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This tube contains a valve that opens and closes. Inadequate opening of this tube can cause a buildup of fluid in the ears, which can lead to a feeling of pain and pressure in the ear. A tube that is too open can also cause a persistent feeling of pressure as well as hearing unusual sounds such as your own breathing or your own voice too loudly. Eustachian tube disorders are common and one of the leading causes of ear infections (otitis media).

Patulous Eustachian tube dysfunction is a disorder of the valve of the Eustachian tube that causes it to remain open. When this valve remains open, sound can travel from the nasal-sinus cavity to the ears, allowing you to hear your own voice or your own breathing too loudly, or even the sound of blood pumping. Patulous Eustachian tube dysfunction can also alternate with obstructive Eustachian tube dysfunction.

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Your doctor may use a variety of techniques to diagnose patulous Eustachian tube dysfunction while viewing your ear drum (tympanic membrane). Your doctor may ask you to breathe deeply and swallow to see how the ear drum responds. Your doctor may also measure the pressure inside your ear using specialized tools.

The surgical method will be determined by your doctor. In some cases, tympanostomy tubes (ear tubes) may make the condition worse. Implants, fillers, grafts and fat transfers act to fill out the tissue in the surrounding area so the Eustachian tube can close properly and return to normal function. Sometimes grafts are applied to the ear drum.

A common course of treatment for Eustachian tube dysfunction is the use of decongestants or antihistamines. In some cases, this treatment may make the condition worse. If decongestants or antihistamines do not provide relief, contact your doctor. You may need to see an ear, nose and throat specialist for treatment.

The Johns Hopkins Eustachian Tube Health Center provides comprehensive evaluation, diagnosis and management of Eustachian tube dysfunction that include medical, multidisciplinary and surgical approaches.

Neural tube defects are birth defects of the brain, spine, or spinal cord. They happen in the first month of pregnancy, often before a woman even knows that she is pregnant. The two most common neural tube defects are spina bifida and anencephaly. In spina bifida, the fetal spinal column doesn't close completely. There is usually nerve damage that causes at least some paralysis of the legs. In anencephaly, most of the brain and skull do not develop. Babies with anencephaly are usually either stillborn or die shortly after birth. Another type of defect, Chiari malformation, causes the brain tissue to extend into the spinal canal.

Neural tube defects are usually diagnosed before the infant is born, through lab or imaging tests. There is no cure for neural tube defects. The nerve damage and loss of function that are present at birth are usually permanent. However, a variety of treatments can sometimes prevent further damage and help with complications.

The type known as a thermionic tube or thermionic valve utilizes thermionic emission of electrons from a hot cathode for fundamental electronic functions such as signal amplification and current rectification. Non-thermionic types such as a vacuum phototube, however, achieve electron emission through the photoelectric effect, and are used for such purposes as the detection of light intensities. In both types, the electrons are accelerated from the cathode to the anode by the electric field in the tube.

These devices became a key component of electronic circuits for the first half of the twentieth century. They were crucial to the development of radio, television, radar, sound recording and reproduction, long-distance telephone networks, and analog and early digital computers. Although some applications had used earlier technologies such as the spark gap transmitter for radio or mechanical computers for computing, it was the invention of the thermionic vacuum tube that made these technologies widespread and practical, and created the discipline of electronics.[6]

In the 1940s, the invention of semiconductor devices made it possible to produce solid-state devices, which are smaller, more efficient, reliable, durable, safer, cooler, and more economical than thermionic tubes. Beginning in the mid-1960s, thermionic tubes were being replaced by the transistor. However, the cathode-ray tube (CRT) remained the basis for television monitors and oscilloscopes until the early 21st century.

Thermionic tubes are still employed in some applications, such as the magnetron used in microwave ovens, certain high-frequency amplifiers, as well as high end audio amplifiers, which many audio enthusiasts prefer for their "warmer" tube sound, and amplifiers for electric musical instruments such as guitars (for desired effects, such as "overdriving" them to achieve a certain sound or tone).

Not all electronic circuit valves / electron tubes are vacuum tubes. Gas-filled tubes are similar devices, but containing a gas, typically at low pressure, which exploit phenomena related to electric discharge in gases, usually without a heater.

One classification of thermionic vacuum tubes is by the number of active electrodes. A device with two active elements is a diode, usually used for rectification. Devices with three elements are triodes used for amplification and switching. Additional electrodes create tetrodes, pentodes, and so forth, which have multiple additional functions made possible by the additional controllable electrodes.

Vacuum tubes may have other components and functions than those described above, and are described elsewhere. These include as cathode-ray tubes, which create a beam of electrons for display purposes (such as the television picture tube, in electron microscopy, and in electron beam lithography); X-ray tubes; phototubes and photomultipliers (which rely on electron flow through a vacuum where electron emission from the cathode depends on energy from photons rather than thermionic emission).

The earliest vacuum tubes evolved from incandescent light bulbs, containing a filament sealed in an evacuated glass envelope. When hot, the filament in a vacuum tube (a cathode) releases electrons into the vacuum, a process called thermionic emission, originally known as the Edison effect. A second electrode, the anode or plate, will attract those electrons if it is at a more positive voltage. The result is a net flow of electrons from the filament to plate. However, electrons cannot flow in the reverse direction because the plate is not heated and does not emit electrons. The filament has a dual function: it emits electrons when heated; and, together with the plate, it creates an electric field due to the potential difference between them. Such a tube with only two electrodes is termed a diode, and is used for rectification. Since current can only pass in one direction, such a diode (or rectifier) will convert alternating current (AC) to pulsating DC. Diodes can therefore be used in a DC power supply, as a demodulator of amplitude modulated (AM) radio signals and for similar functions.

Early tubes used the filament as the cathode; this is called a "directly heated" tube. Most modern tubes are "indirectly heated" by a "heater" element inside a metal tube that is the cathode. The heater is electrically isolated from the surrounding cathode and simply serves to heat the cathode sufficiently for thermionic emission of electrons. The electrical isolation allows all the tubes' heaters to be supplied from a common circuit (which can be AC without inducing hum) while allowing the cathodes in different tubes to operate at different voltages. H. J. Round invented the indirectly heated tube around 1913.[10]

The filaments require constant and often considerable power, even when amplifying signals at the microwatt level. Power is also dissipated when the electrons from the cathode slam into the anode (plate) and heat it; this can occur even in an idle amplifier due to the quiescent current necessary to ensure linearity and low distortion. In a power amplifier, this heating can be considerable and can destroy the tube if driven beyond its safe limits. Since the tube contains a vacuum, the anodes in most small and medium power tubes are cooled by radiation through the glass envelope. In some special high power applications, the anode forms part of the vacuum envelope to conduct heat to an external heat sink, usually cooled by a blower, or water-jacket.

Klystrons and magnetrons often operate their anodes (called collectors in klystrons) at ground potential to facilitate cooling, particularly with water, without high-voltage insulation. These tubes instead operate with high negative voltages on the filament and cathode.

Except for diodes, additional electrodes are positioned between the cathode and the plate (anode). These electrodes are referred to as grids as they are not solid electrodes but sparse elements through which electrons can pass on their way to the plate. The vacuum tube is then known as a triode, tetrode, pentode, etc., depending on the number of grids. A triode has three electrodes: the anode, cathode, and one grid, and so on. The first grid, known as the control grid, (and sometimes other grids) transforms the diode into a voltage-controlled device: the voltage applied to the control grid affects the current between the cathode and the plate. When held negative with respect to the cathode, the control grid creates an electric field that repels electrons emitted by the cathode, thus reducing or even stopping the current between cathode and anode. As long as the control grid is negative relative to the cathode, essentially no current flows into it, yet a change of several volts on the control grid is sufficient to make a large difference in the plate current, possibly changing the output by hundreds of volts (depending on the circuit). The solid-state device which operates most like the pentode tube is the junction field-effect transistor (JFET), although vacuum tubes typically operate at over a hundred volts, unlike most semiconductors in most applications. e24fc04721