Inhalation flow rate

Pitcairn, G., Lunghetti, G., Ventura, P., and Newman, S.P., A comparison of the lung deposition of salbutamol inhaled from a new powder inhaler at two inhaled flow rates, Int. J. Pharm., 102 11-18 (1994). 

Ross DL, Schulz RK. Effect of inhalation flow rate on the dosing characteristics of dry powder inhaler (DPI) and metered dose inhaler (MDI) products. J Aerosol Med 1996 9(2) 215-26. 

Every DPI device will exhibit an internal resistance which will determine the inhaled flow rate that a patient can achieve when using the device. As flow rate will inevitably be linked with inhaler performance, it is essential such factors be considered in any in vitro comparative testing of DPIs. 

Table 14 Emitted dose (% of loaded dose) vs. inhalation flow rate (n = 5)...

Fig.8. Real vs mean inhaled flow rate (individual filter)...

A number of pharmaceutical companies are developing INH dehvery systems using both liquid and dry-powder insulin formulations [34,35]. Table 4 briefly indicates those arrived at in phase HI studies. A few companies have developed systems based on hquid formulations, which utilize relatively complex pressurized metred-dose devices or nebuUzation systems to generate appropriately sized aerosolized doses, hi the AERx system inhalation flow rate, inhaled volume and duration are patient-controlled... 

For active devices the situation can be similar to the passive case in terms of the device resistance dictating the inhaled flow rate and hence the flow rate at which the device should be tested. However, just like the pMDI, if the device generates an aerosol that has a velocity relative to the inspired airstieam, some form of stopping distance measurement, such as an oropharyngeal cast or inlet bend, is mandatory. 

Newman S, Moren F, Trofast E, Talaee N, Clarke S. Terbutahne sulphate terbu-taline effect of inhaled flow rate on drug deposition and efficacy. Int J Pharm 1991 74 209-213. 

This is a compact device (Fig. 7) it is quiet in operation and functions at a low inhaled flow rate that is easily achieved by patients with obstructive airways disease (67). 

Figure 4 The relationship between the inhaler resistance and peak inhalation flow rate for healthy volunteers. The two curves indicate a maximum effort and a comfortable effort at inhalation. (From Ref. 28.)...

An experimental relationship between impaction parameter (based on inhaled flow rate) and oropharyngeal deposition from a study with monodisperse particles is shown in Fig. 6.5. The highest value in this relationship is for 6 pm particles inhaled at a flow rate of 67 L/min the lowest for 1.5 pm particles inhaled at 31 L/min [6]. 

Figure 4 The relation between AD F and traeheobronchial deposition in percentage of all inhaled partieles, ealeulated from the regression lines in Figures 2 and 3 The curve has its maximum, 30% traeheobronehial deposition of all inhaled particles, at a AD F of 1365 0,m L/min, whieh eorresponds to an aerodynamie particle size of 6 pm at an inhalation flow rate of 30 L/min.

In general, during normal inhalation flow rates, deposition in the oropharynx may be estimated by the impaetion factor AD F (see Fig. 2). In the future, it would be desirable to develop methods for clinieal use in evaluating oropharyngeal, as well as lung deposition of inhaled drugs. 

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