Jeffrey P. Mansfield

An acoustical guidance and position monitoring system for endotracheal tubes

A prototype instrument to guide the placement and continuously monitor the position of an endotracheal tube (ETT) was developed. An incident audible sound pulse is introduced into the proximal ETT and detected as it travels down the ETT via a miniature microphone located in the wall. This pulse is then emitted from the tube tip into the airways and the reflected signal from the airways is detected by the microphone. A well defined reflection arises from the point where the total cross sectional area of the airways increases rapidly, and the difference in timing between detection of the incident pulse and this reflection is used to determine ETT position or movement. This reflection is not observed if the ETT is erroneously placed in the esophagus. The amplitude and polarity of an additional reflection that occurs at the ETT tip is used to estimate the cross-sectional area of the airway in which the ETT is placed. This combined information allows discrimination between tracheal and bronchial intubation and can be used to insure an adequate fit between the ETT and trachea. The instrument has proven extremely reliable in multiple intubations in eight canines and offers the potential to noninvasively and inexpensively monitor ETT position in a continuous manner.<<ETX>>

Miniature acoustic guidance system for endotracheal tubes

Ensuring that the distal end of an endotracheal tube (ETT) is properly located within the trachea, and that the tube is not obstructed by mucus deposition, is a major clinical concern in patients that require mechanical ventilation. A novel acoustic system was developed to allow for the continuous monitoring of ETT position and patency. A miniature sound source and two sensing microphones are placed in-line between the ventilator hose and the proximal end of the ETT. Reflections of an acoustic pulse emitted into the ETT lumen and the airways are digitally analyzed to estimate the location and degree of lumen obstruction, as well as the position of the distal end of the tube in the airway. The system was evaluated through in vitro studies and in a rabbit model. The system noninvasively estimated tube position in vivo to within roughly 4.5 mm, and differentiated between proper tracheal, and erroneous bronchial or esophageal intubation in all cases. In addition, the system estimated the area and location of lumen obstructions in vitro to within 14% and 3.5 mm, respectively. These findings indicate that this miniature technology could improve the quality of care provided to the ventilated adult and infant.

Acoustic method to quantitatively assess the position and patency of infant endotracheal tubes : Preliminary results in rabbits

In this preliminary laboratory study, an acoustical method was evaluated to quantitatively assess the position and patency of an infant‐size endotracheal tube (ETT) by in vivo and in vitro measurements. The method consists of emitting an audible sound pulse into the ETT and the airways, and deriving position and patency information from the timing and characteristics of the returning echoes. The methods capacity to measure ETT changes of position in the tracheae of five anesthetized New Zealand white rabbits (weight, 4.3–4.9 kg; age, 1.5–3 years) was found to be accurate to 0.7 ± 3.6 mm (mean ± 95% CI) over a distance of 5 cm. The method was also shown to reliably differentiate between tracheal, bronchial, and esophageal intubations by means of an acoustically inferred diameter of the passageway just beyond the ETT tip. To assess the accuracy of estimating lumen obstruction, in vitro acoustical measurements were performed in different size ETTs (2.5, 3.0, 3.5, and 4.0 mm inner diameter), with obstructions ranging from 5–100% reduction in cross‐sectional area. The system identified the sizes of these obstructions to within ±7%. This technology has the potential for continuous, computer‐based monitoring of breathing‐tube function through instantaneous detection of ETT malposition or obstruction before it leads to a serious medical condition. Pediatr Pulmonol. 1998; 26:354–361.

Detection of respiratory sounds at the external ear

Several clinical and ambulatory settings necessitate respiratory monitoring without a mouthpiece or facemask. Several studies have demonstrated the utility of breathing sound measurements performed on the chest or neck to detect airflow. However, there are limitations to skin surface measurements, including susceptibility to external noise and transducer motion. Thus, this two-part study investigated a novel location for breathing sound measurements: the external ear. The first study investigated characteristics of sound transmission from the oropharynx to the external ear in 19 adults (nine males). Broadband noise was directed into the oropharynx through a tube and mouthpiece and measured indirectly via an accelerometer affixed to the cheek. Resultant transmission to the external ear was measured with a microphone inserted into an earplug that provided acoustic isolation from ambient noise. Near-unity coherence estimates (>0.9) between the sounds recorded at the external ear and the oropharynx were observed up to approximately 800 Hz, indicating a low-frequency region of preferred transmission. In the second study, each of 20 subjects (nine males) breathed through a pneumotachograph at targeted shallow (3.0 mL/s/kg) and tidal (7.5 mL/s/kg) flows normalized to body mass, and the resulting sounds were recorded at the external ear. Recordings during breath hold measured background noise. Shallow and tidal expiratory flows, respectively, produced signal-plus-noise-to-noise [(S+N)/N] ratios of 6.7/spl plusmn/4.1 dB and 14.0/spl plusmn/5.3 dB (mean/spl plusmn/standard deviation) across all subjects between 150 and 300 Hz. Concurrent inspiration demonstrated (S+N)/N ratios of 6.6/spl plusmn/3.9 dB and 14.9/spl plusmn/6.3 dB. Thus, the external ear shows promise as an anatomic site to detect and monitor breathing in a relatively noninvasive and unobtrusive manner.

In-line acoustic system to position and monitor infant-sized endotracheal tubes

Ensuring that the distal end of an endotracheal tube is properly located within the trachea, and that the tube is not obstructed by mucous deposition, is a major clinical concern. This concern is heightened in infant care, where the relatively small geometries predicate higher risks. A novel acoustic system was developed to allow for the continuous monitoring of endotracheal tube position and patency. A miniature sound source and two sensing microphones are placed in-line between the ventilator hose and the proximal end of the endotracheal tube. Reflections of an acoustic pulse from the endotracheal tube lumen and the airways are digitally analyzed to estimate the location and degree of obstruction, as well as the position of the distal end of the tube in the airway. The system was evaluated in a rabbit model. During advancement and retraction of the distal end of the tube within the trachea, changes in position were estimated acoustically to within -0.4/spl plusmn/2.0 mm (mean /spl plusmn/95% CI). Through reflection analysis, the system reliably differentiated tracheal from improper bronchial or esophageal placement in all cases. In addition, the system acoustically estimated the area of intralumenal obstruction to within 5.4/spl plusmn/8.6%.

Echo‐based neonatal breathing tube monitoring system.

A device to monitor the position and patency of neonatal breathing tubes (endotracheal tubes, ETT) was developed based on a pulse‐echo technique originally employed in a system for adult breathing tubes [J. P. Mansfield and G. R. Wodicka, J. Sound Vib. 188(2), 167–188 (1995)]. A 100 μs duration sound pulse is emitted into the neonatal ETT via a wave tube containing a miniature sound source and a miniature microphone. The microphone detects echoes from acoustic impedance changes arising largely from changes in cross‐sectional area within the ETT lumen and airways. The delays and amplitudes of echoes from obstructions within the ETT are used to estimate their respective locations and sizes. An echo arising from the ETT tip provides an estimate of the cross‐sectional area just beyond the tube tip and is used to distinguish between proper tracheal and erroneous bronchial or esophageal intubations. Determination of tracheal position is accomplished by tracking the delay of a characteristic echo which arises fr...

Monitoring of breathing tube position and patency in situ using reflected sound

A new technique that acoustically interrogates an intubated breathing tube to yield clinically useful patency and position information was developed. A miniature speaker connected to the proximal tube end generates a sonic pulse that propagates down the tube, and the resulting echoes from within the tube and airways are measured by a miniature microphone. During intubations of anesthetized canines, the technique: 1) reliably differentiated between tracheal, bronchial, and esophageal intubations; 2) accurately quantified tube movements; 3) provided the location and degree of lumenal obstructions; and 4) detected extubation or disconnection from the ventilator hose. This technique offers an inexpensive and noninvasive mechanism to monitor breathing tubes in situ.

Determination of breathing tube position and patency using acoustic reflectometry

A new technique for determining the position and patency of tubes placed within the body using acoustic reflectometry was developed. The technique was used to guide and monitor endotracheal tubes (ETT) in four canines requiring breathing assistance during surgery. An incident sound pulse, generated by a small speaker in a tube, was injected into the proximal end of the ETT. The pulse then traveled down the ETT, was emitted into the airways, and the resulting reflections were measured by a microphone as they propagated back up the tube toward the speaker. A characteristic inverted reflection from the airways was measured and its timing was used to determine ETT position or movement. In addition, the reflection from the distal end of the ETT was used to estimate the diameter of the intubated airway. The location and degree of obstruction in the ETT was also estimated. The information provided by the device insured proper tracheal placement, patency, and accurate detection of ETT movement. [Work supported by...