Particle Velocity Is Important in Drug Delivery
- Particle velocity depends on two main factors: (1) Particle Diameter and (2) IFR (Inspiratory Flow Rate)
- Particle size is determined by drug formulation. HFA formulation results in finer particle size resulting in better drug deposition. CFC formulations are no longer available as of 2012.
- Slow particle velocity is a key determinant in drug deposition.
- Low flow rates allow small particles or the respirable particles (2-3 microns in size) to deposit more deeply into the lung.
- High flow rates tend to allow the large non-respirable particles (greater than 3 microns in size) to be deposited mainly in the oral cavity.
Particle Velocity Varies Directly With IFR or Inversely With Airway Diameter
- This physiologic relationship is defined by the equation of V=IFR/A
- V is defined as particle velocity
- IFR is defined as Inspiratory Flow Rate generated by a patient
- A is defined as Airway Diameter
- As IFR increases or airways narrow, particle velocity increases
- High IFR results in turbulent airflow as does narrowed airways
Flow Rate Determines Gas Patterns
- Inspiratory flow rate determines the type of gas pattern that enters the respiratory tract.
- High inspiratory flow rates produce turbulent flow patterns, low inspiratory flow rates produce laminar flow patterns.
- Both in vitro and in vivo studies revealed that laminar flow patterns deposit inhaled medication deeper into the bronchi.
- Turbulent air flow patterns repeatedly have been shown to result in deposition of most of the medication plume into the oral cavity or upper airways.
- Prescribers of medications have no control over drug formulations. However, through the use of the RiteFlo™ you can obtain for your patients repeatedly the correct IFR, resulting in ideal respirable particle size deposition into your patients lungs.
Why Small Airways Are Targeted For Therapy?
- Distal airways are a major site of airway caliber obstruction. They are also a site of airway hyper-responsiveness
- Even with normal lung function tests, distal airways show high airflow resistance
- Small airways in chronic asthmatics contribute 51% of total airway resistance compared to 24% in normal patients
- Greater percentage of activated eosinophils and their mediators are found in the distal airways compared to the proximal airways
- Disease of the small distal airways is more intense compared to central airways
- Distal airways have a greater concentration of steroid receptors
Steroid Particle Size of Different Steroid Formulations
The NHLBI/EPRIII 2007 and WHO/Global Initiative For Asthma Guidelines Recommend A Spacer/Holding Chamber Emit An Optimum Flow Rate of 30 L / min For MDI’s
- RiteFlo™ Assures this guideline recommendation of 30 L/min flow rate
- 30 L/min flow rate allows for ideal particle (1-2.5 microns) deposition
- No training or coaching required with RiteFlo™ to obtain ideal flow rate
- Consistent performance with every inhalation
- Minimal time for health care professionals to educate patients