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APAPARI Workshop Hanoi 2017 Lung function tests Dr Michael Lim Division of Paediatric Pulmonary and Sleep Khoo Teck Puat - National University Childrens Medical Institute (KTP-NUCMI) National University Hospital Singapore 29th April 2017 Overview • • • • Spirometry Body plethysmography Helium dilution Carbon monoxide transfer Introduction • Spirometry – Measure dynamic lung volumes and flow rates during forced ventilatory manoeuvres • Plethysmography – Measure static lung volumes (TLC, RV) Effort independent measures of airway obstruction may also be generated • Gas diffusion techniques – To measure static lung volumes, and to determine the efficiency of gas exchange Indications • Diagnosis – Characterise impairment in physiological function – Quantification of impairment in physiological function • Monitoring of chronic disease – Asthma – Neuromuscular disease • Establishing the effectiveness of therapeutic intervention – Asthma – Bronchiectasis • Assessing risk of an intervention – Chemotherapy – Anaesthetic Spirometry • Uses forced ventilatory manoeuvres to assess maximal flow rates and dynamic lung volumes • Flow and time measured • Volumes derived from these • Flow measured using pneumotachometer (measures pressure change across a fixed resistance) or speed of rotating fan • Two curves: – Flow volume curve – Volume time curve Flow depends on: • • • • Elastic recoil of the lung Dimensions of the airway Stiffness of the airway Lung volume (airway supported open in inflated lungs, but narrows down as the lung empties) • (Density and viscosity of the gas) Physiology behind forced expiratory manoeuvres • Flow limitation theory – Dynamic compression of the airways – Wave speed theory spirxpert P mo=pressure at mouth P br=pressure inside the airway P pl=intrapleural pressure P alv=intra alveolar pressure P L.el=elastic recoil pressure of Wave speed theory • Flow in elastic tubes limited by the ability of elastic tubes to propagate pressure waves • Bulk flow cannot occur at speeds above which pressures driving the flow can be propagated along the tube (tube wave speed) • At tube wave speed – choke point • Increasing driving pressure above choke point does not lead to increased flow • Max flows proportional to density of gas, airway wall compliance, and surface area of lumen Case • year-old boy presents with history of recurrent pneumonia, never needing hospital admission • Presents with a blue spell Fixed upper airway obstruction tracheal stenosis Case • year-old ex-prem girl presents with history of recurrent croup • Noted to have biphasic stridor Subglottic stenosis before and after treatment Variable upper airway obstruction laryngeal polyp Case • 16 year-old athletic girl presents with history of difficulty taking in breath • On presentation, stridor, hoarse voice Vocal cord dysfunction Case • 10 year-old boy with history of complex cyanotic heart disease (post-op TGA repair) with recurrent wheezing Bronchomalacia Baseline and After with Predicted Value Flow [l/s] Flow [l/s] Vol [l Vol [l] Vol [l] ] Restrictive pattern Reversible expiratory airflow obstruction Fixed large airway obstruction Variable extrathoracic Look at FEV1/FVC % More than or equal to 80% What is the FVC? Less than 80% What is the FVC? ≥ 80% ≥ 80% Normal < 80% < 80% Restrictive Pattern Obstructive Pattern Mixed Pattern ... • • • • Elastic recoil of the lung Dimensions of the airway Stiffness of the airway Lung volume (airway supported open in inflated lungs, but narrows down as the lung empties) • (Density and viscosity... static lung volumes, and to determine the efficiency of gas exchange Indications • Diagnosis – Characterise impairment in physiological function – Quantification of impairment in physiological function. .. or growth • Progression of disease ͚͚Spiroŵetry is aŶ effort-dependent manoeuvre that requires understanding, co-ordination, and co-operation by the subject/patient, ǁho ŵust ďe The person making
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