Novel, Noninvasive Parameter Useful in Measuring Lung Function

SAN DIEGO—The Pleth Variability Index (PVI)—an automated measure derived from the pulse oximetry wave form of the dynamic change in the perfusion index (PI) that occurs during the respiratory cycle—offers a quick, noninvasive way to reflect degree of airway obstruction in patients with lung disease, and may be used to determine the adequacy of exercise, according to the findings of two separate studies presented at Chest 2009.

AIRWAY OBSTRUCTION

In a pilot study of patients with severe airway obstruction in a small pulmonary practice, researchers used a pulse co-oximeter capable of deriving PVI and compared the results with spirometry tests performed during the same visit. Patients were divided into two groups, more obstructed (ie, mean FEV₁ to FVC ratio of 0.44) and less obstructed (mean FEV₁ to FVC ratio of 0.72). PVI in the more obstructed group (n = 54) was significantly higher at 29.7, compared with the less obstructed group (n = 55) at 25.2.

“Patients with obstructive lung disease need to be evaluated regarding their severity of obstruction in a quick and easy fashion,” suggested Mary L. Zaremba, APRN-BC, and colleagues from St. Clair Pulmonary and Critical Care, Port Huron, Michigan. “Pulse oximetry with PVI may be a useful way to screen patients for airway obstruction where spirometry is not readily available or patients are unable to perform adequate spirometric maneuvers. In acute care settings, PVI may be a quick and useful adjunct in evaluating severity of obstruction in patients with obstructive lung disease.”

PULMONARY REHABILITATION

In another study, Ms. Zaremba and colleagues found that PVI also may be a useful parameter for measuring exercise adequacy in patients with obstructive lung disease during pulmonary rehabilitation. In addition, this may help in setting individualized goals for adequate intensity of exercise for each patient, they noted.

The researchers monitored patients’ PVI, PI, and heart rate before and after exercise therapy and found that PVI was significantly higher after adequate exercise than before, with increases similar to those in heart rates. Before exercise, PVI averaged 27.33 and heart rates averaged 77.37. After exercise, PVI averaged 32.04 and heart rates averaged 85.67. PI rates were not significantly different.

“Pulsus paradoxus may be accentuated in patients with lung disease particularly obstructive due to the influence of intrathoracic pressure changes on cardiac output. Increase in PVI may reflect those changes quickly and noninvasively and may be a useful measure of adequacy of exercise in a pulmonary rehabilitation program,” Dr. Zaremba and colleagues explained. “Further, physiological testing of PVI in relation to other metabolic and cardiac parameters during exercise may help define its role in a pulmonary rehabilitation program.”

—Rebecca K. Abma

Suggested Reading
Abu-Hilal MA, Mookadam F. Pulsus paradoxus; historical and clinical perspectives. Int J Cardiol. 2009 May 21; [Epub ahead of print].

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