The present invention relates to a dual body plethysmography apparatus and process for measuring the blood flow between the trunk and the body periphery.
The measurement of the blood flow between the trunk and the body periphery (term by which the upper limbs, the lower limbs and the head are designated) is extremely important in the understanding of the physiology and physiopathology of cardiopulmonary interaction.
Changes of the pleural and abdominal pressure have important implications for cerebral blood flow, pulmonary blood volume, cardiac output and ventricular afterload. Changes in these parameters affect alveolar gas exchange and skeletal muscle perfusion particularly during physical exercise with or without limitation of expiratory flow as frequently occurs in chronic obstructive lung disease and asthma. These parameters are also affected by positive pressure mechanical ventilation, negative inspiratory pressures during obstruction of the upper respiratory tract (for instance in obstructive sleep apnoea), strongly positive expiratory pressures as occurs in Valsalva's maneuver, expulsive maneuvers, and cough.
Some of the aforesaid implications have been described in the following papers:
There are currently no devices or processes which can measure blood shifts between the trunk and the extremities.
It is known that, during every respiratory act or maneuver, the variations of the volume defined by the thoraco-abdominal wall (hereafter also indicated by the symbol ΔVcw, with reference to the term “chest wall”) are determined by the sum of the variations of gas volume in the lung (hereafter also indicated by the symbol ΔVL) and variations of blood volume contained within the trunk. (Vb) according to the equation
ΔVcw=ΔVL+Vb.
There are known systems to measure ΔVL, by total body plethysmographies or by the acronym WBP, “Whole Body Plethysmography”, described in U.S. Pat. No. 3,511,237) and consisting in measuring the variations of air flow or volume in a constant pressure booth in which a subject under examination is seated; furthermore, the subject breathes through a mouthpiece which is connected to the outside; finally, there is an opening provided with a special sensor that measures the ΔVL. Two embodiments of such plethysmographies are considered here:
There are also known systems for the measurement of the variations of the volume of the trunk (ΔVcw), known as thoraco-abdominal plethysmographs or by the acronym TAP, “Thoraco-Abdominal Plethysmography”.
A first example of thoraco-abdominal plethysmography is given by the opto-electronic plethysmography (also known by the acronym OEP, “Opto-Electronic Plethysmography”), described in patent ITMI001188A1 and by the papers:
Said opto-electronic plethysmography uses digital video cameras to film a subject under examination; reflective markers are applied on the chest and abdomen of such a subject. The markers are filmed by the video cameras, which transmit the filmed sequences to a microprocessor system, which traces the position in space of the markers, and computes the variations of the volume enclosed in the trunk (Vcw) on the basis of a pre-established geometrical model.
A second example of thoraco-abdominal plethysmography is given by the respiratory inductance plethysmography (also known by the acronym RIP), described by U.S. Pat. Nos. 5,331,968, 3,731,184, 4,308,872, 4,373,534, 4,433,693, 4,452,252, 4,494,553, 4,807,640, 4,815,473, 4,817,625 and 4,834,109.
Such a respiratory inductance plethysmography uses two separate windings of wire, stitched within an elastic band which is about 10 cm broad, positioned just under the armpits and at the level of the umbilicus. The wires of the two bands, which are equivalent to as many coils, display a self-inductance that varies according to the surface thereof, which in turn depends on the volume variations of the thoraco-abdominal compartment (ΔVcw); in this manner, the volume variations of the thoraco-abdominal compartment (ΔVcw) may be traced by traditional electronic means.
A third example of thoraco-abdominal plethysmography is described by patent GB2116725A, which discloses a thoraco-abdominal plethysmograph integrated in clothing; in this case, the measurement of the volume is obtained by the measurement of appropriate resistances.
Scientific papers in this respect are:
It is the object of the present invention to obtain an apparatus that measures the blood flow between the trunk and the extremities in a non-invasive manner.
According to the invention, such an object is achieved by means of an apparatus for measuring the blood flow between the trunk and the extremities (Vb), which comprises a whole body plethysmograph for measuring ΔVL, a thoraco-abdominal plethysmograph for measuring the volume variations of the trunk (ΔVcw) and processing means to analyze said ΔVL with said ΔVcw in order to measure the blood flow between the trunk and the extremities Vb, as the difference between ΔVcw and ΔVL:
V
b
=ΔV
cw
−ΔVL.
The invention also relates to a process for measuring the blood flow between the trunk and the body periphery (Vb), comprising:
By means of an apparatus or a process according to the invention, the blood flow from the trunk to the extremities may be derived from the equation
V
b
=ΔV
cw
−ΔVL.
Furthermore, by knowing the instantaneous values of the volume variations of the trunk and the values of the variations of gas volume in the lungs, the instantaneous flow rates (indicated by the symbol P(t)) of the blood flowing from the trunk to the extremities and vice versa, may be derived from the formula
These and other features of the present invention will become more apparent from the following detailed description of an embodiment thereof by way of no limitation in the accompanying drawings, in which:
An apparatus 1 according to the invention, diagrammatically shown in
The whole body plethysmograph 102 is structured as follows. The booth 12 has a volume of 600 dm3 and is adapted to allow the seating of a subject 11 whose blood flow dynamics between the trunk and the extremities is to be studied. The booth 12 comprises non-transparent parts and transparent parts. Approximately at the level of the mouth of the subject 11, a mouthpiece 15 allows the passage of air from the outside to the inside.
On the upper wall of the booth 12, openings 4 allow the passage of air between the outside and the inside of said booth 12; a traditional flow sensor 40 with a pneumotachograph (provided with Lilly or Silverman or Fleisch resistors) to measure the air flow passing through the openings 4 is applied to each of said openings 4.
The opto-electronic thoraco-abdominal plethysmograph 101 is structured as follows. In front of the booth 12, video cameras 3 are arranged so as to film inside the booth. Such video cameras 3 are connected with an output to an electronic detection device 21.
A plurality of markers 2, consisting of small plastic half-spheres covered by reflective material is applied to the subject 11 at preset positions on the surface of the trunk. The application of such markers 2 is performed by means of the application of double-sided hypoallergenic paper tape.
Said electronic detection device 21 is an electronic system which provides the value of the volume variation of the trunk (ΔVcw) on the outside on the basis of processing performed on the digital images obtained from said video cameras 3 by means of the tracing of the positions in space of the markers 2.
The microprocessor system 20 comprises an integrating circuit 27, an anti-filter 41, an operation block 23 and a differentiator circuit 24.
The flow sensor 40 provides the value of the gas flow in and out of the lungs. Such a value is integrated by the integrating circuit 27 in order to obtain the changes in gas volume of the lungs.
Such a value is anti-filtered by the anti-filter 22 (the explanation will be carried out hereafter).
Downstream of the anti-filter 22 there is a clamping circuit 41. The reason for the use of such a clamping circuit 41 will be explained hereafter.
The values of the outputs of the electronic detection device 21 and clamping circuit 41 are subtracted in the operation block 23 in order to obtain the value of the amount of blood flowing between the trunk and the extremities (Vb) and is provided on the outside.
Finally, such a value Vb is provided on the outside, and also differentiated by the differentiator circuit 24 to compute the flow rate P(t) thereof.
The reason for the use of the anti-filter 22 is explained hereafter. The dynamical phenomena occurring within the booth 12 must indeed be taken into account. For this purpose, it is helpful to refer to an equivalent circuit shown in
is associated to the capacitance C,
which is the equation of a low pass filter having a cut-off frequency fb equivalent to
To correct the attenuation and the phase shift introduced by the booth dynamics it is therefore necessary to apply an appropriate anti-filter consisting of a filter, the transfer function of which is:
with cut-off frequency fh at high frequencies being for instance 20 Hz.
The reason for the use of the clamping circuit 41 is now explained. Within the booth 12, the subject 11 produces heat giving rise to a thermal drift which must be corrected by means of high pass filtering of the signal, which however may be difficult to define. A correction of the drift is therefore obtained by aligning the ΔVcw plots (which are not subject to drift) from the output of the electronic detection device 21 with the output of the anti-filter 22 at the end of the inspiration (when there is usually no blood flow and therefore the two plots coincide) breath by breath and by linearly correcting the signal ΔVL in the segment between the two points of zero flow at the beginning and end of the inspirations. Such a function is performed by the clamping circuit 41.
There may be variants to the embodiment of the present invention.
For instance, as shown in
According to a further variant, shown in
In the two variants just described above, the booth 12 does not need to be transparent, as the use of video cameras is not necessary.
Variants may also be used for the whole body plethysmograph 102, by using, for instance, a volume displacement plethysmograph instead of a variable flow plethysmograph.
The latter processing 120 comprises:
differentiation 124 of Vb to obtain the flow of blood P(t) between the trunk and the extremities
Number | Date | Country | Kind |
---|---|---|---|
MI 2006A 001540 | Aug 2006 | IT | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2007/057919 | 7/31/2007 | WO | 00 | 1/29/2009 |