Indexes vs. “true” qualities

Background General principle: Observables concepts should represent qualities of the patient (or environment) + observation procedure Examples An X-ray image shows a fracture, not just black pixels where there should be white “Serum tests” (generally) inhere plasma Core body temperature vs. axillary temperature

Example BMI - 1 BMI WHO: “Body Mass Index (BMI) is a simple index of weight-for-height that is commonly used to classify underweight, overweight and obesity in adults. It is defined as the weight in kilograms divided by the square of the height in metres (kg/m2).” How would BMI be represented? What is the quality?

Example BMI - 2 'Body Height Squared' equivalentTo 'Calculated observable entity' and (SQUARE_OF some 'Body Height') 'Body Mass Index' equivalentTo 'Calculated observable entity' and (HAS_NOMINATOR some 'Body Mass') and (HAS_DENOMINATOR some 'Body Height Squared')

Example BMI - 3 'Body Mass Index v2' equivalentTo 'Observable entity' and (IS_ABOUT some ('Quality' and (PROPERTY_TYPE some 'Relative mass') and (INHERES_IN some 'Entire human body'))) and (IS_SPECIFIED_BY some ('Observation procedure' and (TECHNIQUE some 'BMI calculation')))

Example GFR - 1 GFR Glomerular Filtration Rate – related to renal function Wikipedia: “(GFR) describes the flow rate of filtered fluid through the kidney” Hard to measure accurately Different filtered substances have different properties – Creatinine Vs. Cystatin-C Various estimations are used (eGFR) The Estimated GFR calculation has a number of variables including age, race, gender. Some calculations include height and weight. There are a number of different ways to calculate eGFR –e.g. Cockcroft-Gault, abbreviated MDRD, Jelliffe using serum Creatinine as a marker and the serum cystatin C-based equations - (Larsson, Hoek, Filler, leBricon, Grubb and Orebro-cyst DAKO. http://ndt.oxfordjournals.org/content/23/1/154.full.pdf

Example GFR - 2 LOINC NPU The formula matters – between the commonly used formulas MDRD and Cockcroft-Gault the is something like a 30% difference in the calculated values (in favour of Cockcroft-Gault). MDRD also adjusts for race, so African Americans have a slightly higher eGFR than caucasians. Note LOINC makes use of the aric volume rate property (volume per unit time per unit), whereas NPU use volume rate.

Example GFR - 3 'Urine concentration' … INHERES_IN 'Urine' ... 'UrineSubstanceRate' equivalentTo 'Calculated observable entity' and (HAS_FACTOR some 'Urine concentration') and (HAS_FACTOR some 'Urine flow') 'GFR' equivalentTo 'Calculated observable entity' and (HAS_NOMINATOR some 'UrineSubstanceRate') and (HAS_DENOMINATOR some 'Plasma concentration') Note : this doesn’t accurately reflect the formula and there is no mention of which formulae this observable applies to.

Example GFR - 4 'GFR v2' equivalentTo 'Observable entity' and (IS_ABOUT some ('Quality' and (PROPERTY_TYPE some 'Volume rate') and (INHERES_IN some ('Substance' and (IS_OUTPUT_OF some ('Glomerular filtration' and (HAS_AGENT some 'Kidney'*) and (HAS_DURATION some 'Time frame'))))) This is a generic GFR observable * or ' 'Nephron' or 'Parenchyma'...

Example GFR 5 'eGFR, MDRD formula' equivalentTo 'Observable entity' and (IS_ABOUT some ('Quality' and (PROPERTY_TYPE some 'Volume rate') and (INHERES_IN some ('Substance' and (IS_OUTPUT_OF some ('Glomerular filtration' and (HAS_AGENT some 'Kidney'*) and (HAS_DURATION some 'Time frame'))))) (SPECIFIED_BY some ('Observation procedure' and (TECHNIQUE some 'MDRD formula'))) Nice way of pushing the complexity out to the Procedure.

Cardiac Indices - overview Doppler echocardiography enables noninvasive determination of blood velocity and flow area through which quantitation of blood flow in vessels and across valvular orifices can be achieved. The stroke volume is rendered as the product of the flow area and the area beneath the velocity curve; on taking the heart rate into consideration, the cardiac output can be calculated. (Herz. 1986 Oct;11(5):258-68. Determination of cardiac output by Doppler echocardiography: a critical appraisal. Zoghbi WA, Quinones MA.) CO indexed to body surface area (BSA) or cardiac index (CI), is an important clinical parameter used in the assessment of patients with heart disease as well as critically ill patients and patients under anesthesia. CI is also of interest in pharmacological studies [2] and the definition of forward failure in patients with heart failure is a decrease in CI. http://www.jcmr-online.com/content/pdf/1532-429X-14-51.pdf Techinques for measuring cardiac output include Doppler Echocardiography and CMR (Cardiovascular Magnetic Resonance)

Cardiac indices Systolic index (ml/m2)= Stroke volume / body surface area Cardiac output (l/min) = Stroke volume x Heart Rate Cardiac index (l/min/m2) = Cardiac output / body surface area There are a number of indices in echocardiography Cardiac index is similar to eGFR in that the property it is measuring is volume rate per Body surface area

Systolic Index as a process All of these indices can be modelled as either a process or a quality (using the IS_OUTPUT_OF object property)

Systolic index as a quality

Cardiac output as a process

Cardiac output as quality

Cardiac index – built in calcn Modelling the index using calculation based on two observable entities

Cardiac Index – using technique Modelling the index using the procedure ‘technique’ part

Lung functions – FEV1/FVC ratio e.g. 1 'FEV1/FVC' equivalentTo ('Ratio observable entity' and (HAS_NOMINATOR some 'Forced expiratory volume, first second') and (HAS_DENOMINATOR some 'Forced vital capacity')) This is a lung function calculated observable defined as “standardisation of FEV1 for expired volume”, Where FEV1 is the forced expiratory volume in one second

FEV1/FVC e.g. 2 ‘FEV1/FVC’ equivalentTo 'Observable entity' and (IS_ABOUT some ('Quality' and (PROPERTY_TYPE some 'VolumeRatio') and (INHERES_IN some ('Air' and (IS_OUTPUT_OF some ('Expiration process' and (HAS_DURATION some 'Maximal expiration period')))) and (PRECONDITION some 'Maximal inspiration'))) and (SPECIFIED_BY some ('Observation procedure' and (TECHNIQUE some ‘FEV1/FVC ratio formula'))))) This pushes the complexity out to the procedure and technique part of the model