting venous pulsation). This is the first
time that the local oxygen difference between arterial and venous saturation (oxygen
consumption) is measurable.
We applied the thin and flexible PPG sensor to the lower extremity to a sedentary
subject/patient, (e.g. ankle area, toes, or on the longitudinal arches of the foot; Fig. 5.5
left).
After an auto-calibration of the measuring system, the patient performs an
extended leg exercise (15 dorsal extensions in 2 s intervals). It this time sequence,
there are two recorded perfusion signals available, one at λ 1 (preferably 940 nm)
and another one at λ 2 (preferably 660 nm); the combined arterial and venous blood
volume variations in the measurement area at the extremity are recorded (Fig. 5.5
right). These signals are forwarded to two digital filter groups with different spectral
signal characteristics. One of the filters or filter groups calculates DC and AC components of the arterial signal component, the other filter then calculates DC and AC
signal components of the venous signal component (Fig. 5.6). The resulting signal
99
5.6 Extended Multi-Wavelength Venous Muscle Pump Test
for the Assessment of the Venous Blood Oxygen
Saturation Level
As already mentioned, the term “oxygen saturation“ means the ratio of oxygen
present in the blood to the maximum oxygen carrying capacity of the blood. In
the normal case, the arterial saturation is around 98% and the peripheral venous
saturation is around 73% to 75%.
Local disturbances in the human oxygen consumption chain are naturally
extremely important because, without oxygen, the cells can not assimilate nutrients and hence, cannot survive. Thus, without our cells burning oxygen, there is no
energy infused into the cells and thus no healthy metabolism. Usually, by puncturing
a central artery and vein and performing invasive blood gas analysis on the samples
collected from the vein and the artery, both arterial saturation and global (central)
venous saturation can be measured.
The non-invasive arterial pulse oximetry evaluates the local arterial oxygen saturation utilizing the heart synchronous pulsation in the arterial blood by analyzing
dual wavelength PPG signal from that local site. However, a pulse oximeter does
not provide information about the local hypoxia in terms of oxygen consumption,
because the method of oxygen saturation estimation used in a pulse oximeter can
not be used to detect the venous saturation and thus the local oxygen consumption
(the difference between the arterial and venous oxygen saturations) can not be ascertained with a pulse oximeter. The difference between the arterial and venous oxygen
saturations determines the metabolism “on-site” and thus diagnostically very important especially in patients with peripheral vascular disease. Such conditions are quite
normal in patients with diabetes, patients suffering from peripheral arterial disease
or patients with difficult to heal wounds (ulcers).
In this case, the arterial oxygen saturation is determined from the arterial pulsation,
and in addition, by applying an embossed leg exercise, the local venous oxygen
saturation can be assessed (from the resulting venous pulsation). This is the first
time that the local oxygen difference between arterial and venous saturation (oxygen
consumption) is measurable.
We applied the thin and flexible PPG sensor to the lower extremity to a sedentary
subject/patient, (e.g. ankle area, toes, or on the longitudinal arches of the foot; Fig. 5.5
left).
After an auto-calibration of the measuring system, the patient performs an
extended leg exercise (15 dorsal extensions in 2 s intervals). It this time sequence,
there are two recorded perfusion signals available, one at λ 1 (preferably 940 nm)
and another one at λ 2 (preferably 660 nm); the combined arterial and venous blood
volume variations in the measurement area at the extremity are recorded (Fig. 5.5
right). These signals are forwarded to two digital filter groups with different spectral
signal characteristics. One of the filters or filter groups calculates DC and AC components of the arterial signal component, the other filter then calculates DC and AC
signal components of the venous signal component (Fig. 5.6). The resulting signal