Workshop 1 - respiratory function

Spirometry

Measures lung volumes and flows

Useful for diagnosis of respiratory diseases

Capnography

Measure CO2 concentration in airway during respiration

Volumes and capacities

Spirometric values

FVC - forced vital capacity - total air exhaled after maximum exhale effort

FEV1 - forces expiratory volume in 1 second - air exhaled in the first second of forced exhalation

FEV1/FVC ratio - determines airway obstruction severity

Graphical representation of spirometry - volume/time curve

Shows how quickly a person exhales

Relates volume expired with time taken for inspiration

Graphical representation of spirometry - flow/volume curve

Relates flow expired at each instant with the volume expired at that instant

Harder to interpret but are more detailed

Flow volume loop

Expiration is above horizontal axis, inhalation under axis

Expiration - starts at total lung capacity → reaches peak expiratory flow → after PEF, flow declines as lung volume decreases → ends at residual volume

Inspiration - starts at RV → airflow increases until reaches TLC → flow reduces back to 0

Spirometry alternations - volume/time curve

Obstructed - reduced airflow due to airway resistance

Restricted - reduced lung volume due to stiffness of deformation

Spirometry alternations - volume/flow curve

Obstructive - difficulty exhaling, resistance in airway, reduction airflow

Restrictive - limited lung expansion

Spirometry loops

Capnography

A-B : dead space ventilation, no CO2 detected

B-C : expiratory phase, CO2 starts increasing

C-D : alveolar plateau, steady CO2 levels

D-E : inspiration phase, CO2 drops as fresh air enters

Clinical importance of capnography

Shape change indicated respiratory disease

End tidal CO2 helps assess ventilation efficiency, treatment effectiveness and correct endotracheal tube placement

Capnography alternations 1

Capnography alternations 2