Bias Flow Research Articles

The damping of flexural and acoustic waves by a bias-flow perforated elastic plate

An analysis is made of the damping of sound and structural vibrations by vorticity production in the apertures of a bias flow, perforated elastic plate. Unsteady motion causes vorticity to be generated at the aperture edges; the vorticity and its energy are swept away by the bias flow and result in a net loss of acoustic and vibrational energy. In this paper we investigate the interaction of an arbitrary fluid-structure disturbance with a small circular aperture in the presence of a high Reynolds number, low Mach number bias flow. By considering the limit in which the aperture is small compared to the length scale of the impinging disturbance, it is shown that the effect of the interaction can be represented by a concentrated source in the plate bending wave equation consisting of a delta function and two of its axisymmetric derivatives. A generalized bending wave equation is then formulated for a plate perforated with an homogeneous distribution of small, bias flow circular apertures. This equation is used to predict the attenuation of sound and resonant bending waves by vorticity production. Acoustic damping is found to be significant provided the fluid loading is sufficiently small for the plate to be regarded as rigid (e.g. for an aluminium plate in air when the frequency is not too small). On the other hand, a bending wave is effectively damped only when the fluid loading is large enough for the wave to produce a substantial pressure drop across the plate; when this occurs the predicted attenuations are comparable with those usually achieved by the application of elastomeric damping materials. Numerical predictions are presented for steel and aluminium plates in air and water.

Ventilation‐perfusion relationships during graded exercise in the Standardbred trotter

SummaryThe aim of this study was to evaluate pulmonary function in Standardbred trotters during graded exercise. The exercise test consisted of 4 work loads corresponding to 10%, 42%, 70% and 96% of the individual V̇O2max. Oxygen uptake was detected from an open bias flow system without valves. Cardiovascular and haemodynamic data were recorded at walk and during steady state exercise in 7 horses. Pulmonary gas exchange was assessed by conventional blood gas variables (arterial and mixed venous blood gas tensions) and the ventilation‐perfusion distribution V̇A|Q̇ as estimated by the multiple inert gas elimination technique. The dispersion of perfusion and ventilation distribution respectively (SDQ) and the difference between measured PaO2 and that predicted on the basis of amount of ventilation‐perfusion mismatching and shunt that was observed (predicted‐measured), were determined. The latter reflects mostly diffusion limitation. At the highest work load the PaCO2 increased to 50.3 torr. V̇A|Q̇ inequality increased significantly with exercise [mean log = 0.32 ± 0.03 (walk) and 0.46 ± 0.06 (heavy exercise), P < 0.01]. Alveolar‐capillary diffusion limitation of oxygen was evident at and above exercise at 70% of V̇O2max. The arterial hypoxaemia seen during the highest work load was a result of a) hypoventilation, accounting for 4%, b) increase in V̇A|Q̇ mismatch, accounting for 41% and c) considerable diffusion limitation of oxygen, accounting for 55%.

High-frequency ventilation: Oscillatory dynamics

To determine the influence of the dynamic properties of the oscillator on the oscillatory volume delivered through the endotracheal tube to the lung or lung surrogate (delivered volume) under conditions of high-frequency ventilation. In particular, the relation between the tidal volume of the pump (oscillator) and the delivered volume was analyzed. PaCO2 was measured further as a function of the delivered volume in a number of experiments performed with healthy dogs. Laboratory study. Engineering and animal laboratory. Lung surrogates and healthy dogs. An experimental oscillatory system was connected to various lung surrogates. In addition, six beagle dogs received high-frequency ventilation with different delivered volumes during the study. Control of the mean airway pressure was achieved by a peripheral pressure chamber located at the exhaust port of the bias flow tube. The delivered volume, which is the quantity of interest from a physiologic point of view, can deviate considerably from the tidal volume of the pump due to dynamic (particularly resonance) effects. Because the delivered volume and the mean airway pressure have to be controlled independently, two independent quantities are necessary for control purposes (e.g., the tidal volume of the pump and the mean pressure at the exhaust port). Furthermore, it was found that a minimal condition for adequate gas exchange is a delivered volume that exceeds the machine-related deadspace. For this reason, and in order to maximize the CO2 gradient, the exhaust tube must be as short as possible. a) The delivered volume has to be monitored under clinical conditions; b) however, because the impedance of the endotracheal tube in general considerably exceeds the impedance of the lung, the influence of the impedance of the lung on the delivered volume is generally small, and thus an in vitro calibration may serve as a useful approximation; c) at least two independent quantities are needed for an adequate oscillatory control; d) a necessary (not necessarily sufficient) condition for adequate CO2 removal is that the delivered volume must exceed the machine-related deadspace; e) in a clinical environment involving extremely pathologic lung conditions, e.g., adult respiratory distress syndrome, mechanical lung characteristics may deviate substantially from those characteristics used in this study (i.e., the results obtained may not necessarily be applicable under all clinical situations).

High-frequency oscillation in an adult porcine model.

Controversy exists as to whether high-frequency oscillatory ventilation can be used on babies and small laboratory animals only, or whether high-frequency oscillatory ventilation can also be efficient in the adult patient and large (> 65 kg body weight) laboratory animals. Moreover, controversy exists as to whether limitations in high-frequency oscillation efficiency are caused by the size and shape of the bronchial system, by the lack of low impedant intersegmental gas flow in lung parenchyma, or by inappropriate high-frequency ventilators and ancillary hardware. Therefore, our objective in this study using the adult pig as a model of the adult patient was to test whether the adult airway system is suited to the use of high-frequency oscillatory ventilation or whether there are geometrical, structural, or functional limitations to efficient ventilation by high-frequency oscillation. Prospective, controlled, randomized comparison over 8 to 16 hrs of ventilatory management. Experimental thoracovascular surgery laboratory in a university hospital. Fifteen adult, female, house swine (weight 90 to 140 kg). We evaluated the ventilatory effect of a wide range of oscillation frequencies (10-15 to 35-45 Hz), tidal volumes (0.5 to 2.2 mL/kg), and bias flow volumes (10 to 70 L/min) at a mean airway pressure of 12 +/- 1 cm H2O in anesthetized and relaxed pigs who did not have lung injury. Arterial blood gases are mainly dependent on tidal volume, frequency, and mean airway pressure. A threshold bias flow volume of 35 +/- 5 L/min is required to prevent CO2 rebreathing. In the group of lightweight animals (65 to 99 kg), the most efficient frequency band for CO2 elimination was approximately 25 Hz. The most efficient frequency band for arterial oxygenation was found to vary between individuals more than the most efficient frequency band for CO2 elimination. In the group of heavy animals (100 to 140 kg), no most efficient mean frequency could be assessed, probably because the excitation system was limited. We confirmed that tidal volume on its own had an effect on CO2 elimination ("tidal-volume effect"), although CO2 elimination was mainly determined by the product of tidal volume and oscillation frequency (oscillated minute volume), at least up to a critical frequency. Beyond that frequency, CO2 elimination could not be enhanced. The most efficient mean airway pressure in unimpaired lungs was assessed at 12 +/- 1 cm H2O. Adult pigs with a body weight in the range of the weight of clinical adult patients can be ventilated by high-frequency oscillation at tidal volumes smaller than, equal to, or slightly more than anatomical deadspace. The most efficient frequency for gas exchange varied between individuals. Tidal volume had an enhancing effect on CO2 elimination. The frequency dependency of PaO2 may have been related to a frequency-dependent structural remodeling of the airway system, which occurred even though the mean airway pressure was kept constant. These results demonstrate that failure of adequate ventilation by high-frequency oscillation is caused by a) CO2 rebreathing, b) the avoidance of an appropriate alveolar recruitment strategy, and c) an underpowered, high-frequency ventilatory system (oscillator) that is unable to deliver appropriate pressure oscillations. These limitations led to insufficient CO2 elimination and/or inadequate arterial oxygenation.

Estimation of Triggering Work of Breathing: The Dependence on Lung Mechanics and Bias Flow During Pressure Support Ventilation

Work of breathing necessary to trigger a ventilator (WOBtr) was calculated during pressure support ventilation (PSV), and the effect of bias flow on WOBtr was evaluated. A spring-loaded bellows type lung model with two bellows placed in series was used to simulate spontaneous breathing. A Venturi mechanism of jet flow generated subatmospheric pressure inside the diaphragm bellows simulated inspiratory effort. The lung compliance (CL) was set at 0.3 L/cm H2O or 0.05 L/cm H2O. The airway resistance (Raw) was set at 5, 20, or 50 cm H2O/L/s. Pressure support levels were increased from 0 to 45 cm H2O. Sensitivity was set at 2 cm H2O. No bias flow was used at first. The WOBtr was calculated using a pressure-volume (P-V) loop derived from the diaphragm bellows movement during the triggering period. We determined WOBtr and its dependence on the various pressure support (PS) levels, CL and Raw. To evaluate the effects of bias flow on WOBtr and triggering delay, a ventilator was put in the PSV mode, with various bias flow rates (from 0 to 20 L/min) at a sensitivity of 2 cm H2O. We found that when no bias flow was used, WOBtr increased with an increase in both Raw and end-expiratory lung bellows pressure which was considered as auto-PEEP. With bias flow, both triggering delay and WOBtr increased. An increase in bias flow at a given PS level resulted in both decreased pressure support time and tidal volume (VT). It is concluded that the bias flow system is not desirable for use during PSV.

Trigger sensitivity of Servo 300 (Siemens Elema) for pressure support ventilation in an infant

SummaryThe trigger sensitivity for pressure support ventilation (PSV) with a Servo 300 ventilator was evaluated in a 6‐month‐old male infant ventilated with synchronized intermittent mandatory ventilation (SIMV) of 14 c.min−1 and PSV of 4 cmH2O. The delay time between onset of inspiration and the trigger signal was 42 and 139 msec for trigger sensitivity of –2 and –4 cmH2O, respectively. On the former sensitivity, the inspiration was sensed by a decrease of expiratory bias flow before the airway pressure decreased to the set level. The time between the trigger signal and the flow delivery was 7 msec. The supplied volume exceeded the spontaneous breath on both trigger sensitivities. Using Servo 300, the constant expiratory bias flow, the use of a flow trigger and the mechanical improvement of the inspiratory valve contribute to reduced delay time in the trigger function, making the ventilator well suited, set in the PSV mode, even at high spontaneous respiratory rates for infants.

Aeroallergen‐induced dyspnea in freely moving guinea pigs: quantitative measurement by bias flow ventilated whole body plethysmography

Guinea pigs were sensitized and boostered with i.p. injections of ovalbumin (OA) 10 micrograms + Al(OH)3 100 mg. Thirteen days after the last injection animals (800-1100 g) were placed in bias flow ventilated whole body plethysmographs and allowed to stabilize for 2 h. Lung function was recorded for up to 2 h before and 5 h after aeroallergen challenge (OA 20 mg/ml, 60 s, 20 psi) by a noninvasive pulmonary analyzer for unrestrained rodents. Aeroallergen challenge produced immediate dyspnea and gasping (peaking between 8 and 17 min). Gasping was associated with an increase in amplitude in the box pressure fluctuations (93%), and in the slope of the fluctuations (391%). Respiratory rate increased (103 to 175 breaths/min, 78%), the product of breathing rate times box pressure amplitude increased (161 to 432, 180%). Relaxation time (the time it takes the box pressure signal to drop from its peak to 1/3 of its peak value) declined (0.16 to 0.05 s, 72%). All of these lung dysfunction changes were highly significant (p < 0.001). Lung dysfunction persisted for 60 to 120 min after challenge. One of 8 animals tested died within 10 min. None of the animals exhibited late asthmatic responses during the 5 h post-challenge period. Based on these data we conclude that this technique allows quantitative analysis of dyspnea, gasping, and an abnormal pattern (waveform) of breathing.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrical and optical properties of heterostructures made from diamond-like carbon layers on crystalline silicon

Thin films of amorphous, diamond-like carbon (DLC) were deposited in a capacitively coupled RF-plasma discharge on n- or p-type silicon substrates with different bias voltages, pressures and flow rates. The produced DLC/Si heterostructures show a broad variety of electrical and optical properties depending on the deposition parameters. The investigations concentrated on C—V measurements and on the photo-electrical properties of the DLC/Si heterostructure. The quantum efficiency of the heterostructure DLC on crystalline p-type silicon (specific resistance 10–20 Ω · cm) is 0.5 at a wavelength of 980 nm and a reverse bias of 2.7 V.

Sound absorption by a screen with a regular array of slits

Perforated plates are used extensively to absorb sound. A screen perforated by a regular array of parallel slits, with a mean bias flow through the slits, is investigated. The interaction between an incident sound wave and this mean flow converts acoustical energy into unsteady vortical motion. This vorticity radiates sound ineffectively, so that a significant proportion of the incident energy may be absorbed. The presence of a mean bias flow therefore leads to a linear mechanism of sound absorption. The maximum absorption coefficient from an isolated screen is found to be 1 2 , but it can be greatly increased by placing a rigid surface behind the screen. It is predicted theoretically that a backed screen with parallel slits can absorb all the sound incident on it, provided the gap between the screen and the rigid surface is approximately one-quarter of a wavelength and the mean flow velocity through the slits is chosen appropriately. Experimental results are presented which show encouraging agreement with the theory.

Ventilatory and metabolic responses to acute hyperoxia in newborns.

Hyperoxia has previously been found to increase metabolic rate (oxygen consumption [VO2] and CO2 production [VCO2]) in newborn mammals. We asked whether the same occurs in the newborn infant. Breathing pattern was measured in 25 full-term infants, 1 to 2 days of age, from the spirometric record obtained with a pneumotachograph attached to a face mask. Concentrations of O2 and CO2 were continuously measured at the mouth; VO2 and VCO2 were computed as the product of VE and the difference between inspired and expired concentration of the respective gases, 5 min of air (FIO2 = 0.21) and 5 min of O2 (FIO2 = 1). A bias flow through the mask and pneumotachograph delivered the inspired gas and eliminated the effects of the instrumental dead space. In neither case did measurements at 1 min significantly differ from those taken at 5 min. In hyperoxia VE increased in 22 of the 25 infants, in average +18% (p less than 0.001, paired two-tailed t test). Because of a rise in tidal volume (+35%, p less than 0.001) and a decrease in breathing rate (-11%, p less than 0.005) alveolar ventilation (VA) increased by about 58% (p less than 0.001). VO2 and VCO2 increased by 25% and 17%, respectively (p less than 0.001). The rise in VO2 was too large to be explained by the greater respiratory work of the hyperventilation, whereas that of VCO2 was not large enough to fully explain the increase in VA. We conclude that in newborn humans, as in other newborn species, the normoxic metabolic rate seems to be limited by the availability of O2.(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of Feed Water Recovery and Entrainment Solids Recovery in Flotation Columns

AbstractThe hydraulic entrainment recovery of gangue particles in a flotation process acts to decrease froth quality and is directly related to the quantity of feed water recovered. In this study, feed water recovery in column flotation has been measured using two techniques, one based on temperature differences around the froth, and the other based on a tracer (potassium permanganate) balance. There is similarity between the water recovery measured by the two methods. The results of experiments on a 3.8 cm diameter column are presented as a correlation between water recovery and bias flow. The effects of froth height, gas rate and feed rate on bias are also presented. Solid recovery by entrainment was measured using hydrophilic silica and hydrophilic galena. The results show that the degree of entrainment decreases with both increasing particle size and solids specific gravity. The effect of solids specific gravity is not as large as would first be expected. Resume Dans le procede de flottation, Le recup...

Vorticity production at the edge of a slit by sound waves in the presence of a low-Mach-number bias flow

Vorticity production by low-frequency sound waves impinging on a screen perforated with a slit is studied in the presence of a steady low-Mach-number mean flow through it. A Kutta condition is invoked at the rim of the slit to determine the strength of the shed vortex sheets. It is found that, unlike the case of a circular aperture, the strength depends not only on the Strouhal number but also on the Mach number. An attempt is made to apply the results to the problem of transmission of sound waves through a uniformly perforated screen.

Measurement of total respiratory impedance in infants by the forced oscillation technique

The forced oscillation technique according to Làndsér et al. (J. Appl. Physiol. 41:101-106, 1976) was modified for use in infants. Adaptations, including a flexible tube to connect the infant to the measuring system and a bias flow to avoid rebreathing, did not influence impedance values. The linearity of the respiratory system was assessed and confirmed by 1) applying pseudo-random noise oscillations at three different amplitudes to 7 infants and 2) comparing in 12 infants impedance values obtained with pseudo-random noise and with sinusoidal oscillations at 12 and 32 Hz. Intersubject variability, averaged for all frequencies, was 6%. In 17 infants the relative error (+/- SD) between two series of five measurements within a time interval of 15 min was 0.5 +/- 5.7%. No statistically significant difference was found between impedance values before and after repositioning of the infant's head, whereas rotation resulted in a decrease in resistance and no effect on reactance. Our results indicate that the infant-adapted forced pseudo-random noise oscillation technique has the potential to give valuable information about ventilatory lung function in infants.

Electron emission characteristics of sputtered lanthanum hexaboride

Magnetron sputtering was used to deposit a thin film of lanthanum hexaboride for cathode structures. The chemistry of the coatings was studied with x-ray diffraction, Auger electron spectroscopy, and x-ray photoelectron spectroscopy. The work function and electron emission characteristics of the coating have been studied in a diode test cell using tungsten and rhenium as substrates and controls. After optimization of sputtering parameters such as sample bias, forward power, base pressure, and argon flow rates, coatings were obtained with a work function of 2.4–2.6 eV. At 1200 K, the emission density of a lanthanum hexaboride coated tungsten filament was 8.8 mA/cm2 while the emission density of a clean tungsten filament was 9.7×10−12 A/cm2. Coated tungsten filaments ran over 1000 h without any reduction in the emission current in a vacuum of 10−7 Torr. Coated filaments were flexed with moderate severity without microcracking, spalling, or a detectable difference in emission characteristics. After an initial activation, the lanthanum hexaboride-coated filaments were exposed to the atmosphere without a subsequent reduction in emission current density. Surface analysis indicated that the surface of the cathode was primarily lanthanum oxide.

Isocapnic high frequency jet ventilation: dead space depends on frequency, inspiratory time and entrainment

Twelve healthy pigs were ventilated with high frequency jet ventilation via a Mallinckrodt HiLo jet tube. The expired gas was led to a conventional ventilator and CO2 analyzer which were used to measure CO2 elimination. There was no bias flow, so that the jet entrained only expired gas, i.e. rebreathing occurred. Frequency was varied between 2 and 11 Hz and the duration of inspiration, as a fraction of the ventilatory cycle (Ti/Ttot), from 5 to 20%. The minute ventilation, Vjet, delivered by the jet ventilator was adjusted to maintain a constant PaCO2. At 2 Hz and a Ti/Ttot of 5%, Vjet was of the same magnitude as ventilation during conventional intermittent positive pressure ventilation, and the total dead space fraction, VD/VT was 0.32. Both increasing frequency at a constant Ti/Ttot, and increasing Ti/Ttot at a constant frequency, increased VD/VT which was maximal (0.8) at 11 Hz and a Ti/Ttot of 20%. When entrainment was blocked, tidal jet volume had to be greatly increased. The continuous measurement of CO2 elimination was found to be useful for maintaining isocapnia when the jet ventilator setting was changed.

Influence of lung volume on collateral resistance in normal man

We measured the influence of changing the end-expiratory lung volume (EELV) on collateral resistance (Rcoll) in 6 normal volunteers (5 male, 1 female, aged 23–45 years). With subjects lying supine in an iron lung, a 5.3 mm fibroscope was introduced under local anesthesia and wedged into a sub-segmental bronchus of the right lower lobe. A truncated 5f Swan-Ganz catheter was tightly fitted into the suction port of the fibroscope. One lumen of the catheter served to deliver a constant flow (200 ml/min) of 5% CO 2 in air. The pressure in the wedged segment (Ps) was measured by the other channel. Airway pressure (used as alveolar pressure (Palv)) was determined with a low bias flow catheter taped to the side of the bronchoscope, its tip positioned 20 cm from the end of the bronchoscope. Rcoll was obtained by the formula: Rcoll = (Ps - Palv)/flow. EELV was passively changed by applying a constant extrathoracic pressure in the iron lung at 5 cm H 2O steps from 0 to + 15 and from 0 to −20 cm H 2O. The changes obtained in Rcoll (% baseline, mean ± SEM) at each extrathoracic pressure (ETP) were: − 5 cm H 2O, 73 ±4%; −10, 56 ± 7%; − 15, 56 ± 9%; − 20, 35 ± 10%; + 5, 118 ± 6%; + 10, 129 ± 7%; + 15, 118 ± 11%. Rcoll progressively decreased with increasing EELV (negative ETP) and increased slightly as EELV was reduced (positive ETP). The relationship between the log Rcoll and ΔEELV was linear; the slope of this line was 9.8%.

High-frequency oscillation during simulated altitude exposure

Ventilatory requirements using high-frequency oscillation (HFO) during simulated altitude exposure were investigated in control dogs and animals with oleic acid-induced lung injury. FIO2 values of 0.21 and 1.0 were supplied by bias flow to the normal and injured dogs, respectively. After a control period, animals were exposed to a simulated altitude of 8,000 ft (barometric pressure 564 torr), followed by a second control period at ground level. Both experimental groups had similar values of PaCO2 at ground level and during exposure to reduced barometric pressure. The tidal volume necessary to maintain eucapnia was higher in oleic acid-injured animals compared with the control group; cardiac output and functional residual capacity were lower. The alveolar-arterial oxygen difference was substantially larger in the oleic acid group. Adequate gas exchange can be maintained with HFO during exposure to altitude provided that ventilation and inspired PO2 are not reduced below normobaric levels.

The absorption of sound by perforated linings

The efficiency of a perforated screen as a sound absorber can be greatly increased when a rigid surface is placed behind the screen, essentially because the sound can then interact many times with the perforations. We consider a practical application for a backed perforated screen with a bias flow through the perforations: the ‘screech liner’. This is a perforated lining which is inserted in the afterburner section of jet engines to suppress the acoustically driven combustion instability commonly known as screech. A pressure drop across the screen ensures that a bias flow of cool air is produced; this flow protects the liner from the intense heat in the afterburner.Our analysis was developed in answer to a clear need for a theory which can predict the optimal geometry and bias flow to produce a highly absorptive liner. We show that it is theoretically possible to absorb all the sound at a particular frequency. Experimental results are presented which show encouraging agreement with the theoretical predictions.Screech is thought to be the excitation of a transverse resonant oscillation in the jet pipe, but the insertion of a liner inevitably changes the frequency of such resonances because the boundary condition at the wall is altered. We examine the effect of a liner on the resonances which occur in a cylinder and show that a well-designed liner may suppress resonances over a range of frequencies.The effect of the hot axial jet flow on the performance of a liner has not previously received attention. A simple model to account for this flow is included in our analysis.

MEASUREMENT OF ENTRAINMENT RATIO DURING HIGH FREQUENCY JET VENTILATION

We have measured tidal (VT), entrained (Ve) and "blowback" (Vbb) volumes during high frequency jet ventilation (HFJV) through a Mallinckrodt Hi-Lo Jet tracheal tube in anaesthetized patients. The above volumes were calculated by digital integration of the appropriate regions of flow curves derived from a pneumotachograph placed between the bias flow tubing and the tracheal tube. At a driving pressure of 1 bar, lung minute ventilation increased with increasing ventilatory frequency, whilst tidal volumes decreased. The contribution of entrainment to tidal volume (Ve/VT) remained constant, although the volumes entrained were relatively small and varied widely from subject to subject. Blowback volumes were considerable, especially at ventilatory frequencies used clinically (1-2 Hz). We conclude that it is not possible to entrain predictable concentrations of volatile agents from the low pressure bias flow during HFJV.

Alcohol and the response of upper airway resistance to a changing respiratory drive in normal man

We studied the effects of alcohol ingestion on the response of upper airway resistance (UAR) to changing respiratory motor output in 9 normal subjects. Nasal and pharyngeal pressures were measured with two low bias flow catheters placed at the tip of the epiglottis and in the posterior nasopharynx. Respiratory flow was measured with a Fleisch no. 3 pneumotachograph connected to a tightly fitting mask. Breath-by-breath inspiratory upper airway resistances were calculated at isoflow during 1) a CO 2 rebreathing (increase in drive),2) 2 min following five slow vital capacities of 100% O 2 (decrease in drive) (Post-O 2 period), and 3) 1 min before each procedure (baseline measurements). The respiratory motor output was estimated by the pressure developed 0.1 sec after the onset of inspiration (P 0.1) during rebreathing and by the mean inspiratory flow ( Vt/Ti) during the post-O 2 period. Measurements were performed before and after the ingestion of 1.5 ml/kg of 40% alcohol. Blood alcohol level rose from 0 to 14.9 ± 1.8 mmol · L −1(Mean ± SD) and total supralaryngeal resistance increased from 2.8 ± 1.8 cm H 2O·L −1·sec to 4.2 ± 1.8 cm H 2O·L −1·sec ( P < 0.001, Student's paired t-test). During CO 2 rebreathing UAR decreased exponentially as P 01. increased both before and after alcohol intake. The slope of the plot Log (pharyngeal resistance) against P 0.1 decreased from −17.0·10 −3 ± 9.3·10 −3 before alcohol to −11.0·10 −3 ± 6.6·10 −3 after alcohol intake ( P = 0.03). The slope of the decrease in nasal resistance remained unchanged. A decrease in Vt/Ti occurred during the Post-O 2 period and was accompanied by an exponential increase in UAR at each experiment. The slope of Log (pharyngeal resistance) over Vt/Ti was significantly higher after (−27.0·10 −3 ± 7.1·10 −3) than before alcohol (−12.0·10 −3 ± 4.2·10 −3, P < 0.001). The slope of the increase in nasal resistance with decreasing Vt/Ti rose from −8.4·10 −3 ± 6.5·10 −3 to −13.0·10 −3 ± 7.4·10 −3 after alcohol ingestion ( P = 0.06). We conclude that alcohol ingestion depresses the pharyngeal responses to changing central drive in normal subjects.