H2 Receptor-High Frequency Ventilation

H2-receptor antagonist chemical agent that blocks the interaction of histamine or acetylcholine with receptors in stomach cells; drugs that inhibit secretion of gastric acid

Hagen-Poiseuille equation flow measure that calculates volume per unit time, not distance or flow velocity, relating volume flow to the fourth power of the radius, directly and inversely related to the viscosity of the fluid and the length of the tube through which the fluid passes, while directly related to the pressure gradient; if these variables are kept constant, the pressure gradient over the length of the tubular structure in question is directly proportional to flow.

Haldane effect influence of O2 on the CO2 dissociation curve; ensures that the CO2 content of deoxygenated blood is greater than oxygenated blood at any Pco2.

half-life time required for a drug's concentration to be reduced by half.

hallucination a false perception of reality; may be visual, auditory, or olfactory

hamburger phenomenon during carbon dioxide transport, as HC03 moves out of the red blood cells, the Cl- (which has been liberated from the NaCl compound) moves into the red blood to maintain electric neutrality. This movement is known as the Hamburger phenomenon, or the chloride shift.

Hb common abbreviation for hemoglobin

HbA abbreviation for hemoglobin A, or normal adult hemoglobin

HbCO abbreviation for carboxyhemoglobin, hemoglobin saturated with carbon monoxide

HbF abbreviation for fetal hemoglobin  

health belief model theory focusing on prevention of disease and asserting that taking action depends on one's perception of four issues: one's level of susceptibility to the condition, degree of severity of the consequences that might result from contracting the condition, potential benefits of the health action in preventing or reducing susceptibility, and the barriers or costs related to starting or continuing the proposed behavior.

Health Care Financing Administration (HCFA) branch of the U.S. Department of Health and Human Services that administers the Medicare and Medicaid programs. HCFA is responsible for setting the coverage policy, payment, and other guidelines and directing the activities of government contractors.

health maintenance organization (HMO) type of group health care practice that provides basic and supplemental health maintenance and treatment services to voluntary enrollees who prepay a fixed periodic fee that is set without regard to the amount or kind of services received.

heart the muscular cone-shaped hollow organ, about the size of a clenched fist, that pumps blood throughout the body and beats normally about 70 times per minute by coordinated nerve impulses and muscular contractions.

heart rate the number of heart beats, QRS complexes, or R-R intervals per minute.

heart rate calculator ruler a ruler like device used to calculate the heart rate.

heat capacity the number of calories required to raise the temperature of 1 g of a substance 10 C (cgs) or 1 lb of a substance 10 F (fps); by definition, the heat capacity of water is 1 cal in the cgs system and 1 BTU in the fps system

heated blow-by humidifier a type of pass-over humidifier where the gas flow is exposed to a heated water reservoir.

heated wire circuit a type of ventilator circuit in which the inspiratory tubing is heated to reduce water vapor "rain­out" and to ensure delivery of gas at 100% relative humidity at body temperature.

Heimlich maneuver an emergency procedure for dislodging a bolus of food or other obstruction from the trachea to prevent asphyxiation

helical diffusion variant of spike theory that may also play a role in high-frequency ventilation (HFV).

heliox gas mixture of helium and oxygen; used clinically because of its low density.

helium dilution one of the most commonly used methods for measuring functional residual capacity (FRe).

hematemesis vomiting of blood

hematocrit proportion of whole blood that is red blood cells (the hemoglobin-carrying cells).

hematogenous originating or transported in the blood hematology the branch of medicine involved in the study of blood morphology, physiology, and pathology

hematopoiesis, hematopoietic pertaining to the production and the development of blood cells or a substance that stimulates their production

heme the pigmented iron-containing, nonprotein portion of the hemoglobin molecule

hemiblock blockage to the conduction of electrical impulses in one of the fascicles (anterior or posterior) of the left bundle branch. See left anterior fascicular block (LAFB), left posterior fascicular block (LPFB).

hemidiaphragm pertaining to the left or right dome of the diaphragm

hemiparesis paralysis affecting one side of the body

hemithorax either the left or right side of the thorax

hemizygous vein a large vein of the lower left thoracic wall that empties into the azygous vein (trunk connecting the superior and inferior vena cavae)

hemoccult trademark for a guaiac reagent strip test for occult blood

hemodialysis a procedure in which impurities or wastes are removed from the blood, used in treating renal insufficiency and various toxic conditions

hemodynamically stable (or unstable) refers to a patient who is normotensive, without chest pain or congestive heart failure, and not having an acute myocardial infarction or ischemic episode. A patient who is hemodynamically unstable, on the other hand, is hypotensive with evidence of poor peripheral perfusion, has chest pain or congestive heart failure, or is having an acute myocardial infarction or ischemic episode.

hemodynamics the study of the physical aspects of blood circulation, including cardiac function and peripheral vascular physiologic characteristics.

hemoglobin iron-containing globular protein consisting of two pairs of polypeptides; primary function is the transport of oxygen from the lungs to the tissues.

hemolysis process in which water passes through a cell, possibly bursting it, as occurs when the water concentration is higher outside the cell, that is, osmotic pressure is lower outside the cell.

hemoptysis spitting up blood  

hemorrhage the escape of blood from the vascular system

hemorrhagic diathesis any tendency to spontaneous bleeding or bleeding from minor trauma caused by a defect in clotting or a defect in the structure of blood vessels.

hemostasis the condition of controlled bleeding

hemostatic defects abnormal conditions that stop the flow of blood within the vessels.

hemothorax blood trapped in the pleural space, causing a space-occupying lesion; source of blood is typically from fractured ribs lacerating the intercostal blood vessels or lacerating the lung.

Henderson-Hasselbalch equation assertion that the pH of a buffer is determined by the ratio of the concentration of base to the concentration of weak acid.

Henry's law (in physics) a law stating that the solubility of a gas in a liquid is proportional to the pressure of the gas if the temperature is constant and if the gas does not chemically react with the liquid

HEPA abbreviation for high efficiency particulate air, usually applied to air filtration devices capable of 99.99% efficacy on particulate matter down to 0.3 µm Size

HEPA filter a 'high efficiency particulate air' filtration device, usually capable of 99.99% efficacy on particulate matter down to 0.3 µm in size

heparin an anticoagulant. Types of heparin include low-molecular-weight (LMW) heparin and unfractionated heparin. See Anticoagulant.

heparin-induced thrombocytopenia (HIT) complication of heparin use consisting of a platelet count less than 150,000 mm3 that typically develops 5 to 10 days after the initiation of heparin therapy.

hepatojugular reflux inappropriate elevation of a usually normal jugular venous pressure (JVP) when the abdomen is compressed for 1 minute over the liver.

hepatomegaly enlargement of the liver

Hering-Breuer inflation reflex a parasympathetic inflation reflex mediated via the lung's stretch receptors that appears to influence the duration of the expiratory pause occurring between breaths

herniation a protrusion of a body organ or portion of an organ through an abnormal opening in a membrane

herpes any inflammatory disease caused by a herpesvirus, especially herpes zoster or herpes simplex

hertz unit of measure for wave frequency; equal to 1 cycle per second.

heterodisperse referring to an aerosol consisting of particles of varying diameters and sizes

hexachlorophene a topical bacteriocide and detergent

hexaxial reference figure a guide for determining the direction of the QRS axis in the frontal plane, formed by the lead axes of the three limb leads and three augmented leads, spaced 300 apart around a zero reference point.

HHA abbreviation for home health agency; a public or private provider of home healthcare services, usually regulated by state departments of health; HHAs can provide a broad range of services, including the provision of home health aids, nursing care, and rehabilitative personnel

HHb symbol for reduced (deoxygenated) hemoglobin

high-breathing rate alarm a ventilator warning system that indicates rapid respirations in excess of the set rate.

high flow system oxygen therapy equipment that supplies inspired gases at a consistent preset oxygen concentration (see also fixed performance device)

high-frequency airway oscillation technique used to enhance clearance of secretions through a variety of mechanisms, including alteration of mucus rheology, enhanced mucus-airflow interaction, and reflex mechanisms; oscillations can be mechanically generated and administered to the patient, or they can be self-generated by expiration through an oscillatory device.

high frequency chest wall compression (HFCC) a mechanical technique for augmenting secretion clearance; small gas volumes are alternately injected into and withdrawn from a vest by an air-pulse generator at a fast rate, creating an oscillatory motion against the patient's thorax

high-frequency flow interrupter (HFFI) ventilation one of four general types of high-frequency ventilation;. delivers inspiratory flow to the patient in short bursts via a rotating ball valve or microprocessor-controlled solenoid valve, producing breath rates of 2 to 22 Hz (l Hz = 60 breaths/min); inspiration and exhalation are both active.

high-frequency jet ventilation (HFJV) one of four general types of high-frequency ventilation; delivers short pulses of gas directly into the trachea through a narrow­bore cannula or jet injector.

high-frequency oscillatory (HFO) ventilation one of four general types of high-frequency ventilation; essentially an airway vibrator, usually using piston pumps or a vibrating diaphragm that operates at frequencies ranging from 400 to 2400 breaths/min both inspiration and expiration are active.

high-frequency positive-pressure ventilation (HFPPV) conventional positive-pressure ventilation at high breath rates (> 150/min) and small tidal volumes with short inspiratory time to facilitate the increased respiratory rate; exhalation is passive.

high-frequency ventilation (HFV) widely accepted mode of mechanical ventilation in neonatal and pediatric critical care; positive pressure ventilation at rates greater than 150/minute and tidal volumes approximating anatomic dead space with an ability to deliver an adequate minute volume with a lower airway pressure, often when conventional mechanical ventilation has failed.

Hilum-Hz

hilum depression in the lung where the vessels and nerves enter.

his-Purkinje system (of the ventricles) the part of the electrical system consisting of the bundle of His, bundle branches, and Purkinje network.

histamine a substance that is normally present in the body and exerts a pharmacologic action when released from injured cells. It is produced from the amino acid histidine.

histoplasmosis a systemic respiratory disease caused by a fungus

histotoxic hypoxia a type of hypoxia that develops in any condition that impairs the ability of tissue cells to utilize oxygen.

HIV abbreviation for the human immunodeficiency virus, the cause of AIDS

HME abbreviation for heat and moisture exchanger; a passive device used to humidify and warm the inspired air of patients receiving ventilatory support

HMO abbreviation for health maintenance organization; an organized system providing a comprehensive range of healthcare services to a voluntarily enrolled consumer population; in return for a prepaid, fixed fee, the enrollee is guaranteed a defined set of benefits

"Hockey stick" pattern the ventricular "strain" pattern in the QRS-ST-T complex produced by a downsloping ST segment depression and T wave inversion; characteristic of long-standing right or left ventricular hypertrophy. Synonymous with left or right ventricular strain pattern.

holistic of or pertaining to the whole; in healthcare, a philosophy whereby the person is viewed in totality as a mental, physical, and emotional being interacting with the environment  

home health provision of services and equipment to the patient in the home for the purpose of restoring and maintaining his or her maximal level of comfort, function, and health; home health services fall into five different categories: home health agencies, hospice, home medical equipment, home infusion therapy, and homemaker services/private duty nursing.

homeostasis the tendency for physiologic parameters to be maintained within stable limits that best support continued well-being. A tendency for an organism to maintain a stable physiologic state (e.g., maintenance of a stable, normal body temperature).

homogenous something is homogenous when the substances that compose it are uniformly distributed within its volume.

horizontal plane a flat surface passing through the body at right angles to the sagittal and frontal planes and, in the case of electrocardiography, dividing the chest into an upper and a lower half at the level of the heart.

hormone a substance originating in an organ or gland that is conveyed through the body to another part of the body, which it stimulates by chemical action to increased functional activity and/ or increased secretion.

hood an environmental control device that covers the head and regulates the humidity, gas concentration, and temperature of the inspired gases.

hospital-acquired pneumonia pneumonia that develops after hospital admission, excluding any infection that is incubating at the time of admission.

hot film anemometer a flow sensing device used in the Bennett 7200 ventilators that works by measuring the temperature of the gas flow. They are similar to hotwire flow transducers.

House of Delegates (HOD) one of several governance and advisory entities of the AARC, which exists as a representative body for the chartered affiliates to contribute to the growth, existence, governance and future of the respiratory care profession; the HOD exists to bring the wishes and concerns of the general membership to the national organization through local representation; serves as a communication bridge reporting activities, data, information, and needs back to the AARC chartered affiliates and members; serves an advisory role to the BOD and participates in governance of the AARC; and contributes to the governance of the AARC through approval of bylaws, budgets, nominations, and audits and through consideration of resolutions and motions that are forwarded to the BOD for consideration.

huff coughing forced expiratory technique (FET) that is performed by sharply exhaling from high-to mid-lung volumes through an open glottis; used for patients unable to generate an effective cough.

human chorionic gonadotropin (hCG) hormones produced by the placenta and detected in the urine and blood of a pregnant woman

humidifier a device that adds molecular water to gas

humidity water in molecular vapor form; absolute humidity is a measure of the actual content or weight of water present in a given volume of air; relative humidity is the ratio of actual water vapor present in a gas to the capacity of the gas to hold the vapor at a given temperature

humidity deficit a condition in which the available humidity is less than the potential humidity; that is, the percentage relative humidity is less than 100.

humoral of or pertaining to the body fluids; used especially to denote physiological activity occurring via chemical or biological mediators in the body fluids (as opposed to neurological stimulation)

hyaline membrane a membrane that forms in the lung sacs of a developing fetus; a respiratory distress syndrome of the newborn

hyaline membrane disease acute lung disease affecting newborns (usually premature), characterized by airless alveoli, inelastic lungs, more than 60 respirations per minute, nasal flaring, intercostal and subcostal retractions, grunting on expiration, and peripheral edema.

hydrogen bond connection holding adjacent water molecules together in a liquid state and requiring a significant amount of heat to be absorbed to change this water from a liquid to a gas.

hydronephrosis accumulation of urine in the renal pelvis caused by obstruction, forming a cyst

hydrophilic water-loving; describes molecules that tend to be attracted to, and mix well with, water molecules.

hydrophobic water-hating.

hydrostatic pressure static water pressure, generated by the water's weight and which varies on the basis of the density of fluid and height, reflecting the force of gravity; with other fluids, this pressure is called manometric pressure.

hydrostatic testing process that measures the expansion characteristic of the cylinder when exposed to internal pressures two-thirds greater then normal; performed by totally suspending the cylinder in a tank of water and pumping water into the cylinder.

hydrothorax a noninflammatory accumulation of serous fluid in one or both pleural cavities

hydrous containing water, usually chemically combined.

hygrometer an instrument that directly measures relative humidity of the atmosphere or the proportion of water in a specific gas or gas mixture, without extracting the moisture

hygroscopic the property of a substance to readily take up and retain moisture.

hyperalimentation infusion of life-sustaining fluids, electrolytes, and elements of nutrition intravenously or via the gastrointestinal tract

hyperbaric oxygen treatment modality in which a patient breathes 100% oxygen intermittently while the pressure of the treatment chamber is increased to a point higher than sea-level pressure.

hyperbaric oxygenation inhalation of oxygen at greater than normal atmospheric pressure in a specially designed chamber; considered a controversial means of improving the prognosis of those suffering serious CO exposures.

hyperbasemia the abnormal presence of an excess of total buffer base in the blood; a base excess (BE)> +2.0

hyperbilirubinemia greater-than-normal amounts of the bile pigment bilirubin in the blood, often characterized by jaundice, anorexia, and malaise

hypercalcemia increased calcium serum levels characterized by anorexia, vomiting, polyuria, mental confusion, obtundation, and death.

hypercapnia excess carbon dioxide in the blood; can be caused by hypoventilation, increased dead space, and increased CO2 production.

hypercapnic respiratory failure the inability to maintain the normal removal of carbon dioxide from the tissues. It may be indicated by a Paco2 of more than 50 torr in an otherwise healthy individual (also called ventilatory failure)

hyperchloremia excessive chloride in the blood.

hypercoagulability tendency of the blood, to coagulate, or clot, more rapidly than is normal.

hyperemic refers to an excessive amount of blood in a part or area

hyperesthesia increased sensitivity to pain

hyperextension a position of maximum extension

hyperglycemia an increase in the normal blood glucose level

hyperinflation condition in the lung in which air is not easily exhaled, resulting from decreased lung elasticity and subsequent increased expiratory airway resistance and air trapping as a result of dynamic airway compression.

hyperkalemia serum potassium levels above normal; can produce hyporeflexia and muscle weakness; paralysis can occur in severe cases, but death because of cardiac arrhythmias usually takes place before this occurs.

hyperlipidemia an increase of fat levels in the blood

hyperlucent extremely clear or transparent; as applied to x-rays, allowing easy x-ray penetration and thus appearing black on the negative film

hypermagnesemia high magnesium serum levels.

hypernatremia high sodium serum levels.

hyperosmolarity a state of condition of abnormally increased osmolarity in the blood or body fluids

hyperoxia a condition of abnormally high oxygen tension in the blood

hyperoxygenation mechanism of action, along with bubble reduction, in hyperbaric oxygen therapy, which is the primary therapy for decompression sickness and arterial gas embolism; a secondary effect of hyperbaric oxygen therapy.

hyperoxia an arterial P02 greater than the upper limits of normal.

hyperparathyroidism a condition caused by overactive parathyroid glands

hyperphosphatemia greater-than-normal concentration of phosphate ions in the blood

hyperpnea rapid, deep, labored breathing.

hyperpyrexia an extremely elevated temperature sometimes occurring in acute infectious diseases, especially in young children

hyperresonance sound, often produced in percussion technique, that is loud, low-pitched, and long; often heard over an emphysematous lung.

hypersecretion substance or fluid produced by cells or glands in an excessive amount or more than normal.

hypersensitivity abnormal sensitivity to a stimulus of any kind.

hypersensitivity pneumonitis an inflammatory form of interstitial pneumonia that results from an immunologic reaction in a hypersensitive person. The reaction may be provoked by a variety of inhaled organic dusts, often those containing fungal spores. The disease can be prevented by avoiding contact with the causative agents. Also called extrinsic allergic alveolitis

hypersomnolence a condition characterized by pathologically excessive drowsiness or sleep hypertension persistently high blood pressure hyperthyroidism a condition characterized by hyperactivity of the thyroid gland

hypertension higher than normal blood pressure.

hyperthermia higher than normal body temperature.

hypertonic property existing in a solution with an osmotic pressure greater than that within the cell.

hypertrophy, hypertrophic enlargement of an organ or structure

hyperuricemia excessive uric acid levels in the blood

hyperventilation rapid, deep, labored breathing resulting in a lowered Pco2

hypervolemia an increase in the amount of extracellular fluid, particularly in the volume of circulating blood or its components

hypnotic a drug or chemical agent that induces sleep

hypoalbuminemia low albumin levels in the blood

hypobasemia the abnormal presence of a deficit of total buffer base in the blood; a negative base excess (BE) < -2.0

hypocalcemia low ionized serum calcium usually resulting from either decreased absorption or decreased mobilization of calcium from the bones.

hypocapnia an arterial PC02 less than the lower limits of normal (less than 35 mm Hg).

hypochloremia low levels of chloride in the extracellular space.

hypoglycemia a less-than-normal amount of glucose in the blood, usually caused by administration of too much insulin, excessive secretion of insulin by the islet cells of the pancreas, or by dietary deficiency (normal blood glucose levels range from 70 to 105 mg/dL)

hypokalemia low serum potassium level

hypomagnesemia low serum magnesium levels.

hyponatremia low serum sodium levels, creating a significant shift in the relationship between intracellular and extracellular fluid compartments.

hypoparathyroidism a condition caused by greatly reduced function of the parathyroid glands

hypoperfusion deficiency of blood coursing through the vessels of the circulatory system.

hypopharynx the lower portion of the airway between the epiglottis and larynx

hypophosphatemia low serum phosphorus levels primarily caused by decreased absorption, intracellular shifts, or increased excretion.

hypopneas abnormally slow, shallow respiration.

hypotension an abnormal condition in which the blood pressure is not adequate for normal perfusion and oxygenation of the tissues

hypothalamus portion of the brain that controls certain metabolic activities.

hypothermia an abnormal and dangerous condition in which the temperature of the body is below 32° C, usually caused by prolonged exposure to cold hypothyroidism a condition characterized by decreased activity of the thyroid gland

hypotonia a condition characterized by decreased muscle tone or strength

hypotonic property of any solution with an osmotic pressure less than that within the cell.

hypoventilation ventilation less than that necessary to meet metabolic needs; signified by a Pco2 greater 45 mm Hg in the arterial blood

hypovolemia decreased amount of blood in the body's cardiovascular system.

hypovolemic shock a condition that occurs when blood in the circulatory system is decreased (e.g., hemorrhage)

hypoxemia deficiency in blood oxygenation may be caused by inadequate ventilation relative to perfusion (that is, low VA/Q and shunt), which has a great effect on oxygen uptake by the lung hypoxemia in adults is usually defined as Pao2 of less than 80 mm Hg.

hypoxemic respiratory failure the inability to maintain the normal delivery of oxygen to the tissues. It may be indicated by a Pao2 of less than 60 mm Hg in an otherwise healthy individual breathing supplemental oxygen

hypoxia decreased tissue oxygenation below adequate levels, disabling adequate blood perfusion of the tissue.

hypoxic pulmonary vasoconstriction narrowing of the lumen in a pulmonary blood vessel because of inadequate oxygen at the cellular level a mechanism that is normally protective, but which, by some disturbance, can contribute to shunt physiology and hypoxemia.

hysteresis the failure of two associated phenomena to coincide, as in the observed difference between the inflation and deflation volume-pressure curves of the lung

Hz (Hertz) a unit of frequency equal to one cycle per second (60 Hz indicates a frequency of 60 cycles per second).