A kidney stone is a solid deposit that forms over time. Kidney stones are composed of acid salts and various minerals. Scientists aren’t sure exactly why these minerals accumulate in the kidneys instead of being passed through urine, but the most widely accepted theory is that when certain substances concentrate in the kidneys, they form a nucleus around which other minerals can cling. Because the kidneys are essentially filters that work via gravity, kidney stones eventually work their way into the bladder, making an exit through the urethra.
Unfortunately, kidney stones can become so large while in the kidney that they do not pass easily. In extreme cases, doctors must manually remove stones through surgery. These troublesome stones cause several symptoms, including painful, cloudy urination, nausea, and fever. Surgery is not the favored option, however. Before doctors go digging for kidney stones, they attempt to break them up with sound waves. This process is called lithotripsy.
In lithotripsy, a medical practitioner sends shock waves through the kidneys, bladder and ureter. This procedure breaks large kidney stones down so that they can pass through the urine. Unfortunately, the procedure only hastens the natural process, passing the remaining stones is still quite painful. The patient receives pain medication and antibiotics before the procedure starts, and the patient may feel a slight tingling or pinging feeling when the sound waves are passed through the body.
Lithotripsy lasts between 45 minutes to an hour in order to ensure that all problematic stones are pulverized. In complex cases, the doctor may drain urine from the kidney via a tube so that the liquid can’t provide a buffer for the stones. Unfortunately, while the procedure itself is sound, individual success rates vary. Before now, there has been no reliable way to determine whether all of the stones have been broken into small enough pieces to allow the body to deal with them on its own. This can extend patient discomfort, require additional exposure to x-rays and can even result in repeat procedures.
Scientists from the University of Southampton are working on a new listening device—a type of stethoscope—that can monitor the effectiveness of lithotripsy in real time. The stethoscope was developed in the school’s Faculty of Engineering and the Environment, with funding from Guy’s and St Thomas’ NHS Foundation Trust and Precision Acoustics Ltd. Project leader Tim Leighton describes the invention this way: “It’s an imperfect analogy, but consider a railway man walking along the length of a train, hitting the metal wheels with a hammer. If the wheel rings nicely, he knows that it’s not cracked. If the wheel is cracked, it gives a duller sound.”
Like other stethoscopes, the university’s invention works on the surface of the skin. It listens to the echos that ring out at the beginning of lithotripsy, when the stones are still intact, and then compares them to the duller echoes that result from sound waves impacting much smaller stones. As the procedure progresses, the stethoscope can inform medical staff as to whether there are any large stones remaining. This may result in lithotripsy taking longer in general, but it will render it a one-time procedure. Dr. Leighton’s research was published in the journal Proceedings of the Royal Society A.