Steve S. Kraman

Fundamentals of lung auscultation.

Computer-assisted techniques allow detailed analysis of the acoustic and physiological aspects of lung sounds. This short review of classic lung sounds includes both audio clips and interpretations made in the light of modern pulmonary acoustics.

Renal failure in the respiratory intensive care unit.

The development of renal failure during respiratory failure is of grave prognostic significance. In 686 patients with respiratory failure, 74 developed renal failure; these had a mortality of 80%. The leading predisposing factors are: 1) gastrointestinal bleeding with hypovolemic shock; 2) sepsis with shock; 3) drug induced nephrotoxicity; and 4) hypotension. With antacid gastric neutralization, judicious use of nephrotoxic antibiotics, the incidence of renal failure can be reduced. Once renal failure occurs, early dialysis may increase the chances of recovery in these critically ill patients.

An acoustic model of the respiratory tract

With the emerging use of tracheal sound analysis to detect and monitor respiratory tract changes such as those found in asthma and obstructive sleep apnea, there is a need to link the attributes of these easily measured sounds first to the underlying anatomy, and then to specific pathophysiology. To begin this process, we have developed a model of the acoustic properties of the entire respiratory tract (supraglottal plus subglottal airways) over the frequency range of tracheal sound measurements, 100 to 3000 Hz. The respiratory tract is represented by a transmission line acoustical analogy with varying cross sectional area, yielding walls, and dichotomous branching in the subglottal component. The model predicts the location in frequency of the natural acoustic resonances of components or the entire tract. Individually, the supra and subglottal portions of the model predict well the distinct locations of the spectral peaks (formants) from speech sounds such as /a/ as measured at the mouth and the trachea, respectively, in healthy subjects. When combining the supraglottic and subglottic portions to form a complete tract model, the predicted peak locations compare favorably with those of tracheal sounds measured during normal breathing. This modeling effort provides the first insights into the complex relationships between the spectral peaks of tracheal sounds and the underlying anatomy of the respiratory tract.

Effects of lung volume and airflow on the frequency spectrum of vesicular lung sounds

UNLABELLED The purpose of this study was to determine whether the vesicular lung sound frequency spectrum is affected by changes in lung volume and airflow. Nine healthy young nonsmokers were studied. The dependent variables were the points that divide the power spectrum of the vesicular lung sound into quarters (1st, 2nd and 3rd quartiles (Q1, Q2 and Q3]. Recording sites were the right upper anterior (RUL) and lower posterior (RLL) chest wall. Lung sounds were high-pass filtered at 100 Hz. To evaluate the effect of volume, lung sounds were recorded during an inspiratory vital capacity (VC) maneuver at near constant airflow rates. The spectral parameters were determined at each sixth of the VC. To assess the effects of airflow, 5 of the subjects breathed from resting lung volume at peak inspiratory airflows of between 1 and 3.0 L/sec for a total of 16 breaths each and the frequency parameters of the lung sounds occurring during peak inspiratory airflows were determined. RESULTS Volume effects: only at the RUL was there a small but significant decrease in all three parameters with increasing lung volume. Airflow effects: all parameters were independent of airflow except for a weakly positive relationship (r = 0.285, P less than 0.05) for Q3 at the RUL location. Individually, there were weakly significant trends in three of the five subjects. These data suggest that the frequency composition of the vesicular lung sound in groups of healthy adults is not systematically affected by changes in lung volume or airflow.

The Forced Expiratory Wheeze

When a subject exhales forcefully, a wheeze is usually heard during the latter part of the maneuver. The origin and mechanism of this wheeze has been the subject of speculation but this has never been

Bilateral asymmetry of respiratory acoustic transmission

Sonic noise transmission from the mouth to six sites on the posterior chest wall is measured in 11 healthy adult male subjects at resting lung volume. The measurement sites are over the upper, middle and lower lung fields and are symmetric about the spine. The ratios of transmitted sound power to analogous sites over the right (R) and left (L) lung fields are estimated over three frequency bands: 100–600 Hz (low), 600–1100 Hz (mid) and 1100–1600 Hz (high). A R-L dominance in transmission is measured at low frequencies, with a statistically significant difference observed at the upper site. No significant asymmetry is observed in any measurement site at mid or high frequencies. A theoretical model of sound transmission that includes the asymmetrical anatomy of the mediastinal structures is in agreement with the observed asymmetry at low frequencies. These findings suggest that the pathway of the majority of sound transmission from the trachea to the chest wall changes from a more radial to airway-borne route over the measured frequency range.

Effects of breathing pathways on tracheal sound spectral features

The spectra of sounds recorded over the trachea of adults typically reveal peaks near 700 and 1500 Hz. We assessed the anatomical determinants of these peaks and the conditions contributing to their presence. We studied five adult subjects with normal lung function, measuring sounds at the suprasternal notch and on the right cheek. The subjects breathed at target airflows of 15 and at 30 ml sec(-1) kg(-1) both through the mouth with nose clips and then through the mouth and nose using a cushioned face mask. The mouth breathing maneuvers were performed with three lengths (3.6, 21.1 and 38.6 cm) of 2.6 cm diameter tubing between the mouth and the pneumotachograph. The nose breathing maneuver was performed with the longest tube (between the mask and pneumotachograph). The signals occurring at the target flows +/- 20% were used to create averaged, spectral estimates. We found that all subjects had two predominant spectral peaks; a approximately 700 Hz peak loudest over the cheek and a approximately 1500 Hz peak loudest over the trachea. The frequency of both peaks negatively correlated with body height (and presumably, airway length). There was no systematic effect of breathing phase, flow rate or length of the tube connecting the mouth to the pneumotachograph on the spectral peaks. Breathing into the mask and breathing through the nose did markedly alter the spectra. We conclude that the higher tracheal sound peak reflects resonance within the major airways and is relatively independent of extrathoracic influences during mouth breathing through a tube.

Air-Borne and Tissue-Borne Sensitivities of Bioacoustic Sensors Used on the Skin Surface

Measurements of body sounds on the skin surface have been widely used in the medical field and continue to be a topic of current research, ranging from the diagnosis of respiratory and cardiovascular diseases to the monitoring of voice dosimetry. These measurements are typically made using light-weight accelerometers and/or air-coupled microphones attached to the skin. Although normally neglected, air-borne sounds generated by the subject or other sources of background noise can easily corrupt such recordings, which is particularly critical in the recording of voiced sounds on the skin surface. In this study, the sensitivity of commonly used bioacoustic sensors to air-borne sounds was evaluated and compared with their sensitivity to tissue-borne body sounds. To delineate the sensitivity to each pathway, the sensors were first tested in vitro and then on human subjects. The results indicated that, in general, the air-borne sensitivity is sufficiently high to significantly corrupt body sound signals. In addition, the air-borne and tissue-borne sensitivities can be used to discriminate between these components. Although the study is focused on the evaluation of voiced sounds on the skin surface, an extension of the proposed methods to other bioacoustic applications is discussed.

Advocacy: The Lexington Veterans Affairs Medical Center

BACKGROUND: After the Veterans Affairs Medical Center (VAMC) in Lexington, Kentucky, lost two major malpractice cases in the mid-1980s, leaders started taking a more proactive approach to identifying and investigating incidents that could result in litigation. An informal risk management team met regularly to discuss litigation-prone incidents. During one in-depth review, the team learned that a medication error had caused the patients death. Although the family would probably never have found out, the team decided to honestly inform the family of exactly what had happened and assist in filing for any financial settlement that might be appropriate. This decision evolved into an organization wide full disclosure policy and procedure. DISCLOSURE POLICY AND PROCEDURE: The Lexington VAMCs policy on full disclosure includes informing patients and/or their families of adverse events known to have caused harm or injury to the patient as a result of medical error or negligence. The disclosure includes discussions of liability and also includes apology and discussion of remedy and compensation. RESULTS: Full disclosure is the right thing to do and the moral and ethical thing to do. Moreover, doing the right thing actually seems to have mitigated the financial repercussions of inevitable adverse events that result in injury to patients. As reported in 1999, Lexington VAMC was in the top quarter of medical centers for number of tort claims filed but was in the lowest quarter for malpractice payouts resulting from these torts.

Lung sounds: Relative sites of origin and comparative amplitudes in normal subjects

Little is known about the comparative amplitude of the vesicular lung sounds heard over the lung apices and bases. Neither is the site of origin of these sounds known. Recent studies suggest that differences in amplitude between the left and right sides of the chest may be considerable. In order to better assess these differences, and to determine the relative sites of origin of these sounds, a new computerized lung sound measurement technique was employed to study the lung sound amplitude and phase relationships over the left and right posterior lung bases and anterior apices in 9 healthy volunteers. Twenty-four inspiratory breath sounds were recorded simultaneously using 2 microphones at 8 different intermicrophone separations (1 to 8 cm) at those locations. The mean amplitude of the lung sounds so recorded at each location was determined by automated flow-gated measurement at an inspiratory air flow rate of 1.3 l/s. Simultaneously, the degree of similarity of phase between the sounds from both microphones (Subtraction intensity index — SII) was determined. In addition, 3 inspirations were recorded simultaneously by 1 microphone on either side of the sternum in the second intercostal space in order to assess the phase similarity of the lung sounds at these positions. The results showed that the sound intensity at one base (left or right) was significantly greater than at the opposite base in 7 of the 9 subjects. The sound intensity at the left apex was always louder than or equal to that at the right. The subtraction patterns suggested that the sound sources at the apex were more central than at the bases but that additional phase shifting may have occurred during transmission to the chest wall. The sounds recorded from opposite sides of the sternum showed little or no similarity indicating that the sound at this location, though bronchial in character, was not transmitted from the trachea. It is concluded that significant inequality in lung sound amplitude between homologous areas on opposite sides of the chest is a common finding and that the vesicular sounds over the lung apices are possibly produced more centrally than those at the bases but that the trachea is not the source of these sounds.