Proceedings of The Physiological Society
University of Birmingham (2010) Proc Physiol Soc 20, C18 and PC18
Classical model of ventilation applied to exercise in occupational lung disorders.
J. E. Cotes1,2, J. W. Reed1, D. W. Wilson2
1. School of Medicine and Health, Durham University, Durham City, United Kingdom. 2. Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne, United Kingdom.
Introduction. The classical model portrays ventilation as the sum of alveolar and airway deadspace components . The latter is the product of anatomical deadspace and breathing frequency. It is commonly overlooked, yet in healthy shipyard workers the term was significant . Here the model is used with an additional disease-specific term to examine ventilation in men referred for assessment for suspected occupational lung disorders (OLD); they comprised 54 men with coalworkers’ pneumoconiosis (CWP), 26 with work-related wheeze (WRW), 11 with diffuse pleural thickening (DPT) and raised ventilation, 14 with diffuse pulmonary fibrosis and 9 with presumed centriacinar emphysema. 44 referred men who were found to have normal function formed a comparison group (CG). Methods. The subjects completed a respiratory questionnaire (MRC) and lung function assessment by standard methods. Progressive treadmill exercise was used to derive ventilation (V'expst) and respiratory exchange ratio (RERst) at an O2 uptake of 1.0 l min-1 (45 mmol min-1), and tidal volume and respiratory frequency (designated Vt30 and fR30) at a ventilation of 30 l min-1. Special care was taken over the derivation of RERst because the relationship was non-linear. The model of V'expst on RERst and fR30  was extended by the inclusion of a disease-specific constant term. Outliers with valid data were not excluded. Significance (*) was at the 5% level. Results. Mean V'expst in OLD was 33.1 (range 36.7 to 26.9) l min-1 and exceeded that in CG (23.4 l min-1)*. In CWP mean values for V'expst, RERst and fR30 were respectively 34.6 l min-1, 0.83 and 26 min-1. The corresponding means for the coefficients in CG were 0.77 and 20.3 (min-1)*. For these two groups together the extended model yielded: V'expst = 32.2 RERst* + 0.42 fR30* + 6.6 CWP (yes or no)* -9.84 (R2 = 0.67). The constant, interactions between the variables, also terms for age and smoking were not significant. From the model the factors contributing to increased V'expst in CWP were alveolar drive (17%), shallow breathing (24%) and deadspace ventilation (59%). In DPT restriction to lung expansion was not a consistent feature, yet mean fR30 was 33.3 min-1, an increase compared with CG *. By contrast in WRW, fR30 (mean 17.1 min-1) was reduced*. Conclusion. Breathing frequency contributes to ventilation under standard conditions in chest disorders as well as in health. Thus it should be taken into account whenever ventilation is an issue. In DPT, unexplained tachypnoea is often assumed to be functional. The present results suggest it could be of reflex origin. This possibility might usefully be explored.
Where applicable, experiments conform with Society ethical requirements