Assessment of intraluminal impedance for the detection of pharyngeal bolus flow during swallowing in healthy adults

Intraluminal impedance, a nonradiological method for assessing bolus flow within the gut, may be suitable for investigating pharyngeal disorders. This study evaluated an impedance technique for the detection of pharyngeal bolus flow during swallowing. Patterns of pharyngoesophageal pressure and impedance were simultaneously recorded with videofluoroscopy in 10 healthy volunteers during swallowing of liquid, semisolid, and solid boluses. The timing of bolus head and tail passage recorded by fluoroscopy was correlated with the timing of impedance drop and recovery at each recording site. Bolus swallowing produced a drop in impedance from baseline followed by a recovery to at least 50% of baseline. The timing of the pharyngeal and esophageal impedance drop correlated with the timing of the arrival of the bolus head. In the pharynx, the timing of impedance recovery was delayed relative to the timing of clearance of the bolus tail. In contrast, in the upper esophageal sphincter (UES) and proximal esophagus, the timing of impedance recovery correlated well with the timing of clearance of the bolus tail. Impedance-based estimates of pharyngoesophageal bolus clearance time correlated with true pharyngoesophageal bolus clearance time. Patterns of intraluminal impedance recorded in the pharynx during bolus swallowing are therefore more complex than those in the esophagus. During swallowing, mucosal contact between the tongue base and posterior pharyngeal wall prolongs the duration of pharyngeal impedance drop, leading to overestimation of bolus tail timing. Therefore, we conclude that intraluminal impedance measurement does not accurately reflect the bolus transit in the pharynx but does accurately reflect bolus transit across the UES and below.     

Ventilatory effect of acute pulmonary hypothermia

The isolated effect of cooling the pulmonary circulation on ventilation was quantified in nine anesthetized dogs. The right pulmonary artery (RPA) was cannulated within the pericardium, and systemic blood was pumped from the left atrium to the RPA between, but not during, periods of cooling. Cooled blood boluses were injected into the RPA under conditions in which either bolus temperature (5-35 degrees C) or volume (0-1.5 ml/kg body wt) varied. Inspiratory time (TI), expiratory time (TE), breath duration (TT), and peak integrated activity (PEAK) were determined from diaphragm EMG. Results for five postinjection breaths were converted to a percent of the values from five preinjection breaths. There was a linear relationship between bolus temperature and TI [r = 0.61, slope (x) = 0.59%/degrees C, P less than 0.001), TE (r = 0.73, x = 1.43%/degrees C, P less than 0.001] as well as TT (r = 0.74, x = 1.10%/degrees C, P less than 0.001), whereas PEAK was unaffected (n = 9). When injection temperature was 5 degrees C, an inverse linear relationship existed between bolus volume and TI (r = 0.75, x = -15.2%.ml-1.kg-1, P less than 0.001) and TE (r = 0.78, x = -23.4%.ml-1.kg-1, P less than 0.001) (n = 4). In two dogs tested the effect of bolus injection was minimal at residual volume and progressively increased with lung volume. The effect of cold bolus injection was eliminated after right vagotomy in three dogs. Results indicate that cooling of some vagal receptor in the lung increases breathing frequency primarily by shortening TE.     

Effect of dry swallows and wet swallows of different volumes on esophageal peristalsis.

The effect of dry swallows and wet swallows of various volumes on esophageal function was studied in normal subjects. An intraesophageal transducer assembly was used to measure the dynamics of esophageal peristalsis. The strength of esophageal contraction (amplitude) following a 1-ml liquid bolus was similar to that following a dry swallow but was significantly less than that following a wet swallow of a larger volume. There was no difference in strength of esophageal squeeze following swallows ranging from 2 to 20 ml. In addition, a wet swallow was associated with slower wave speed, greater duration of the contraction wave, and later time of appearance of the peristaltic wave in the distal esophagus than a dry swallow. Futhermore, the incidence of peristalsis was greater with a wet swallow than a dry swallow. The results of our studies indicate that although the act of swallowing alone in man initiates peristalsis, afferent information contributes to the regulation of primary peristalsis.     

Nutrient modulation of intestinal gas dynamics in healthy humans: dependence on caloric content and meal consistency

The actions of nutrients on gut transit of liquids and solids have been extensively studied, but the effects of meal ingestion on intestinal gas flow are unexplored. We hypothesized that meals of varying caloric content and consistency modulate gas transit to different degrees. Nine healthy volunteers underwent jejunal perfusion of physiological gas mixtures at 12 ml.min(-1).3 h, with ingestion of nothing (control), water (240 ml), 240-kcal liquid meals, and 240-kcal solid meals at the end of the second hour in separate studies. Gas was quantified from an intrarectal catheter. After an initial lag phase, gas evacuation approached steady state by the end of the fasting period. Solid and liquid caloric meals increased total gas volumes evacuated from 5-40 min after ingestion vs. control studies (P < 0.05). These increases resulted from increased numbers of bolus gas evacuations (P < 0.05), whereas bolus volumes, pressures, and flow rates were similar for all test conditions. Solid and liquid caloric meals elicited similar effects on bolus gas dynamic parameters, whereas water did not affect these measures vs. control (NS, not significant). Both caloric meals and the noncaloric liquid meal increased continuous gas flow, which represented <2% of total gas expulsion. In conclusion, caloric meals promote bolus gas transit in healthy humans, whereas noncaloric liquids have no effect. Solids stimulate early postprandial gas dynamics to the same extent as liquid meals of similar caloric content. Thus modulatory effects of meals on intestinal gas transit depend on their caloric content but not their consistency.     

Measuring esophageal distension by high-frequency intraluminal ultrasound probe

Distension of the esophagus can cause heartburn and chest pain; however, none of the available techniques to study the esophagus measure esophageal distension. We evaluated the technique of high-frequency intraluminal ultrasound probe (HFIUS) to measure the esophageal cross-sectional area (CSA) during gastroesophageal reflux (GER). The following methods were used: 1) the CSA of agarose gel tubes of known dimensions were measured using ultrasound probes; 2) seven normal subjects were studied to evaluate the esophageal CSA during different bolus volumes (1, 5, 10, 15, and 20 ml) of water swallows (WS); and 3) simultaneous pressures, pH, and ultrasound images of the esophagus were recorded in healthy subjects. In vitro studies showed that the HFIUS measured the CSA of the tubes accurately. The maximal CSA of the distal esophagus during WS with boluses of 1, 5, 10, 15, and 20 ml were 54, 101, 175, 235, and 246 mm(2), respectively. Esophageal contents during 62 episodes of transient lower esophageal sphincter relaxations, 29 pH positive, and 33 pH negative GER episodes revealed that reflux of air into the esophagus occurred more frequently than liquid. The median CSA and estimated diameter of the esophagus during liquid GER was 44.1 mm(2) and 7.5 mm, respectively. We conclude that HFIUS is a valid technique to measure the CSA of the esophagus in vivo during GER. Distension of the esophagus during physiological GER is relatively small.     

Electromyographic activity from human laryngeal, pharyngeal, and submental muscles during swallowing.

The durations and temporal relationships of electromyographic activity from the submental complex, superior pharyngeal constrictor, cricopharyngeus, thyroarytenoid, and interarytenoid muscles were examined during swallowing of saliva and of 5- and 10-ml water boluses. Bipolar, hooked-wire electrodes were inserted into all muscles except for the submental complex, which was studied with bipolar surface electrodes. Eight healthy, normal, subjects produced five swallows of each of three bolus volumes for a total of 120 swallows. The total duration of electromyographic activity during the pharyngeal stage of the swallow did not alter with bolus condition; however, specific muscles did show a volume-dependent change in electromyograph duration and time of firing. Submental muscle activity was longest for saliva swallows. The interarytenoid muscle showed a significant difference in duration between the saliva and 10-ml water bolus. Finally, the interval between the onset of laryngeal muscle activity (thyroarytenoid, interarytenoid) and of pharyngeal muscle firing patterns (superior pharyngeal constrictor onset, cricopharyngeus offset) decreased as bolus volume increased. The pattern of muscle activity associated with the swallow showed a high level of intrasubject agreement; the presence of somewhat different patterns among subjects indicated a degree of population variance.     

Lung volume effects on pharyngeal swallowing physiology.

The experiment was a prospective, repeated-measures design intended to determine how the variation of lung volume affects specific measures of swallowing physiology. Swallows were recorded in 28 healthy subjects, who ranged in age from 21 to 40 yr (mean age of 29 yr), by using simultaneous videofluoroscopy, bipolar intramuscular electromyography, and respiratory inductance plethysmography. Each subject swallowed three standardized pudding-like consistency boluses at three randomized lung volumes: total lung capacity, functional residual capacity, and residual volume. The results showed that pharyngeal activity duration of deglutition for swallows produced at residual volume was significantly longer than those occurring at total lung capacity or at functional residual capacity. No significant differences were found for bolus transit time or intramuscular electromyography of the superior constrictor. The results of this experiment lend support to the hypothesis that the respiratory system may have a regulatory function related to swallowing and that positive subglottic air pressure may be important for swallowing integrity. Eventually, new treatment paradigms for oropharyngeal dysphagia that are based on respiratory physiology may be developed.     

Multichannel intraluminal impedance accurately detects fasting,recumbent reflux events and their clearing

Multichannel intraluminal impedance (MII) is a new diagnostic test for gastroesophageal reflux disease (GERD). The objective of this report is to determine the accuracy of MII in detecting individual reflux events (REs) identified by pH probe and manometry, as well as their clearing in patients with severe GERD compared with normal volunteers. Ten severe GERD patients and 10 normal volunteers underwent simultaneous manometry [7 sites: gastric, lower esophageal sphincter, esophagus (4), pharynx], pH, and MII (6 sites in esophagus) for 15 min in the left and right recumbent posture while fasting. We found that patients had 30-fold more REs than normal volunteers (41 +/- 11 vs. 1.3 +/- 0.4), and 95% of all REs were detected by MII. An average 15-fold fall in impedance with liquid and fivefold rise with gas made REs and their composition easy to detect with MII. In the right recumbent posture, nearly all REs detected by MII were liquid (98%, 98/100). In contrast, all 283 REs detected by MII in the left recumbent posture were gas. Nearly all REs detected by MII were cleared (98%, 368/374). Mean acid clearing time was threefold longer (47 s) than clearing time by either manometry (15 s) or MII (13 s), primarily due to acid rereflux, i.e., additional acid REs during acid clearing. We conclude that MII is accurate in detecting REs identified by manometry and/or pH probe, their composition, and their clearing.     

Dosimetric characterization of 3D printed bolus at different infill percentage for external photon beam radiotherapy

Background and purpose3D printing is rapidly evolving and further assessment of materials and technique is required for clinical applications. We evaluated 3D printed boluses with acrylonitrile butadiene styrene (ABS) and polylactide (PLA) at different infill percentage.Material and methodsA low-cost 3D printer was used. The influence of the air inclusion within the 3D printed boluses was assessed thoroughly both with treatment planning system (TPS) and with physical measurements. For each bolus, two treatment plans were calculated with Monte Carlo algorithm, considering the computed tomography (CT) scan of the 3D printed bolus or modelling the 3D printed bolus as a virtual bolus structure with a homogeneous density. Depth dose measurements were performed with Gafchromic films.ResultsHigh infill percentage corresponds to high density and high homogeneity within bolus material. The approximation of the bolus in the TPS as a homogeneous material is satisfying for infill percentages greater than 20%. Measurements performed with PLA boluses are more comparable to the TPS calculated profiles. For boluses printed at 40% and 60% infill, the discrepancies between calculated and measured dose distribution are within 5%.Conclusions3D printing technology allows modulating the shift of the build-up region by tuning the infill percentage of the 3D printed bolus in order to improve superficial target coverage.     

THE RELATION BETWEEN THE ELECTRICAL CONDUCTIVITY OF THE EXTERNAL MEDIUM AND THE RATE OF CELL DIVISION IN SEA URCHIN EGGS

Dilution of sea water with isotonic sugar solution leaves the rate of cleavage of Arbacia eggs almost unchanged until the proportion of sea water is decreased to 20 or 25 volumes per cent. From this point cleavage becomes progressively slower with further dilution. Many eggs fail to cleave at dilutions of 5 to 6 volumes per cent. No cleavage occurs in 2 volumes per cent sea water or in pure sugar solution. Eggs returned from these media to sea water resume cleavage and development. There is thus no relation between the rate of cleavage and the electrical conductivity of the medium, except possibly within the range of dilutions from 20 to 5 volumes per cent sea water. In this range cleavage rate decreases as conductivity decreases, but the relation is not a linear one.     

Fundamental cryobiology of rat immature and mature oocytes: hydraulic conductivity in the presence of Me(2)SO, Me(2)SO permeability, and their activation energies

The hydraulic conductivity in the presence of dimethyl sulfoxide Me(2)SO (L(p)(Me(2)SO)), Me(2)SO (P(Me(2)SO)) permeability and reflection coefficient (sigma) of immature (germinal vesicle; GV) and mature (metaphase II; MII) rat oocytes were determined at various temperatures. A temperature controlled micropipette perfusion technique was used to conduct experiments at five different temperatures (30, 20, 10, 4, and -3 degrees C). Kedem and Katchalsky membrane transport theory was used to describe the cell volume kinetics. The cell volumetric changes of oocytes were calculated from the measurement of two oocyte diameters, assuming a spherical shape. The activation energies (E(a)) of L(p)(Me(2)SO) and P(Me(2)SO) were calculated using the Arrhenius equation. Activation energies of L(p)(Me(2)SO) for GV and MII oocytes were 34.30 Kcal/mol and 16.29 Kcal/mol, respectively; while the corresponding E(a)s of P(Me(2)SO) were 19.87 Kcal/mol and 21.85 Kcal/mol, respectively. These permeability parameters were then used to calculate cell water loss in rat oocytes during cooling at subzero temperatures. Based on these values, the predicted optimal cooling rate required to maintain extra- and intracellular water in near equilibrium for rat GV stage oocytes was found to be between 0.05 degrees C/min and 0. 025; while for rat MII oocytes, the corresponding cooling rate was 1 degrees C/min. These data suggest that standard cooling rates used for mouse oocytes (e.g., 0.5-1 degrees C/min) can also be employed to cryopreserve rat MII oocytes. However, the corresponding cooling rate required to avoid damage must be significantly slower for the GV stage rat oocyte. J. Exp. Zool. 286:523-533, 2000.     

Regional deposition and retention of particles in shallow, inhaled boluses: effect of lung volume

The regionaldeposition of particles in boluses delivered to shallow lung depths andtheir subsequent retention in the airways may depend on the lung volumeat which the boluses are delivered. To evaluate the effectof end-inspiratory lung volume on aerosol bolus delivery, we hadhealthy subjects inhale radiolabeled, monodisperse aerosol(^99mTc-iron oxide, 3.5-µm massmedian aerodynamic diameter) boluses (40 ml) to a volumetric frontdepth of 70 ml into the lung at lung volumes of 50, 70, and 85% oftotal lung capacity (TLC) end inhalation. By gamma camera analysis, wefound significantly greater deposition in the left (L) vs. right (R)lungs at the 70 and 85% TLC end inhalation; ratio of deposition in Lto R lung, normalized to L-to-R ratio of lung volume (mean L/R), was1.60 ± 0.45 (SD) and 1.96 ± 0.72, respectively(P < 0.001 for comparison to 1.0) for posterior images. However, at 50% TLC, L/R was 1.23 ± 0.37, not significantly different from 1.0. These data suggest that the L andR lungs may be expanding nonuniformly at higher lung volumes. On theother hand, subsequent retention of deposited particles at 2 and 24 hpostdeposition was independent of L/R at the various lung volumes. Thusasymmetric bolus ventilation for these very shallow boluses does notlead to significant increases in peripheral alveolar deposition. Thesedata may prove useful for 1)designing aerosol delivery techniques to target bronchial airways and2) understanding airway retention ofinhaled particles.

     

Water- and cryoprotectant-permeability of mature and immature oocytes in the medaka (Oryzias latipes)

The permeability of the plasma membrane plays a crucial role in the successful cryopreservation of oocytes/embryos. To identify a stage feasible for the cryopreservation of teleost oocytes, we investigated the permeability to water and various cryoprotectants of medaka (Oryzias latipes) oocytes at the germinal vesicle (GV) and metaphase II (MII) stages. In sucrose solutions, the volume changes were greater in GV oocytes than MII oocytes. Estimated values for osmotically inactive volume were 0.41 for GV oocytes and 0.74 for MII oocytes. Water-permeability (microm/min/atm) at 25 degrees C was higher in GV oocytes (0.13+/-0.01) than MII oocytes (0.06+/-0.01). The permeability of MII oocytes to various cryoprotectants (glycerol, propylene glycol, ethylene glycol, and DMSO) was quite low because the oocytes remained shrunken during 2 h of exposure in the cryoprotectant solutions at 25 degrees C. When the chorion of MII oocytes was removed, the volume change was not affected, except in DMSO solution, where dechorionated oocytes shrunk and then regained their volume slowly; the P(DMSO) value was estimated to be 0.14+/-0.01x10(-3) cm/min. On the other hand, the permeability of GV oocytes to cryoprotectants were markedly high, the P(s) values (x10(-3) cm/min) for propylene glycol, ethylene glycol, and DMSO being 2.21+/-0.29, 1.36+/-0.18, and 1.19+/-0.01, respectively. However, the permeability to glycerol was too low to be estimated, because GV oocytes remained shrunken after 2 h of exposure in glycerol solution. These results suggest that, during maturation, medaka oocytes become less permeable to water and to small neutral solutes, probably by acquiring resistance to hypotonic conditions before being spawned in fresh water. Since such changes would make it difficult to cryopreserve mature oocytes, immature oocytes would be more suitable for the cryopreservation of teleosts.     

Assessment of papain-induced lung injury in isolated lungs by measurements of aerosol deposition and mixing.

Aerosol bolus inspirations were used to assess lung injury in 15 isolated dog lungs exposed to low (0-375 units) or high doses (600-1,200 units) of papain. Effective air space size (EAD) was determined from aerosol deposition during a 5-s breath hold. Convective mixing was assessed by the spreading of the expired bolus with respect to expired volume, quantified by a coefficient of dispersion (CD) equal to the square root of the difference in the variances of the expired and inspired boluses divided by the volumetric penetration of the bolus. After exposure, CD measured with deeply penetrating boluses increased by an average of 2.5% in the low-exposure group (P greater than 0.05) and 28.0% in the high-exposure group (P less than 0.0001). CD measured with shallowly penetrating boluses decreased by 4.3% (P less than 0.0001) in the low-exposure group and increased by an average of 18.3% in the high-exposure group (P less than 0.05). Papain exposure caused EAD to increase in some lungs and decrease in others. For deep bolus penetrations, EAD changed by an average of -0.8% in the low-exposure group (P greater than 0.05) and +21.1% in the high-exposure group (P greater than 0.05). Both EAD and CD appeared to be sensitive to lung injury. However, changes in EAD were less consistent than those in CD, possibly due to changes caused by lung injury in the regional distribution of inspired aerosol.     

Adaptation of swallowing hyo-laryngeal kinematics is distinct in oral vs. pharyngeal sensory processing

Before a bolus is pushed into the pharynx, oral sensory processing is critical for planning movements of the subsequent pharyngeal swallow, including hyoid bone and laryngeal (hyo-laryngeal) kinematics. However, oral and pharyngeal sensory processing for hyo-laryngeal kinematics is not fully understood. In 11 healthy adults, we examined changes in kinematics with sensory adaptation, sensitivity shifting, with oropharyngeal swallows vs. pharyngeal swallows (no oral processing), and with various bolus volumes and tastes. Only pharyngeal swallows showed sensory adaptation (gradual changes in kinematics with repeated exposure to the same bolus). Conversely, only oropharyngeal swallows distinguished volume differences, whereas pharyngeal swallows did not. No taste effects were observed for either swallow type. The hyo-laryngeal kinematics were very similar between oropharyngeal swallows and pharyngeal swallows with a comparable bolus. Sensitivity shifting (changing sensory threshold for a small bolus when it immediately follows several very large boluses) was not observed in pharyngeal or oropharyngeal swallowing. These findings indicate that once oral sensory processing has set a motor program for a specific kind of bolus (i.e., 5 ml water), hyo-laryngeal movements are already highly standardized and optimized, showing no shifting or adaptation regardless of repeated exposure (sensory adaptation) or previous sensory experiences (sensitivity shifting). Also, the oral cavity is highly specialized for differentiating certain properties of a bolus (volume) that might require a specific motor plan to ensure swallowing safety, whereas the pharyngeal cavity does not make the same distinctions. Pharyngeal sensory processing might not be able to adjust motor plans created by the oral cavity once the swallow has already been triggered.     

Contribution of upper airway geometry to convective mixing

We investigated the axial dispersive effect of the upper airway structure (comprising mouth cavity, oropharynx, and trachea) on a traversing aerosol bolus. This was done by means of aerosol bolus experiments on a hollow cast of a realistic upper airway model (UAM) and three-dimensional computational fluid dynamics (CFD) simulations in the same UAM geometry. The experiments showed that 50-ml boluses injected into the UAM dispersed to boluses with a half-width ranging from 80 to 90 ml at the UAM exit, across both flow rates (250, 500 ml/s) and both flow directions (inspiration, expiration). These experimental results imply that the net half-width induced by the UAM typically was 69 ml. Comparison of experimental bolus traces with a one-dimensional Gaussian-derived analytical solution resulted in an axial dispersion coefficient of 200-250 cm(2)/s, depending on whether the bolus peak and its half-width or the bolus tail needed to be fully accounted for. CFD simulations agreed well with experimental results for inspiratory boluses and were compatible with an axial dispersion of 200 cm(2)/s. However, for expiratory boluses the CFD simulations showed a very tight bolus peak followed by an elongated tail, in sharp contrast to the expiratory bolus experiments. This indicates that CFD methods that are widely used to predict the fate of aerosols in the human upper airway, where flow is transitional, need to be critically assessed, possibly via aerosol bolus simulations. We conclude that, with all its geometric complexity, the upper airway introduces a relatively mild dispersion on a traversing aerosol bolus for normal breathing flow rates in inspiratory and expiratory flow directions.     

Effect of bleeding on hemoglobin contents and lipid oxidation in the skipjack muscle

Skipjack samples were prepared using two different killing methods, namely, struggling death in iced sea water (control) and instant death by mechanical bleeding. The hemoglobin content in the bled muscles was significantly lower than that in the control. 4-Hydroxyhexenal content in the bled muscles was significantly lower than that in the control over 2 d of storage at 0 degrees C.     

Role of physical bolus properties as sensory inputs in the trigger of swallowing

Background

Swallowing is triggered when a food bolus being prepared by mastication has reached a defined state. However, although this view is consensual and well supported, the physical properties of the swallowable bolus have been under-researched. We tested the hypothesis that measuring bolus physical changes during the masticatory sequence to deglutition would reveal the bolus properties potentially involved in swallowing initiation.

Methods

Twenty normo-dentate young adults were instructed to chew portions of cereal and spit out the boluses at different times in the masticatory sequence. The mechanical properties of the collected boluses were measured by a texture profile analysis test currently used in food science. The median particle size of the boluses was evaluated by sieving. In a simultaneous sensory study, twenty-five other subjects expressed their perception of bolus texture dominating at any mastication time.

Findings

Several physical changes appeared in the food bolus as it was formed during mastication: (1) in rheological terms, bolus hardness rapidly decreased as the masticatory sequence progressed, (2) by contrast, adhesiveness, springiness and cohesiveness regularly increased until the time of swallowing, (3) median particle size, indicating the bolus particle size distribution, decreased mostly during the first third of the masticatory sequence, (4) except for hardness, the rheological changes still appeared in the boluses collected just before swallowing, and (5) physical changes occurred, with sensory stickiness being described by the subjects as a dominant perception of the bolus at the end of mastication.

Conclusions

Although these physical and sensory changes progressed in the course of mastication, those observed just before swallowing seem to be involved in swallowing initiation. They can be considered as strong candidates for sensory inputs from the bolus that are probably crucially involved in the triggering of swallowing, since they appeared in boluses prepared in various mastication strategies by different subjects.     

Convective and diffusive gas transport in canine intrapulmonary airways.

The significance of convective and diffusive gas transport in the respiratory system was assessed from the response of combined inert gas and particle boluses inhaled into the conducting airways. Particles, considered as "nondiffusing gas," served as tracers for convection and two inert gases with widely different diffusive characteristics (He and SF6) as tracers for convection and diffusion. Six-milliliter boluses labeled with monodisperse di-2-ethylhexyl sebacate droplets of 0.86-microns aerodynamic diameter, 2% He, and 2% SF6 were inspired by three anesthetized mechanically ventilated beagle dogs to volumetric lung depths up to 170 ml. Mixing between inspired and residual air caused dispersion of the inspired bolus, which was quantified in terms of the bolus half-width. Dispersion of particles increased with increasing lung depth to which the boluses were inhaled. The increase followed a power law with exponents less than 0.5 (mean 0.39), indicating that the effect of convective mixing per unit volume was reduced with depth. Within the pulmonary dead space, the behavior of the inert gases He and SF6 was similar to that of the particles, suggesting that gas transport was almost solely due to convection. Beyond the dead space, dispersion of He and SF6 increased more rapidly than dispersion of particles, indicating that diffusion became significant. The gas and particle bolus technique offers a suitable approach to differential analysis of gas transport in intrapulmonary airways of lungs.     

Effect of protein hydration on receptor conformation: decreased levels of bound water promote metarhodopsin II formation.

Neutral solutes were used to investigate the effects of osmotic stress both on the ability of rhodopsin to undergo its activating conformation change and on acyl chain packing in the rod outer segment (ROS) disk membrane. The equilibrium concentration of metarhodopsin II (MII), the conformation of photoactivated rhodopsin, which binds and activates transducin, was increased by glycerol, sucrose, and stachyose in a manner which was linear with osmolality. Analysis of this shift in equilibrium in terms of the dependence of ln(Keq) on osmolality revealed that 20 +/- 1 water molecules are released during the MI-to-MII transition at 20 degrees C, and at 35 degrees C 13 +/- 1 waters are released. At 35 degrees C the average time constant for MII formation was increased from 1.20 +/- 0.09 ms to 1.63 +/- 0.09 ms by addition of 1 osmolal sucrose or glycerol. The effect of the neutral solutes on acyl chain packing in the ROS disk membrane was assessed via measurements of the fluorescence lifetime and anisotropy decay of 1,6-diphenyl-1,3,5-hexatriene (DPH). Analysis of the anisotropy decay of DPH in terms of the rotational diffusion model showed that the angular width of the equilibrium orientational distribution of DPH about the membrane normal was progressively narrowed by increased osmolality. The parameter fv, which is proportional to the overlap between the DPH orientational probability distribution and a random orientational distribution, was reduced by the osmolytes in a manner which was linear with osmolality. This study highlights the potentially opposing interplay between the effect of membrane surface hydration on both the lipid bilayer and integral membrane protein structure. Our results further demonstrate that the binding and release of water molecules play an important role in modulating functional conformational changes for integral membrane proteins, as well as for soluble globular proteins.