Inspiratory Flow Rate and Dynamic Lung Function in Cystic Fibrosis and Chronic Obstructive Lung Diseases

¹ From the Pulmonary and Critical Care Medicine Section, Department of Medicine, VA Palo Alto Health Care System, Palo Alto, CA; and the Division of Pulmonary and Critical Care Medicine, Department of Pediatrics, Stanford University Medical Center, Stanford, CA
² From the Division of Pediatric Pulmonology, Department of Pediatrics, Stanford University Medical Center, Stanford, CA
³ From the Genentech, Inc, South San Francisco, CA.
⁴ From the Pulmonary and Critical Care Medicine Section, Department of Medicine, VA Palo Alto Health Care System, Palo Alto, CA
⁵ From the Pulmonary and Critical Care Medicine Section, Department of Medicine, VA Palo Alto Health Care System, Palo Alto, CA; and the Division of Pulmonary and Critical Care Medicine, Department of Pediatrics, Stanford University Medical Center, Stanford, CA; and Genentech, Inc, South San Francisco, CA.

Priscilla S.A. Sarinas, MD, FCCP, Pulmonary and Critical Care Medicine, VA Palo Alto Health Care System, 3801 Miranda Ave-111P, Palo Alto, CA 94304; email: sarinas{at}icon.palo-alto.med.va.gov

Study objectives: The peak inspiratory flow rates (PIFRs) generated by cystic fibrosis (CF) and COPD patients through a range of clinically relevant resistances have not yet been reported (to our knowledge). The objectives of this study were to (1) explore a relevant range of resistive loads and address whether patients with stable CF and COPD can generate the PIFR sufficient to disperse dry-powder inhalants (DPI) and (2) determine whether the optimal inspiratory flow rate effective for delivery of aerosolized pharmacologic therapeutic agents can be attained with a comfort rating acceptable to subjects.

^Design: Prospective, controlled, subject-blinded study.

Setting: Pulmonary function laboratory at the VA Palo Alto Health Care System.

Patients or participants: Thirty-six subjects, including 12 healthy volunteers, 12 subjects with CF, and 12 subjects with COPD were studied.

Measurements: Studies of dynamic lung function and PIFR without and with varying resistances were obtained at a single laboratory visit.

Results: Dynamic lung function and PIFR varied inversely with the resistive load for all patient groups and did not correlate with the disease severity, as indicated by FEV₁ of percent predicted. The average subjective comfort rating for any given resistive load was similar for subjects with CF and COPD.

Conclusions: These results support the conclusion that subjects with stable CF and COPD of varying severity can comfortably generate the necessary flow rates to operate new and currently available DPIs over a wide range of inspiratory resistances.

Key Words: chronic bronchitis • COPD • cystic fibrosis • therapy • emphysema • inspiratory flow rate • inspiratory resistance • inspiratory volume

Submitted on March 17, 1997
Accepted on March 16, 1998