What Does Airway Resistance Tell Us About Lung Function?

Abstract

SummarySpirometry is considered the primary method to detect the air flow limitation associated with obstructive lung disease. However, air flow limitation is the end-result of many factors that contribute to obstructive lung disease. One of these factors is increased airway resistance. Airway resistance is traditionally measured by relating air flow and driving pressure using body plethysmography, thus deriving airway resistance (R aw ), specific airway resistance (sR aw ), and specific airway conductance (sG aw ). Other methods to measure airway resistance include the forced oscillation technique (FOT), which allows calculation of respiratory system resistance (R RS ) and reactance (X RS ), and the interrupter technique, which allows calculation of interrupter resistance (R int ). An advantage of these other methods is that they may be easier to perform than spirometry, making them particularly suited to patients who cannot perform spirometry, such as young children, patients with neuromuscular disorders, or patients on mechanical ventilation. Since spirometry also requires a deep inhalation, which can alter airway resistance, these alternative methods may provide more sensitive measures of airway resistance. Furthermore, the FOT provides unique information about lung mechanics that is not available from analysis using spirometry, body plethysmography, or the interrupter technique. However, it is unclear whether any of these measures of airway resistance contribute clinically important information to the traditional measures derived from spirometry (FEV 1 , FVC, and FEV 1 /FVC). The purpose of this paper is to review the physiology and methodology of these measures of airway resistance, and then focus on their clinical utility in relation to each other and to spirometry.

Pulmonary Function Testing

“…However, measurement of airway resistance (and derived parameters) has not always been viewed as a complement of spirometry. 18 The availability of body plethysmography allows measurement of the pressure drop across the airways and relates this pressure to flow at the mouth. Because lung volume (V TG ) can be measured in the same session, it is useful to express resistance and its reciprocal, conductance, as specific for the lung volume at which they are measured (sR aw and sG aw , respectively).…”

“…These include the FOT, 18 enhanced use of transcutaneous P O 2 and P CO 2 sensors (for adults as well as children), uptake of NO to measure D LNO (membrane transfer factor), 44 impedance cardiography to measure cardiac output, 19 and analysis of exhaled NO (F ENO ) to assess airway inflammation. 35 Some technologies are on the horizon that are "brand new" and may have a role in the PFT lab of the future.…”

Trajectories of Lung Function during Childhood

“…We have previously shown that as early as age 3 years, sRaw differs between children with a history of wheezing and those without (9), and higher sRaw at age 3 years is associated with subsequent persistence of wheezing (14). In childhood, sRaw is considered to be independent of age, height, and sex, thus facilitating the interpretation of longitudinal measurements in individual subjects (5,8,12,13). Previous data from our group indicated a possible increase in sRaw through early childhood (14).…”

“…For younger children, the techniques that can be performed during tidal breathing are more practical (7). One such method is measurement of specific airway resistance (sRaw) using plethysmography (8)(9)(10)(11)(12)(13), which can be a useful measure in clinical practice and research studies (11). We have previously shown that as early as age 3 years, sRaw differs between children with a history of wheezing and those without (9), and higher sRaw at age 3 years is associated with subsequent persistence of wheezing (14).…”

Bronchoconstriction in Response to Deep Inhalation During Spirometry Testing

“…1 Moreover, deep inhalation is thought to maintain airway smooth muscle homeostasis and to possess bronchodilating and bronchoprotective properties against challenge agents. [2][3][4][5][6] The bronchodilatory effect of deep inhalation is clearly impaired in asthma patients 2,7,8 ; however, the bronchoprotective properties of deep inhalation against challenge test agonists (eg, methacholine) remain robust in many asthma patients with mild airway hyper-responsiveness.…”