Eleven volunteers (9 men and 2 women),
with median age of 39 years (range: 26-50) were recruited for the study.
They stayed supine for the entire examination,
lying on an electro-mechanical tilting chair (Givas AP4295,
A head support was used in order to have the subject’s neck in the proper position,
avoiding hypo- or hyper-extensions.
The respiratory activity was measured simultaneously with the US examination for all the subjects.
For two subjects,
the ECG was also recorded.
All the signals were displayed on the US screen at the same time,
with aligned temporal axis.
VV and BVR of all subjects were bilaterally examined by an expert vascular sonographer with the US system MyLabVinco (Esaote S.p.A.,
A linear array transducer probe (LA332,
Operating bandwidth 3 – 11 MHz; imaging frequencies: 3.5 – 5.0 - 6.6 - 10.0 MHz; Doppler frequencies: 3.3 – 5.0 MHz) was used for the IJV and VV examination.
A phased array transducer probe (PA240,
Operating bandwidth: 1 - 4 MHz; B-Mode frequencies: 2.0 - 2.5 - 3.3 MHz; CFM-PW Frequencies: 1.6 - 2.0 - 2.5 MHz) was used for examining the BVR.
A thick layer of US gel (Aquasonic 100 – Parker Laboratories Inc,
New Jersey USA) was used to ensure a complete coupling between the transducer and the examined subject’s skin,
so to avoid black cones and dark areas on the US image.
The sonographer paid particular attention to prevent excessive pressure on the examined subject’s neck,
in order not to change the IJV shape and the dimension.
ECG and respiratory activity recording
The ECG signal was recorded with a standard 3-leads configuration: the hardware is fully integrated in the US system and detects automatically the heart rate (40-240 bpm).
For every subject the respiratory activity was acquired with a sensor developed for this application (Fig.
It is based on a low noise analog output triaxial accelerometer (ST Microelectronics LIS344ALH).
placed on the subject’s thorax or abdomen and fixed using an elastic band,
acts like an inclinometer,
sensing the variations of underlying geometry caused by respiratory movements,
thus providing information on the subject’s inhalation/exhalation/apnea phases.
The signal is filtered (frequency response 0.02 – 14.5Hz) and amplified to meet the US system specifications.
The respiratory sensor was connected to the US system through the auxiliary (AUX) parallel port (DB25 connector,
input signal ±5mV,
max current 250mA) on the rear panel of the system.
Another input port was used for the ECG (Fig.
The respiratory sensor was placed on the subject's thorax or abdomen,
depending on the type of respiration,
in order to obtain the best signal quality.
For the two subjects whose ECG was recorded,
the respiratory sensor was not placed over the clothes,
because they were bare-chested for ECG electrodes positioning.
For the remaining 9 subjects the respiratory sensor was placed on the clothes.
Gain and position of the trace were individually adjusted on the US system to get the best signal visualization.
IJV was examined at the level of the thyroid cartilage (J2 segment) ,
for morphological and hemodynamic evaluations and at its confluence to the subclavian vein for valve movement analysis .
VV was examined at the level between the 5th and 6th cervical vertebrae .
BVR was insonated through the transtemporal US window in the midbrain plane,
considering its segment adjacent to the segment P2 of the posterior cerebral artery .
IJV was imaged with B-Mode for studying the cross sectional area changes in different breathing phases and conditions.
IJV and VV hemodynamic were measured with the classic Color Doppler (CD) and Pulsed Wave Doppler (PW) and also with the Multigate Quality Doppler Profiles (QDP) technology [16,
The last technique overcomes the limitations of the first ones in terms of flow direction sensitivity,
spatial and temporal resolution.
in the particular application of neck venous flow measurement,
QDP can detect flows with slow velocity and also different directions both present in the same vessel at the same time,
as described in previous works .
QDP was used for checking the PW Sample Volume (SV) position in real time,
compared to the venous flow position.
the B-Mode plus CD (B-ref) modalities were first used for guiding the QDP multigate line of sight position,
then the B-Ref was switched off and the PW was activated.
Since the PW SV position is marked along the QDP line of sight,
it is possible to detect if it is providing the correct measure or if it is sampling outside the vessel.
For a better visualization of the IJV valve,
being only a fraction of a millimeter (approximately 100µm)  thick,
XView and MView technologies were used,
for reducing artifacts,
shadowing and speckle .
The IJV valve was also investigated with M-Mode technology.