Ventilation during submaximal exercise ([vdot]E,ex) can be represented as the sum of the ventilations per min of (1) anatomical deadspace, (2) any pathological tidal deadspace in continuity with airways and (3) alveoli that participate in gas exchange. The last component is increased by uneven lung function ([vdot]A/[qdot]inequality). These causes of increased ventilation have been attributed collectively to a ‘physiological deadspace effect’ [1] or a distribution of [vdot]A/[qdot] ratios [2]. In the present model the ventilation under standard conditions ([vdot]E,ex_st) is partitioned into components that are respectively proportional to and independent of respiratory frequency, represented by two coefficient terms in a multiple regression equation. [vdot]E,ex_st = a. standardised CO₂ output + b. standardised respiratory frequency + c. [vdot]E,ex_st and standardised CO₂ output were at the O₂ uptake of 1.0 l min^-1 (45 mmol min^-1), and standardised respiratory frequency at ventilation 30 l min^-1 (designated fR₃₀). The corresponding tidal volume is 30/fR₃₀, hence the fR₃₀ reflects the pattern of breathing. Subjects were 136 working shipyard tradesmen [3] and 69 applicants for respiratory disability benefit who had impaired function. Lung function and responses to progressive exercise were by standard methods. Indices under standard conditions were by interpolation. Stepwise multiple regression analysis (SPSS) was performed, with terms that were not significant (p>0.05) eliminated progressively. In the tradesmen, terms for age and smoking did not contribute to the regression. The presence of wheeze did contribute and was allowed for. The values for ‘a’,‘b’ and ‘c’ were respectively 17.1, 0.19 l and 4.48 l min^-1; ‘a’ and ‘b’ were independent of each other (p<0.01). The residual standard deviation (RSD) about this equation (Eqn 1) was 2.02 l min^-1. For pooled data from applicants ‘a’, ‘b’,’c’ and RSD were 40.1, 0.45, -11.4 and 7.14 (Eqn 2). All coefficients were significant (p< 0.01). ‘a’ differed between the two equations (p< 0.01). For ‘b’ the probability of a real difference was p=0.10. A two compartment model is realistic, precise and can be used to deconstruct [vdot]E,ex_st. Eqn 1 gives the parameters for working men. They can provide an expected (reference) value for [vdot]E,ex_st at a man’s own standardised CO₂ output and fR₃₀. Eqn 2 illustrates the application of the model to data for men with abnormal lung function. The method can be used to estimate the relative contributions of uneven alveolar ventilation, tidal deadspace and pattern of breathing to an increased [vdot]E,ex_st and hence to breathlessness in different chronic respiratory disorders.