Health Talk: Sleeping foot
Have you ever tried to get up and take a step after sitting in a strange position, only to find that one of your feet has “fallen asleep”?
Yet, after a tingling or burning sensation in the affected limb subsides, the foot returns to normal. However, the process is more complicated than that; “sleeping foot,” or “paresthesia,” is actually caused by blocked nerve pathways or arteries, preventing the regular flow of electrochemical impulses from reaching the brain. Electrochemical impulses are transmitted by the body’s neurons, cells in the nervous system that are responsible for transmitting information. This process allows for rapid communication between different parts of the body.
When pressure is exerted on a foot, arm, or leg over a sustained period of time, it can compress arteries in that area, which means that the arteries lose the ability to transport nutrients like oxygen and glucose to the tissues and nerve cells in the affected area, which they need to function normally. Once the limb is moved, nutrient-fortified blood returns to the area, which results in the familiar “pins and needles” feeling.
The sensation is caused by an abnormal transmission of signals to the brain. Nerve pathways become blocked, and the body can no longer send electrochemical impulses to the brain. As a result, the nerves begin to behave erratically, sending “mixed signals” to the brain. These signals result in a tingling sensation in the affected area.
Once the body changes position, the electrochemical impulses begin to flow properly. However, from the time that the body changes position until the time when the exchange of electrochemical impulses is completely restored, the intensity of the tingling increases, causing the “pins and needles” feeling.
The “pins and needles” sensation may dissolve into an uncomfortable burning feeling before the affected area of the body feels normal. The nerve fibers that regulate pain, temperature, and motor control are thin, allowing the victim to move the affected limb before regaining feeling in it, and to feel the tingling sensation rather quickly. The burning, however, is caused by separate thicker nerve fibers that may take longer to begin transmitting electrochemical impulses again.
Certain areas of the body are more prone to this sensation than others. Specifically, nerves that are close to the body’s surface and near a bone are more susceptible to paresthesia, such as the median nerve in the wrist, which causes Carpal Tunnel Syndrome if damaged.
Other common conditions of this type include Ulnar Nerve Palsy, which occurs from repeatedly hitting the nerve close to the elbow, or “funny bone”; Peroneal Nerve Palsy, also called “footdrop,” which is damage to the nerve at the lower part of the knee and results in inability to flex one’s foot upward; and Radial Nerve Palsy, prolonged pressure on the nerve on the underside of the upper arm. Radial Nerve Palsy is also called “Saturday Night Palsy” because it often occurs in people who sleep soundly after drinking heavily.
Although uncomfortable, paresthesia can actually be beneficial, as the sensation alerts an individual to change his or her position to restore blood flow. If the blood flow is restricted and nerves are compressed for several hours, the victim could suffer permanent nerve damage, called mononeuropathy. This results more often from prolonged pressure on a nerve that occurs during sleep or from staying in a crouched position for a sustained period of time.
However, mononeuropathy can also result from accidents, extreme cold or heat, radiation therapy for some types of cancer, and having a cast or crutches that do not fit correctly. “Sleeping foot” is considered a temporary mononeuropathy, which can be cured by resting, not putting pressure on the area, or applying heat to the site of the discomfort.
More serious cases of prolonged nerve compression, however, may require physical therapy or surgery. Such cases can usually be diagnosed via physical examination by a medical professional.