This appendix is a list of key definitions that are common to many topics.
Mass of water vapour in a given volume of air. Measured in mg.L-1.
The rate at which a drug leaves its site of administration and the extent to which this occurs.
The ability of a measuring device to match the actual value of the quantity being measured.
A proton donor.
Arterial blood pH < 7.35.
A process which leads to an excess of hydrogen ions, and may lead to acidaemia if there is inadequate compensation. Can be subdivided into:
- Respiratory acidosis: PaCO2 > 45
- Metabolic acidosis: HCO3- < 22
The effective concentration of a substance in a reacting system.
- Acute Pain
Defined as pain of:
- Recent onset
- Limited probable duration
- Identifiable causal and temporal relationship to injury or disease
A process that occurs without transfer of heat or matter. For example, gases heat up when compressed (greater than the energy used to compress them), and cool when allowed to expand (adiabatic cooling).
Ability of a drug to bind to a receptor.
Ventricular wall stress at the onset of systole.
Naturally occurring, physiological decline in the structure and functional reserve of all organ systems.
Drug which produces a maximal response at receptor site.
Arterial blood pH > 7.45.
A process which leads to a deficit of hydrogen ions, and may lead to alkalaemia if there is inadequate compensation. Can be subdivided into:
- Respiratory alkalosis: PaCO2 < 35
- Metabolic alkalosis: HCO3- > 26
Pain caused by a previously non-painful stimulus.
Substance which binds a receptor distant to the ligand-binding site, and modifies (positively or negatively) the effect of the ligand. Has no activity in absence of a ligand.
Where the output of the transducer varies with the input signal.
Negatively charged ion.
The electrode which conventional current flows into.
Method of myocardial autoregulation in which an increase in afterload causes an increase in contractility.
Drug which produces no response at the receptor, but prevents other ligands binding.
Ability of an organ to maintain homeostasis in the presence of dynamic physiological conditions.
A mixture of two substances that cannot be separated by fractional distillation, as each component shares same boiling point. This is typically temperature dependent.
Amount of acid that must be added to a solution to lower its pH to 7.4, at 37°C and with a PaCO2 of 40mmHg.
Degree of myocardial excitability. Used with either positive or negative bathmotropy.
The principle that in the spinal cord the dorsal roots are sensory and the ventral roots are motor.
The systematic distortion of the estimated intervention effect away from the “truth”, caused by inadequacies in the design, conduct, or analysis of a trial.
Electromagnetic radiation given off by all bodies at greater than 0°K. Wavelength of radiation emitted depends on the temperature of the body.
An increase in [H+] or PaCO2 decreases Hb affinity for O2.
- Boiling Point
The temperature at which the vapour pressure of a liquid equals the environmental pressure surrounding the liquid.
- Therefore boiling point decreases as environmental pressure falls, as there is less external pressure keeping molecules in their liquid state
- Boiling differs from evaporation as molecules anywhere in the liquid may enter the gaseous phase, whilst evaporation occurs only at the surface
Increase in contractility seen with an increase in HR. Also known as the Treppe effect.
Pressure of a gas is inversely proportional to volume.
Solution containing a weak acid and its conjugate base and will resist a change in pH when a stronger acid of base is added.
A process of checking a monitoring device for linearity of correlation between actual and measured values over a given measurement range.
Ability of a system to store electrical charge. Measured in Farads.
Central Blood Volume
Volume of blood in heart and lungs.
Increased responsiveness of nociceptive neurons in the central nervous system (i.e., post-synaptic) to their normal or subthreshold afferent input.
Movement of cells along a gradient of increasing concentration of an attracting molecule.
- Chronic Pain
- Persists beyond the time of tissue healing
- Frequently has no clearly identifiable cause
Volume of plasma completely cleared of a substance per unit time.
Coronary Blood Flow
At rest is ~5% of CO, or 225 ml.min-1, and may increase 3-4x during exercise.
Substance evenly dispersed throughout another solution in which it is insoluble.
- Colligative Properties
The properties of a solution that depend on the ratio of solute to solvent, and not on the type of molecules present. These include:
- Vapour pressure
- Boiling point
- Freezing point
- Osmotic pressure
Distensibility of a system. Expressed as the change in volume for a given change in pressure.
Describes the disproportionately rapid rise in Fi/FA ratio of nitrous oxide, as its rapid diffusion across the alveolar membrane increases the concentration of alveolar gas, and also augments respiration by drawing in dead space gas.
Time taken for plasma drug concentration to fall to 50% of its starting value after cessation of a drug infusion aimed to maintain a constant plasma concentration. Varies with the context, or duration, of drug infusion.
Factors affecting myocardial performance, independent of preload and afterload.
- Critical Length
The length of axon which must be blocked in order to prevent action potential transmission. It is dependent on myelination and fibre diameter.
- Critical Point
The point on a phase diagram where the liquid and gas phases of a substance have the same density, and are therefore indistinguishable.
- This point is where a substance is at both its critical temperature and critical pressure
Pressure required to liquefy a vapour at its critical temperature.
Temperature above which a substance cannot be liquified, irrespective of how much pressure is applied.
The volume occupied by a given amount of substance at its critical point.
Unit of mass equal to 1/12th of the mass of Carbon-12.
The partial pressure of a gas in a mixture is equal to the pressure that gas would exert if it occupied the volume alone.
- Dead Space
Inspired gas not participating in gas exchange. Includes:
- Apparatus dead space
Gas in the ventilator or breathing circuit.
- Anatomical dead space
Gas in the conducting zone of the lung.
- Alveolar dead space
Alveolar gas not participating in gas exchange. Also known as West Zone 1.
- Physiological dead space
Sum of alveolar and anatomical dead space.
- Apparatus dead space
Mass per unit of volume.
When a characteristic withdrawal syndrome occurs when a drug is withdrawn, or an antagonist administered.
Passive movement of a substance down an activity gradient by Brownian motion.
Fall in alveolar PAO2 due to dilution of alveolar gas by N2O diffusing from blood to alveoli.
Process of breaking down macromolecules into readily absorbed compounds.
- Doppler Effect
Alteration in frequency of a signal due to a relative difference in velocity between the emitter and observer. Detected frequencies will be:
- Higher if the emitter is moving toward the observer
- Lower if the emitter is moving away from the observer
Decrease in receptor number due to chronic agonist exposure.
A fixed deviation from the true value at all points in the measured range.
Substance administered to cause a change in a physiological system.
Where the same set of results are published in multiple journals. Academically unethical, and will cause a systematic bias in a meta-analyses as the same set of patients are included twice.
Force required to accelerate 1g by 1cm.sec-2.
Maximal effect produced by a drug. Analogous to intrinsic activity.
Graphical recording of the vector sum of cardiac electrical activity, as measured by electrodes on the skin.
A fine dispersion of minute droplets of one liquid in another in which it is not soluble or miscible.
A mixture of substances with the lowest possible melting point than any other mixture of the same substances (and lower than that of either substance).
How rapidly an excitable cell depolarises. Given by the gradient of phase 0 of the action potential, and is dependent on the function of voltage-gated sodium channels.
Mathematical function where the rate of change is proportional to the current value.
How well findings from one setting can be applied to another.
Decrease in apparent viscosity that occurs when a suspension (e.g. blood) flows through a tube of smaller diameter.
Metabolic state achieved after complete digestion and absorption of a meal prior to the onset of starvation.
Blood flow to an organ equals the uptake of a tracer substance by that organ, divided by the arterio-venous concentration difference.
Quantity of fluid passing a point per unit time.
- Fourier Analysis
Deconstruction of a complex waveform by separating it into its constituent sine waves. The slowest component is known as the fundamental frequency.
- Free radical
Extremely reactive molecular constituent carrying an unpaired electron.
- Freezing point
Temperature at which molecular movement begins.
- Functional Residual Capacity
Volume of gas in the lungs at the end of a normal tidal expiration, when the recoil pressure of the lungs equals the expansile pressure of the chest wall.
Device to measure electrical current, usually via deflection of a wire in a magnetic field.
Substance above its critical temperature.
Drug induced, controlled, and reversible production of unconsciousness.
Describes the tendency of diffusable ions to distribute themselves such that the ratios of the concentrations are equal when they are in the presence of non-diffusable ions.
The speed of diffusion of a gas through a membrane is inversely proportional to the square root of the molecular weight.
Deoxygenated blood forms carbamino compounds and buffers H+ better than oxygenated blood.
Time taken for drug concentration (typically in plasma) to fall by half.
Describes the transfer of thermal energy from one body to another body; measured in Joules.
Amount of gas dissolved in a substance is directly proportional to the partial pressure of gas at the gas-liquid interface.
Change in ventricular function based on myocardial fibre length. Also known as Starling's Law.
Mechanisms which alter myocardial performance independent of fibre length.
Chemical messenger secreted by a ductless gland and has action on a distant target cell.
Greater than normal amount of pain from a noxious stimulus. May be:
Occurring in the region of tissue damage, e.g. in an inflamed area around a wound.
Extending beyond the region of tissue damage.
When PaO2 is less than 60mmHg.
The point at which inadequate oxygenation of tissues results in anaerobic metabolism.
When the future state of a system depends not only on its current state, but on the states preceding it.
- Ideal Gas
A gas which will obey the ideal gas law. An ideal gas must have:
- Negligible intermolecular attraction
- A small molecular volume compared to the space between the molecules
An effect of a drug affecting only a small number of patients, typically due to the action of a particular metabolite.
Property of a conductor by which a change in current induces an electromotive force in the conductor and any nearby conductors.
Drug which alters myocardial contractility.
Maximal effect produced by a drug. Analogous to efficacy.
Resistance to alternating current.
Where a causal relationship between variables has been properly demonstrated, i.e. a lack of bias.
How easily an excitable cell can be stimulated. Given by how close the resting membrane potential is to threshold potential.
Compound with the same chemical formula, but different chemical structure or arrangement of atoms.
Line of constant temperature drawn on a pressure-volume graph for a gas, which describes the relationship between pressure, temperature, and volume for a particular gas.
Energy transfered to an object when it is acted on by 1N for 1m.
Flow occurring smoothly and without turbulence.
Drug which reversibly prevents the conduction of the nerve impulse in the region to which it is applied, without affecting consciousness.
The minimal alveolar concentration (measured in % of 1 atm) at steady state which prevents a movement response to a standard surgical stimulus (midline incision) in 50% of a population.
Device which measures gas pressure.
Mean Systemic Filling Pressure
The pressure measured anywhere in the systemic circulation when all flow of blood is stopped.
Amount of a substance which contains as many representative particles as there are atoms in 12g of carbon-12.
Number of moles of solute per kg of solvent.
Number of moles of solute per L of solvent. Varies with:
- Solvent density
- Solute volume
Frequency at which a system will oscillate at if disturbed and left alone.
Unpleasant subjective sensation associated with urge to vomit.
Pain caused by a lesion or disease of the somatosensory nervous system.
Neural process of encoding a noxious stimulus.
Estimate of risk, where the OR is the ratio of odds of an outcome in those treated vs. those not treated. OR = 1 suggests no effect, ≤1 suggests reduced risk >1 suggests increased risk.
Resistance which will allow one ampere of current to flow per volt of potential difference.
Naturally occurring substance with morphine-like properties.
Proportion of osmotic pressure due to colloid.
Describes any substance with activity at opioid receptors, and which can be reversed by naloxone.
Movement of a solvent across a semipermeable membrane to an area of greater solute concentration.
Pressure that must be applied to a solution to prevent the movement of a solvent from entering a solution with higher osmolality.
Volume of oxygen delivered to the tissues per minute.
The partial pressure at which an oxygen-carrying protein is 50% saturated.
Unpleasant sensory and emotional experience associated with actual or potential tissue damage, or expressed in terms of such damage.
Describe the relative affinity of an agent for two phases. It is defined as the ratio of the concentration of agent in each phase, when both phases are of equal volume and the partial pressures are in equilibrium at STP.
PO2 at which oxidative phosphorylation ceases.
Supra-atmospheric airway pressure at the end of expiration.
The power of hydrogen. Describes the activity of hydrogen ions in a solution, and is expressed as .
Load imposed on a muscle before contraction, and measured as the average myocardial fibre length at the onset of systole. May be approximated clinically using EDV.
The ability of a measurement device to provide reproducible results upon repeated measurement.
Temperature at which a gas mixture will separate into its constituent components.
Transfer of energy via electromagnetic radiation.
Component of a cell which binds to a ligand and results in a change in function.
Reaction which results in a gain of an electron.
Unconscious, predictable response to a stimulus.
Passive passage of gastric contents into the mouth.
Ratio of mass of water vapour in a given volume of air, to the mass required to saturate that volume at that temperature. Expressed as a percentage.
Respiratory Exchange Ratio
Ratio of CO2 produced to O2 consumed at any given point.
Ratio of CO2 produced to O2 consumed at steady-state.
Dimensionless index which predicts the likelihood of turbulent flow.
- Saturated Vapour
Vapour which is in equilibrium with its own liquid state, i.e. there are as many molecules entering the vapour phase as there there are those condensing into the liquid phase.
- A saturated vapour contains the least amount of energy possible without condensing
Saturated Vapour Pressure
Pressure exerted by a vapour which is in equilibrium with its liquid state. Increases with temperature, since as the kinetic energy (heat) content of molecules increase, more of them enter the vapour phase.
Second Gas Effect
Disproportionately rapid rise in FA/Fi ratio seen when an anaesthetic agent is co-administered with nitrous oxide.
The generation of a potential difference at the junction of two dissimilar metals, with its value dependent on the temperature of the junction.
Involuntary, oscillatory, muscular activity that augments metabolic heat production.
Blood entering the left side of the circulation without being oxygenated via passage through the lungs.
Density of a liquid, in mass per unit volume.
Specific Heat Capacity
Amount of heat energy required to raise the temperature of 1kg of a substance by 1°K without a change in state.
Describes the tendency of a fluid to minimise its surface area.
Particles of any phase dispersed in a liquid.
When two drugs interact to produce a greater effect than would be expected.
Average kinetic energy of molecules within a material, measured in degrees.
Conscious sensation of the physiological urge to drink.
- Time constant
Time it would take for an exponential function to complete if the initial rate of change continued. A process is:
- 63% complete at 1T
- 86.5% complete at 2T
- 95% complete at 3T
Effective osmolality of a solution. Given by the osmolality, minus the concentration of freely diffusable osmoles (in plasma, these are urea and glucose).
Device which measures pressure of liquid.
Device which changes a signal from one energy form to another.
Increase in contractility with an increase in HR. Also known as the Bowditch effect.
Irregular movement in radial, axial, and circumferential axes.
Forced expiration against a closed glottis.
Substance in a gaseous phase below its critical temperature.
Pressure experted by a vapour.
Amount of mixed venous blood that must be added to pulmonary end-capillary blood to give the observed arterial oxygen content.
Describes the tendency of a fluid to resist flow.
Potential difference which dissipates 1W of energy per 1A of current.
Volume of Distribution
Apparent volume into which a drug is distributed to produce the identified plasma concentration.