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Tidal breathing analysisReliability and Clinical Relevance of Tidal Breathing Analysis H.J. Smith Product Manager Pneumonology Respiratory Care Turkish Thoracic Society 2014
Workshop tidal breathing analysis Forced spirometry • Education and training in all levels on all issues • European spirometry driving licence • Everlasting problems • Quality of spirometry and test results will ever depend on efforts of patients and medical stuff • Interpretation of flow limitation needs expertise of physician Tidal breathing analysis • Little offers for specific training or education • Knowledge and skills are very often out-of-date • Misunderstanding in methodological potential, quality issues, relevance of test results • Promoted mostly by paediatricians Why not in combination with spirometry?
Introduction “Pro” tidal breathing analysis Tidal breathing lung function testing • Physiologic • Usual way of breathing • Effort independent (all subjects can be measured – from infants to elderly and severe diseased) • Maximal manoeuvres are limited in describing tidal breathing conditions • Of interest in diagnostics of the lung • Differentiated, informative, sensitive • Direct measurements of specific characteristics of the respiratory system
Spirometry tidal breathing analysis Mostly in infant lung function testing • Flow-volume pattern • Flow-time pattern • Rather often adaptation of interpretation strategies from adults V.P. Seppä et al. Tidal breathing flow measurements in awake young children by using impedance pneumotachography. J ApplPhysiol. 2013; 115: 1725-1731
Tidal breathing analysis in practice (adults) Adult subject (a) Normal / obstructive ? Adult subject (b) Normal / obstructive ?
Tidal breathing in spirometry Subject (a) Emphysema Subject (b) Healthy
“Contra” tidal breathing analysis • Variability • Freedom of the subject to breath slower, faster, deeper or more shallow • No standards for achieving reproducibility • In the past: Metronome; BF=constant • Sensitivity and specificity of flow pattern • Nearly all respiratory problems lead to flow limitation • Only severe degrees of disability become visible • Usually more complex technology needed • Specific quality, best selection and classification concepts
Specific methods for (clinical) evaluation • Problems: • Standardisation of breathing • Intra-breath variability • Limitations not yet visible at tidal breathing • Flow-volume pattern ambiguous • Solutions: • Statistical methods for evaluation • Long term recording • Individual trend analysis • Pre-post assessment • Intra-breath variability of 2 flow-volume-parameters: • Tpef%Tex • Vpef%Vex Still the flow-volume recording of tidal breathing lacks information!
Survay of methods (applications) Flow (volume) in combination with one ore more additional signals (simultaneous recording) • Rint, Rocc Occlusion pressure - Pint/Pocc • sRaw, Bodyplethysmography - Vshift • R5, X5, Oscillometry - Pmouth (ext. generator) • P0.1 Breathing pump - Pint/Pocc • FRCHe, FRC-Rebreathing - %He • Cdyn, Compliance - Poes • CO2/O2, Capnography/Oxymetry - %CO2/O2 • RAAR, Rhinomanometry - Pchoanae • Wheezing, Lung sound analysis - Sound • Zimp, Impedance tomography - Impedance
FRC-stability (EEL) • Common long term stability of flow channel > 5 min • Offset of flow transducer stays within “dead zone” • New, high stable and temperature compensated pressure transducers Volume drift upwards • Physiologic criteria for FRC-stability • Regularity of breathing • BF constant • VT constant FRC-stability line Volume drift downwards
Sources of drift • Drift of volume is an technical issue – ATP-BTPS correction • It is not possible to eliminate this drift • In future statistical methods • Sources of drift • Approximation of ATP-BTPS correction • Correction depends / varies with: • Changes in ATP • Use of filters • Breathing pattern (flow profile) • Ratio of dead space / alveolar ventilation • Adaptation of Patient • Calibration • Solution • Post processing • Depending on measurement application • Applied on specific breaths or entire recording • Excludes physiological changes of EEL • Visual inspection of adaptation • Offset correction Volume drift
Repeatability (within trial / between tests) Standardisation ? • Patient has all degrees of freedom to increase, lower VT, BF • What is the standard? In the past • Standardization of BF – Metronome • Need of corrective action of patient • Shift of FRC Nowadays • Non-restricted spontaneous breathing is requested • Confirmation of normal resting breathing • The point of lowest WOB is highly reproducible Respiratory system always tries to minimise WOB • Regulation / optimisation of BF and VT Obstruction BF i, VT hRestriction BF h, VT i
Decreasing variability of measurement • Edit capabilities • Selection, deselection • Manual corrections • Resultc Subjective influence increases variability of results
Reliable concepts to improve quality • Adaptation phase until regular tidal breathing • Familiarisation with mouth breathing through instrument • Instruction/confirmation of spontaneous breathing (at individual lowest WOB) In case of insufficient cooperation • Increase of number of breathing cycles • Increase of number of trials • Repeated recording after optimised instruction • Rejection of artefact affected trials • Editing artefact effected trials is not recommended !
BEST selection in tidal breathing analysi • Maximum / Minimum • Not applicable in tidal breathing analysis • Median (usually) • Arranging all the observations from lowest value to highest value and picking the middle one • Advantage: Robust against artefacts • Disadvantage: BEST as good as single trial • Average • Sum of a list of numbers divided by the size of the list • Advantage: Improves with number of trials BEST is better than a single trial • Disadvantage: Strongly effected by artefacts • Use requires prior artefact rejection
Comparisonof median – meancalculation Low variability of sReff (Reff, TGV)and FRC Median = mean
Full body plethysmography Characteristic and clinical usefulness / interpretation of breathing (resistance) loops.
Breathing loop without Raw 0 Flow [L.s-1] Flow sReff DVm 0 Shift volume Shift volume [mL] TGV DVth DVthorax = DVmouth No compression / decompression of air in lungs. Movement of thorax is NOT detected by box! No Shift volume!
Breathing loop with Raw >> 0 Flow Flow [L.s-1] sReff Fraction Raw sReff DVm Raw>> Alveolar pressure >> 0 + PA + Shift volume Compression / decompression DVth Sift volume [mL] Shift volume= proportional to Raw
Breathing loop with Raw >> & TGV 0 Flow Flow [L.s-1] Fractions RawTGV DVm Raw>> sReff + PA + Alveolar pressure >> 0 Shift volume Compress. / decompress. TGV DVth Sift volume [mL] Shift volume=further increased by TGV Alveolar pressure = constant!
Summary - breathing loop Specific resistance (sRaw) incorporates (Raw, TGV) Flow [L.s-1] • sRaw breathing loop • Specific Resistance • Related to WOB, efforts for breathing • Without shutter measurement! • Proportional to Raw and TGV • Not a resistance loop! (Alveolar pressure ~ Raw only) Pecularitiesof the sRaw breathing loop • Low variability as primary measure • High clinical relevance / significance • Answer on relevant clinical questions: abnormality, local distribution, reversibility, hyperresponsiveness sReff Parameters sRtot Shift volume [mL]
Weibel: Morphometry of the human lung Cross sectional area [cm²] 2.5 2.0 5.0 1.8 x 10² 9.4 x 10² 5.8 x 10³ 56 000 000 Resistance [kPa/(L/s)] 0.05 0.05 0.02 Genera- tion 8-10 17 24 Larynx Trachea Bronchi Bronchioles Alveolar Ducts Alveoli Central airways R ~ 80% Peripheral airways R < 20% TGV > 60 % Weibel, Morphometry of the Human Lung, Springer 1963
Raw-TGV dependency Raw > Raw < TGV < TGV > = sRaw = Rawhigh & TGVlow Rawlow & TGVhigh Specific Resistance (sRaw) • Normalises airways resistance to lung volume • Low dependence on biometrical data • Reference values are constant
Clinical information based on sRaw Threshold to abnormal lung function • Adults sRaw > 1.2 kPa.s (Raw & TGV) • Children sRaw > 1.0 kPa.s (Raw & TGV) Reversibility • No…………No significant change of sRaw • Partial…….Significant decrease of sRaw • Complete….sRaw becomes normal Hyperresponsiveness • PD/C+100sRaw & > 2.0 kPa.s • PD/C-40sGaw & < 0.5 kPa-1.s-1 Important clinical questions are answered based on tidal breathing! Incorporating the entire respiratory tract. Flow V‘ [L.s-1] Clockwise turn sReff Approximation TGV Reff Shift volume [mL]
Differential diagnsotics via sRaw- loop Degree of opening, separately for in- and expiration K1 closed, steepc Normal lung function K2 little opened, clockwise turned cCentral obstruction K3 Golf club cPeripheral end-expiratory inhomogeneity K4 V-shapecElevated diaphragm and/or end-expiratory „closing“ K5 Markable S-shapecExtra thoracic stenosis
Impulse Oscillometry New multiple trial concept.
Tidal breathing analysis • Spontaneous breathing pattern • Physiologic, effortless, patient friendly • No age limitation • Highly reproducible (Point of lowest WOB) • Variety of different methods available • Global information (sReff) • Highly differentiated (Raw, FRC; R5, X5) • New concepts for artefact elimination • Median >> automated artefact rejection and mean calculation