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The purpose of the study was to measure nasal passageway dimensions in guinea pigs and rats by use of acoustic rhinometry (AR) and by a previously described fluid-displacement method (FDM) (Straszek SP, Taagehoej F, Graff S, and Pedersen OF. J Appl Physiol 95: 635–642, 2003) to investigate the potential of AR in pharmacological research with these animals. We measured the area-distance relationships by AR of nasal cavities postmortem in five guinea pigs (Duncan Hartley, 400 g) and five rats (Wistar, 250 g) by using custom-made equipment scaled for the purpose. Nosepieces were made from plastic pipette tips and either inserted into or glued onto the nostrils. We used liquid perfluorocarbon in the fluid-displacement study, and it was carried out subsequent to the acoustic measurements. We found for guinea pigs that AR measured a mean volume of 98 mm3 (95–100 mm3) (mean and 95% confidence interval) of the first 2 cm of the cavity. FDM measured a mean volume of 146 mm3 (117–175 mm3), meaning that AR only measured 70% (50–90) of the volume by FDM. For rats, the volume from 0 to 2 cm was 58 mm3 (55–61 mm3) by AR and 73 mm3 (60–87 mm3) by FDM, resulting in AR only measuring 83% (66–100%) of volume by FDM (see Table 2 ). We conclude that absolute nasal cavity dimensions are underestimated by AR in guinea pigs and rats. This does not preclude that relative changes may be correctly measured. In vivo trials with AR using rats have not yet been published. The FDM is possibly the most accurate alternative to AR for measurements of the nasal cavity geometry in small laboratory animals, but it can only be used postmortem.

An increasing number of studies have used acoustic rhinometry (AR) for study of pharmacological interventions on nasal cavity dimensions in dogs and cats, but there have been no attempts to validate AR in these species. This is done in the present study. We compared area-distance relationships of nasal cavities from five decapitated dogs (3.5–41 kg) and cats (3.8–6 kg). AR was compared with magnetic resonance (MR) imaging and a fluid-displacement method (FDM) using perfluorocarbon. AR measured 88% (98–79%) (mean and 95% confidence interval) of nasal cavity volume in dogs determined by FDM and 71% (83–59%) in cats. AR markedly underestimated nasal cavity dimensions when minimum areas were below 0.1 cm2 in dogs and 0.05 cm2 in cats. AR underestimation increased with the severity of the constriction and with distance. Cross-sectional areas in the deeper parts of the cavity measured 76% (99–54%) of FDM in dogs and 52% (66–39%) in cats. AR agreed well with MR, especially in the deeper part of the cavity. MR images showed that the nasal cavities had a very complex structure not expected to be reproduced by AR. MR could not be considered a “gold standard” because definition of the cross-sectional area of the lumen depended critically on subjective choices. FDM produced repeatable measurements and possibly offers the most adequate reference in future evaluation of AR. AR underestimated what we believed were the most correct cross-sectional areas determined by FDM, especially in the deeper part of the dog and cat nasal cavities. Despite these difficulties, AR has been shown to be useful to describe qualitative changes in cross-sectional area.

Pedersen, O. F., H. J. L. Brackel, J. M. Bogaard, and K. F. Kerrebijn. Wave-speed-determined flow limitation at peak flow in normal and asthmatic subjects. J. Appl. Physiol. 83(5): 1721–1732, 1997.—The purpose of this study was to examine whether peak expiratory flow is determined by the wave-speed flow-limiting mechanism. We examined 17 healthy subjects and 11 subjects with stable asthma, the latter treated with inhaled bronchodilators and corticosteroids. We used an esophageal balloon and a Pitot-static probe positioned at five locations between the right lower lobe and midtrachea to obtain dynamic area-transmural pressure ( A-Ptm) curves as described (O. F. Pedersen, B. Thiessen, and S. Lyager. J. Appl. Physiol. 52: 357–369, 1982). From these curves we obtained cross-sectional area ( A) and airway compliance (Caw = d A/dPtm) at PEF, calculated flow at wave speed {V˙ws = A[ A/(Caw∗ρ)0.5], where ρ is density} and speed index is (SI =V˙/V˙ws). In 13 of 15 healthy and in 4 of 10 asthmatic subjects, who could produce satisfactory curves, SI at PEF was >0.9 at one or more measured positions. Alveolar pressure continued to increase after PEF was achieved, suggesting flow limitation somewhere in the airway in all of these subjects. We conclude that wave speed is reached in central airways at PEF in most subjects, but it cannot be excluded that wave speed is also reached in more peripheral airways.

Pedersen, O. F., T. F. Pedersen, and M. R. Miller. Gas compression in lungs decreases peak expiratory flow depending on resistance of peak flowmeter. J. Appl. Physiol. 83(5): 1517–1521, 1997.—It has recently been shown (O. F. Pedersen T. R. Rasmussen, Ø. Omland, T. Sigsgaard, P. H. Quanjer, and M. R. Miller. Eur. Respir. J. 9: 828–833, 1996) that the added resistance of a mini-Wright peak flowmeter decreases peak expiratory flow (PEF) by ∼8% compared with PEF measured by a pneumotachograph. To explore the reason for this, 10 healthy men (mean age 43 yr, range 33–58 yr) were examined in a body plethysmograph with facilities to measure mouth flow vs. expired volume as well as the change in thoracic gas volume (Vb) and alveolar pressure (Pa). The subjects performed forced vital capacity maneuvers through orifices of different sizes and also a mini-Wright peak flowmeter. PEF with the meter and other added resistances were achieved when flow reached the perimeter of the flow-Vb curves. The mini-Wright PEF meter decreased PEF from 11.4 ± 1.5 to 10.3 ± 1.4 (SD) l/s ( P < 0.001), Pa increased from 6.7 ± 1.9 to 9.3 ± 2.7 kPa ( P < 0.001), an increase equal to the pressure drop across the meter, and caused Vb at PEF to decrease by 0.24 ± 0.09 liter ( P < 0.001). We conclude that PEF obtained with an added resistance like a mini-Wright PEF meter is a wave-speed-determined maximal flow, but the added resistance causes gas compression because of increased Pa at PEF. Therefore, Vb at PEF and, accordingly, PEF decrease.

in a current paper in the Journal of Applied Physiology ([3][1]) the authors have tried to find out whether the compression of the gas in the lungs during a forced expiration influences the grading of decreased lung function in patients with sick lungs either due to emphysema or chronic bronchitis.