Fig. 4.

Ventilatory response panels

Panel 5: Relationship between minute ventilation ($\dot{\mathbf{V}}\mathbf{E}$) and work rate (WR) vs. time (x-axis). The maximum voluntary ventilation (MVV) is calculated indirectly as forced expiratory volume in 1 s (FEV₁) × 40 or can be determined by direct measurement of MVV (preferred option in restrictive lung disease). Exercise is usually not limited by breathing.

Analysis (target values and response kinetics): Is $\dot{\text{V}}\text{E}$ adequate relative to work rate (see main text: validity check, 9-point rule)? Is $\dot{\text{V}}\text{E}$ vs. work rate sharply increased at the start of exercise (suggestive of R-L shunting) or decreased (e.g., mask or mouthpiece leakage)? Impaired ability to increase $\dot{\text{V}}\text{E}$ in response to enhanced CO₂ production and/or acidaemia (e.g., severe lung disease, obesity)?

Panel 8: Respiratory exchange rate (RER) and breathing reserve (BR). RER describes the ratio of CO₂ output to O₂ uptake (${\dot{\text{V}}\text{CO}}_2$/${\dot{\text{V}}\text{O}}_2$) as a function of time and reflects patient effort (RER at least ≥ 1). RER depends on the rate of lactate increase during progressive exercise. BR indicates the actual percentage of the maximum ventilatory capacity (MVV-V̇E). Validity depends on adequate spirometry.

Analysis (target values and response kinetics): RER values at rest: normal, high or low? RER > 1 at rest (indicative of hyperventilation). RER ≥ 1 achieved in early exercise (work rate already above lactate threshold) or in late exercise? An abrupt, persistent RER increase during early exercise suggests exercise-induced R-L shunt. RER < 1 during exercise (e.g., poor effort, severe lung disease [$\dot{\text{V}}\text{E}$ cannot be adequately increased], myopathy, PAD, hyperventilation prior to testing)? Delayed decrease in RER in early recovery (indicates delayed CO₂ elimination, e.g., severe COPD) or rapid RER decrease in early recovery (indicates delayed recovery of ${\dot{\text{V}}\text{O}}_2$ vs. ${\dot{\text{V}}\text{CO}}_2$ due to a high O₂ deficit during exercise)? BR normal or low? A low BR indicates reduced ventilatory capacity due to impaired lung mechanics and increased ventilatory demands during exercise.

Panel 9: Breathing pattern. Relationships of tidal volume (V_T) (y-axis), minute ventilation ($\dot{\mathbf{V}}\mathbf{E}$) (x-axis) and breathing frequency (BF). BF is indirectly presented in the form of isopleths (= line with the same numerical values. Upper isopleth: low BF [= 20 breaths/min]. Lower isopleth: high BF [= 50 breaths/min]). Physiologically, V̇E increases until V_T is fully utilised (≈ 60% of VC), thereafter V̇E increases with a rise in BF.

Analysis (target values and response kinetics): Normal breathing pattern? The values in the area of the upper isopleths indicate a high V_T and a low BF. Obstructive breathing pattern? The increase in ventilation during exercise is limited because V_T is already fully utilised and eventually falls off. BF cannot be adequately increased due to the prolonged expiration time. This results in slow, deep breathing. Restrictive breathing pattern? The increase in ventilation during exercise is limited because V_T cannot be sufficiently increased due to the reduced lung volume (VT/IC ratio ↑ [> 0.8]). Hence, ventilation can only be increased by elevated BF. V_T runs low and flat in the direction of the lower isopleth. This results in rapid, shallow breathing.