Technique for measurement of oropharyngeal clearance in the elderly

Real-Time In Vitro Assessment of Aerosol Delivery During Mechanical Ventilation

Background: A new real-time method for assessing factors determining aerosol delivery is described.

Methods: A breath-enhanced jet nebulizer operated in a ventilator/heated humidifier system was tested during bolus and continuous infusion aerosol delivery. ^99mTc (technetium)/saline was either injected (3 or 6 mL) or infused over time into the nebulizer. A shielded gamma ratemeter was oriented to count radioaerosol accumulating on an inhaled mass (IM) filter at the airway opening of a test lung. Radioactivity measured at 2–10-minute intervals was expressed as % nebulizer charge (bolus) or % syringe activity per minute infused. All circuit parts were measured and imaged by gamma camera to determine mass balance.

Results: Ratemeter activity quantitatively reflected immediate changes in IM: 3 and 6 mL bolus IM% = 16.1 and 18.8% in 6 and 14 minutes, respectively; infusion IM% = 0.64 + 0.13 (run time, min), R² 0.999. Effect of nebulizer priming and system anomalies were readily detected in real time. Mass balance (basis = dose infused in 90 minutes): IM 39.2%, breath-enhanced jet nebulizer residual 35.5%, circuit parts including humidifier 23.4%, and total recovery 98.1%. Visual analysis of circuit component images identified sites of increased deposition.

Conclusion: Real-time ratemeter measurement with gamma camera imaging provides operational feedback during in vitro testing procedures and yields a detailed analysis of the parameters influencing drug delivery during mechanical ventilation. This method of analysis facilitates assessment of device function and influence of circuit parameters on drug delivery.

Deposition and clearance: unique problems in the proximal airways and oral cavity in the young and elderly

Prospective longitudinal studies measuring aerosol behavior in the respiratory tract as humans age have not been performed. The present paper reviews observations related to aging of the respiratory tract and other effects more likely due primarily to disease and iatrogenic causes. Upper airway deposition was found to approximate 50% in children during inhalation of drugs thought to be designed primarily for deposition in the lower respiratory tract. In older subjects, aging per se did not have a major impact on the deposition of aerosols. Disease processes that develop with age were shown to be the primary cause of deposition abnormalities. Flow-limitation in central airways was proposed as a major factor responsible for central airway deposition as well as abnormal clearance in common obstructive lung diseases. The oral cavity, a source of pathogenic organisms causing pneumonia, was also studied in the elderly. Salivary clearance, often abnormal in the aged, was related to colonization with pathogenic bacteria. Salivary clearance was not obviously reduced by aging per se but by iatrogenic sources such as drug therapy for other diseases.

Oral clearance and pathogenic oropharyngeal colonization in the elderly

The elderly have an increased incidence of oropharyngeal colonization with respiratory pathogens, a well-known risk factor for the development of pneumonia. Changes in the oral milieu may occur secondary to decreased salivary production and abnormalities in swallowing. These abnormalities, common in the elderly, may result in impaired clearance of organisms, allowing pathogenic colonization. To test this hypothesis, we performed a prospective cross-sectional analysis of 75 elderly institutionalized patients and measured oral clearance using (99m)Tc-human serum albumin (HSA) administered to the oropharynx. Oropharyngeal cultures, salivary cell populations, elastase activity, and clinical parameters were measured simultaneously. Retention of radiolabel ranged from 100% to 2.3% over 120 min of observation. Clearance in the oropharynx was significantly decreased in those patients who had oropharyngeal colonization with gram-negative bacilli (GNB), Staphylococcus aureus (SA), or yeast compared with those demonstrating normal flora by 95% confidence intervals. Decreased clearance was also seen in patients on antidepressants by 95% confidence levels. The absolute number of salivary lymphocytes/ml and buccal cells/ml was increased in colonized patients versus noncolonized persons (mean +/- SEM, 128 x 10(3) +/- 49 x 10(3), 25.4 +/- 11.6 x 10(3)). Elastase activity was elevated in patients who had GNB compared with patients without GNB (mean +/- SEM, 10.6 nM +/- 5.7, versus 2.2 nM +/- 1.2, p = 0.036). We conclude that a decrease in salivary clearance of potentially pathogenic organisms may be a major risk factor for the development of colonization in the elderly.