Breath–to–breath crackle rate variability

1. Crackle Pitch and Rate Do Not Vary Significantly During A Single Examining Session In Patients With Pneumonia, CHF, and IPF Raymond Murphy and Andrey Vyshedskiy, Brigham and Women’s / Faulkner Hospitals, Boston MA Introduction Breath–to–breath crackle rate variability • We have been studying lung sounds using computerized acoustic technology under the assumption that these sounds reflect the underlying pulmonary pathophysiology and that technologic advances now allow decoding of the complex acoustic signals emanating from the lung during respiration. As crackles are an important abnormal lung sound and observer variability in detection of crackles can be large, we were interested in how much variability was present in the crackle rate (CR) and crackle pitch (CP) as determined by computer and the effect of breathing maneuvers on this variability. • The purpose of this study was to determine the breath-to-breath crackle variability during a single examining session and also the influence of breathing effort and cough on the crackle rates in patients with pneumonia (PN), congestive heart failure (CHF), and interstitial pulmonary fibrosis (IPF). 49 patients with Pneumonia Crackle pitch as a function of breathing maneuver. Each patient’s average crackle pitch during the 1st deeper than normal breathing maneuver was compared to that individual’s crackle pitch at each of the other maneuvers. The crackle pitch in each maneuver was expressed as a percentage of the crackle pitch during the 1st deeper than normal breathing. The absolute pitch of crackles during the 1st deeper than normal breathing is shown in brackets. * Pneumonia IPF CHF Between-maneuver crackle variability Examples of crackle variability in individual patients Protocol Materials and Methods • Each patient’s crackle rate during the 1st deeper than normal breathing maneuver was compared to that individual’s crackle rate at each of the other maneuvers. • Crackle rate in each maneuver was expressed as a percentage of the crackle rate during the 1st deeper than normal breathing maneuver. • t-Tests were performed on this data. Statistically significant changes are indicated by a star *. All other changes are not statistically significant. • In 80% of pneumonia patients crackle rate increased in deeper than normal breathing as compared to normal breathing. Notice that crackle pitch varies little between breathing maneuvers in all three conditions. • A convenience sample of 49 patients with PN, 52 patients with CHF, and 18 patients with IPF in a community teaching hospital were examined with a 16 channel lung sound analyzer (Stethographics, Inc., Model 1602). • The Stethograph (STG) automatically identifies and quantifies a number of acoustic parameters including the crackle rate (CR). • Patients selected for the study had CR > 2cr/breath during deeper than normal breathing and wheeze rates < 20% • Note the small number of crackles during shallow breathing in this patient. This was a common finding in patients with PN. Within-maneuver crackle rate variability (expressed as a percentage of CR during complete 20 second recordings ± SD): Between-maneuver crackle variability Within-maneuver crackle rate variability Summary 18 patients with IPF * Within-maneuver crackle pitch variability (expressed as a percentage of crackle pitch during complete 20 second recordings ± SD): Clinical Implications All patients were instructed to perform several breathing maneuvers in the following sequence: 1. normal breathing, 2. deeper than normal breathing, 3. coughing,4. deeper than normal breathing, 5. a vital capacity maneuver, and 6. repeat deeper than normal breathing. • Note: The crackle rate was greater during shallow breathing compared to deeper than normal breathing. • In 67% of patients crackle rate decreased in deeper than normal breathing as compared to normal breathing. • Crackles in all three conditions were surprisingly stable. • Neither the average crackle rate, nor the average crackle pitch changed significantly from breath to breath or from one deeper than normal breathing maneuver to another even when these maneuvers were separated by the cough and the vital capacity maneuvers. 52 patients with CHF • The finding that the assessment of crackle rate is relatively reproducible on repeated measurements on a single examination provides evidence that it can be used to follow the course of patients with CHF, PN and IPF. • We found significant changes in CR from normal breathing to deeper than normal breathing in PN and IPF patients. During deeper than normal breathing crackle rates on average were higher in pneumonia patients and lower in IPF patients. We realize that this may have limited clinical value, but it may help clinicians considering the diagnosis of IPF in cases where they might otherwise not suspect it. • Each breathing maneuver was recorded for 20 seconds. • The CR in each breathing maneuver was expressed as a percent of the CR during the first “deeper than normal” breathing maneuver. • Crackle rates were relatively stable from maneuver to maneuver. This was a common finding in patients with CHF. • In 50% of patients crackle rate decreased in deeper than normal breathing compared to normal breathing.