Automatic blood pressure measuring apparatus having pressure chamber-relieving means

An apparatus for automatically measuring a blood pressure of a subject, including a device for defining an inflatable pressure chamber, the device being set on a body portion of the subject, a flexible piping, a device for supplying a pressurized fluid to the inflatable pressure chamber via the flexible piping so as to increase fluid pressure in the pressure chamber and thereby press the body portion of the subject, and a relief device for discharging the pressurized fluid in the inflatable pressure chamber, into atmosphere, if the fluid pressure in the pressure chamber exceeds a predetermined value, the relief means being supported by the means for defining the pressure chamber.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to an automatic blood pressure (BP) 
measuring apparatus and particularly to such an apparatus which has an 
inflatable pressure chamber for pressing a body portion of a subject. 
2. Discussion of the Prior Art 
There is known an automatic BP measuring apparatus of the type having (a) a 
pressing device which has an inflatable pressure chamber and which is set 
around a body portion of a subject, (b) a flexible hose, (c) a supply 
device for supplying pressurized fluid to the inflatable pressure chamber 
via the flexible hose so as to increase fluid pressure in the pressure 
chamber and thereby press the body portion of the subject, and (d) a 
relief-valve device for discharging the pressurized fluid in the 
inflatable pressure chamber if the fluid pressure in the pressure chamber 
exceeds a predetermined value as the pressurized fluid is supplied to the 
pressure chamber. 
However, in the BP measuring apparatus of the above-described type, the 
relief-valve device is associated with the main body of the apparatus 
which is spaced apart from the pressing device or inflatable pressure 
chamber via the flexible hose provided therebetween. Accordingly, if the 
flexible hose is bent double, the relief-valve device may erroneously be 
operated, that is, placed in its operative position in which the device 
permits a decrease in the fluid pressure in the inflatable pressure 
chamber, though the fluid pressure in the pressure chamber may not have 
exceeded the predetermined value. In the case where the relief-valve 
device is provided with a manually operated reset mechanism for restoring 
the device from its operative position to its inoperative position, the 
operator or subject must operate the reset mechanism each time the 
relief-valve device is changed from its inoperative position to its 
operative position due to bending of the flexible hose. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an automatic 
blood pressure measuring apparatus in which the relief means for 
discharging the pressurized fluid in the inflatable pressure chamber, is 
operated with high reliability. 
The above object has been achieved by the present invention, which provides 
an apparatus for automatically measuring a blood pressure of a subject, 
comprising (i) means for defining an inflatable pressure chamber, the 
means being set on a body portion of the subject, (ii) a flexible piping, 
(iii) means for supplying a pressurized fluid to the inflatable pressure 
chamber via the flexible piping so as to increase fluid pressure in the 
pressure chamber and thereby press the body portion of the subject, and 
(iv) relief means for discharging the pressurized fluid in the inflatable 
pressure chamber, into atmosphere, if the fluid pressure in the pressure 
chamber exceeds a predetermined value, the relief means being supported by 
the means for defining the pressure chamber. 
In the automatic BP measuring apparatus constructed as described above, the 
relief means is directly associated with the inflatable pressure chamber, 
in constrast to the previously-indicated conventional apparatus in which 
the relief-valve device is disposed apart from the inflatable pressure 
chamber via the flexible hose provided therebetween, that is, on the 
upstream side of the flexible hose regarding the pressurized fluid 
supplied from the supply means to the pressure chamber. Therefore, the 
relief means of the invention apparatus is operated directly depending on 
the level of the fluid pressure in the inflatable pressure chamber. 
Consequently the present apparatus is free from the conventionally 
encountered problem that the relief-valve device or other relief means 
erroneously is operated due to bending of the flexible hose. Moreover, the 
present apparatus has eliminated the trouble of manually restoring the 
relief-valve device from the operative position to the inoperative 
position each time the relief-valve device erroneously is operated. 
Preferably the apparatus further comprises means for detecting pulse waves 
produced from an artery running beneath the body portion of the subject, 
and means for determining a blood pressure of the subject based on the 
detected pulse waves. 
According to a preferred feature of the present invention, the relief means 
comprises a cylindrical valve member formed of a rubber material, one of 
opposite axial ends of the cylindrical valve member being closed, while 
the other end of the valve member being open, the open end of the valve 
member communicating with the atmosphere, the valve member having at least 
one cut of a predetermined length which is made through the thickness of a 
cylindrical side wall of the valve member and extends axially of the valve 
member, the valve member being operated such that, while the fluid 
pressure in the inflatable pressure chamber is below the predetermined 
value, the valve member is in an inoperative condition thereof in which 
the at least one cut is fluid-tightly closed, and that, when the fluid 
pressure exceeds the predetermined value, the valve member is placed in an 
operative condition thereof in which the at least one cut is opened due to 
elastic deformation of one of a pair of lips adjacent to the at least one 
cut so that the pressurized fluid in the pressure chamber is discharged 
into the atmosphere through the opened at least one cut. 
In a preferred form of the above-indicated embodiment, the means for 
defining the inflatable pressure chamber comprises an inflatable cuff 
formed of a rubber material, the cylindrical valve member being formed 
integral with the inflatable cuff such that the open end of the valve 
member is exposed to the atmosphere and the closed end thereof is located 
in the pressure chamber. 
In another form of the same embodiment, the means for defining the 
inflatable pressure chamber comprises an inflatable cuff formed of a 
rubber material, the relief means further comprising a fixture member 
fluid-tightly secured to the inflatable cuff, the fixture member having a 
stepped cylindrical shape which includes a small-diameter portion and a 
large-diameter portion connected to each other at an intermediate shoulder 
portion thereof, the cylindrical valve member further including a 
large-diameter cylindrical portion which extends axially outwardly from 
the open end thereof and which has an outer diameter sufficiently larger 
than an outer diameter of a cylindrical main body of the valve member and 
slightly smaller than an inner diameter of the large-diameter portion of 
the fixture member, the valve member being press-fitted in the 
large-diameter portion of the fixture member such that the large-diameter 
cylindrical portion of the valve member is held in fluid-tight contact 
with the shoulder portion of the fixture member and communicates with the 
small-diameter portion of the fixture member, the small-diameter portion 
of the fixture member being exposed to the atmosphere, while the 
large-diameter portion of the fixture member being located in the pressure 
chamber. 
In yet another form of the same embodiment, the at least one cut consists 
of a pair of opposite cuts made in the cylindrical side wall of the 
cylindrical valve member. 
In a further form of the same embodiment, the at least one cut is opened 
when the fluid pressure in the inflatable pressure chamber exceeds 350 
mmHg. 
In a still further form of the same embodiment, the cylindrical valve 
member once placed in the operative condition thereof continues to be in 
the same condition due to radial overlapping of the pair of lips adjacent 
to the opened at least one cut, thereby permitting the pressurized fluid 
in the inflatable pressure chamber to be discharged through the opened at 
least one cut, even if the supply means continues to supply the 
pressurized fluid to the pressure chamber. In this case, the fluid 
pressure in the inflatable pressure chamber may be decreased down to about 
20 mmHg while the cylindrical valve member continues to be in the 
operative condition thereof. 
According to a feature of the same embodiment, the cylindrical valve member 
is restored from the operative position thereof to the inoperative 
condition thereof by blowing air into a cylindrical main body of the valve 
member through the open end thereof. 
According to another aspect of the present invention, there is provided a 
pressing device for pressing a body portion of a subject, comprising (i) 
means for defining an inflatable pressure chamber, the means being set on 
the body portion of the subject, (ii) means for supplying a pressurized 
fluid to the inflatable pressure chamber so as to increase fluid pressure 
in the pressure chamber and thereby press the body portion of the living 
body, and (iii) relief means for discharging the pressurized fluid in the 
inflatable pressure chamber, into atmosphere, if the fluid pressure in the 
pressure chamber exceeds a predetermined value, the relief means being 
supported by the means for defining the pressure chamber.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring first to FIG. 1 there is diagrammatically shown a portable blood 
pressure monitoring system embodying the present invention. In the FIGURE 
reference numeral 10 designates a pressing device which is set around an 
upper arm or the like of a living body. The pressing device 10 includes an 
inflatable enclosure or cuff 14 of rubber which defines an inflatable 
pressure chamber 12 (see FIG. 2) therein, and a fabric bag 15 which 
accommodates the inflatable cuff 14 therein. The inflatable cuff 14 is 
connected to the main body of the monitoring system via a flexible piping 
in the form of a hose 16, the main body being interpreted to include all 
the members shown in FIG. 1 except for the cuff 14 and the hose 16. More 
specifically described, the cuff 14 is connected to a pressure sensor 20, 
a cylinder 22 containing compressed gas therein, a solenoid valve 23 for 
opening and closing the cylinder 22, a low-rate deflation device 24 and a 
high-rate deflation device 26 via piping 18 in the main body. The pressure 
sensor 20 supplies a pressure signal SP representative of variation in 
fluid pressure in the pressure chamber 12, to a first and a second 
detector circuit 28, 30. The first detector circuit 28 includes a low-pass 
filter and, upon reception of pressure signal SP, supplies a cuff-pressure 
signal SK representative of variation in static pressure of the fluid 
pressure in the pressure chamber 12, to a central processing unit (CPU) 34 
via an analog/digital (A/D) converter 32. Meanwhile, the second detector 
circuit 30 includes a band-pass filter and, upon reception of pressure 
signal SP, supplies a pulse-wave signal SM representative of pulse waves 
applied to the cuff 14, to the CPU 34 via the A/D converter 32. The pulse 
waves are oscillatory pressure waves produced from an arterial vessel 
running beneath the pressing device 10, in synchronization with pulsation 
of the heart of the subject. 
The CPU 34 is coupled via data bus to a read-only memory (ROM) 36, a random 
access memory (RAM) 38, a writing device 40 and an output interface 42, 
and processes signals according to software programs pre-stored in the ROM 
36 by utilizing the temporary-storage function of the RAM 38. The CPU 34 
controls the operations of the solenoid valve 23 and the low- and 
high-rate deflation devices 24, 26 via the output interface 42 so as to 
effect a blood pressure measurement on the subject. Further, the CPU 34 
operates to determine a blood pressure of the subject based on pulse-wave 
signal SM and cuff-pressure signal SK, and commands the writing device 40 
to write data indicative of the determined blood pressure together with 
the current time, on a memory card 44. The more detailed description of 
the blood pressure measurement is omitted since such description is not 
very important in understanding the present invention. 
As clearly shown in FIG. 2, the pressure chamber 12 is provided with a 
relief-valve device 46. The relief-valve device 46 includes a fixture 
member 52 and a valve member 58. The fixture member 52 has a stepped 
cylindrical shape including a small-diameter portion 48 and a 
large-diameter portion 50 connected to each other at an intermediate 
shoulder portion 49 thereof. The valve member 58 is formed of rubber and 
has a generally cylindrical shape, one of opposite axial ends thereof 
being closed and the other end being open. The valve member 58 includes, 
on the open-end side thereof, a large-diameter portion 54 whose outer 
diameter is slightly larger than an inner diameter of the large-diameter 
portion 50 of the fixture member 52 and is sufficiently larger than an 
outer diameter of the remaining, small-diameter portion 56 of the valve 
member 58. The fixture member 52 is fluid-tightly secured to the 
inflatable cuff 14 such that the small-diameter portion 48 is exposed to 
the atmosphere while the large-diameter portion 50 is located in the 
pressure chamber 12. The valve member 58 is press fitted in the 
large-diameter portion 50 of the fixture member 52 such that the 
large-diameter portion 54 of the valve member 58 is in fluid-tight contact 
with the shoulder portion 49 of the fixture member 52. Thus, it needs a 
predetermined drag force to draw the valve member 58 out of the fixture 
member 52. 
The small-diameter portion 56 of the valve member 58 has a pair of opposite 
cuts 60 of a predetermined length made through the thickness of the 
cylindrical side wall of the small-diameter portion 56. The cuts 60 extend 
axially of the valve member 58, namely, in parallel to the longitudinal 
axis of the valve member 58. These cuts 60 normally are closed in a 
fluid-tight manner, as shown in FIG. 3. Meanwhile, if the fluid pressure 
in the pressure chamber 12, accordingly, pressure applied to the outer 
circumferential surface of the small-diameter portion 56 of the valve 
member 58, exceeds a predetermined value, the cuts 60 are opened such that 
one of a pair of lips 56a, 56a adjacent to each cut 60 is more largely 
elastically deformed radially inwardly than the other lip, as shown in 
FIG. 4. The hardness, diameter, thickness and other parameters of the 
small-diameter portion 56 of the valve member 58 are predetermined to 
exhibit the above-indicated effect. 
There will be described the operation of the relief-valve device 56 
constructed as described above. 
Initially, pressurized gas is supplied from the cylinder 22 to the pressure 
chamber 12 of the cuff 14 via the piping 18 and the hose 16, so as to 
inflate the pressure chamber 12 and thereby increase fluid pressure in the 
pressure chamber 12 up to 180 mmHg, for example. In this situation, the 
cuts 60 of the valve member 58 are fluid-tightly closed as shown in FIG. 
3. Meanwhile, if the fluid pressure in the pressure chamber 12 exceeds the 
predetermined value, for example 350 mmHg, due to a failure caused in the 
main body of the monitoring system, the relief-valve device 46 is placed 
in an operative position thereof in which the cuts 60 of the 
small-diameter portion 56 are opened such that one of the pair of lips 
56a, 56a adjacent to each cut 60 is largely deformed radially inwardly of 
the small-diameter portion 56 (or valve member 58). As a result, the 
pressure chamber 12 is brought into fluid communication with the 
atmosphere via the relief-valve device 46 in the operative position, and 
the pressurized fluid in the pressure chamber 12 is discharged into the 
atmosphere and the fluid pressure in the pressure chamber 12 is decreased. 
A test using a valve member having a hardness of 65 degree (according to 
the testing method of JIS (Japanese Industrial Standard)--K 6301), a 
small-diameter portion of 4 mm outer diameter and 0.75 mm thickness and a 
pair of cuts of 6 mm length, showed that the fluid pressure in the 
pressure chamber 12 was decreased to about 20 mmHg as a result of the 
discharge of the pressurized fluid from the pressure chamber 12, though 
the supply of the pressurized fluid from the cylinder 22 to the pressure 
chamber 12 had been continued. 
Even after the pressurized fluid in the pressure chamber 12 has been 
discharged into the atmosphere and the fluid pressure of the pressure 
chamber 12 has been decreased to the minimum level, the valve member 58 
continues to be in a condition thereof as shown in FIG. 5 in which the 
pair of lips 56a, 56a adjacent to each cut 60 overlap each other in the 
radial direction of the small-diameter portion 56. With the valve member 
58 being in this condition, it is not permitted to increase the fluid 
pressure in the pressure chamber 12. An air-blowing device (not shown) is 
used to blow air into the valve member 58 from the small-diameter portion 
48 of the fixture member 52, so as to release the overlapping of the pair 
of lips 56a, 56a as shown in FIG. 6 and thereby restore the valve member 
58 to the condition shown in FIG. 3, namely restore the relief-valve 
device 46 to the inoperation position thereof. 
In the illustrated embodiment, the relief-valve device 46 for preventing an 
excessively high fluid pressure in the pressure chamber 12, is directly 
associated with the pressure chamber 12 of the pressing device 10, in 
contrast to the conventional apparatus in which the relief-valve device is 
disposed on the upstream side of the flexible hose regarding the 
pressurized fluid fed from the main body of the apparatus to the pressure 
chamber via the hose. Therefore, the relief-valve device 46 of the present 
monitoring system is operated directly depending on the level of the fluid 
pressure in the pressure chamber 12. Accordingly, the present BP 
monitoring system is free from a problem that the relief-valve device 46 
erroneously is operated due to bending of the flexible hose 16, thereby 
eliminating the trouble of restoring the relief-valve device 46 to its 
inoperative position. Since, in the present portable system, the flexible 
hose 16 is normally held inside the clothes of the subject and likely is 
bent double inside the clothes, the above-indicated advantage is more 
significant. 
In the instant embodiment the rubber valve member 58 having the axial cuts 
60 in the small-diameter cylindrical portion 56 thereof, serves as a valve 
mechanism for relieving the pressurized fluid in the pressure chamber 12 
into the atmosphere. This valve mechanism is not operated, namely, not 
changed from the inoperative position in which the pair of lips 56a, 56a 
adjacent to each cut 60 are in fluid-tight contact with each other, to the 
operative position, until the fluid pressure in the pressure chamber 12 is 
increased up to a comparatively high level such as 350 mmHg. However, in 
the operative position of the valve mechanism, one of the pair of lips 
56a, 56a is largely deformed radially inwardly and the lips 56a, 56a 
overlap each other in the radial direction of the small-diameter portion 
56. Consequently, the valve mechanism is not automatically restored from 
the operative position to the inoperative position even if the pressure 
level in the pressure chamber 12 is lowered to a comparatively low level. 
As described above, even with the pressurized fluid being supplied from 
the cylinder 22 to the pressure chamber 12, the valve mechanism in the 
operative position permits the fluid pressure in the pressure chamber 12 
to be reduced to a sufficiently low level such as about 20 mmHg. The valve 
mechanism or relief-valve device 46 of the present monitoring system is 
simple in construction and is constituted by the least number of parts. 
The valve mechanism serves to avoid an unnecessary, excessively high 
pressure applied to the subject. 
While in the illustrated embodiment the fixture member 52 is used to secure 
the valve member 58 to the cuff 14, it is possible to directly secure the 
valve member (58) to the cuff (14). In this case, it is preferred that the 
valve member (58) be formed integral with the cuff (14). 
Although in the illustrated embodiment the two cuts 60 are used, it is 
possible to make and use a single cut (60). 
The relief-valve device 46 consisting of the fixture member 52 and the 
valve member 58 may be substituted for by other types of relief means. 
While in the illustrated embodiment the rubber cuff 14 is used as the means 
for defining the inflatable pressure chamber, it is possible to employ, in 
place of the rubber cuff 14, a pair of superimposed vinyl sheets adhered 
to each other at the peripheral portions thereof and defining an 
inflatable pressure chamber therein. 
Although the illustrated BP monitoring system is of the portable type, it 
is possible to apply the principle of the present invention to other BP 
measuring apparatus which is adapted to feed pressurized fluid from a main 
body thereof to an inflatable pressure chamber via a flexible piping. 
While the present invention has been described with particularities for 
illustrative purposes only, it is to be understood that the present 
invention may be embodied with various changes, improvements and 
modifications that may occur to those skilled in the art without departing 
from the scope and spirit of the invention defined in the appended claims.