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Biomedical subjects

J M Fouke

Publications and source records attributed to J M Fouke.

34 records · Page 2Linked to original sources
PubMed1988

Airway response to ultra short-term exposure to ozone.

To determine whether acute short-term exposure to oxidant pollutants can cause changes in respiratory mechanics, we gave 0.5 ppm ozone for 5 min to 7 baboons. We measured pulmonary resistance (RL) and obtained dose response curves to methacholine before and after the exposures. This brief insult increased resistance (control RL = 1.53 +/- 0.21 cm H2O.L-1 s; post-ozone RL = 3.53 +/- 0.54 cm H2O.L-1 s). On a second occasion, 6 of these animals were restudied before and after the administration of cromolyn sodium. Although this drug had no effect on the measurements of mechanics made in the control period, it significantly reduced the ozone-induced changes in mechanics. The increase in RL was 52% of that produced in the first study. The results demonstrated that the ozone injury with its acute and subacute airway sequelae occurs quite rapidly and after very brief exposure. The time course of the change in mechanics and the effects of cromolyn suggest the hypothesis that surface epithelial cells are disrupted, causing subsequent release of bronchoconstricting agents.

Air Pollutants↗
PubMed1987

Phasic changes in upper airway impedance.

To identify within breath variations in the mechanical properties of the isolated upper airway, we examined changes in impedance spectra over the course of the respiratory cycle. Changes were evaluated with a modified forced oscillation technique applied to the isolated, sealed upper airways of nine anesthetized mongrel dogs. Upper airway impedance spectra were studied during sequential 350 msec epochs. We found spectral changes which were reproducible within the respiratory cycle. Impedance spectra revealed that during mid-inspiration at the point of peak upper airway muscle activity, the low frequency real part decreased and the imaginary part was less negative and less steep. During late inspiration and early expiration the impedance values returned to their end-expiratory values. The only significant change in parameter estimates from a three-parameter model indicated an increase in compliance. Since these changes correlated not only with tidal flow through the lower trachea and lung but also with upper airway muscle activation, we reasoned that changes in impedance could have resulted from an increase in upper airway size. Therefore, we used a sealed speaker system and, while the animal was apnoeic, evaluated impedance at two different airway pressures and the resultant volumes. The changes in impedance spectra with a volume increase were similar to those seen during spontaneous breathing efforts. We conclude that the mechanical properties of the upper airway change during the respiratory cycle and that these changes correlate with the respiratory activation of upper airway muscles. We suspect that these changes in input impedance could reflect a change in the size of the airway rather than a true increase in elasticity.

Airway Resistance↗
PubMed1987

Comparison of volume changes in the upper airway and thorax.

To describe the mechanical cycles of the upper and lower portions of the respiratory system, we measured volume change in and out of the isolated upper airway in 13 anesthetized dogs and compared volume changes in the upper airway with tidal volume change during spontaneous respiratory efforts. During inspiration the onset and peak increase in volume into the upper airway preceded the onset and peak of inspiratory tidal volume by 84 +/- 8 and 638 +/- 47 ms, respectively. The volume cycle of the upper airway was nearly complete by the end of inspiratory airflow into the thorax. With progressive hypercapnia there was an increase in the change in both upper airway volume and tidal volume but the temporal sequence was preserved. End-expiratory tracheal occlusion increased the volume change in the isolated upper airway at any level of CO2; however, the effect was disproportionately greater at low rather than at high levels of CO2. Following hyperventilation-induced apnea, a change in volume in the upper airway and thorax occurred on the first inspiratory effort. In most animals at lower levels of CO2, the percent change in upper airway volume with inspiration was relatively less than tidal volume, but the reverse was true at higher levels of CO2. These differences represent dissimilarities in the mechanical forces occurring as the result of upper airway and chest wall muscle contraction during inspiration.

Animals↗
PubMed1987

Effect of position and lung volume on upper airway geometry.

The occurrence of upper airway obstruction during sleep and with anesthesia suggests the possibility that upper airway size might be compromised by the gravitational effects of the supine position. We used an acoustic reflection technique to image airway geometry and made 180 estimates of effective cross-sectional area as a function of distance along the airway in 10 healthy volunteers while they were supine and also while they were seated upright. We calculated z-scores along the airway and found that pharyngeal cross-sectional area was smaller in the supine than in the upright position in 9 of the 10 subjects. For all subjects, pharyngeal cross-sectional area was 23 +/- 8% smaller in the supine than in the upright position (P less than or equal to 0.05), whereas glottic and tracheal areas were not significantly altered. Because changing from the upright to the supine position causes a decrease in functional residual capacity (FRC), six of these subjects were placed in an Emerson cuirass, which was evacuated producing a positive transrespiratory pressure so as to restore end-expiratory lung volume to that seen before the position change. In the supine posture an increase in end-expiratory lung volume did not change the cross-sectional area at any point along the airway. We conclude that pharyngeal cross-sectional area decreases as a result of a change from the upright to the supine position and that the mechanism of this change is independent of the change in FRC.

Adult↗
PubMed1987

Heat and water flux in the intrathoracic airways and exercise-induced asthma.

To explore the relationship between the flux of heat and water within the respiratory tract during exercise and recovery to the development of exercise-induced asthma (EIA), we recorded airstream temperature at multiple points throughout the tracheobronchial tree in 10 normal and 10 asthmatic subjects before, during, and after cycle ergometry. In both groups, the intra-airway temperature fell progressively as ventilation increased, and there were no significant differences between the thermal profiles of the two populations at rest or during exercise. Calculation of water losses and the osmolality of the airway surface fluid failed to demonstrate significant airway drying in either group. With cessation of the work load, the airstream temperature increased abruptly, rising two times more rapidly in the asthmatics than the normals. Since the major source of heat in these experiments is the bronchial circulation, our findings suggest a reaction sequence consisting of vasoconstriction and airway cooling during exercise followed by a rapid resupply of heat when exercise ceases. The latter may cause the hyperplastic capillary bed in the airways of asthmatics to develop an exaggerated rebound hyperemia which may lead to airway edema and EIA.

Adult↗
PubMed1987

Assessment of muscle action on upper airway stability in anesthetized dogs.

Skeletal muscle activation is believed to be important in the maintenance of upper airway patency. To determine where and how muscles affect pharyngeal stability, we assessed in heavily anesthetized, ventilated dogs, the negative pressure required to close the nasopharynx and the passage from the oral to the pharyngeal airway before and after electrical stimulation of six pairs of upper airway muscles: the sternohyoid, sternothyroid, ceratohyoid, thyrohyoid, genioglossus, and geniohyoid. Before muscle stimulation, the pressures required to close the nasopharynx and the oral passage were -9.8 +/- 2.3 (mean +/- SEM) and -4.9 +/- 1.9 cm H2O, respectively. Submaximal electrical stimulation of each of the six muscle pairs caused consistent and substantial improvements in nasopharynx closing pressure. In contrast, the stabilizing actions of these muscles on the oral passage was less consistent and smaller in magnitude. Using pressure in the sealed upper airway as an index of forces acting on the airway, we found a strong association between the effect of muscle stimulation on the closing pressure and the effect of muscle stimulation on producing a dilating force on the airway. We conclude that muscles in the anterior and lateral pharyngeal wall improve nasopharynx stability to a greater extent than oral passage stability and that the action by any of these six muscle pairs improves airway stability through their ability to dilate the upper airway.

Airway Resistance↗
PubMed1986

Effects of sodium cyanide and nicotine on upper airway resistance in anesthetized dogs.

The purpose of this study was to determine whether pharmacologic interventions which increase respiratory drive could also reduce flow resistance in the upper airway. Studies were performed in twelve anesthetized supine dogs. In six animals breathing spontaneously through the intact upper airway, intravenous administration of respiratory stimulants (sodium cyanide and nicotine) produced a dose-related decrease in upper airway. In nine animals, upper airway resistance was measured across the isolated upper airway. The stimulants produced a dose-related decrease in upper airway resistance. In both preparations inspiratory resistance fell at lower doses than expiratory resistance. Eventually a dose could be given which resulted in comparable, minimal values of resistance during both inspiration and expiration. Mechanisms for changes in resistance were clarified using lateral radiographs of the neck and transbronchoscopic views of the upper airway. Pharmacologic challenge resulted in a change in the route of airflow (from nose only to nose-and-mouth breathing) as well as a change in caliber of the airway at the level of the naso-pharynx and hyoid apparatus. In anesthetized dogs, respiratory stimulants will decrease upper airway resistance by increasing activation of upper airway muscles which may enlarge the airway, change the route of flow, and thus overcoming collapsing forces produced by increased chest wall muscle activation.

Airway Resistance↗
PubMed1986

Effect of varying inspiratory and expiratory times during high-frequency jet ventilation.

Although high-frequency jet ventilation may reduce barotrauma, the optimal ventilator settings at which complications are minimized have not been determined. To develop ventilator strategies applicable to the human infant, we studied six New Zealand rabbits before and after saline lung lavage. Changes in functional residual capacity (delta FRC) and airway pressure gradient (peak inspiratory pressure minus positive end-expiratory pressure) were measured while inspiratory time (TI) and expiratory time (TE) were varied. Frequencies of 120, 240, and 480 cycles per minute and inspiratory to expiratory ratios of 1:1, 1:3, 1:5, and 1:9 resulted in TI that varied from 12 to 250 msec, and TE from 62 to 450 msec. Analysis of variance demonstrated that as TI was shortened, a significantly higher airway pressure gradient was necessary to maintain a constant tidal volume. As TE was shortened, air trapping, as determined from both inadvertent positive end-expiratory pressure and delta FRC, significantly increased. Lung lavage increased the airway pressure gradient at each TI, but decreased air trapping at each TE. At no time did entrainment contribute to the delivered tidal volume. We conclude that a relatively narrow range of TI and TE may be necessary for optimal use of high-frequency jet ventilation to reduce airway pressures and minimize the risk of air trapping.

Animals↗
PubMed1986

Pressure-volume behavior of the upper airway.

The study was performed to investigate the relationship between force generation and upper airway expansion during respiratory efforts by upper airway muscles. In 11 anesthetized dogs we isolated the upper airway (nasal, oral, pharyngeal, and laryngeal regions) by transecting the cervical trachea and sealing the nasal and oral openings. During spontaneous respiratory efforts the pressure within the sealed upper airway, used as an index of dilating force, decreased during inspiration. On alternate breaths the upper airway was opened to a pneumotachograph, and an increase in volume occurred, also during inspiration. Progressive hyperoxic hypercapnia produced by rebreathing increased the magnitude of change in pressure and volume. At any level of drive, peak pressure or volume occurred at the same point during inspiration. At any level of drive, volume and pressure changes increased with end-expiratory occlusion of the trachea. The force-volume relationship determined from measurements during rebreathing was compared with pressure-volume curves performed by passive inflation of the airway while the animal was apneic. The relationship during apnea was 1.06 +/- 0.55 (SD) ml/cmH2O, while the force-volume relationship from rebreathing trials was -1.09 +/- 0.45 ml/cmH2O. We conclude that there is a correspondence between force production and volume expansion in the upper airway during active respiratory efforts.

Airway Resistance↗
PubMed1986

Measurement of tidal volume during high-frequency jet ventilation.

The measurement of tidal volume during high-frequency jet ventilation is difficult due to the high-frequency components of the inspiratory flow. To validate tidal volume measured with a screen pneumotachograph placed on the expiratory limb, we simultaneously determined tidal volume with a body plethysmograph in seven anesthetized normal adult New Zealand rabbits before and after saline lung lavage. Four to six comparisons of tidal volume were obtained by varying peak inspiratory pressures at each combination of frequency (120, 240, and 480/min) and inspiratory to expiratory time ratio (1:1, 1:3, 1:5, 1:9). Overall, 90% of the tidal volumes measured with the pneumotachograph were within 10% of 1 ml of the volumes determined with the plethysmograph, independent of frequency, inspiratory to expiratory time ratio, and lung compliance. There was unidirectional outward flow at the pneumotachograph during inspiration when both normal and saline lavaged lungs were being ventilated, suggesting a lack of gas entrainment. We conclude that a pneumotachograph on the expiratory limb may be used to measure tidal volume and gas entrainment in vivo during high-frequency jet ventilation. Determination of tidal volume may serve to optimize ventilator settings during high-frequency jet ventilations and facilitate an understanding of the mechanism involved in gas exchange.

Animals↗
PubMed1985

Oral breathing in newborn infants.

Newborn infants are considered obligate nasal breathers, hence dependent on a patent nasal airway for ventilation. The conditions under which oral breathing could occur and the contribution of oral ventilation to total ventilation were studied in 30 healthy term infants (aged 1 to 3 days). Nasal and oral airflow were measured using two resistance-matched pneumotachometers, and heart rate, tcPO2, etCO2, and sleep state were continuously recorded. In three of 10 infants studied in undisturbed sleep, spontaneous oronasal breathing was noted during both active and quiet sleep (mean duration 19 +/- 25 minutes), the distribution of tidal volume being 70% +/- 12% nasal and 30% +/- 12% oral. Episodes of oronasal breathing were also observed after crying in six infants (mean duration 21 +/- 19 seconds). In an additional 20 infants, multiple 15-second end-expiratory nasal occlusions were performed; eight (40%) of these infants initiated and sustained oral breathing in response to nasal occlusion. Respiratory rate, tidal volume, heart rate, and tcPO2 did not change when oral breathing occurred in response to nasal occlusion, although minute ventilation decreased from 265 to 199 ml/min/kg (P less than 0.05). These results demonstrate that newborn infants may use the oral airway for ventilation, both spontaneously and in response to complete nasal occlusion.

Airway Obstruction↗
PubMed1985

Dilating forces on the upper airway of anesthetized dogs.

We reasoned that in an isolated sealed upper airway a pressure change would be caused by a change in airway volume. In eight spontaneously breathing anesthetized dogs, we isolated the upper airway by transecting the cervical trachea and sealing it from the lung and from the atmosphere. Pressure changes in this isolated upper airway were studied in relation to respiratory phase as evidenced by alae nasi electromyographic (EMG) activation and tidal volume measured at the distal trachea. A fall in pressure, indicating airway dilation, occurred with each spontaneous respiratory effort. Like the moving average of the alae nasi EMG, the pressure drop reached a peak value early in inspiration, was inhibited by further lung inflation, and was absent during passive mechanical ventilation. End-expiratory tracheal occlusion or vagotomy prolonged and augmented EMG activity and also the inspiratory fall in upper airway pressure. Increased levels of CO2 increased the magnitude of change in pressure during inspiration. An inhibiting effect of lung inflation was present to an equal extent at low and high levels of chemical drive. We show that dilation of the airway is concurrent with upper airway muscle activation during early inspiration, that this dilation increases with increasing chemical drive, and that vagal reflexes during lung inflation inhibit this dilation during the latter half of inspiration.

Airway Resistance↗
PubMed1981

Direct dynamic measurements of tracheal diameter.

Methods of monitoring airway caliber as an indicator of bronchomuscular tone have been indirect, static, and invasive. A diameter transducer has been developed the static and dynamic characteristics of which indicate that it should overcome some methodological problems. The catheter-mounted spring-loaded braces of the transducer track the motion of the airway wall, which is reflected in the output changes of a linear-variable transformer. The range of the transducer was 5.3-24.3 mm. The amplitude response was flat up to 8 Hz, and the phase difference between the forcing signal and the response of the gauge was 0 degrees up to 8 Hz. The minimum specific compliance was 0.15 cmH2O-1, an order of magnitude larger than the specific compliance of isolated trachea, indicating that the airway was not significantly loaded by the transducer. In vivo studies in ventilated dogs revealed tidal changes in tracheal diameter and marked constriction during apnea. Bilateral vagotomy increased diameter up to 20%, and vagal stimulation decreased diameter as much as 30% below postvagotomy levels. It appears that this transducer is suitable for measuring resting diameter, tidal changes in diameter, and changes in diameter induced by alteration in bronchomotor tone.

Animals↗
PubMed1981

Time-constant histograms from the forced expired volume signal.

The forced expired volume signal was analyzed using a parallel compartment model in which each compartment emptied exponentially. With this model the forced expired volume signal was represented by a histogram showing the fraction of the vital capacity as a functional of compartmental time constants. We developed an algorithm to compute this histogram from the volume signal. The algorithm used the least-squares criterion function with both smoothness and nonnegativity constraints. In a stimulation study reasonable histograms were obtained even in the presence of realistic random error. Three dependent forced expired volume signals from 16 subjects were analyzed, and the histograms were reproducible. Most histograms were bimodal with fast time constants of 0.12-0.55 s and slow time constants of 1.3-2.7 s. In all normal subjects and patients with restrictive disease more than 75% of the vital capacity was in the fast time-constant mode. Subjects with obstructive disease had more than 40% of the vital capacity in the slow time-constant mode.

Adult↗
PubMedDate not supplied

Comparison of three transmittance oximeters.

Estimates of oxygenation from three transmittance oximeters, Hewlett-Packard 47201A, Nellcor, and Biox III, were obtained simultaneously in ten healthy human subjects during isocapnic progressive hypoxia and under conditions of episodic hypoxemia. In the oxygen saturation range studied (approximately 95-75%), results showed that values from the Nellcor finger oximeter were 2-4% lower than values from the Hewlett-Packard ear oximeter. Values from the Biox III oximeter, using either the ear or finger probe, were 3-7% higher than those from the Hewlett-Packard, and the biggest discrepancies were seen as oxygen saturation fell below 80%. This often resulted in an estimation of the ventilatory response to hypoxia as measured using the Biox III oximeter that was higher than estimates using the Nellcor or the Hewlett-Packard (P less than 0.005). Hypoxic ventilatory responses using the Nellcor and the Hewlett-Packard oximeters gave similar values. During rapidly changing oxygenation, the distribution of values for oxygen saturation were significantly different for the three oximeters. For example, the median of the distribution for Nellcor values was 89 +/- 1.5% (mean +/- SEM); for the Hewlett-Packard, it was 92 +/- 1.3%; and for the Biox III, it was 93 +/- 0.8% (finger) and 95 +/- 1.6% (ear). The authors conclude that differences between the three non-invasive transmittance oximeters will affect clinical measurement of the ventilatory responsiveness to hypoxia and the estimation of the stimulus for hypoxic complications in respiratory diseases.

Adult↗