Source: Annual Congress 2003 - Respiratory structure and mechanisms: current concepts

Abstract

Aim: To reinterpret measurements by Weiss et al. (JAP 52:874-878,1982) of maximum expiratory flows (V’max) and static lung elastic recoil pressure (Pel) before and after bronchodilatation in 6 healthy subjects breathing air and 80% He in oxygen (He/O₂).
Methods: From maximum flow-static recoil (MFSR) curves on air and He/O₂, a MFSR curve for "frictionless" flow was derived under the assumption of laminar flow upstream to the choke point (CP). The cross-sectional area (A) and airway compliance (Caw) at CP, was calculated from the derived MFSR-curve by use of the "inverse" wave speed flow equation (Pedersen et al. JAP 52:357-369,1982). Furthermore the resistance of the airway upstream to CP was calculated as the horizontal distance between the derived MFSR curve and the curve for air.

Table 1: Model input

	Before bronchodilation			After bronchodilaion
%FVC	Pel (kPa)	V‘max(air) (L/s)	V‘max(He) L/s)	Pel (kPa)	V‘max(air) (L/s)	V‘max (He) (L/s)
50%	0.860	5.39	8.62	0.860	6.19	10.3
25%	0.536	3.63	5.38	0.536	3.95	6.37

Results

Table 2: Model output

	Before bronchodilatation			After bronchodilatation
%FVC	A (cm2)	Caw (cm2/kPa)	Rfr (kPa/(L/s))	A (cm2)	Caw (cm2 /kPa)	Rfr (kPa/(L/s))
50%	1.60	1.31	0.016	2.02	2.08	0.004
25%	1.32	1.60	0.043	1.64	2.60	0.011

Conclusion: .The original paper concluded by indirect assessment that upstream frictional pressure loss was decreased by bronchodilatation. In addition to that conclusion the present model indicates that bronchodilation also increases airway area and airway compliance at CP, which intuitively seems correct.

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Citations should be made in the following way:
O. F. Pedersen (Aarhus, Denmark). Bronchodilatation, lung recoil, and density dependence of maximal expiratory flow. New interpretation of old data. Eur Respir J 2003; 22: Suppl. 45, 160

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