Paper 5 Answers
James Day, Amy Thomson, Tamsin McAllister, Nawal Bahal in Get Through, 2014
The Fick principle states that the amount of substance taken up by an organ per unit time is equal to the arterial concentration minus the venous concentration of the substance, multiplied by the blood flow through the organ. This can be used to calculate flow (or cardiac output), where: or where Q = blood flowVO2 = oxygen consumptionCA = oxygen content of arterial bloodCV = oxygen content of venous blood
Non-invasive physiological monitoring
John Edward Boland, David W. M. Muller in Interventional Cardiology and Cardiac Catheterisation, 2019
Arterial and venous blood sampling and blood oxygen quantification can provide Ca and Cv. VO2 can be measured as the difference of inspired and expired oxygen (see Chapters 16 and 17). The Fick principle can be applied to any gas that diffuses easily in blood. Various devices use gas rebreathing to estimate arterial and venous levels of the gas. Measurement of inspired and expired carbon dioxide can provide cardiac output estimation without blood sampling,16 but this technique suffers from accuracy problems at higher pulmonary shunt levels.17 Rebreathing a combination of two inert gases (nitrous oxide, soluble in blood, and sulphur hexafluoride, insoluble in blood) allows for correction for pulmonary shunt and has good agreement with other estimates of cardiac output such as thermodilution, the Fick principle by oxygen measurement and cardiac magnetic resonance imaging.18 Measurements of cardiac output using the Fick principle are not useful for continuous monitoring purposes, but it is a relatively easy, if demanding, non-invasive method to estimate cardiac output at a single point in time.
Gas Exchange in the Lungs
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal in Principles of Physiology for the Anaesthetist, 2020
Quantitative assessment: Measurement of shunt using the shunt equation or estimating of shunt using iso-shunt lines.Measurement of dead space using Bohr equation.The multiple inert gas elimination technique (MIGET) test is a technically demanding and laborious one used only in research laboratories. Six tracer gases with different blood-gas solubilities (ranging from very soluble [acetone] to very insoluble [sulphur hexafluoride]) are dissolved in saline and administered intravenously as a constant infusion. When a steady state is reached, the levels of the tracer gases in arterial blood are measured and levels in the mixed venous blood are derived using the Fick principle. Retention and elimination of each tracer gas are determined by the blood-gas solubility. The results of this technique are plotted as amount of ventilation and the amount of perfusion against V/Q ratio (i.e. they tell us how much blood or air is coming from a region with a particular ratio).
Percutaneous ASD closure of children weighing less than 10 kg
Published in Acta Cardiologica, 2020
Nazmi Narin, Osman Baspinar, Ozge Pamukcu, Suleyman Sunkak, Aydin Tuncay, Onur Tasci, Ali Baykan
The ratio of pulmonary blood flow to systemic blood flow (Qp/Qs) was calculated based on the Fick principle. Percutaneous ASD closure was done by the technique that has been published previously [4]. Successful implantation was defined as the device being properly placed and deployed without malposition or embolisation in the catheterisation laboratory. Major complications were defined as any life-threatening event and/or need for immediate surgical intervention like cardiac arrest, device embolisation, cardiac tamponade, cardiac arrhythmia, hypotension, bleeding (requiring blood transfusion), vascular complications (femoral arteriovenous fistula, femoral haematoma, and femoral thrombosis), and stroke. Minor complications were defined as transient complication with no long-term sequela. Physical examination, ECG, TTE examinations were done in all patients immediately after procedure, at 24th hour, 1st and 6th months after procedure. After the 6th month control, it was done annually. All patients routinely received aspirin therapy (3–5 mg/kg) for 6 months after the procedure.
Cardiopulmonary exercise testing – refining the clinical perspective by combining assessments
Published in Expert Review of Cardiovascular Therapy, 2020
Ross Arena, Justin M. Canada, Dejana Popovic, Cory R. Trankle, Marco Giuseppe Del Buono, Alexander Lucas, Antonio Abbate
Of the numerous measures that can be derived from CPX, measures of exercise capacity and ventilatory efficiency garner the greatest focus in the clinical and research settings. With respect to exercise capacity, maximal VO2 (VO2max) obtained during exercise defines the upper limits of the cardiopulmonary system as illustrated through the Fick principle wherein VO2max is the product of cardiac output (CO) and the arteriovenous oxygen content difference [C(a-v)O2] at peak exercise. However, it is important to note that aerobic capacity is more commonly defined as peak VO2 (highest level obtained during exercise) versus VO2max as the latter implies attainment of a physiologic plateau not often observed in clinical populations. Peak VO2 reflects both central and peripheral functioning of the cardiopulmonary system and is influenced by age, sex, disease states, genetics, and physical activity levels[6]. The VE/VCO2 slope has been the most widely used index of ventilatory efficiency [5] and is attractive due to its high test–retest reliability [40]. Like peak VO2, although inversely, VE/VCO2 broadly reflects disease severity with higher values indicating worse prognosis in cardiopulmonary disease populations[2]. Moreover, the OUES has independent value in the prognostication of patients with cardiopulmonary disease [41–44] Furthermore, it has high reliability, is independent of exercise intensity, and is sensitive to therapeutic interventions such as exercise training regimens [45–47].
Preventing disease progression in Eisenmenger syndrome
Published in Expert Review of Cardiovascular Therapy, 2021
Ana Barradas-Pires, Andrew Constantine, Konstantinos Dimopoulos
The direct Fick method is recommended for the calculation of Qp in cardiac catheterization laboratories but requires ‘direct’ measurement of oxygen consumption with equipment that may not be widely available. The thermodilution method is considered a reliable technique in PH practice but should be avoided in patients with cardiac shunts. The less accurate indirect Fick method (that uses nomograms to obtain oxygen consumption) is commonly used in patients with simple cardiac defects, despite its limitations. Cardiovascular magnetic resonance (in a hybrid catheterization laboratory) can provide accurate estimates of Qp and Qs, especially in patients with complex cardiac anatomy in whom the Fick principle may be difficult to apply.
Related Knowledge Centers
- Arteriovenous Oxygen Difference
- Carbon Dioxide
- Molecule
- Oxygen
- Pulmonary Vein
- Blood
- Cardiac Output
- Spirometer
- Hemoglobin
- Body Surface Area