Lung deposition of inhaled particles depending on respiratory profile
Impaction of particles is dependent on size and velocity of flow. While slowly inhaled particles may follow the inspiratory flow unhindered through narrowings and curves faster travelling particles deposit already in the upper respiratory tract. Particles smaller then 2 to 3 µm are not affected by impaction and reach peripheral airways even more effectively during slow inhalation (< 30 l/min).
Regarding sedimentation the inspiratory flow rate does not play a crucial role. However protracted flow expands the time in which the amount of aerosol taken with one breath stays in the respiratory tract, thus leading to a higher rate of deposition by sedimentation.
Following permanent aerosol generation the applied dose increases the deeper the breath. Since the volume of functional dead space in the respiratory tract averages about 150-300 ml particles only reach more distal parts of the lung with an inspiratory volume of more than 300 ml. Additionally the duration of a breath increases with its volume also leading to a higher lung deposition.
Voshaar T. Therapie mit Aerosolen. 2005. Uni-Med: Bremen
DEPOSITION OF PARTICLES DEPENDING ON SIZE, INSPIRATORY VOLUME, AND AIR FLOW
-video to be updated-
In this interactive tool sliders can be moved to choose a certain inspiratory flow rate, inspiratory volume or particle size. Colouring of the respiratory tract indicating the amount of inhaled aerosol reaching certain regions will change according to the chosen values. Additionally, clicking on the buttons “extra-thoracic”?, “bronchial”? or “alveolar”? will shift the sliders to values, which most likely lead to aerosol deposition in the chosen region.
INFLUENCE OF OBSTRUCTION IN THE RESPIRATORY SYSTEM ON AEROSOL DEPOSITION
Morphological alterations of airways in asthmatics do not seem to have much impact on the efficacy of inhaler devices in average. Interindividual variability of the anatomical conditions of the pharyngeal area play a more important role concerning lung deposition of aerosols. Comparative narrowing in this region leads to a higher rate of oropharyngeal particle deposition. Concerning spirometric measures in contrast to expiratory flow the peak inspiratory flow rate (PIF) in asthmatics normally does not differ considerably from the PIF generated in normal subjects. Even in people with chronic obstructive lung disease (COPD) and cystic fibrosis no significant differences are observed between patients and healthy volunteers. Only few studies exist exploring inspiratory parameters. Mostly variables like inspiratory flow rates are studied in trials on the efficacy of inhaler devices. However in these studies patients with obstructive lung diseases are assessed concerning their ability to generate sufficient inspiratory flows but rarely in comparison with normal subjects. One study investigated dynamic lung functions in patients with obstructive lung diseases compared with healthy people. Inspiratory manoeuvres performed against increasing resistive loads only slightly reduced the inhaled volumes probably due to fatigue. Simultaneously the degree of comfort experienced by the subjects decreased monotonically with increasing resistance. No significant differences were observed between patients and normal subjects in any variable studied.
Colasanti RL, Morris J, Madgwick RG, Sutton L, Williams EM. Analysis of tidal breathing profiles in cystic fibrosis and COPD. 2004. Chest; 125:901-908
Hnatiuk OW, Sierra A, Chang AS. Evaluation of the normal inspiratory flow-volume curve. 1998. Respiratory Care; 43 (12): 1058-1063
Sarinas PSA, Robinson TE, Clark AR, Canfield J, Chitkara RK, Fick RB. Inspiratory flow rate and dynamic lung function in cystic fibrosis and chronic obstructive lung disease. 1998. Chest; 114: 988-992
Svartengren K, Lindestad PA, Svartengren M, Philipson K, Bylin G, Canner P. Deposition of inhaled particles in the mouth and throat of asthmatic subjects. 1994. European Respiratory Journal; 7 (8): 1467-1473
DEPOSITION IN MOUTH AND THROAT DEPENDENT ON CHARACTERISTICS OF PHARYNX AND LARYNX
PSYCHOSOCIAL AND DEVICE-RELATED ASPECTS OF PATIENT COMPLIANCE
Studies in adults and children have shown that about 50% of patients are not compliant concerning application of regular treatments. Noncompliance may be defined as the failure of treatment to be taken as agreed upon by the patient and health care professional. Several factors are related with noncompliance like regression of the diagnosis and its severity, communication and beliefs of the patient concerning treatment safety and disease control.
However even if these psychosocial factors are balanced still many patients fail to comply with the treatment due to problems in the correct use of their inhalation devices. Even investigator-independent assessment of inhalation technique with a computerized device revealed problems in using a metered-dose inhaler of 42% concerning inspiratory flow rate, 47% regarding coordination, 24% holding breath at the end of inspiration, and 39% inhaling acceptably deeply.
Several features, which can be implemented in inhalation devices, are thought to rise patient compliance. Feedback mechanisms support the patient concerning correct inhalation manoeuvre thereby improving the user’s technique and compliance. Dose counters will give patient control over number of doses applied and help to reassure, whether daily doses have been taken or not. Many patients, especially on corticosteroid treatment, may be afraid of overdosing. Therefore an overdose prevention mechanism will surely improve compliance with the treatment.
Crompton GK. How to achieve good compliance with inhaled asthma therapy. 2004. Respiratory Medicine; 98 (Suppl.2): S35-S40
Goodman D, Israel E, Rosenberg M, et al. The influence of age, diagnosis, and gender on proper use of metered-dose inhalers. 1994. Am J Crit Care Med; 150: 1256-1261
O´Byrne P. GINA Executive Committee. Global strategy for asthma management and prevention. 2004. National Institutes of Health. Publication No 02-3659
ASPECTS OF IMPROVED PATIENT COMPLIANCE