Basics | body plethysmography | flow-pressure-curve
Important parameters for the differentiation of obstructive ventilation disturbances are FEV1, FEV1/VC (spirometry | quantitative assessment), residual volume and airway resistance. Residual volume and airway resistance can only be measured by means of body plethysmography. In order to determine resistance, oral pressure is measured. This value can then be illustrated graphically in a flow-pressure curve ( = “respiratory loop”). Flow and oral pressure are plotted against displacement volume, creating two loops. In the case of obstruction, both loops intersect at an angle of > 90°. In the absence of obstruction (healthy individuals or those with restriction), the angle is < 90°. If emphysema is present, the respiratory loop takes on a typical club shape.
Obstructive respiratory disturbances with possible emphysema or air trapping such as chronic obstructive pulmonary disease (COPD), asthma bronchiale, α1-antitrypsin deficiency
67-year-old female patient.
Findings: the intersection angle of the loops > 90° as a sign of obstruction. Marked club form as an indication of emphysema. Virtually no difference between before (blue) and after (red) bronchodilation.
77-year-old male patient.
Findings: intersection angle of the loops > 90 as a sign of obstruction. Club form as an indication of emphysema. Under bronchodilation, minimal lessening of the angle, with slight narrowing of the club shape as an indication of minor air trapping.
55-year-old female patient.
Findings: intersection angle of the loops > 90° as a sign of obstruction. Club form recognizable as an indication of increased residual volume. Under bronchodilation (red) normal respiratory loop as an indication of reversible obstruction and air trapping.