Choke
A choke is a condition or action that obstructs or restricts the normal passage of air to the lungs, often by compressing or blocking the trachea, leading to difficulty breathing, suffocation, or death if not relieved.[1] This physiological response can occur due to foreign objects, swelling, or external pressure, and it triggers immediate physiological reactions such as coughing or gagging to clear the airway.[2] In medical contexts, choking is a life-threatening emergency requiring interventions like the Heimlich maneuver to dislodge obstructions.[3] Beyond its primary physiological sense, choke denotes various mechanical and electrical devices designed to control or restrict flow. In automotive and small engine systems, a choke is a valve in the carburetor that limits air intake during cold starts, enriching the fuel-air mixture to aid ignition and prevent stalling.[4] This component, common in older gasoline engines, operates by partially closing off the air pathway, allowing more fuel to vaporize for easier combustion.[5] In electronics, a choke functions as an inductor that blocks high-frequency alternating current (AC) while permitting direct current (DC) or low-frequency AC to pass, often used in power supplies to filter noise and stabilize signals.[6] In firearms, particularly shotguns, a choke refers to a tapered constriction at the muzzle end of the barrel that narrows the shot pattern, increasing accuracy and range by controlling the spread of pellets.[7] Choke types, such as full, modified, or improved cylinder, are measured in thousandths of an inch and are either fixed or interchangeable to suit different shooting scenarios like hunting or clay target sports.[7] In sports psychology, to choke describes a sudden decline in performance under high-pressure conditions, where skilled individuals fail to execute routine actions despite their abilities, often due to anxiety, distraction, or overthinking.[8] This phenomenon, studied extensively since the 1980s, involves cognitive overload where worry diverts mental resources from automatic skills to explicit monitoring, leading to suboptimal outcomes in critical moments like penalty shots or closing games.[9] Choking is not mere poor play but a specific response to situational demands exceeding perceived resources, affecting athletes across disciplines and even non-sporting high-stakes scenarios.[10] In biology and botany, choke refers to certain plants, such as the chokecherry (Prunus virginiana), a North American shrub or small tree known for its tart fruit, and the chokeberry (Aronia spp.), a genus of deciduous shrubs producing astringent berries.[11] In entertainment, Choke is the title of various works, including a 2001 novel by Chuck Palahniuk, a 2008 film adaptation directed by Clark Gregg, and albums or songs by artists such as I Prevail (2019) and Alice in Chains (1996).[12][13] Other uses include a strategic chokepoint, a geographical feature that restricts movement or access, such as narrow passages in military or trade contexts, and a chokehold, a grappling technique that compresses the neck to restrict blood flow or airflow.[14]Engineering and technology
Electrical choke
An electrical choke is an inductor that restricts the flow of alternating current (AC), particularly at higher frequencies, while permitting direct current (DC) and lower-frequency AC to pass with minimal opposition.[15] This behavior arises from the principles of electromagnetic induction, where a coil of wire generates a magnetic field that induces a voltage opposing changes in current, as described by Faraday's law and Lenz's law.[16] The opposition to AC flow is quantified by inductive reactance, given by the equation X_L = 2\pi f L where X_L is the inductive reactance in ohms, f is the frequency in hertz, and L is the inductance in henries; this reactance increases linearly with frequency, effectively "choking" high-frequency signals by presenting a high impedance to them.[17] Electrical chokes are classified by their core materials, which influence inductance, frequency response, and suitability for specific applications. Air-core chokes, constructed with a coil wound around empty space or non-magnetic supports, provide low inductance and are ideal for radio frequency (RF) circuits where minimal core losses are essential at high frequencies.[18] Iron-core chokes use a ferromagnetic iron core to achieve higher inductance values, making them suitable for filtering lower-frequency AC noise in applications requiring greater energy storage, though they suffer from higher core losses at elevated frequencies.[18] Ferrite-core chokes employ a ceramic ferrite material as the core, offering a balance of high inductance and low losses, which renders them versatile for high-frequency filtering in power supplies and RF circuits.[18] The development of electrical chokes traces back to the early 20th century, coinciding with the rise of radio technology, where they were essential for blocking high-frequency signals in early wireless circuits.[15] During the vacuum tube era from the 1910s to the 1950s, chokes were commonly integrated into rectifier power supplies for radio receivers and amplifiers to smooth DC output and suppress AC ripple.[19] In modern electronics, chokes have evolved for use in switched-mode power supplies (SMPS), where they store and release energy to regulate voltage and filter noise, enabling compact and efficient designs since the late 20th century.[20] Key applications of electrical chokes include electromagnetic interference (EMI) suppression, where common-mode chokes attenuate noise on power lines and data cables to ensure electromagnetic compatibility in electronic devices.[21] In audio systems, chokes serve as inductors in crossover networks, directing low-frequency signals to woofers while blocking higher frequencies to tweeters, thereby improving sound clarity without significant power loss.[22] Additionally, in fluorescent lamp ballasts, chokes limit current to the gas discharge tube, preventing damage and stabilizing operation in lighting circuits.[23]Automotive choke
In carbureted internal combustion engines, the automotive choke serves to enrich the air-fuel mixture during cold starts by restricting airflow into the carburetor. It functions via a butterfly valve—a flat, disc-shaped plate mounted on a shaft across the air intake passage, typically positioned upstream of the venturi. When partially or fully closed, this valve limits air entry while the engine's intake vacuum draws fuel from the carburetor jets, creating a richer mixture that promotes easier ignition and smoother initial operation in low temperatures.[24] Chokes operate by inducing incomplete combustion initially, as the excess fuel vaporizes more readily in the warm exhaust gases, helping the engine reach operating temperature faster. The valve's partial closure increases the fuel-to-air ratio to approximately 9:1, compared to the stoichiometric 14.7:1 for normal running. In older vehicles, the choke links mechanically to the throttle linkage and is controlled by a dashboard pull knob or lever via a cable, allowing the driver to adjust it as the engine warms; automatic (thermostatic) versions use a bimetallic spring or electric heater linked to the cooling system or intake manifold temperature to open the valve gradually without manual input. Manual chokes provide direct driver control for precise enrichment, while automatic ones reduce user error but can fail if the thermostat sticks.[25][26] Historically, the automotive choke was a standard feature in carbureted engines from the early 1900s through the 1980s, with manual versions prominent in vehicles like the Ford Model T during the 1910s, where a dashboard lever controlled the valve for gravity-fed fuel systems. Its use peaked in mass-produced automobiles reliant on carburetors for fuel delivery, but it was largely phased out by the late 1980s as electronic fuel injection (EFI) systems became widespread, offering superior precision and emissions control.[27] In modern EFI-equipped engines, the choke's role is replicated electronically by the engine control unit (ECU), which adjusts injector pulse width and timing based on coolant temperature sensors to enrich the mixture during cold starts, eliminating the need for physical valves. This approach provides more accurate control, reducing fuel waste and emissions without the mechanical complexity of a traditional choke.[28] Common troubleshooting issues with chokes include sticking due to gummed linkages or corrosion, leading to symptoms such as engine flooding (excess fuel causing wet spark plugs and hard starting), black exhaust smoke from unburned fuel, rough idling, or stalling once warmed. To adjust, remove the air cleaner for access, loosen the choke housing screws with the engine cold, rotate the housing to align the index mark for ambient temperature (typically fully closed below 60°F/15°C), and retighten while verifying smooth operation via the control cable.[25]Firearms choke
A firearms choke is a tapered constriction at the muzzle end of a shotgun barrel designed to control the spread of shot pellets, thereby influencing the density and diameter of the shot pattern downrange. This constriction narrows the bore diameter from its standard size—typically 0.729 inches for a 12-gauge shotgun—to a smaller exit diameter, measured in thousandths of an inch of constriction relative to the bore. For example, a full choke in a 12-gauge shotgun provides approximately 0.040 inches of constriction, resulting in a tighter pattern suitable for longer ranges.[29] The primary ballistic effect of a choke is to regulate pellet dispersion without significantly altering individual pellet velocity, as the constriction primarily affects the shot column's expansion after exiting the barrel. In a cylinder bore with no constriction (0.000 inches), pellets spread rapidly, producing a wide pattern ideal for close-range targets up to 20 yards, whereas a full choke maintains a denser cluster, achieving a 30-inch pattern diameter at 40 yards or more by compressing the shot charge and promoting uniform pellet flight. This control over spread enhances effective range and hit probability; for instance, tighter chokes like improved modified (0.035 inches constriction) are used for targets at 30-40 yards, balancing density and coverage to minimize wasted shot while maximizing energy delivery on game. Pellet velocity remains largely consistent across choke types, typically around 1,200-1,300 feet per second for standard loads, but pattern uniformity improves with progressive constriction due to reduced tumbling and deformation in the shot cloud.[30][31][32] Shotgun chokes are categorized into fixed and interchangeable types, each suited to different applications. Fixed chokes are integrally machined into the barrel during manufacturing, offering permanence and simplicity for dedicated uses like upland bird hunting, where a consistent modified choke (0.020 inches constriction) suffices. In contrast, interchangeable or screw-in chokes, threaded into the barrel's muzzle, allow quick swaps to adapt to varying conditions; these emerged prominently in the late 20th century and are constructed from durable materials such as stainless steel for corrosion resistance or titanium for lightweight performance in competitive shooting. A notable example is the Rem Choke system, introduced by Remington in 1986 for models like the 870 and 1100, featuring standardized threads for interchangeable tubes in improved cylinder, modified, and full constrictions.[33][34][35] The concept of the shotgun choke originated in the mid-19th century with the development of purpose-built shotgun barrels, where early patents for tapered muzzles date to 1866, enabling controlled shot dispersion in hunting arms. Fixed chokes became standard in the late 1800s as double-barrel shotguns proliferated, with American manufacturers like Winchester incorporating them into models such as the Model 12 by the early 1900s to improve patterns for waterfowl and small game. Interchangeable systems marked a major evolution in the 1950s and 1960s, with Winchester's Model 59 in 1959 introducing the first factory removable choke sleeves, paving the way for modern versatility in both hunting—where chokes target specific game like doves at 25 yards with skeet constrictions (0.005 inches)—and sport shooting disciplines like trap and skeet. Today, chokes remain essential for optimizing performance in these pursuits, with advancements in precision machining ensuring consistent patterning across loads.[36][37][38] Selecting the appropriate choke involves matching constriction to target distance, game size, and shooting scenario, often verified through pattern testing. For close-range upland hunting (under 25 yards), a cylinder or improved cylinder choke provides a broad 40-50 inch pattern at 30 yards for flushing birds, while full chokes suit waterfowl or turkey at 40+ yards to concentrate pellets on vital areas. In clay target sports, such as sporting clays, shooters may alternate between light modified for crossing targets at 20-30 yards and improved modified for longer quartering shots. Pattern testing, the standard evaluation method, entails firing at a 30-inch paper circle target from 40 yards and assessing pellet density—ideally 70-80% within the circle for hunting effectiveness—adjusting based on load type, as non-toxic steel shot requires one size looser choke than lead to avoid excessive constriction.[32][39][40]Network choke
In computer networking, a network choke refers to mechanisms designed to limit the rate of data packet transmission and prevent overload in communication pathways, thereby maintaining efficient traffic flow. These techniques involve routers or network devices detecting impending congestion—often through monitoring buffer occupancy or queue lengths—and responding by signaling sources to reduce their sending rates. A classic example is the choke packet, a control message sent by a congested router directly to the source host, instructing it to lower its transmission rate until the network stabilizes.[41] This approach contrasts with implicit signals like packet loss but provides proactive feedback to avoid full congestion collapse. The concept of choke packets originated in the 1970s with the ARPANET, the precursor to the modern Internet, where early packet-switched networks faced frequent congestion due to limited bandwidth and growing traffic. In ARPANET implementations, mechanisms like source quench messages—essentially choke packets—were used to notify sources of overload, marking an initial effort at explicit congestion signaling.[41] This evolved in the 1980s with the adoption of TCP/IP protocols, where congestion control became integral to reliable data transfer. By the late 1980s, research formalized choke-based avoidance strategies to predict and mitigate bottlenecks before they caused widespread packet drops.[41] As of 2025, these principles persist in cloud computing environments, where virtualized networks employ choke-like throttling to manage dynamic workloads across distributed data centers, and in 5G networks, which integrate advanced congestion signaling to support ultra-reliable low-latency communications amid high device densities.[42] Key protocols incorporating choke signals include TCP congestion control, which traditionally relies on packet loss as an implicit choke but has been enhanced with explicit mechanisms. In TCP, algorithms like slow start and congestion avoidance adjust the congestion window based on feedback, effectively acting as a self-throttling response to network pressure; modern variants interpret delayed acknowledgments or duplicates as choke indicators to halve the sending rate. Complementing this is Explicit Congestion Notification (ECN) in IP networks, defined in 2001, where routers mark packets with congestion experienced (CE) bits instead of dropping them, allowing endpoints to reduce rates without packet loss— a direct evolution of choke packet ideas for lossless signaling. ECN is particularly vital in environments requiring high throughput, as it enables finer-grained control over traffic bursts. Choke point detection often relies on monitoring queue lengths at routers, where thresholds trigger responses to preempt overflow. A seminal algorithm for this is Random Early Detection (RED), introduced in 1993, which probabilistically drops or marks packets when average queue size exceeds a minimum threshold (e.g., 10-20% of buffer capacity) and ramps up to a maximum (e.g., 30-50%), signaling senders via implicit loss or ECN to achieve fair bandwidth allocation across flows.[43] RED's design avoids global synchronization of drops during spikes, promoting stable network behavior by differentiating aggressive flows early. Applications of network chokes span various domains, including bandwidth throttling by Internet Service Providers (ISPs) to enforce fair usage policies during peak hours, where traffic shaping algorithms limit per-user rates based on detected congestion.[44] In Voice over IP (VoIP) systems, Quality of Service (QoS) frameworks use choke mechanisms to prioritize low-latency packets, ensuring clear audio by throttling non-critical traffic when queues build. For DDoS mitigation, edge routers deploy rate-limiting chokes to identify and slow anomalous high-volume sources, absorbing floods before they overwhelm core infrastructure.[45]Medicine and physiology
Airway obstruction
Airway obstruction, commonly known as choking, is a medical emergency characterized by the partial or complete blockage of the upper respiratory tract, which impedes the flow of air and prevents effective breathing. This condition arises when an object or substance obstructs the trachea or larynx, leading to immediate respiratory distress and potential hypoxia if not addressed promptly. In the United States, choking accounts for over 5,500 deaths annually as of 2023, making it the fourth leading cause of unintentional injury death overall, with children under 5 years old at particularly high risk due to their exploratory behaviors.[46][47][48] The primary causes of airway obstruction include foreign body aspiration, such as food items like hot dogs, grapes, nuts, and candy, or non-food objects like toys, coins, and small batteries, which are especially hazardous in young children. Anatomical issues, including laryngospasm—a sudden involuntary contraction of the vocal cords often triggered by irritation from reflux or anesthesia—can also cause temporary blockage. Medical conditions like anaphylaxis, an severe allergic reaction leading to swelling of the airway tissues, contribute to obstruction as well. Physiologically, the epiglottis normally folds over the larynx during swallowing to prevent aspiration into the lungs, but in obstruction cases, a foreign body may bypass this barrier, increasing risks of aspiration pneumonia if material enters the lower airways. Obstruction progresses from partial blockage, where some air passes but causes turbulent flow and reduced oxygenation, to complete blockage, resulting in rapid hypoxia, elevated carbon dioxide levels, and potential loss of consciousness within minutes due to depleted oxygen reserves.[49][50][51][52][53][54][55] Symptoms of airway obstruction vary by severity but typically include violent coughing or wheezing in partial cases, signaling the body's attempt to expel the blockage. In complete obstruction, the individual cannot speak, cry, or cough effectively, often displaying the universal choking signal of clutching the throat with one or both hands, alongside signs of distress like anxiety, stridor (high-pitched breathing sounds), and cyanosis—a bluish discoloration of the skin due to oxygen deprivation. Risk factors encompass age groups such as toddlers, who frequently place objects in their mouths, and the elderly, who may have impaired swallowing from neurological disorders or dentures. Behavioral risks include talking, laughing, or running while eating, which can precipitate aspiration. As of 2025, U.S. Consumer Product Safety Commission regulations continue to ban toys and children's products with small parts that fit within a 1.25-inch diameter cylinder for items intended for children under 3 years, with enhanced labeling requirements for potential choking hazards to mitigate non-food risks.[49][56][57][58][49][59][60][61] Diagnosis of airway obstruction relies on clinical assessment, including observation of symptoms and history of recent ingestion or exposure. In severe or suspected cases, direct visualization via flexible fiberoptic laryngoscopy is performed to identify the obstruction's location and nature, guiding further management without delaying intervention.[54][52][62]First aid for choking
First aid for choking involves immediate actions to dislodge a foreign object from the airway, primarily through established techniques recommended by major health organizations. The primary method for conscious adults and children is the Heimlich maneuver, also known as abdominal thrusts, which was introduced by surgeon Henry Jay Heimlich in 1974 as a simple, non-surgical intervention to expel obstructions by increasing intrathoracic pressure.[63] Updated guidelines from the American Heart Association (AHA) in 2025 emphasize alternating back blows and abdominal thrusts for enhanced effectiveness.[64] For a conscious adult or child over one year old who is choking (unable to cough, speak, or breathe effectively), follow these steps:- Position yourself slightly behind and to the side of the victim.
- Deliver 5 firm back blows between the shoulder blades using the heel of your hand.
- If the object does not dislodge, perform 5 abdominal thrusts: wrap your arms around the victim's waist, make a fist with one hand above the navel but below the ribcage, grasp it with the other hand, and deliver quick upward thrusts.
- Repeat cycles of 5 back blows and 5 abdominal thrusts until the object is expelled, the victim can breathe or cough, or they become unresponsive. Call emergency services (911) immediately if available.[65]
- Support the infant's head and neck, positioning them face-down along your forearm with their head lower than their chest.
- Deliver 5 back blows between the shoulder blades using the heel of your hand.
- Turn the infant face-up, supporting the head, and give 5 chest thrusts using two fingers on the breastbone just below the nipples.
- Repeat cycles until the object is expelled or the infant becomes unresponsive; call 911 after the first cycle if alone.[65][64]