pox As with a throat culture, material from the site is sent to a laboratory, where it is placed in a growth medium to see what types of bacteria grow. ELECTROCARDIOGRAM An electrocardiogram, or ECG, is a recording of the electrical impulses of the heart. These impulses are what make the heart beat in a regular rhythm. To make such a record, the patient is attached to an ECG machine with electrodes (metal plates that are placed on the arms, legs, and chest). These electrodes pick up the electrical impulses that move through the body. The impulses cause a needle in the machine to move on a piece of paper as the paper moves through the machine. Where the needle touches the paper, it makes a line. The physician studies the pattern on the paper to see if the heart rhythm is normal. The ECG does not hurt the patient, but it is important for the patient to stay very still while the recording is being done. All muscle movements, not just movements of the heart muscle, are caused by electrical impulses. Therefore, any movement can affect the ECG recording and give an inaccurate picture of the heartbeat. An ECG is done to check for arrhythmias (irregular heart rhythms), an enlarged heart, heart valve disorders, heart malformations, and many other heart disorders. The test can be done in a doctor's office or an outpatient laboratory. ELECTROENCEPHALOGRAM An electroencephalogram, or EEG. is a recording of electrical activity in the brain. It is a painless procedure similar to an ECG. The metal plates known as electrodes are attached to the patient's head and to an EEG machine. The electrodes pick up the brain's electrical impulses. These impulses activate a needle, which traces the pattern of the impulses on a piece of paper moving through the machine. The physician compares the pattern on the recording with patterns of normal brain activity and determines if there is an abnormality. Recordings from opposite sides of the brain can also be compared to see if the patterns match. An EEG is done to test for epilepsy, brain tumors, encephalitis (inflammation of the brain), and other brain disorders. LUMBAR PUNCTURE A lumbar puncture, or spinal tap, is the method used to obtain a sample of cerebrospinal fluid for testing. Cerebrospinal fluid is a clear liquid that surrounds the brain and the spinal cord. In a lumbar puncture. a needle is used to penetrate into the lumbar spine (the lower portion of the spine) between two vertebrae (the bones that make up the spine) and to draw out some fluid. The pressure in the spinal column can be measured at the same time. The fluid is examined to see if it is clear or cloudy and to see if it contains any blood. It is then tested for viruses, bacteria, and other signs of infection. A lumbar puncture may be done to test for meningitis, encephalitis, brain hemorrhage (bleeding in the brain), polio, and other nervous system disorders. Under the usual circumstances, there is no risk from a lumbar puncture. pox