to increasing concentrations of methacholine was determined by the double-chambered whole body plethysmograph and reported as lung resistance (RL, cm[H.sub.2]O x [s.sup.-1] x [mL.sup.-1]).
The mechanical bronchodilation or splinting of the airways will have the effect of decreasing total airways resistance
whilst the increased alveolar surface area will increase total lung compliance.
Airway resistance was measured using an 8-second forced oscillation, composed of nonoverlapping, nonharmonic frequencies that were used to produce an index of central airways resistance
, [R.sub.n] (Newtonian resistance).
Sleep specialists have carved out a diagnostic niche called upper airways resistance
syndrome (UARS) for children (and adults) who don't have overt sleep apnea and may not even snore but still can't get a good night's sleep.
With volume-cycled breaths, worsening airways resistance
or lung/chest wall compliance results in increases in peak inspiratory pressure with continued delivery of set tidal volume (unless peak pressure limit is exceeded).
Single short-term exposures are known to cause acute changes in pulmonary function, such as increased specific airways resistance
(S[R.sub.aw]) and decreased forced expiratory volume in 1 sec (FE[V.sub.1]) and forced vital capacity (FVC) (Aris et al.
TESTING: Shane Mansfield, a volunteer at the Common Cold Centre at Cardiff University, has his airways resistance
measured as part of the university's research work Picture: NICK TREHARNE
The Pulmonary Time Constant (TC, Kt), is the product of the airways resistance times the static lung compliance in seconds that will allow for 63% of transferred volume to equilibrate.
NOTE: Frequently expiratory airways resistance is greater than inspiratory airways resistance.
Lung units with high compliance will have a longer time constant; as will lung units with high airways resistance
. Conversely, lung units with low compliance and low airways resistance
will have a shorter time constant.