Surgery – Diagnostic testing – Cardiovascular
Reexamination Certificate
2002-09-04
2004-06-22
Hindenburg, Max F. (Department: 3736)
Surgery
Diagnostic testing
Cardiovascular
C600S498000, C073S385000
Reexamination Certificate
active
06752764
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a mercury sphygmomanometer that is compact, easy to manufacture, and safe from mercury spillage.
A mercury sphygmomanometer is one of several blood pressure-measuring devices currently available. Other measuring devices include aneroid pressure measuring manometers and electronic manometers. Aneroid and electronic manometers tend to be smaller in size, lighter in weight, and more compact than mercury sphygmomanometers, but their accuracy is always in doubt. For most assured accuracy the standard among different blood pressure measuring devices is the mercury sphygmomanometer. The mercury sphygmomanometer measures arterial blood pressure and indicates its measurement by the height of a mercury column. The conventional mercury sphygmomanometer uses a transparent rigid plastic or glass tube through which a mercury column rises and falls during blood pressure measurement. In a typical mercury sphygmomanometer, the mercury tube is tall enough to allow the mercury column to reach a maximum height of 300 mm. Thus, the height of the mercury tube establishes the minimum height or length of the mercury sphygmomanometer when the device is stored or carried.
In order to obviate the size limitation of the conventional mercury sphygmomanometer and to allow a compact size for easy portability and storage, three approaches have been taken. One approach is to use a flexible tube for the mercury column, which could be folded during storage for compactness, e.g. as disclosed in U.S. Pat. No. 2,603,210. Another approach is to provide an articulation or a hinge located part way along the tube and to fold and unfold the mercury tube at the articulation or hinge for storage and usage of the device, e.g. as disclosed in U.S. Pat. Nos. 1,093,199 and 1,077,365. In another approach using a hinge mechanism, as described in U.S. Pat. No. 1,474,853, the mercury column used for blood pressure reading is a single tube. But this device requires a third tube to act as a mercury reservoir which is placed between a tube for the mercury column used for blood pressure readings and another tube connected to the air inflation cuff.
Repeated folding of a flexible tube can damage the tube and cause mercury spillage. Use of a hinge or an articulation would add complexity and cost to the manufacturing process in order to minimize risk of mercury spillage along the hinge or the articulation.
The third type of device is based on reducing the height of the mercury column based on Boyle's Law, which states: if the volume of a gas and its temperature are kept constant, the pressure of the gas is inversely proportionate to its volume. Unlike a conventional mercury sphygmomanometer with a mercury tube in communication with an outside air, the mercury tube in this device is in a closed system. It is in communication with an air reservoir having a fixed volume through a passageway containing a filter, which allows air to pass through the filter between the two compartments, but blocks mercury from entering the reservoir.
Because the air valve that connects the air reservoir to the outside air is closed, pressure develops in the air reservoir as well as in the air compartment above the mercury column. This air pressure will be exerted on the rising mercury column. Hence, the pressure at the bottom of the mercury column is equal to the air pressure on the top of the mercury column plus the pressure generated by the weight of mercury, which is proportionate to the height of the mercury column. The maximum height of mercury column needed to obtain a certain maximal pressure measurement (e.g. 300 mmHg) can be reduced to a length that is much shorter than 300 mmHg. This feature allows easy portability of the device.
The present invention enables the measurement of blood pressure using a variation of the third principle described above. The invention involves blood pressure measurements using two separate scales that are displayed along the mercury column, e.g. at opposite sides of the column or at one side. One scale, e.g. along one side of the mercury column, represents blood pressure measurements made with the air valve open. The other scale, e.g. along the other side of the mercury column, represents the pressure measurements with the air valve closed. The maximum blood pressure scale with the open air valve is dictated by the desired maximal blood pressure readings. For example, if a maximal blood pressure reading of 180 mmHg is desired, the required height of the mercury column would be 7.086 inches (180/25.4=7.086). If a maximal pressure reading of 200 mmHg is desired, the required maximal height would be 7.874 inches). In either example, the overall length of the device would be considerably shorter than the conventional mercury sphygmomanometer.
The advantage of the dual scale system (one scale, e.g. on one side with a closed air valve, and the other scale, e.g. on the other side with an open air valve) is in the easy readability of the blood pressure scales. When blood pressure is measured entirely with the air valve closed (as claimed by the U.S. Pat. No. xx), the advantage in compactness is counterbalanced by reduced readability of the blood pressure scales. In a conventional mercury sphygomomanometer, the blood pressure scales are depicted alongside the mercury column at intervals of about 2 mm in length. If the device were to be created using the principles claimed by U.S. Pat. No. xxx, the blood pressure scales would have to be depicted at shorter intervals than 2 mm. For example, if the overall length of the mercury column were to be reduced from 300 mmHg to 180 mmHg (reduced to 60%), the actual distance of each 2 mm scale would be only 1.2 mm (reduced to 60%). In the device to be produced using the principle claimed by the present invention, the actual distance of the blood pressure scales with the open air valve would be the same as that of the conventional device. With the open air valve, no additional pressure is exerted on the mercury column, and the pressure at the bottom of the mercury column depends solely on the height of the mercury column. Normotensive subjects and most hypertensive subjects with adequate blood pressure control will only need to use the scale with the open-valve system if the maximal pressure of such device is 180 mmHg. The pressure readings using the device with the open air valve would be as accurate and easy as using the conventional mercury manometer, since the scale of pressure readings are the same as those of a conventional mercury manometer.
When the blood pressure to be measured is higher than the maximal reading possible with the open air valve, measurement would then be repeated with the closed air valve. However, pressure readings made with a closed air valve would not be as accurate as those made with the open air valve for two reasons. 1) The air pressure that develops on the top of the mercury column may vary with variations in the atmospheric pressure. 2) Cramming of the displayed pressure scales into a shorter height space makes it harder to read the scales. However, A slight error in readings with the closed air valve is clinically unimportant, because the closed air valve scale would be used only when the pressure is higher than the maximal readings possible with the open air valve scale; when the pressure is lower, the open air valve scale is used. For example, a distinction between a pressure difference of 85 and 90 mmHg would be more important while the distinction between 250 and 255 mmHg is likely less important.
A second feature of the present invention relates to minimizing errors in pressure measurement resulting from variation in atmospheric pressure due primarily to a change in the altitude at which the measurement is made. When blood pressure is measured using the closed air valve, the air in the mercury tube above the mercury column is compressed within a closed system that communicates with the air reservoir when the mercury column rises. The rise in pressure in the air reservoir system d
Hindenburg Max F.
Natnithithadha Navin
Ostrolenk Faber Gerb & Soffen, LLP
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