A 15,000 dwt freighter was broken in two by a freak wave on its maiden voyage. In 1973 the 12,000 grt Bencruachan had the whole bow section forward of the break of the 36.6 m long forecastle bent downwards at 7 degrees by the impact of a 15 m wave. At the bottom it may meet a steep wall of water, perhaps 18 m high and about to break, bearing down on it at 30 knots. A ship may be heading into waves 8 m high when suddenly the bow falls into a long, sloping trough so that in effect it is steaming downhill. Tupper BSc, CEng RCNC, FRINA, WhSch, in Basic Ship Theory (Fifth Edition), 2001 Abnormal WavesĪbnormal waves can be created by a combination of winds, currents and seabed topography. Rawson MSc, DEng, FEng RCNC, FRINA, WhSch, E.C. Be sure to speak up if there’s anything about your results that you don’t understand.K.J. Before you review the results, it may be helpful to write down any questions you might want to ask. It’s very important to discuss your test results with your doctor.
dead tissue due to a blockage of blood flow. The EEG will show if the frequency of waves or patterns is normal. For example, the wave patterns move faster when you’re awake than when you’re asleep. Different levels of consciousness, like sleeping and waking, have a specific range of frequencies of waves per second that are considered normal. Normal resultsĮlectrical activity in the brain appears in an EEG as a pattern of waves. Your doctor may schedule an appointment to go over the test results with you. However, it does not always show past abnormalities related to a seizure.Ī neurologist (someone who specializes in nervous system disorders) interprets the recordings from the EEG and then sends the results to your doctor. The EEG may show abnormalities even if the seizure does not occur during the test. These EEGs use video to capture seizure activity. In some instances, a person may undergo a 24-hour EEG. They may ask you to lie still, close your eyes, breathe deeply, or look at stimuli (such as a flashing light or a picture).ĭuring the test, very little electricity passes between the electrodes and your skin, so you’ll feel very little to no discomfort. The technician may instruct you to do certain things while the test is in progress. 
This machine converts the electrical impulses into visual patterns that appear on a screen.
Once the test begins, the electrodes send electrical impulse data from your brain to the recording machine. The technician will put a sticky gel adhesive on 16 to 25 electrodes and attach them to spots on your scalp. These spots are scrubbed with a special cream that helps the electrodes get a high-quality reading. A technician will measure your head and mark where to place the electrodes. 
You’ll lie down on your back in a reclining chair or on a bed. The test usually takes roughly 30 to 60 minutes to complete and involves the following steps: Specialized technicians administer EEGs at hospitals, doctor’s offices, and laboratories. The electrodes transfer information from your brain to a machine that measures and records the data. An electrode is a conductor through which an electric current enters or leaves. Other factors that can influence your EEG reading include:Īn EEG measures the electrical impulses in your brain by using several electrodes attached to your scalp. The person responsible for interpreting your EEG will take these movements into account. Several types of movements can potentially cause “artifacts” on an EEG recording that mimic brain waves. Factors that could interfere with an EEG reading Some people may not be able to hyperventilate safely, such as people with a history of stroke, asthma, or sickle cell anemia. Hyperventilation is also commonly induced during an EEG to produce abnormalities. The technician performing the EEG is trained to safely manage any situation that might occur. When someone has epilepsy or another seizure disorder, there’s a small risk that the stimuli presented during the test (such as a flashing light) may cause a seizure. If an EEG does not produce any abnormalities, stimuli such as strobe lights, or rapid breathing may be added to help induce any abnormalities.
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