title: Comparison of direct and indirect measurements of respiratory airflow: implications for hypopneas.
abstract: The purpose of this study was to compare indirect methods for measuring respiratory airflow, such as temperature difference between inspired and expired air, thoracoabdominal movements, and nasal respiratory-airflow pressures-with a more direct measurement of minute ventilation using a head-out body plethysmograph. Measurements were obtained in healthy, awake, seated subjects during sequences of different levels of voluntary hypoventilations at 20 breaths/minute and analyzed to determine how well different methods could identify hypopneas (defined as reduction in minute ventilation by 50% or more). The results varied widely between different methods. Sensitivities ranged from 0 to 1, specificity ranged from 0.33 to 1, positive predictive values (PPV) ranged from 0 to 0.73, negative predictive values (NPV) ranged from 0.68 to 0.93. Cohen's kappa varied between 0 and 0.65 The poorest agreement was for the thermistor method, and the best agreement was obtained when a combination of thoraco-abdominal movements and nasal respiratory-airflow pressure was employed (sensitivity = 0.86, specificity = 0.83, PPV = 0.71, NPV = 0.92, Cohen's kappa = 0.65). We conclude that none of the indirect methods investigated, individually or in combination, proved adequate for identification of voluntary hypopneas in awake individuals.
authors.affiliation: ENT Department, University of Lund, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Berg
authors.forename: J S
authors.initials: JS
authors.lastname: Haight
authors.forename: V
authors.initials: V
authors.lastname: Yap
authors.forename: V
authors.initials: V
authors.lastname: Hoffstein
authors.forename: P
authors.initials: P
authors.lastname: Cole
mesh_terms: D006801:Humans; D010991:Plethysmography; D012123:Pulmonary Ventilation; D012891:Sleep Apnea Syndromes / Q000175:diagnosis*; D014851:Wakefulness