A system for acquiring data representing sound in a human or animal body

Abstract

 A system (10) for acquiring data representing sound in a human or animal body. The system comprises a disk shaped piezoelectric element (30) with a fist side (31) and a second side (32) opposite the first side (31). The piezoelectric element (30) is capable of generating, when exposed to the sound, an analogue electrical signal representing the sound, and the first side (31) is adapted for placing in acoustic contact with the skin of an animal or a human being, and the second side (32) is directly exposed to ambient air, and a device (20) for receiving the electrical signal generated by the piezoelectric element (30). The piezoelectric element (30) can be covered by a protective coating. The electrical signal is sampled at a sampling frequency as high as 96 kHz.

Description

FIELD OF THE INVENTION

[0001] The invention relates to recording, measurement and analysis of sounds in human and animal bodies.

BACKGROUND OF THE INVENTION

[0002] Sound in human and animal bodies is vibrations, which propagate in the tissue. When the vibrations reach the skin (or other accessible surface) the vibrations can be picked up by a transducer, which generates and outputs an electrical signal representing the vibrations. The sounds are vibrations with frequencies below, in or above the range of audible frequencies, such as from a few Hz or a fraction of one Hz up to several tens of kHz and possibly 100 kHz or more. Such wide frequency bands are yet relatively unexplored.

[0003] Audible sounds in human and animal bodies can be picked up by a stethoscope placed on the skin of the body and listened to. Stethoscopes range from simple tubular devices as a transmission medium from the skin to the ear of the person listening to the sounds, and to advanced electronic devices with an electroacoustic transducer and one or more connected devices for recording and analysing the signals representing the sounds in the body. Sounds from organs like heart and lungs typically have a maximum frequency of a few kHz.

[0004] For human and veterinarian medical purposes sounds originating from processes and movements in soft tissue such as heart, lungs, intestines, and digestion, and in solid tissue such as bones and joints, are of interest.

[0005] Sound recording from skeletal muscles, acoustic myography (AMG), has been known as a useful method for assessing muscle force and fatigue for a period of time, but it is only recently that microphones and contact transducers, in particular piezoelectric devices, as well as recording systems, have become available in a size and of a quality that enables them to be applied to a normal daily setting outside the clinic and the laboratory setting. These new possibilities provide a clinical tool for the assessment of patients with musculoskeletal complaints during daily activities, or assessment of athletes in terms of efficiency in use of muscles. With the improved accessibility of piezoelectric crystals, enabling accurate muscle sound recordings transdermally, AMG has had a revival.

[0006] WO 2004/002191 A1 discloses an electronic stethoscope with a piezoelectric element in a housing with a noise attenuation arrangement.

SUMMARY OF THE INVENTION

[0007] The invention aims at evaluating whether the recorded signal could be used to determine coordination, as well as aspects of muscle function, in physically active human subjects with a view to its application in clinical practice.

[0008] Thus, the invention provides a system for acquiring data representing sound in a human or animal body, the system comprising a disk shaped piezoelectric element with a first side and a second side opposite the first side, the piezoelectric element being capable of generating, when exposed to the sound, an electrical signal representing the sound, wherein the first side is adapted for placing in acoustic contact with the skin of an animal or a human being, and the second side is directly exposed to ambient air, and a device for receiving the electrical signal generated by the piezoelectric element. Such system with an uncovered or "naked" piezoelectric element, i.e. without a housing or other encapsulation, is extremely simple since the second side, which faces away from the skin of the human or animal body is uncovered and thus directly exposed to ambient air.

[0009] In an advantageous embodiment of the first and second sides of the piezoelectric element are covered by a protective coating, which protects the piezoelectric element from being damaged by e.g. scratches and influenced by fluids such as acoustic contact gel. Advantageously, the protective coating is a thin sheet of a rubber-like substance, which is transparent to the sounds to be picked up by the piezoelectric element.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] 

Figure 1 shows schematically a system according to the invention, and

Figures 2 and 3 show examples of graphic representations of sound recordings from skeletal muscles.

DETAILED DESCRIPTION OF THE INVENTION

[0011] In figure 1 is shown a system 10 for acquiring data representing sound in a human or animal body. The system 10 has an analyser 20 with a disk shaped piezoelectric element 30 electrically connected to the analyser 20. Also in figure 1 is shown the piezoelectric element 30 seen from its edge to show that the piezoelectric element 30 has a first side 31 and a second side 32 opposite the first side 31. The first side 31 is adapted for placing in acoustic contact with the skin of an animal or a human being, and the second side 32 is directly exposed to ambient air. When the piezoelectric element 30 is placed in acoustic contact with the skin of an animal or a human being the piezoelectric element 30 will receive sound originating from the body of the animal or a human being, and the sound signals will cause the piezoelectric element 30 to generate an analogue electrical signal representing the sound. The analyser 20 receives electrical signal from the piezoelectric element 30 and records, processes and/or analyses the electrical signals.

[0012] The analyser 20 performs a sampling of the received electrical signal. AMG signals turn out to have content of high frequencies up to several tens of kHz, and it is therefore important to use a corresponding high sampling frequency in the analogue-to-digital conversion of the analogue electrical signals representing the sound in the animal or human body in order to avoid losing information of interest. It has been found that sampling frequencies as high as 22, 44 and 96 kHz or even higher can provide useful information about both short and long muscle fibres.

[0013] Figure 2 is a typical AMG and sEMG trace obtained from a healthy subject. Upper trace = sEMG and Lower trace = AMG recordings from m. gastrocnemius during a heal-to-toe rise and fall form of physical activity.

[0014] Figure 3 is a graph of an AMG signal from m. biceps femoris showing the response to an arm lift without a weight (upper panel), an arm lift with a weight (middle panel), and the signal obtained when the arm is passively lifted by another individual (lower panel).

[0015] The invention can be used both on humans and on small as well as larger animals such as horses where non-invasive studies of their skeletal muscles can give useful information, which can be used e.g. in breeding horses for equestrian sports.

Claims

1. A system (10) for acquiring data representing sound in a human or animal body, the system comprising
a disk shaped piezoelectric element (30) with a fist side (31) and a second side (32) opposite the first side (31), the piezoelectric element (30) being capable of generating, when exposed to the sound, an analogue electrical signal representing the sound, wherein the first side (31) is adapted for placing in acoustic contact with the skin of an animal or a human being, and the second side (32) is directly exposed to ambient air, and
a device (20) for receiving the electrical signal generated by the piezoelectric element (30).

2. A system (10) according to claim 1 wherein the first and second sides (31, 32) of the piezoelectric element (30) are covered by a protective coating.

3. A system (10) according to any one of the preceding claims wherein the device (20) for receiving the electrical signal converts the analogue electrical signal to a digital signal with a sampling frequency of at least 22 kHz.

4. A system (10) according to claim 3 wherein the sampling frequency is at least 44 kHz.

5. A system (10) according to claim 3 wherein the sampling frequency is at least 96 kHz.

Drawing