Biomedical subjects

N Gavriely

Publications and source records attributed to N Gavriely.

At least 37 records · Page 2Linked to original sources

PubMed1995

Electrically-activated dilator muscles reduce pharyngeal resistance in anaesthetized dogs with upper airway obstruction.

There is current controversy as to whether electrical stimulation of upper airway musculature can be used us a beneficial treatment modality in patients with obstructive sleep apnoea syndrome. Increased upper airway (UAW) muscle activity decreases UAW resistance (Ruaw) in isolated UAW of dogs. In the present study, we evaluated the effect of UAW muscle contraction on UAW patency in anaesthetized dogs in vivo breathing spontaneously through partially and completely obstructed UAW. Airflow and supraglottic pressure were measured to obtain Ruaw. Ruaw could be regulated by inhalation of a rubber balloon implanted transcutaneously in the pharyngeal submucosa to produce partial or complete obstruction. Wire electrodes were implanted bilaterally into the genioglossus (GG), geniohyoid (GH), sternothyroid (ST), and sternohyoid (SH) muscles for electrical stimulation (ES), and into the alae nasi for electromyographic (EMG) recording. Three levels of electrical stimulation were delivered to each muscle before and during partial or complete UAW obstruction. Genioglossus and geniohyoid stimulation both resulted in a significant reduction in Ruaw, which was most pronounced during partial obstruction, reducing Ruaw from 54 +/- 11 to 14 +/- 3 and from 74 +/- 12 to 31 +/- 5 cmH2O.L-1.s, respectively. At low voltage, stimulation of the genioglossus was more effective than stimulation of the geniohyoid in reducing Ruaw. Furthermore, electrical stimulation of the genioglossus but not of the geniohyoid released total obstruction. In contrast, electrical stimulation of the sternohyoid and sternothyroid produced no significant change in Ruaw. These findings demonstrate that selective UAW dilatory muscle contraction in spontaneously breathing anaesthetized dogs reduces Ruaw in the presence of UAW obstruction and releases UAW occlusion, with the genioglossus being the most effective muscle. This favours further attempts to investigate the benefits of electrical stimulation of selected upper airway muscles in the treatment of obstructive sleep apnoea syndrome.

Airway Obstruction↗

PubMed1994

Repeatability of measurements of normal lung sounds.

The stability of lung sounds measurements over time may influence their clinical usefulness. In the present study we investigated the temporal variability of the spectral pattern of normal lung sounds. Breath sounds from five healthy men were recorded on the trachea and at four locations over the chest wall. Each subject was studied twice with a time interval of 1 wk. On each occasion, measurements were done in duplicate, with a 30-min interval between recordings. Sounds were amplified, band-pass filtered (75 to 2,000 Hz) and digitized into a computer, and the average spectra of the inspiratory, expiratory, and background sounds were calculated. The variability of corresponding spectra were calculated between the daily duplicate (same-day variability, SDV) and between the two recording sessions (between-day variability, BDV). SDV was 32.8 +/- 12.0% during inspiration and 40.8 +/- 12.6% during expiration (p = 0.005). BDV was 36.9 +/- 11.3% during inspiration and 42.7 +/- 12.7% during expiration. These values were not significantly different from SDV except for sounds recorded from the interscapular region (SR). At this location the SDV was 28.2 +/- 7.2% during inspiration and 40.8 +/- 14.2% during expiration, and the BDV was 48.2 +/- 18.7% during inspiration and 77.6 +/- 22.3% during expiration (p < 0.05). The increased BDV at SR was found to be a result of slight differences in microphone position from the first session to the next. Similar changes in microphone position at the other recording sites did not alter the variability of lung sounds.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

Respiratory health screening using pulmonary function tests and lung sound analysis.

Lung sounds (LS) analysis is a potential source of additional objective, noninvasive and quantitative information on the status of the pulmonary system. We have examined the hypothesis that the addition of lung sounds analysis to spirometry increases the sensitivity of objective population screening, as compared to the use of spirometry alone. Questionnaires, spirometry and lung sounds were obtained in 493 active workers. Lung sounds analysis consisted of the averaged power spectra of breath sounds, measured separately during inspiration and expiration at four standard locations over the trachea and the chest-wall. Of the 493 subjects, 91 had an obstructive lung disease, including 27 with chronic bronchitis identified by a history of prolonged cough and sputum production but with normal spirometry. Twelve additional workers had a restrictive lung disease. Abnormal spirometric results were found in 74 of the patients. Abnormal lung sounds analyses were found in 54 patients, including 14 of the chronic bronchitis cases, so that the overall sensitivity of objective screening tests increased from 71% to 87% by combining the two tests. Thirty three of the subjects considered normal by evaluation of their questionnaire and spirometry had abnormal lung sounds. Of the twenty four who were re-evaluated 12-18 months after the first tests, three had developed a lung or heart disease. We conclude that the combination of spirometry and lung sounds analysis significantly increased the sensitivity of detection of pulmonary diseases by objective tests, and provided an early sign of lung disease that was not detected by spirometry alone.

Adult↗

PubMed1993

Effect of upper airway muscle contraction on supraglottic resistance and stability.

The activation of upper airway (UAW) muscles is believed to increase UAW patency to air flow. To evaluate the mechanisms by which UAW muscles act to prevent UAW collapse, pressure-flow relationships of the isolated UAW as well as the negative pressure required to cause UAW collapse (Pcrit) were assessed before and during electrical stimulation of four UAW muscle pairs in anesthetized dogs. Stimulation of each of the muscles shifted the pressure-flow curve toward lower pressures for any given flow rate, indicating UAW dilatation. UAW resistance decreased from 7.9 +/- 0.6 to 0.4 +/- 0.1, 2.7 +/- 0.6, 2.3 +/- 0.8 and to 4.8 +/- 1.5 cmH2O.L-1.sec during genioglossus, geniohyoid, sternothyroid and sternohyoid stimulation respectively (P < 0.01 in all cases). However, only genioglossus stimulation significantly increased Pcrit (from -3.4 +/- 0.6 to -12.0 +/- 1.8 cmH2O, P < 0.001). Relaxation of the genioglossus thus appears to produce the main impediment to air flow through the UAW, and contraction of this muscle improves UAW patency both by dilating the supraglottic airway and by stiffening its walls.

Airway Resistance↗

PubMed1993

A microcomputer based lung sounds analysis.

The use of a microcomputer in lung sound-analysis is described. The system was used experimentally in order to evaluate automated auscultation as a mean for improving the sensitivity of pulmonary health mass screening. The sound signals from four custom-made piezoelectric transducers, affixed at specific locations on the chest wall, and the breathing flow signal produced by a pneumotachograph were amplified, filtered and digitized simultaneously at 4000 Hz per channel for 512 ms. The acoustic data were transformed to the frequency domain to enable the calculation of the power spectra. Those were averaged over successive runs and displayed as log power vs. frequency. The operator could assess the convergence of the spectral pattern using the on-line graphics and calculated parameters, and store the data once the noise level had reached a preset level. This procedure was repeated during expiration, inspiration and on breath arrest. The results of the off-line analysis of the lung sounds, combined with pulmonary function tests and a questionnaire, were used to identify lung pathology.

Auscultation↗

PubMed1993

Theory and measurements of snores.

Upper airway narrowing, collapsibility, and resistance are recognized predisposing factors for snoring and obstructive sleep apnea, but the mechanisms of their action and interaction are not known. We studied a simple theoretical model of the upper airways, consisting of a movable wall in a channel segment that connects to the airway opening via a conduit with a resistance. Inspiratory flow (V) through the channel segment causes local pressure changes due to viscous losses and the Bernoulli force that may overcome the elastic forces acting on the movable wall. The model predicts instability leading to upper airway closure over a wide range of parameter values. Increasing inspiratory V above a boundary, determined by values of upper airway resistance, segment compliance, length, width, and diameter, as well as gas density, leads to a dynamic airway closure. The mathematical model establishes the power relationships between parameters and provides physiologically realistic quantitative simulation of upper airway closure when values are adapted from literature and from radiographic measurements of upper airway motion induced by negative pressure. The rate of appearance of repetitive sound structures during snoring was favorably compared with the model's prediction of the time course of wall motion during collapse. V measurements during simulated snores revealed an asymmetric oscillatory pattern compatible with repetitive upper airway closure. We conclude that snoring may be modeled as a series of dynamic closure events of the upper airways. The model predicts that the width and length of the movable portion of the upper airways and the gas density are likely to affect the onset of snoring, in addition to other, previously recognized, parameters.

Acoustics↗

PubMed1993

Construction and uses of a concentric catheter for gas sampling in lung airways.

A catheter for intra-airway sampling of gas concentrations was constructed from concentric polyethylene tubes. The internal tube (0.58 mm ID, 0.91 mm OD) was connected to a gas analyzer while the external tube (1.20 mm ID, 1.75 mm OD) was constantly flushed by air or a calibration gas, except during sampling. Injection and sampling dead spaces were 0.35 and 0.28 ml, respectively. Delay at 4-ml/min sampling rate was 4.0 +/- 0.2 s. The 0-90% step response to a sudden change in gas composition was 0.24 s when connected to a mass spectrometer. This catheter was used to assess tracer gas dispersion during oscillatory flow (1-20 Hz) in a straight long tube. Local concentrations measured through the catheter, after a small bolus of tracer gas was injected through the external tube, compared favorably with direct measurements through needles inserted via the tube wall and with theoretical predictions. The catheter was also used to measure intra-airway gas concentrations in dog airways during spontaneous breathing, conventional mechanical ventilation, high-frequency ventilation, high-frequency vibration ventilation, and constant-flow ventilation. It ws placed by a fiber-optic bronchoscope and used to measure local quasi-steady concentrations of CO2 and local dispersion with the bolus method. The occurrence of catheter clogging with secretions was substantially reduced with flow through the external tube. Transmitting a calibration gas through the external tube facilitated in situ recalibration of the gas analyzer without removing the catheter. The use of this catheter improved the efficiency and accuracy of measurements of gas concentrations inside lung airways.

Animals↗

PubMed1993

Hypothermia prolongs survival in a confined atmosphere.

Survival in a confined atmosphere where O2 is limited may be extended by hypothermia. Rats were placed in a thermoregulated sealed chamber which contained a limited amount of air. Rats were studied at low ambient temperatures, in which their terminal rectal temperatures (TB) were 33.2-8.3 degrees C. Rats which had a terminal TB of 20 degrees C achieved maximal O2 extraction. Maximal survival time may be expected with an initial thermoneutral temperature followed by hypothermia with a final TB of 20 degrees C. Resuscitation with no obvious signs of injury was possible after half of the rats succumbed.

Animals↗

PubMed1992

Gas dispersion in volume-cycled tube flow. II. Tracer bolus experiments.

We present a new method for rapid measurement of local gas dispersion in volume-cycled tube flow. After a small bolus of tracer gas (argon) was injected into the oscillating flow, the time-averaged effective diffusion coefficient (mean value of Deff/D) for axial transport of a tracer gas is evaluated from local argon concentration measurements taken by a mass spectrometer. Two methods are presented for the evaluation of mean value of Deff/D from the concentration measurements: one uses all the sampled data, and the other uses only the local peaks of the concentration. Experiments were conducted in two tubes (radius = 0.85 or 1.0 cm) over a range of frequencies (0.42 less than or equal to f less than or equal to 8.5 Hz) and tidal volumes (7 less than or equal to VT less than or equal to 48 ml). The experimental results show very good agreement with the theoretical predictions of Elad et al. (J. Appl. Physiol. 72: 312-320, 1992). In the absence of oscillations (static fluid), the resulting mean value of Deff/D converges to that of molecular diffusion. We also show that concentration data may be acquired at any radial or axial position, not necessarily at the tracer gas injection point, and the resulting mean value of Deff/D is independent of the spatial position of the sampling catheter. This method is of similar accuracy and is substantially faster than previous methods for measuring gas dispersion in oscillatory flows. The rapidity of these measurements may permit this method to be used for the in vivo assessment of gas transport properties within the pulmonary system.

Argon↗

PubMed1992

Spectral content of forced expiratory wheezes during air, He, and SF6 breathing in normal humans.

The effect of gas density on the spectral content of forced expiratory wheezes was studied in the search for additional information on the mechanism of generation of respiratory wheezes. Five normal adults performed forced vital capacity maneuvers through four or five orifice resistors (0.4-1.92 cm ID) after breathing air, 80% He-20% O2, or 80% SF6-20% O2. Tracheal lung sounds, flow, volume, and airway opening (Pao) and esophageal (Pes) pressures were measured during duplicate runs for each orifice and gas. Wheezes were detected in running spectra of lung sounds by use of a frequency domain peak detection algorithm. The wheeze spectrograms were presented along side expiratory flow rate and transpulmonary pressure (Ptp = Pao - Pes) as function of volume. The frequencies and patterns of wheeze spectrograms were evaluated for gas density effects. We found that air, He, and SF6 had similar wheeze spectrograms. Both wheeze frequency and patterns (as function of volume) did not exhibit consistent changes with gas density. Speech tone, however, was substantially affected in the usual pattern. These observations support the hypothesis that airway wall vibratory motion, rather than gas phase oscillations, is the source of acoustic energy of wheezes.

Acoustics↗

PubMed1992

Parametric representation of normal breath sounds.

The spectral content of normal tracheal and chest wall breath sounds has been calculated using the fast Fourier transform (FFT) (J. Appl. Physiol. 50: 307-314, 1981). Parameter estimation methods, in particular autoregressive (AR) modeling, are alternative techniques for measuring lung sounds. The outcome of AR modeling of 38 complete breaths picked up simultaneously over the chest walls and tracheae of five normal males was evaluated. The sounds were treated as noise, bounded by a quasi-periodic envelope generated by the cyclic action of breathing, thus causing the sounds to become inherently nonstationary. Normalization of the sounds to their corresponding variance envelopes eliminated the nonstationarity, an important requirement for most signal-processing methods. Subsequently, the AR model order was sought using formal criteria. Orders 6-8 were found to be suitable for normal chest wall sounds, whereas tracheal sounds required at least orders 12-16. Using orders 6 and 12, we compared the prominent spectral features of chest wall and tracheal sounds calculated by AR with those found in the spectra calculated by FFT. The polar representation of the AR roots, calculated from the AR coefficients, showed that normal lung sounds from a group of individuals are characterized by a low variability, suggesting that this method may provide an alternative representation of the sounds. The data presented here show that normal lung sounds, when measured in the frequency domain by either FFT or AR modeling, have a characteristic pattern that is independent of the analysis method.

Adult↗

PubMed1992

Gas exchange by intratracheal insufflation in a ventilatory failure dog model.

Respiratory insufficiency patients who need only partial ventilatory support are, nevertheless, intubated and connected to a respirator. In search of a partial respiratory assistance method we evaluated the gas exchange, mechanisms, and hemodynamic effects of intratracheal insufflation (ITI) via a narrow (0.2-cm) catheter. The effects of flow rate (0.05-0.2 liter/min per kg), catheter tip position (carina, bronchus, and trachea), and superimposed chest vibration at 22 Hz were studied in seven anesthetized and partially paralyzed dogs. ITI in the carina induced CO2 removal (VCO2) of 48 +/- 16 ml/min in the periods between breaths, which was 39% of the control VCO2. CO2 removal rates between breaths with ITI in a bronchus and in the trachea were 63 and 28% of control, respectively (P < 0.05). ITI at 0.15-0.2 liter/min per kg augmented total VCO2 by > 50% over control (P < 0.05) and decreased PaCO2 by 10% (P < 0.05) despite a 28% fall in VE and 32% lower work of breathing (P < 0.05). Adding vibration to ITI at 0.15 liter/min per kg induced VCO2 of 162 +/- 34 ml/min, which was significantly greater than control, while PaCO2 fell from 69 +/- 24 to 47 +/- 6 mmHg (P < 0.05), despite complete cessation of spontaneous breathing. ITI with or without vibration did not cause any hemodynamic changes, except for a fall in the shunt fraction from 14.6 +/- 9.9% to 5.8 +/- 2.8% with vibration. Thus, ITI at low flow rates can support respiration with no hemodynamic side effects. Adding chest vibration further enhances gas exchange and can provide total ventilation.

Animals↗

PubMed1990

The reproducibility of forced expiratory wheezes.

Previous work has shown forced expiratory wheezes (FEW) to be associated with onset of flow limitation and to have spectral characteristics similar to wheezes heard in patients with obstructive lung diseases. This study was designed to determine whether the acoustic characteristics of FEW are reproducible under controlled lung volume and flow conditions. Six healthy, nonsmoking young adults 28 to 37 yr of age were studied. They performed FVC maneuvers through a set of round apertures (diameters, 14, 12, 10, 8, 6, 4, 2, and 1 mm). Flow, measured with a pneumotachograph, and tracheal lung sounds, recorded with a Hewlett-Packard HP20510A contact sensor, were recorded simultaneously on magnetic tape and analyzed off-line. For each subject, data from three different aperture sizes, measured in triplicates, were analyzed (total of 54 runs); 199 different wheezes were identified (mean, 3.7 wheezes/run), and 56.7 +/- 5.1% (mean +/- SEM) of wheezes found in a certain run (range, 41.7 to 77.8%) were identical to wheezes found in the other two runs of the same aperture size (i.e., same flow rate). In 17 of the 18 sets of triplicate runs analyzed, at least one major wheeze was identical in all three runs of the set. In three of the sets, two different identical wheezes were found. These findings support a deterministic mechanism of generation of wheezes and is in line with the predictions of the "flutter theory."

Adult↗

PubMed1990

[A respiratory health questionnaire for occupational screening].

A Hebrew pulmonary health questionnaire was designed for occupational screening, based on the American Thoracic Society questionnaire but adjusted to conditions in Israel. It was designed for assisted completion using a computer, but can easily be modified to become self-administered. We propose that it be used here as the standard, occupational, pulmonary health questionnaire and as the basis for a standard, general purpose, respiratory health questionnaire.

Humans↗

PubMed1989

Effect of hypercapnia on upper airway resistance and collapsibility in anesthetized dogs.

The upper airway (UAW) is intrinsically unstable and susceptible to collapse when the negative inspiratory intraluminal pressure exceeds the stabilizing forces which prevent obstruction. In the present study we evaluated mechanisms by which UAW patency is maintained in the presence of increased inspiratory flows when respiration is stimulated. In seven anesthetized dogs breathing spontaneously through a low tracheostomy, the UAW was isolated by a second tracheostomy directed rostrally. UAW pressure-flow relationship and stability against collapse were evaluated during steady flow in the inspiratory direction while the animals were breathing 100% O2 or a hypercapnic gas mixture. The pressure-flow curves of the isolated UAW demonstrated the characteristic pattern of collapsible tubes. Steady state hypercapnia resulted in lower UAW resistance during both inspiration and expiration. UAW resistance decreased linearly as PCO2 and ventilation increased over the course of CO2 rebreathing. In addition, during hypercapnia the critical negative intraluminal pressure required to induce UAW collapse and obstruction increased from -4.3 +/- 0.9 to -8.5 +/- 1.5 SE cm H2O (p less than 0.01), indicating increased stability of the UAW. Since hypercapnia is known to stimulate UAW muscles, our findings suggest that increased UAW muscle activity improves UAW patency both by decreasing their resistance to airflow, and by increasing UAW walls rigidity and stability against collapse.

Airway Resistance↗

PubMed1989

Frequency and amplitude effects during high-frequency vibration ventilation in dogs.

High-frequency external body vibration, combined with constant gas flow at the tracheal carina, was previously shown to be an effective method of ventilation in normal dogs. The effects of frequency (f) and amplitude of the vibration were investigated in the present study. Eleven anesthetized and paralyzed dogs were placed on a vibrating table (4-32 Hz). O2 was delivered near the tracheal carina at 0.51.kg-1.min-1, while mean airway pressure was kept at 2.4 +/- 0.9 cmH2O. Table vertical displacement (D) and acceleration (a), esophageal (Pes), and tracheal (Ptr) peak-to-peak pressures, and tidal volume (VT) were measured as estimates of the input amplitude applied to the animal. Steady-state arterial PCO2 (PaCO2) and arterial PO2 (PaO2) values were used to monitor overall gas exchange. Typically, eucapnia was achieved with f greater than 16 Hz, D = 1 mm, a = 1 G, Pes = Ptr = 4 +/- 2 cmH2O, and VT less than 2 ml. Inverse exponential relationships were found between PaCO2 and f, a, Pes, and Ptr (exponents: -0.69, -0.38, -0.48, and -0.54, respectively); PaCO2 decreased linearly with increased displacement or VT at a fixed frequency (17 +/- 1 Hz). PaO2 was independent of both f and D (393 +/- 78 Torr, mean +/- SD). These data demonstrate the very small VT, Ptr, and Pes associated with vibration ventilation. It is clear, however, that mechanisms other then those described for conventional ventilation and high-frequency ventilation must be evoked to explain our data. One such possible mechanism is forcing of flow oscillation between lung regions (i.e., forced pendelluft).

Animals↗

PubMed1989

Critical pressures required for generation of forced expiratory wheezes.

Flow limitation (FL) has recently been shown to be a necessary condition for the generation of forced expiratory wheezes (FEW) in normal subjects. The present study was designed to investigate whether it is also a sufficient condition. To do so we studied the effects of varying expiratory effort on generation of FEW. Six normal subjects exhaled with varying force into an orifice in line with a high-impedance suction pump. Esophageal (Pes), airway opening, and transpulmonary (Ptp) pressures were measured alongside flow rate, lung volume, and tracheal lung sounds. In each subject a certain critical degree of effort had to be attained before FEW were generated. This effort, measured as Pes at the onset of wheezes, varied among the subjects (range -11 to 45 cmH2O). Similarly, a minimal Ptp had to be reached for FEW to evolve (mean +/- SD -34 +/- 12 cmH2O, range -18 to -50 cmH2O). These critical Pes and Ptp values were significantly higher than those required for FL. It was concluded that, in addition to the requirement for FL, sufficient levels of effort and negative Ptp must exist before FEW can be generated. By analogy to experimental and theoretical results from studies on flow-induced oscillations in self-supporting collapsible tubes, it was further concluded that these pressures are required to induce flattening of the intrathoracic airways downstream from the choke point. It is this configurational change that causes air speed to become equal to or exceed the critical gas velocity needed to induce oscillations in soft-walled tubes.

Esophagus↗

PubMed1989

Flutter in flow-limited collapsible tubes: a mechanism for generation of wheezes.

We studied flutter in collapsible tubes as a possible mechanism for the generation of respiratory wheezes. The pressure-flow relationships and the wall oscillations of thick-walled [wall thickness (h)-to-lumen radius (r) ratio 1:1.7 to 1.3] self-supporting latex and Silastic tubes mounted between rigid pipes were measured. A high-impedance vacuum pump was connected to the downstream end. Upstream and downstream valves were used to control corresponding resistances. We found loud honking sounds and tube wall oscillations that occurred only when the tubes were buckled and flow limiting, i.e., when the flow became constant and independent of downstream driving pressure. The overall range of oscillatory frequencies was 260-750 Hz for airflow, presenting as sharp peaks of power on the frequency spectrum. The oscillatory frequencies (f) were higher at higher fluid velocities (u) and with narrower distance between opposing flattened walls (2b), resulting from increasing downstream suction pressure and the transmural pressure becoming more negative. The effect of u and b on f for a latex tube (h-to-r ratio 1:1.7) were found to be f = 228 + 0.021 (u/b). These relationships were valid throughout the range of oscillations in this tube (283-720 Hz) and with flow rates of 12-64 l/min. The experimental data were compared with predictions of the fluid dynamic flutter theory and the vortex-induced wall vibrations mechanism. We conclude that viscid flutter in soft tubes is the more probable mechanism for the generation of oscillations in the soft tube model and is a possible mechanism for the generation of respiratory wheezes.

Humans↗