It has been reported that asthmatic and COPD (chronic obstructive pulmonary diseases) patients struggle to use their inhalers correctly. Studies have shown after training the flow rates achieved by patients can be compromised due to the high resistance of their prescribed inhaler. The aim of this work was to provide preliminary data on the future applicability of a diagnostic tool to guide DPI (dry powder inhaler) choice based on inhalation profiles achieved by patients. Inhalation profiles were recorded using a variable resistance device in series with a conventional clinical spirometer for 20 severe asthmatic and 20 COPD patients. The severity of the disease was assessed following GINA guidelines. The patients were asked to inhale as they would when taking their medication. Descriptive metrics were extracted using a computational curve-stripping approach and preliminary analysis is reported here for peak inspiratory flow (PIF). There was no significant difference between groups for a specific inhaler resistance (e.g. 82.51 ± 28.64 Lmin-1 for 0.158 cmH2O resistance in COPD patients and 77.89 ± 28.05 Lmin-1 in severe asthmatics, p < 0.05). However, the study showed that patients without training achieved flow rates (>100 Lmin-1) when inhaling against low resistance (representing a metered dose inhaler). On the other hand, patients inhaled for longer when a high resistance device was simulated than for a low resistance device. Other parameters such as acceleration of the flow and time of inhalation will be taken into account to use the full inhalation profiles for routine clinical guide for inhaler choice.