Advances in Pulmonary Laboratory Testing: Laboratory Requirements
The cost of NO analyzers is currently quite high, in the range of $20,000 to $40,000. Most analyzers were designed for monitoring the delivery of NO, so they are not designed for documentation of exhaled NO. The ideal instrument for measuring exhaled NO would be easy to calibrate and maintain, and it would be integrated into a system with a mouth pressure transducer and a flowmeter to monitor exhaled volume, and possibly a flow restrictor to reduce nasal contamination and to control for the effects of exhaled flow on the level of NO. Computer software would allow the display of concentration vs time graphs and the calculation of various parameters from the tests. Such instruments are just starting to become available. Thus, to set up exhaled NO measurement for clinical or research applications, one may need a high level of expertise in setting up instrumentation, and in acquiring and analyzing data.
In conclusion, the measurement of exhaled NO is a potentially useful test that could be performed in the setting of routine pulmonary function testing to document the state of airway inflammation in patients with asthma. The test appears to be relatively specific for inflammation related to airway eosino-philia and could prove to be a useful indicator of the effectiveness of antiinflammatory therapy in asthma. However, standard methods must be used to avoid contamination by the nose and to standardize the effects of expiratory flow on the measurement. Furthermore, large population studies using standard methods would be useful to determine precise population 95% confidence intervals for the measurement. there
FO Resistance Measurement
Resistance to the movement of gas is calculated from the ratio of pressure change to flow. Resistance is of interest from both a basic science and a clinical perspective because it is an important determinant of the work of breathing (WOB). Total resistance of the respiratory system is a lumped sum of resistance to movement of lung tissue (Rti) and airway resistance (Raw) to the flow of gas. The sum of Rti and Raw for the lung is often called lung or pulmonary resistance. The measurement of Raw would seem to be the most clinically useful parameter as it reflects the state of the airways, though Rti is increasingly recognized as contributing significantly to the WOB at normal breathing frequencies. However, separating these two components of resistance requires very technically demanding or highly invasive techniques that are available only in animal laboratories.