D-A Converter-Dewar

D-A (digital/analog) converter a device that converts the digital data signal from a computer into a DC analog electrical signal that can be used to control the function of a measuring system's components: This permits the computer to use the electrical data signal from a measuring device.

Dalton's law principle of partial pressures that describes the behavior of physical mixtures of gases and vapors such that each separate gas acts as predicted by the combined gas law, as if it were present alone; in such a mixture, the partial pressure of each particular gas is proportional to the fractional concentration of that gas and equal to the product of fraction concentration and total atmospheric pressure.

damped referring to an analog waveform in which oscillations have a diminished (and erroneous) amplitude data any information or arrangement of a character set meant to represent information

dative bond atomic configuration accomplished when one of the atoms shares two of its valance electrons with another atom.

dead space ventilation volume of gas that is ventilated, but not physiologically effective. There are three types of dead space ventilation: Anatomic dead space-the volume of gas in the conducting airways: the nose, mouth, pharynx, larynx, and lower airways down to, but not including, the respiratory bronchioles. Alveolar dead space-alveoli that are ventilated, but not perfused with blood. Physiologic dead space-the sum of the anatomic dead space and alveolar dead space.

DC analog electrical signal a direct current electrical signal generated by a sensing mechanism. The electrical signal increases or decreases in direct proportion to the measured physical changes in a system.

DC electrical current an electrical signal in the form of a direct current (as opposed to an alternating electrical current).

debride remove foreign material or dead tissue in a wound

decannulation the removal of a tracheostomy tube.

decelerating taper (ramp) a flow curve in which the flow gradually decreases over time.  

decompression a decrease in the pressure of a gas; the opposite of compression.

decompression port a gas channel whose purpose is to relieve pressure within a portion of the gas circuit.

decompression sickness (DeS) painful, sometimes fatal syndrome caused by the formation of nitrogen bubbles in the tissues of divers, aviators, and others who move too rapidly from higher to lower atmospheric pressures; separated into categories, decompression sickness can be Type I, which involves pain only (usually in or around the joints), or Type II, which is neurological; also called the bends.

decompression table schedule of depths at which anyone exposed to increased pressure must stop for a prescribed period of time to avoid decompression sickness.

decongestant of or pertaining to a substance or procedure that eliminates or reduces congestion or swelling

decontamination the process whereby contaminants are removed from objects, usually by simple physical means, such as washing

decubitus ulcer an inflammation, sore, or ulcer in the skin over a bony prominence

deep sulcus sign distinctive radiographic appearance of a pneumothorax in patients in the supine position, with free air in the pleural space rising to the highest portion of the thorax, usually the anterior costophrenic sulcus, and projecting over the upper abdomen and diaphragm.

deep venous thrombosis (DVT) blood clotting in the legs and pelvis, which usually occurs as a result of venostasis; common in surgical patients and with other causes of immobility, damage to the endothelial wall of the blood vessels, and hypercoagulability states.

defendant the person denying the party against whom relief or recovery is sought in an action or suit; also, the accused in a criminal case

defensin a peptide with natural antibiotic activity found within human neutrophils. Three types of defensins have been identified, each consisting of a chain of about 30 amino acids. Similar molecules occur in white blood cells of other animal species. They show activity toward viruses and fungi, in addition to bacteria.

defibrillation use of an electrical current passed through the heart in an attempt to eliminate the chaotic asynchronous activity of ventricular fibrillation by depolarizing cardiac cells and repolarizing them in a uniform manner with resumption of coordinated cardiac contraction; indicated for ventricular fibrillation, pulseless ventricular tachycardia, and asystole (with the possibility that the rhythm is actually fine ventricular fibrillation).

deflection refers to the waves in the ECG. A deflection may be positive (upright), negative (inverted), biphasic (both positive and negative), or equiphasic (equally positive and negative). When a series of waves, such as a QRS complex, is composed of positive and negative deflections, it may be (1) predominantly positive (the sum total of the positive and negative deflections is positive, no matter by how much), (2) predominantly negative (the sum total of the positive and negative deflections is negative, no matter by how much), or (3) equiphasic (the positive deflections are equal to the negative deflections).

delay time control a device that controls the backup rate on a ventilator by setting a maximum time between cycles.

delta wave the slurring of the onset of the QRS complex­the fusion of the depolarization wave of a prematurely activated ventricle, the result of premature ventricular excitation, and the depolarization wave of the other, normally activated ventricle. Present in ventricular preexcitation and nodoventricular/ fasciculoventricular pre excitation.

demand flow accelerator servo an automatic device that increases the patient gas flow in response to patient effort.

demand pacemakers artificial pacemakers that have a sensing device that senses the heart's electrical activity and fires at a preset rate when the heart's electrical activity drops below a predetermined rate level.

demand pacing refers to a mode of pacing by an artificial pacemaker in which the pacemaker is turned on when an appropriate underlying spontaneous atrial or ventricular rhythm fails to occur.

demand sensitivity system a subsystem that sets the level of inspiratory effort needed to cycle a ventilator into the inspiratory phase.

demand valve a mechanism that provides a pressurized flow of gas when the patient makes an inspiratory effort.

demyelination loss of the myelin sheath of a nerve

dendritic cells mobile, irregularly shaped cells derived from bone marrow stem cells that reside in small numbers within the airway epithelium and lung parenchyma as antigen-presenting cells, phagocytosing and processing antigens to present to T-Iymphocytes, activating them; also produce adhesion molecules and cytokines and express class I and II major histocompatibility locus (HLA) molecules.

density mass of a substance per unit of volume (g/cm3) 

deontologic theory ethical theory based on duty, asserting that an act is either right or wrong based on its intrinsic character rather than consequences.

deoxyhemoglobin hemoglobin not bound with oxygen. Also called reduced hemoglobin.

deoxyribonucleic acid (DNA) nucleic acid in which the sugar component is deoxyribose; largest molecule in the body, composed of two long polynucleotide chains running parallel to each other; carries the genetic information necessary for synthesis of proteins specific for a given species.

Department of Health and Human Services (DHHS) a department of the u.s. federal government that has many agencies involved in health delivery, for example, the Food and Drug Administration is an agency that requires a certain level of purity for medical gases

Department of Transportation (DOT) government agency that regulates cylinder manufacture and testing and the transporting of hazardous materials, including compressed gases and cryogenic liquids.

dependent (gravity) being bottom-most relative to the earth's gravitational field

depolarization the electrical process by which the resting potential of a polarized, resting cell of the atria, ventricles, or electrical conduction system is reduced to a less negative value.

depolarization waves the parts of the ECG representing the depolarization of the atria and ventricles-the P wave (atrial depolarization) and the QRS complex (ventricular depolarization).

depolarized state the condition of the cell when it has been completely depolarized.

deposition the testimony of a witness taken upon interrogatories, either oral or in writing

deponent one who testifies to the truth of certain facts; one whose deposition is given

dermatomes a configured zone of skin innervated by a spinal cord segment

dermis the thicker layer of the skin just below the surface layer (epidermis). It consists of dense, vascular connective tissue.

desquamation the process in which the cornified layer of the epidermis is sloughed in fine scales.

dessicant a substance with the property of attracting and absorbing moisture from air or other substances.

detoxify the process of removing toxic agents or poisons dew point the temperature at which water vapor condenses back to its liquid form

Dewar container used to store liquid oxygen; each Dewar has a capacity of several hundred liters of liquid oxygen; invented by Scottish chemist and physicist Sir James Dewar.

Diabetes-Dyssynchrony

diabetes a general term referring to a variety of disorders characterized by excessive urination (polyuria), as in diabetes mellitus and diabetes insipidus.

diabetic hemorrhagic retinopathy a disorder of the retinal blood vessels characterized by degeneration of the blood vessels and hemorrhage within the eye, the result of long­standing, poorly controlled diabetes.

diabetic ketoacidosis an acute, life-threatening complication of uncontrolled diabetes mellitus in which urinary loss of water, potassium, ammonium, and sodium results in hypovolemia, electrolyte imbalance, extremely high blood glucose levels, and the breakdown of free fatty acids, causing a severe metabolic acidosis, often with coma  

diagnostic-related groups (DRGs) form of hospital reimbursement based on a patient classification system consisting of approximately 500 different groups, all entailing a predetermined amount of reimbursement. DRGs establish a rate based on bundled services for a particular diagnosis established at the time of admission. The provider receives this amount regardless of the medical care provided.

diagnostics a function that incorporates aspects of assessment and testing that include (1) blood gas analysis; (2) nutritional, cardiac, pulmonary, exercise, and sleep assessments; (3) chest radiology; (4) bronchoscopy; (5) pulmonary function testing; and (6) hemodynamics and gas exchange monitoring.

dialysate the fluid that passes through a semi­permeable membrane during dialysis

dialysis (dialyses) a procedure that filters out unwanted substances from the blood, usually in cases of renal failure

Diameter Index Safety System one of three indexed safety systems for medical gas distribution station outlets. In this system, a female nut and nipple is manually tightened onto the outlet until contact is made with the plunger, moving it forward until it seats on the stem, thus allowing gas to flow from the piping system.

diameter restrictor a device that controls or reduces flow by reducing the diameter of the flow path.

diapedesis the passage of red or white blood corpuscles through the walls of the vessels that contain them without damage to the vessels.  

diaphoresis, diaphoretic profuse perspiration

diaphragm membranous muscle separating the abdomen and thorax and serving as a major inspiratory muscle.

diaphragm compressor a gas delivery system that operates to reduce gas volume by increasing pressure through movement of a flexible diaphragm.

diaphragm/leaf valves comparatively thin, flat valves that have many applications in respiratory care. They may serve to separate high-and low-pressure areas, as one-way valves or as back flow prevention devices.

diaphragmatic hernia the protrusion of part of the stomach through an opening in the diaphragm, most commonly an abnormally enlarged esophageal hiatus

diaphragmatic pacing use of a radio frequency transmitter and an antenna that discharges signals to a surgically implanted receiver to transmit electrical impulses to a surgically implanted electrode placed over the phrenic nerve to ensure stimulation of all phrenic nerve roots.

diastole part of the cardiac cycle that consists of a period of relaxation during which venous blood returns to the heart.

diastolic blood pressure the baseline blood pressure in the arteries during ventricular relaxation

diastolic dysfunction impaired ventricular filling, recognized increasingly as a cause of congestive heart failure symptoms.

diazepam an antianxiety agent used to produce amnesia in conscious patients before cardioversion of certain arrhythmias. A drug that relieves apprehension and anxiety. Trade name: Valium.

DIC abbreviation for disseminated intravascular coagulation; DIC is a thrombohemorrhagic disorder that accompanies a variety of clinical conditions and involves activation of the clotting cascade, the generation of excess thrombin, intravascular coagulation, occlusion of capillaries and arterioles with fibrin, and tissue ischemia

dicrotic notch a notch on the descending limb of a pulse tracing; especially that seen in the tracing of arterial blood pressure due to closure of the mitral valve

differential area gas blending valve a gas-mixing device that changes the proportions of a gas mixture by varying the size of each gas inlet port.

diffuse alveolar damage constellation of findings including destruction of the Type I alveolar epithelial cells, which rapidly become detached from the underlying basement membrane, contributing to the increased permeability and resultant influx of protein-rich edema fluid into the interstitium and alveolar space.

diffusing capacity number of milliliters of gas that transfer from the lungs across the alveolar-capillary membrane into the bloodstream each minute, for each 1 mm Hg difference in the pressure across the membrane. The average normal DL value for oxygen is 20 ml/min/mm Hg.

diffusing capacity of the lung (DL) the number of milliliters of gas that transfer from the lungs to the pulmonary blood per minute for each torr partial pressure difference between the alveoli and pulmonary capillary blood

diffusing capacity of the lung to alveolar volume ratio (DLCO/VA) an index of the diffusing capacity for each liter of lung volume and an index of the functional alveolar surface area available for diffusion

diffusion the movement of gas molecules from an area of relatively high concentration of gas to one of low concentration. Different gases each move according to their own individual partial pressure gradients. Diffusion continues until all the gases in the two areas are in equilibrium.

diffusion coefficient the rate of diffusion of a gas; in cgs units, the diffusion coefficient is defined as the number of milliliters of a gas at 1 atmosphere of pressure that will diffuse a distance of 1 mm over a square centimeter surface area per minute

diffusion deposition the deposition of aerosol particles on a surface due to their random bombardment by carrier gas molecules

diffuser humidifier a device that forces gas flow through a porous material submerged in water. This causes the gas to form many bubbles that rise to the surface of the gas.

digitalis a cardiac glycoside obtained from the leaves of Digitalis lanata, used to decrease rapid ventricular rate in atrial flutter, atrial fibrillation, and paroxysmal supraventricular tachycardia (PSVT) and to improve ventricular contraction in congestive heart failure.

digitalis effect the changes in the ECG caused by the administration of digitalis. They include prolongation of the PR interval over 0.2 second; depression of the ST segment by 1 mm or more in many of the leads, with a characteristic "scooped-out" appearance; alteration of the T waves so that they appear flattened, inverted, or biphasic; and shortening of the QT interval to less than normal for the heart rate.

digitalis overdose excessive administration of digitalis, often accompanied by signs and symptoms of digitalis toxicity, which includes the appearance of arrhythmias, such as sinus arrhythmia and bradycardia; premature atrial, junctional, and ventricular contractions; atrial, junctional, and ventricular tachycardias; accelerated idioventricular rhythm (AIVR); ventricular fibrillation; and AV blocks. In fact, almost any arrhythmia may be caused by excess digitalis.

digitalis toxicity digitalis overdose.

digitalization the process of administering an adequate amount of digitalis over a period of time in the treatment of certain arrhythmias. See Digoxin.

digitation a fingerlike projection.

digoxin a cardiac glycoside obtained from the leaves of Digitalis lanata, used in the treatment of atrial flutter, atrial fibrillation, and paroxysmal supraventricular tachycardia (PSVT) and to improve ventricular contraction in congestive heart failure.

dilatation and hypertrophy refers to the two kinds of enlargement of the atria and ventricles.

diltiazem hydrochloride a calcium channel blocker drug used to treat atrial tachycardia without block, atrial flutter, atrial fibrillation, and paroxysmal supraventricular tachycardia (PSVT).

dilute relative concentration or strength of a solution indicating that it contains a small amount of solute.

diluter regulator a mechanism that controls the entrained air in an oxygen diluter system.

diplegia bilateral paralysis of both sides of any part of the body or of like parts on the opposite sides of the body

diplopia double vision

direct-current (DC) shock used as defibrillation shock, synchronized countershock, and unsynchronized shock to terminate various arrhythmias. See Defibrillation shock, Synchronized countershock, and Unsynchronized shock.

direct-drive piston ventilator a ventilator in which the gas volume from the piston goes directly to the patient.

direct-acting valve devices that act to provide volume or flow by direct action from a control knob or device. Example: the valve connected to a water faucet. As one turns the faucet, the valve opens or closes.

directional coronary atherectomy (DCA) the mechanical removal of a non calcified thrombus through a catheter inserted in the occluded or narrowed coronary artery.

disability an administrative or legal judgment of an individual's ability to perform certain tasks, generally work related. Disability is often caused by a physical impairment.

disaccharide type of carbohydrate that is a double sugar.

disease management approach to patient care that emphasizes coordinated, comprehensive care along the continuum of disease and across health care delivery systems.

disease prevention individual's conscious choice to learn about and adopt healthy lifestyle practices, implementing behavior modification techniques as needed to reach a higher level of wellness and minimize certain health risks.

disinfectant a chemical agent capable of destroying at least the vegetative phase of pathogenic microorganisms; there are five major categories of disinfectants used in clinical practice: the alcohols, the phenols and their derivatives, the halogens, the aldehydes, and the quaternary ammonium compounds

disinfection the process of destroying at least the vegetative phase of pathogenic microorganisms by physical or chemical means

DISS abbreviation for diameter-indexed safety system; specifications established to prevent accidental interchange of low pressure (less than 200 psig) medical gas connectors. The DISS is used in respiratory care to connect equipment to a low-pressure gas source

dissociation constant a weak acid or base system that has an equilibrium between the molecular form and its ions.

distal away from or being the farthest from any point of reference.

distensibility of or pertaining to the ease of inflation or compliance

distensible capable of being enlarged or expanded under pressure

distillation the condensation of a vapor obtained by heating a liquid; commonly used to separate out liquids with different boiling points as in the production of oxygen by fractional distillation

diuresis, diuretic increased formation and excretion of urine

diuretic a drug used in congestive heart failure to decrease excess body fluid by increasing the secretion of urine by the kidney.

diving reflex the technique of immersing the patient's face in ice water to elicit the parasympathetic reflex in an attempt to terminate paroxysmal supraventricular tachycardia (PSVT) and narrow-QRS-complex tachycardia of unknown origin (with pulse). It should only be tried if other vagal maneuvers are not effective and ischemic heart disease is not present or suspected.

DME company a company that manufactures, sells, or rents durable medical equipment

D02 common abbreviation for delivery of oxygen to the tissues (the product of cardiac output x arterial oxygen content)

dobutamine (Dobutrex) adrenergic agent used to increase cardiac output and elevate the blood pressure.

documentation recording or charting individual patient education, including date and time of intervention, subject matter or content addressed, method of instruction, and response of learner or results of the learning.

documentation system rigorous recording of medical information into a patient's medical record, both paper and electronic records, and including such data as patient assessment, problem identification, care plans, treatments, and outcomes, as well as discharge summaries, progress notes, physician orders, laboratory results, flow sheets, and online reports, photographs, videotapes, films, and audio recordings.

documented event monitoring (DEM) digital recording of chest wall impedance, heart rate, and oxygen saturation.

dominant coronary artery (right, left) refers to the coronary artery, right or left, that gives rise to both the posterior left ventricular arteries and the posterior descending coronary artery.

dominant (or primary) pacemaker of the heart the SA node.

dopamine hydrochloride a sympathomimetic that increases blood pressure; used in the treatment of hypotension and shock.

Doppler echocardiography that uses ultrasound to detect the velocity of blood flow within the heart.

dorsal pertaining to the back or to the posterior portion of a body.

dorsiflexion to bend a joint toward the posterior aspect of the body; for example, the hand is dorsiflexed when it is extended or bent backward at the wrist

DOT Department of Transportation. a federal regulatory agency.

Douglas bag a large plastic bag (approximately 22 liters) designed for the collection of exhaled air.

downsloping ST segment depression a type of ST segment depression that is most specific for myocardial ischemia, including that present in acute subendocardial non-Q-wave MI.

driving pressure pressure difference between two areas in any vessel or airway.

double blinding research technique in which both investigators and participants are unaware of the treatment being studied.

double circuit a ventilator type with two distinct gas flows; one provides power to the other, which goes to the patient.

double-stage reducing valve a pressure control device that lowers line pressure to working pressure in two steps. Generally from 2200 psig to 750 psig to 50 psig.

downstream a relative reference to a point more distal from the source in a stream of flowing fluid

DRG Diagnosis-related group system created by Medicare for establishing basis for payment for diagnostic testing.

drive mechanism a term referring to the method by which gas flow to the patient is achieved.

droplet nuclei the residue of evaporated water droplets; due to their small size (0.5 to 12 mm) droplet nuclei can remain suspended in the air for long periods of time droplet precautions safeguards designed to reduce the risk of droplet transmission of infectious agents

dropped beats nonconducted P waves in AV blocks. Dropped P waves Absent P waves in sinus arrest and sinoatrial (SA) exit block.

drug-related lung disease lung disease caused by a drug

drug signaling the mechanism by which a drug exerts its effect on receptors

dry powder inhaler (DPI) device that creates aerosols by drawing air through a dose of powdered medication. DPIs produce aerosols in which most of the drug particles are in the respirable range, with the distribution of particle sizes differing significantly among various DPIs.

dual-chamber pacemaker an artificial pacemaker that paces the atria, ventricles, or both when appropriate.

dual control ventilatory mode that allows the ventilator to control pressure or volume (but not both at the same time) based on a feedback loop; can be classified as dual control within a breath or dual control breath-to­breath.

Duchenne's muscular dystrophy hereditary familial muscle disease transmitted via an X-linked recessive gene, although about one third of cases may be caused by spontaneous mutation; disease is due to the mutation of the gene for skeletal protein dystrophin; early presenting symptoms are gait disturbances and delayed motor development, as well as limb-girdle muscle weakness and pseudohypertrophy of the calf muscles.

Duckbill/diaphragm/fishmouth valves valves made of elastic materials that have a slit in the middle that opens when pressurized to allow gas flow.

ductus arteriosus vascular channel in the fetus that joins the pulmonary artery directly to the descending aorta; it normally closes after birth.

due process of law law in its regular course of administration through courts of justice

dump port a mechanism that allows expired gas to exit the ventilator; may be part of the expiration valve or the spirometer.

duodenum the shortest, widest, and most fixed portion of the small intestine, taking an almost circular course from the pyloric valve of the stomach so that its termination is close to its starting point

duplex ultrasound combination of real time B-mode and Doppler ultrasound, suitable for the ICU patient because the examination can be performed using a portable unit in the intensive care.

durable medical equipment (DME) umbrella term usually applied to medical equipment leased or borrowed for use outside the hospital by the patient.

durable power of attorney for health care document that names an individual or agent who can make decisions specifically related to health care for another individual.

duty cycle during breathing, the ratio of inspiratory time to the total time for a complete breathing cycle

dying heart a heart with feeble, ineffectual ventricular contractions and an ECG showing markedly abnormal QRS complexes, usually a ventricular escape rhythm.

dynamic airway compression condition occurring as a result of decreased lung elasticity and leading to increased expiratory airway resistance, which ultimately results in air trapping and hyperinflation.

dynamic hyperinflation an increase in functional residual capacity (FRC) above the elastic equilibrium volume of the respiratory system. Causes include increased flow resistance, short inspiratory time, and increased postinspiratory muscle activity (see also auto-PEEP)

dysarthria difficult, poorly articulated speech, resulting from interference in the control over the muscles of speech, usually because of damage to a central or peripheral motor nerve

dysoxia an abnormal metabolic state in which the tissues are unable to properly use the oxygen made available to them

dysphagia difficulty in swallowing

dysphasia difficulty in speaking, usually caused by a lesion in the central nervous system

dysphonia hoarseness; difficulty in speaking

dyspnea shortness of breath or breathlessness; distressing feeling of inability to breathe or great effort required to breathe.

dyspnea index grading scale that measures the ratio of peak exercise ventilation to maximal voluntary ventilation.

dysrhythmia a rhythm other than a normal sinus rhythm. A term more correct than "arrhythmia" but less frequently used.

dyssynchrony pertaining to ventilatory support, a situation in which interaction between the patient and machine is poorly coordinated, causing extra patient effort and discomfort