The Relationship Between Airway Resistance, Airway Conductance and Lung Volume in Subjects of Different Age and Body Size12

Abstract

The resistance of the airways to the airflow through them depends on the radius, length and number of the airways. It has long been apparent (1, 2) that the bronchi are distended as well as lengthened in the inspiratory position of the lung. These two changes in the dimensions of these airways would have opposite effects on their resistance to airflow, lengthening increasing resistance and widening reducing it. More recent measurements of airway resistance have shown that it is reduced in the inspiratory position of the lung (3,4,5) and is more in individuals with small lungs (6).The body plethysmograph affords a good technique for comparing changes in airway resistance with changes in lung volume in an individual, since each measurement of airway resistance includes as an essential stage in its derivation, a measurement of intrathoracic gas volume. It therefore seemed desirable to explore further the relationship between airway resistance and lung volume at different degrees of inflation of the lung in normal subjects. METHODSAirway resistance was measured by the method previously described by DuBois, Botelho and Comroe (7). The method has the advantage that the pressure changes in the body plethysmograph reflect changes in alveolar pressure rather than changes in pleural or esophageal pressure. The resulting measurements are therefore assessments of pure airway resistance uncomplicated by the effects of tissue viscosity which are included with (Figure 1).Each subject sat in the 600 liter body plethysmograph for a few minutes until the air in the box was warm enough and sufficiently saturated with water vapor for spontaneous changes in plethysmograph pressure over a period of 10 seconds to be negligible. During this time the amplification of .the record of plethysmograph pressure was adjusted until a displacement of 30 cc. to or from the plethysmograph gave a deflection of two inches on the oscilloscope face. The subject then put his mouth over the flowmeter shutter assembly which was suspended in the plethysmograph and panted for about six seconds. The observer aligned the plexiglass disc with the midslope of the tracing and read the product (lung volume X airway resistance) off the calibrated scale.The observer then operated a switch, which closed the solenoid shutter at the mouth, and replaced the record of flow rate by one of mouth pressure, on the Y axis of the 5A more detailed description of this modification is being prepared. Meanwhile, the diagram (Figure 1) shows the arrangement of apparatus used in the present study.

Lung Hyperinflation and Its Reversibility in Patients with Airway Obstruction of Varying Severity

“…Reversibility testing (spirometry, body plethysmography) was performed using salbutamol 200 mcg by metered dose inhaler; post-dose measurements were performed 20-min after inhalation. Predicted normal values were those used in the laboratory at the time of testing (22)(23)(24)(25); predicted IC was calculated as predicted TLC minus predicted FRC, predicted ERV was calculated as predicted FRC minus predicted RV.…”

Effect of obesity on breathlessness and airway responsiveness to methacholine in non-asthmatic subjects

“…Baseline lung volumes and airway resistance, measured by plethysmography, and baseline spirometric function were measured before methacholine challenge and are reported as percent predicted. [18][19][20] Atopic status was determined by skin prick tests. Response to methacholine challenge was measured by the change in forced expiratory volume in 1 s (FEV 1 ), and dyspnea was measured by the Borg score.…”

Assessing change in airway calibre‐measurement of airway resistance.

“…Specific airway resistance (sRaw), the product of Raw and thoracic gas volume, corrects to some extent for lung volume though it is a less useful correction than sGaw (see below) because of the shape of the Raw/lung volume plot. The reciprocal of airway resistance, airway conductance (Gaw), shows an approximately linear relationship to both lung recoil pressure and lung volume (Figure 2c and d) (Briscoe & DuBois, 1958;Butler et al, 1959) and this conversion of Raw to Gaw makes the information more convenient to handle. A correction can then be made for lung volume by calculating specific airway conductance (sGaw).…”

“…Some deviation from linearity is well recognized , though problems of reproducibility makes studies in individual patients more difficult to assess. In normal subjects the Gaw/TGV line usually approaches zero Gaw between 0 and 1 litres on the volume scale (Briscoe & DuBois, 1958;Guyatt & Alpers, 1968). In patients with airways obstruction the intercept at zero Gaw is more likely to lie between 1 and 4 litres lung volume Pelzer & Thomson, 1969;Leaver, Tattersfield & Pride, 1973).…”