Definitions Flashcards
Absorption
Absorption - rate & extent to which a drug leaves its site of administration.
The rate and extent of drug movement from the site of administration to the systemic circulation
Acid
Arrhenius
Bronsted-Lowry
Lewis
Acid – proton donor or substance that increases [H+] of a solution
Arrhenius: a substance which is capable of producing hydrogen ions in an aqueous solution
Bronsted-Lowry: a substance which can donate a hydrogen ion to another substance
Donor = conjugate acid
Acceptor = conjugate base
Lewis: any compound that was a potential electron pair acceptor
Additive effect
Additive effect - second drug, acting with the first, produces an effect equal to the algebraic sum of the effects of each drug when administered individually (1 + 1 = 2)
Afterload
Afterload - load the heart is acting against during systole, gives rise to active tension in ventricular wall
- Isolated: force restricting muscle fibre shortening or weight/load that a contracting muscle must overcome prior to shortening.
- Intact: either the stress imposed on the ventricular wall during systole or the arterial impedance to ejection of the stroke volume.
Agonist
Agonist - A drug that binds to a receptor of a cell and triggers a response by the cell. An agonist often mimics the action of a naturally occurring substance.
Full – able to evoke maximal biological response
Partial – can exert a submaximal response despite high doses
Alkaloid
Alkaloid – nitrogen containing base of plant origin
Antagonistic effect
Antagonistic effect - second drug, acting with the first, produces an effect less than the algebraic sum of the effects of each drug administered individually (1 + 1
Baricity
Baricity – density of one solution compared to another
density (mass / volume) of liquid relative to CSF (CSF baricity = 1)
Base
Base – proton acceptor or substance that decreases [H+] when added to a solution
Bioavailability
Bioavailability – the fraction of administered dose which reaches the systemic circulation as intact drug (fraction absorbed x (1-ER)
The rate and extent to which a drug reaches its site of action (or plasma) from its site of administration
Bioequivalence
Chemical
Biological
Therapeutic
Bioequivalence - refers to two formulations of that yield similar concentrations in blood and Tx’s.
Chemical: meets chemical and physical standards
Biological: yields same concentrations in blood and tissue
Therapeutic: provides equal therapeutic benefit
Biophase
Biophase – the zone in which the drug comes into intimate contact with its molecular site of action
Buffer
Buffer – solution containing substances that have the ability to minimize pH changes when an acid or base is added to it
A solution which has the ability to minimise changes in [H+] when an acid or base is added to it.
Clearance
Clearance – volume completely cleared of a substance per unit time (note total body, organ specific)
- the volume of fluid from which a substance is completely removed per unit time (eg. via passage through an organ).
Concentration effect
Concentration Effect – the effect of increasing Fi of agent accelerating the equilibrium of PA/PI, consisting of concentrating component and augmentation component.
The effect which the inspired concentration of the anaesthetic agent exerts on the speed with which that agent attains equilibrium
The higher the inspired concentrations, the more rapid the rise in alveolar concentration
Context senstive half-time
Context sensitive half time – time required following cessation of an infusion designed to maintain a constant plasma concentration, of a given duration (the context) for plasma levels to fall by 50%.
Dead space
Dead space – part of the tidal volume that does not participate in gas exchange
Physiological dead space is divided into alveolar and anatomical:
- Anatomical - the internal volume of the conducting airways or that part of the inspired TV which is expired unchanged.
- Alveolar - Part of inspired gas which passes through the anatomical dead space and enters the alveoli but is not effective in gas exchange given
Apparatus dead space is volume rebreathed from apparatus before fresh gas enters patient airway.
Dependence
Dependence
Psychological – Need for a specific psychoactive substance either for its positive effects or to avoid negative psychological or physical effects associated with its withdrawal
Physical – a physiological state of adaptation to a specific psychoactive substance characterized by a withdrawal syndrome during abstinence, which may be relieved in part or in total by readministration of the substance
Density
Density – weight in grams of 1mL of that solution at STP, mass per unit volume (see universal gas law for gasses)
Drug
Drug - a chemical substance that produces an effect on a biological tissue.
Effect site equilibration time
Effect site equilibration time – time taken for equilibration b/w [drug] in plasma and biophase following an IV bolus
Elimination half time
Elimination half time – time taken for 50% fall in plasma conc during elimination phase – upper limit on how long it will take plasma conc. to fall (0.693 x Cl/VD)_
Emulsion
Emulsion – stable suspension of small globules of 1 liquid in a 2nd liquid
Emulsifier
Emulsifier – surface active agent that promotes the formation of an emotion
Eutetic mixture
Eutetic Mixture – a mixture of constituents at a ratio that produces the lowest temperature melting point
Half life
Half life - time required for elimination of 50% of drug from the body
Time necessary for drug concentration to fall by half whether by redistribution or elimination etc
Half time
Half time – time taken for plasma levels of drug to fall by 50% (0.693 x Cl/VD in single compartment model)_
Hepatic extraction ratio
Hepatic Extraction Ratio – proportion of drug irreversibly removed from each unit volume of blood during a single passage through the liver (0-1)
Hyperactivity
Hyperactivity - usual response achieved at lower than normal dosage (supersensitivity if denervated)
Hypersensitivity
Hypersensitivity - usually implies allergy to the drug
Describes an exaggerated or inappropriate immune response that cause tissue damage and even death of the host
Type I: antigen binds to mast cell IgE, resulting in degranulation (eg. Hay fever, anaphylaxis)
Type II: antibody-antigen reaction, resulting in complement activation and antibody-dependent cell-mediated cytotoxicity (eg. Transfusion reactions)
Type III: deposition of antigen-antibody complexes in the host tissue (eg. Serum sickness)
Type IV: (Delayed hypersensitivity) results from antigen presentation to T lymphocytes causing a release of cytokines. (eg. TB)
Hyporeactivitiy
Hyporeactivity - usual response achieved at larger than normal dosage
Idiosyncrasy
Idiosyncrasy - unusual effect (qualitative difference or extreme quantitative difference) of a drug, usually unrelated to dose, occurring in only a small percentage of patients.
Immunity
Immunity - decreased sensitivity as a result of Ab formation
Inotrope
Inotrope: drug affecting force of muscle contraction (usually used w/ respect to +ve inotropes). Many (though not all) sympathomimetics are useful as inotropes.
Local anaesthetic
Local Anaesthetic - drug producing reversible depression of nerve conduction when placed in close proximity to nerve fibres
Drugs that block, reversibly, the conduction of impulses in the peripheral or central nervous system when applied locally or regionally.
Metabolic rate
Metabolic rate – energy expended per unit time (basal equals 12 hours of fasting at rest)
MAC
Minimum Alveolar Concentration (MAC) – agent at 1 atm preventing gross purposeful movement to supramaximal stimulus in 50% of patients
Minimum alveolar concentration at one atmosphere of an agent that produces immobility in 50% of those subjects exposed to a noxious stimulus
Qualified clinically by: 100% O2, no premedconversionj to a partial pressure, as percentage of 1atm which then represents the tension of anaesthetic at the site of action in the brain; patient aged 25-35yrs
Minimum concentration
Minimum Concentration (Cm) – the minimum conc of LA necessary in vitro to block conduction of all nerve impulses in a given nerve w/n a reasonable time period (usu 10 – 15/60)
Mixed venous blood
Mixed venous blood – blood drawn from pulmonary artery, thus containing entire venous return from systemic circulation and attendant oxygen extraction and carbon dioxide addition
Mixture
Mixture – physical combination of 2 or more substances, each retaining its own properties
Nausea
Nausea – and unpleasant objective sensation referred to the pharynx and upper abdomen assoc with desire to vomit
Unpleasant subjective sensation referred to the pharynx and upper abdomen, associated with a desire to vomit.
Opiate
Opiate – drugs derived from opium
strictly substances derived from Opium ie naturally occurring opioids.
Opioid
Opioid – all exogenous substances that bind specifically to any subtype of opioid receptor to produce some agonist effect
Opioid, endogenous – endorphins, dynorphins, enkephalins
Opium
Opium – dried powdered mixture of alkaloids from unripe seed capsules of Papaver sominiferum (opium poppy)
Pain
Pain - an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage
Physiological pain – operates as a protective system, warning of contact with potentially damaging stimuli. Different receptors (low threshold for innocuous stimuli, high threshold nociceptors) allow such differentiation.
Pathological pain – pain associated with tissue damage or damage to nervous system. Prolonged stimulus causes modification of threshold of nociceptors, hyperalgesia and allodynia.
Acute pain – pain of recent onset and probable limited duration; usually with causal and temporal relationship to injury or disease.
Chronic pain – (usu >3 months) commonly persisting beyond the time of healing of an injury and may not have a clearly identifiable cause.
unpleasant sensory and emotional experience associated with actual or potential tissue damage, or expressed in terms of such damage.
Partition coefficient
Partition coefficient – ratios of concentration of dissolved agents present between two phases at a given temperature at equilibrium (equal partial pressures)
Ratio of amount of gases in two phases, at equilibrium, at stated temperature
Pharmacogenetics
Pharmacogenetics – study of hereditary (genetic) factors in variability of drug response
Preload
Preload - load on the myocardial m’s just prior to the onset of cxn. & determines the end diastolic fibre length prior to onset of contraction.
PRELOAD
- Isolated: load imposed on muscle before contraction, obtained by hanging a small weight at the end of resting muscle.
- Intact: ventricular wall tension at end diastole, determined by EDV, EDP and wall thickness, and approximated by PAWP/CVP.
Potentiation
Potentiation - a non-toxic agent ’ing the toxicity of a toxic agent.
Receptor
Receptor - the molecules of a biological target with which a drug reacts to produce its biological effect
Regurgitation
Regurgitation – passive, not reflex and not forceful
Retching
Retching – may precede vomiting, involves rhythmic contraction of same muscle groups, without expulsion of contents
Second gas effect
Second gas effect – high volume uptake of one agent (N2O usually) to increase the rate of increase of Fa/Fi of a second gas (classically volatile but also O2).
Uptake of one agent can increase the rate of uptake of a second agent
Sensitisation
Sensitization (Reverse tolerance) - acquired hyperactivity due to prior exposure to a drug.
Shock
Shock - physiologic state characterized by a significant reduction in systemic tissue perfusion, resulting in decreased tissue oxygen delivery
Sleep
Sleep – imperative, natural, periodic state of reversible unconsciousness, rousable by sensory stimuli
Solubility
Solubility – amount of specific substance that will dissolve in each vol. of a specified liquid at specified temp and pressure
Solution
Solution – homogenous mixture
Specific gravity
Specific Gravity – ratio of density of a solution compared to water
Suspension
Suspension – heterogenous mixture
SVR
SVR - resistance or impediment of the systemic vascular bed to blood flow, mainly from arterioles
Synergistic effect
Synergistic effect - second drug, acting with the first, produces an effect greater than the algebraic sum of the effects of each drug administered individually (1 + 1 > 2).
Sympathomimetic
Sympathomimetic - sympathomimetic drugs are those which evoke similar responses to those produced by the endogenous activity of the symp. NS.
Tachyphylaxis
Tachyphylaxis - acquired hyporeactivity that develops rapidly (mins/hrs) after only a few doses of a drug.
Rapid deterioration in response to repetitive administration of a pharmacologically active substance.
Tolerance
Tolerance - acquired hyporeactivity over time (days-wks) due to prior exposure to the drug (or another related drug => cross tolerance)
The demonstration of decreased receptor response to a given concentration of agonist
The need to increase the dose of (opioid) agonist to achieve the same (analgesic) effect previously achieved with a lower dose
Vapour
Vapour – gaseous state of a substance that is in equilibrium with the liquid or solid state, which is capable of forming a solid or liquid at the temperature of the vapour (Ie below critical temperature)
The gaseous form of a substance when the ambient temperature is below its critical temperature
Viscosity
Viscosity – fluids resistance to flow (ration of shearing stress to velocity gradient), fluids think honey, but gases get more viscous with increasing temperature
Vomitting
Vomiting – forceful expulsion of gastric contents via mouth, a survival reflex to expel toxins
Volume of distribution
Volume of distribution – the apparent volume which a drug would occupy if all of the drug present in the body distributed uniformly at the concentration present in the blood
Absolute humidity
Weight of H2O vapour in one litre of gas
Units: mg/L or gm / m3
0C= 4.8ml/l, 20C = 17mg/l, 37C = 44mg/l
Adabiatic change in state of a gas
In an isolated system, occurs when a change in pressure or volume results in a change in temperature.
Eg. If a compressed gas expands adabiatically, cooling occurs
Adaption
The temporal progressive reduction in the rate of firing of receptors in response to a continuous sensory stimulus
Eg. Adaption of pressure receptors on bum
Ageing
A normal physiological process of degeneration beginning around 30 and proceeding at a variable rate, with obvious changes becoming apparent around 60, and the end point being death.
Allodynia
Innocuous stimulus leading to pain
Alveolar dead space
That part of the inspired gas, which passes through the anatomical dead space to mix with alveolar gas, but is not perfused with blood and does not contribute to gas exchange. i.e. ventilated but not perfused alveoli
Alveolar gas equation
PAO2=PIO2 – PACO2/R + F
Ampere
A current which if maintained in two straight parallel conductors of infinite length and negligible cross section, placed one metre apart in a vacuum would produce between these conductors a force equal to 0.20 N/m of length
Amphipathic
Part hydrophilic, part hydrophobic
Analysis of variance (ANOVA)
A parametric test used to compare the means of two or more groups
Anaphylactic reaction
An acute hypersensitivity reaction which occurs in patients previously sensitised to the particular antigen.
Mediated by IgE attached to mast cells
Anaphylactoid reaction
Due to direct release of mediators (complement or direct histamine release) from the mast cells by the action of the causative drug or agent
Anatomical dead space
Volume of gas in airways excluding alveoli
Measured by Fowler’s method.
Antigen
A substance capable of stimulating the immune system of the host to produce a specific response to it.
Apparent volume of distribution
The imaginary volume into which a drug would need to distribute so that it has the same concentration as plasma
Autonomic nervous system
Efferent pathway controlling action of involuntary organs and tissues. Main function is homeostasis
Avagadro’s hypothesis
Equal volumes of gases at equal condition of pressure and temperature contain equal number of particles
Bainbridge reflex
Atrial reflex control of HR
Increase in atrial pressure causes increase in HR – stretch receptors transmit afferent signal through vagus to medulla
- infusion of blood or saline in
normovolemic subject causes reflex increase in HR independent of ↑BP
Bartter’s syndrome
Idiopathic hyperplasia of JG cells
Associated with hypokalaemia and increased levels of renin, AII, and aldosterone, but with normal BP
Bezold-Jarisch reflex
Coronary chemoreflex
Injection of vasoactive chemicals into coronary artery leading to apnoea, followed by rapid breathing, hypotension and bradycardia
Bias
Systemic deviation from the truth
Binomial distribution
Exists if a population contains items which belong to one of two mutually exclusive categories (eg male or female)
Biotransformation
The enzymatic conversion of a drug into a more polar, less lipid soluble molecule which is suitable for excretion
Phase I: oxidation, reduction, hydrolysis
Phase II: glucuronidation, sulphation, aceylation
Blood/gas solubility or partition coefficient
Also called “Ostwal solubility coefficient”
The ratio of the concentration of dissolved gas to the concentration in the gas phase at equilibrium
Determines the induction time
Bohr effect
Alteration of blood pH changes haemoglobins oxygen carrying capacity
rightward shift of the oxyhaemoglobin curve with ↑H+ concentration and ↑PCO2 reflecting lower affinity of Hb for oxygen.
Boiling point
The temperature at which its saturated vapour pressure becomes equal to ambient pressure
Temperature at which liquids becomes gases
Boyle’s Law
At a constant temperature the volume of a given mass of gas varies inversely with the absolute pressure
for a given mass, provided the temperature is constant, the volume is inversely proportional to pressure
→ V x P = K
Buffer power
buffer power = d{B+}/dpH
Here d[B+] = change in concentration of base
dpH = change in pH
Bulbs of Krause,
Ruffini
Krause: cold thermoreceptors in dermis
Ruffini: heat thermoreceptors in dermis
Candela
The luminous intensity of a surface of 1/600,000m2of a black body radiator at the temperature of freezing platinum under a pressure of 101,325 kPa
Capnography
The graphical measurement of CO2 vs time
Carotid chemoreceptor reflex of BP control
Decreased perfusion pressure reduces oxygenation, leading to increased pCO2 and stimulation of the vasomotor center of the brain stem, via Hering’s and vagus nerves.
Case control study
An observational study that begins with a definition of the outcome of interest and then looks backward in time to identify possible exposures, or risk factors, associated with that outcome.
Central limit theorem
As the sample size increases, the shape of the sampling distribution approaches normal shape, even if the distribution of the variable in question is not normal.
Charle’s Law
At a constant pressure the volume of a given mass varies directly with the absolute temperature
Chemoreceptor
Those receptors that are stimulated by a change in the chemical composition of the environment in which they are located
Chi square (X2) (Pearson’s)
Used to compare independent groups of categorical data
X^2 = sum (O=E)^2/E
where: O= observed number in each cell; E= the expected number in each cell
Chiral molecule
Describes a molecule that has a centre (or centres) of three-dimensional asymmetry (eg. C, N, S)
Clark’s occupancy theory
There is a dynamic reversible relationship between drug and receptor
Coagulation
Coagulation is a biological amplification system in which a few initial substances activate, by proteolysis, a cascade of circulating precursor enzymes.
Cockcroft-Gault formula
Creatinine clearance = ({140-age} x wt in kg)/[814 x serum cr]
multiply 0.85 for females.
Coefficient of variation
SD/mean
Cohort study
A cohort study observes a group of patients forward in time in order to record their eventual outcome.
Colligative properties
Properties of a solution that depend only on the particle concentration.
Ie the number of particles per unit volume
They are: vapour pressure depression, freezing point depression, boiling point elevation, osmotic pressure
properties of a solution that depend only on the number of freely moving particles and not on the nature of those particles. eg osmotic pressure, freezing point depression, vapour pressure.
Conduction
Transfer of heat at a molecular level. (cannot occur in a vacuum)
Q=KA(t1-t2)/d
Where: Q=heat loss
A= area of transfer
d= thickness of material over which heat has to travel
K= thermal conductivity of the substance
Confidence limits
The lowest and highest values of the CI
Confounding
Effect of imbalance and effect on outcome
Constitutional or structural isomers
molecules with the same empirical formulae whose atoms are connected to each other in a different sequence.
Eg. Isoflurane, enflurane
Contractility
A property of cardiac muscle which defines the work the heart can perform at a specified load.
Convection
A process of heat transfer through a stream of fluid. (Cannot occur in vacuum)
CP50
Plasma concentration required to produce a response in 50% of the population (or to produce a half-maximal effect)
CP95
Plasma concentration required to produce a response in 95% of the population (or to produce 95% of maximal effect)
Critical pressure
Minimum pressure for liquefaction at critical temperature
The vapour pressure of a substance at its critical temperature.
Critical temperature
The temperature above which a gas cannot be compressed into a liquid no matter how high the pressure is increased
Nitrous oxide 36.5 dC
O2 -119 dC
CO2 31 dC
Cushing reflex
Hypertension, bradycardia secondary to an increased ICP
When ICP is increased, the blood supply to the vasomotor area is compromised, and the local hypoxia and hypercapnoea increases its discharge. The resultant rise in BP restores the blood flow to the medulla, but the HR decreases due to the baroreceptor response.
Dalton’s law of partial pressure
In a mixture of gasses the pressure of each gas is the same as that would be exerted if it alone occupied the container.
the pressure exerted by a mixture of gases (or gases and vapour) is equal to the sum of the pressures which each gas would exert if occupying the same space alone.
NB at high pressures, the compressibility of some gases causes deviations in behaviour from predicted values.
Defaecation
The active expulsion of rectal contents to the external environment
Descriptive statistics
Describe a collection of data (mean, median, standard deviation, variance)
Dew point
The dew point is the temperature to which a gas must be lowered in order for water to condense from it. Ie the partial pressure of water vapour equals the saturated vapour pressure
Dibucaine number
Refers to the % inhibition of the esterase (in hydrolysing benzoyl choline) by Dibucaine 10-5 (Nupercaine) The D gene is resistant to inhibition.
Normal activity > 70%, atypical activity
Diffusional hypoxia
Fink effect
Returning N2O displaces the alveolar O2 from the lungs, lowering the alveolar O2 concentration
Distribution
The movement of drug from the systemic circulation to other body compartments
Drug interaction:
Additive
Synergistic
Antagonistic
Additive: the effect of a drug combination is the sum of the effects of each drug (eg potent volatiles)
Synergistic: the effect of a drug combination is greater than the sum of the effects of each drug (eg.opioids and volatiles)
Antagonistic: the effect of a drug combination is less than the sum of the effects of each drug
Eaton-Lambert effect
Myasthenic syndrome – muscle weakness caused by antibodies to presynaptic Ca2+ channels at nerve ending, thus preventing ACh release
ED50
Dose required to produce a response in 50% of the population (or to produce half-maximal effect)
ED95
Dose required to produce 95% depression of the twitch response of the adductor pollicis muscle to stimulation of the ulnar nerve.
Efficacy
The strength of the drug-receptor interaction in causing effect. It describes the response to a certain % receptor occupancy.
Electroencephalogram (EEG)
A continuous register of the summated electrical activity of the brain recorded by electrodes on the scalp
EMF (alternate Nernst equation)
EMF(mv) = +- 61.5log ([] inside/[ ] outside) (at 37 degrees C)
enantiomer
(substances of opposite shape)
a pair of molecules existing in two forms that are mirror images of one another (right and left handed) but cannot be superimposed. Eg. S- and R- bupivacaine
enantiomers and diastereoisomers are subtypes of stereoisomers.
Endocrine gland
Organs that secrete specific substances (hormones) which are released directly into the circulatory system and which influence metabolism and other body processes.
Endocrine system
The system of glands and other structures that elaborate internal secretion (hormones) which are released directly into the circulatory system and which influence metabolism and other body processes
Epidemiology
The study of disease in populations
Excretion
Irreversible elimination of the drug or its metabolites from the body
Exponential function
One where the rate of change of a variable is proportional to the magnitude of the variable
Fenn effect
The greater the amount of work performed by the muscle, the greater the amount of ATP that is cleaved
FEV1
Fraction of the vital capacity expired during the first second of a forced expiration
Fick principle
The amount of a substance taken up by an organ per unit of time is equal to the arterial level of the substance minus the venous level (a-v difference) times the blood flow
Fick’s law of Diffusion
rate = permability coefficient x (C1-C2) x (area/thickness)
First pass effect
Occurs when orally-administered drugs enter the systemic circulation in concentrations that are much lower than if the drug was administered systemically. Eg. Betablocker doses o vs iv
Fisher’s exact test
For use in 2x2 tables, when one or more of the variables
Fluoride number
Refers to the % inhibition of the esterase by fluoride 5 x 105M
Free water
The amount by which the water content of a solution (eg. Urine) exceeds that needed to form a solution isosmotic with plasma
Functional residual capacity
Volume of gas in the lung after a normal expiration
Equals ERV+RV = 0.7+1.1 = 1.8l = 30ml/kg
Gain
The ratio of the secondary change evoked by a given mechanism to the initiating change itself
Gas
The gaseous form of a substance when the ambient temperature is above its critical temperature
Gastro-ileal reflex
Raised secretory and motor activity in stomach increases ileal activity
Gaussian distribution
Normal distribution curve
GFR
GFR = Uw x V / Pw Uw = urine conc of W V = urine volume per unit time Pw = arterial plasma concentration
Goldman equation
Used to calculate the magnitude of the resting membrane potential (RMP)
Dependent on the concentrations and the permeability for each ion species present.
Graham’s law
Rate of diffusion varies with the inverse of the square root of molecular weight
the ratio of diffusion of gases through certain membranes is inversely proportional to the square root of the molecular weight.
Haemopexin
Binds to haem when haptoglobin is saturated
Hair hygrometer
A hair is attached to a dial via a system of levers, and lengthening of the hair is linear with increasing humidity. Accurate over the 30-90% range of relative humidity
Haldane effect
As Hb releases O2 it can carry more CO2 without a rise in pCO2
Deoxygenation of blood increases its ability to carry CO2 since the reduced form of Hb better buffers H+ (more CO2 transported as bicarbonate) and binds CO2 as carbamino groups.
Haptoglobin
An α2-globin. Binds to the globin moiety of free haemoglobin that may be in the plasma
Hawthorne effect
The actual process of study (patient explanation, informed consent, measurement, follow-up) may result in more favourable outcomes in such patients.
Heat
The energy which can be transferred from an object at a higher temperature to one at a lower temperature
A manifestation of the level of molecular kinetic energy present in a substance
Henderson-Hasselbalch equation
pH = 6.1 + log ( HCO3-/ {0.03 Pco2}) pH = pKa + log [HCO3]/ (0.03 x pCO2)
Henry’s law
The concentration of a gas in a liquid is proportional to its partial pressure
Hering-Breuer reflex
Inflation reflex: increase in duration of expiration produced by steady lung inflation
Hormone
A chemical substance that is secreted into the body fluids by one cell or a group of cells that exerts a physiological control effect on other cells of the body
Peptide hormone: hypothalamus, pituitary, pancreas, parathyroid, gut, heart
Amines: thyroid, adrenal medulla
Steroid: sex hormones, adrenal cortex.
Humidity
Amount of water vapour present in air
Hyperalgesia
Mildly painful stimulus leading to severe pain
Immune system
A series of complex cellular and humoral elements that can interact with many different types of foreign molecular structures (antigens) to provide host defence against foreign substances
Incidence
The number of individuals who develop a disease (ie new case) in a given time period
Inferential statistics
That branch of statistics where data are collected and analysed from a sample to make inferences about the larger population (using parametric and non-parametric tests.)
Inspiratory capacity
Maximal inspiration following passive expiration
IC=TV+IRV = 7ml/kg + 45ml/kg = ~50ml/kg
Inspiratory reserve volume
Air inspired with a maximal inspiratory effort in excess of the tidal volume.
45ml/kg
Intestino-intestinal reflex
Over distension of one segment of intestine relaxes the rest of the intestine
Intracranial pressure
The pressure within the cranial vault relative to atmospheric pressure (gauge pressure)
Intravenous anaesthetic agent
A drug or combination of drugs which will induce anaesthesia, safely and reversibly, when injected in sufficient doses and which could also be given intermittently or by infusion for maintenance
Ionic permeability
Net quantity of ion that will diffuse across each unit area of the membrane per unit [ ] gradient
Isohydric principle
An assessment of the concentrations of any one acid-base pair can be utilised to provide a picture of overall acid-base balance in the body.
Isomer
Constitutional: compounds with the same empirical formulae whose atoms are connected to each other in a different sequence. Eg. Isoflurane, enflurane
Stereoisomers: molecules that not only have the same empirical formula but which also have the atoms attached in the same sequence. They differ, however, in the three-dimensional arrangement of those atoms.
Enantiomers: mirror images: eg. S- and R- bupivacaine
Diastereoisomers: oriented around a carbon double bond: eg. Atracurium.
Kelvin
The fraction 1/273.16 of the triple point of water (that temperature at which water can exist as solid and gas = 0.16 dC
Kilogram
The mass of the international prototype kilogram kept at the international Bureau of Weights and measures in France
Kruskal-Wallis test
A non-parametric equivalent of ANOVA
La Chatelier Effect
Shift in equilibrium of carbonic anhydrase reaction to CO2
H+ + HCO3= H2O + CO2
Lambert-Beer Law
There is a non linear, power relationship between the light intensity transmitted, and the incident light intensity
It=Iie-A
the intensity of light passing through a solution decreases exponentially with the concentration of solute and distance traveled through solution
I trans = I incident e^-A
A = DEC
(A = absorption)
D = distance, E = extinction coefficient, C= concentration
Laminar flow
Q proportional to [pi (P1-P2) r^4] / 8nl
n = viscosity (poises)
l = length of tube in cm
Q = flow of gas (ml/sec)
Note that flow is proportional to pressure drop, and to the radius to the power of 4, and inversely proportional to viscosity and length.
Laplace’s law
The equilibrium relationship between transmural pressure difference, wall tension, and radius of curvature in a concave surface, for a sphere: dP=2T/R; for a cylinder: dP=T/R
In a cylinder, for a constant internal pressure, wall tension varies directly with the radius
In a sphere, for a constant internal pressure, wall tension increases at twice the rate as the radius.
Latency
Time from drug introduction to onset of action
Latent heat
The amount of heat required to change the state of a substance, when it is at the temperature required to change state.
Latent heat of vapourization
The amount of heat required to change a liquid to the gaseous phase.
Lissauer’s tracts
Collections of axons that can travel up or down 1-2 segments
MAC awake
MAC at which consciousness is regained or at which 50% of patients will respond to a simple command.
Useful to predict recovery, usually ~0.6 MAC
MAC-95
MAC absolving 95% of the reflex response
MAC-BAR
MAC that blocks adrenergic response in 50% of patients
NA used, measuring BP & HR
MAC required to block adrenalin response (BP and HR increase mediated by catecholamines) in 50% of patients exposed to standard stimulus.
MAC-hr
Duration of exposure to 1 MAC of agent