Transmucosal gas-loss rates in middle ears initially filled with O2 or CO2.

This study investigates the role of different gases in clearance of gas in the middle ear cavity (ME) by its mucosal blood flow. A rat model was used to measure gas volume changes in the ME cavity at constant pressure without ventilation. We disturbed the normal gas composition of the ME by filling it with O2 or CO2, measured the consequent changes in gas volume over time and compared these results with previously obtained ones for air and N2. The first 5 min of the primary transient phase (phase I) for O2 or CO2 was characterized by a volume loss decrease of -0.49 ± 0.34 µL and -46.28 ± 8.49 µL, respectively, with volume loss increase for air and N2 differing greatly, at +0.17 ± 0.17 and +2.31 ± 0.81, respectively. The CO2 value of -46.28 µL showed that a volume of gas equivalent to that of the ME cleft volume was eliminated within the first 5 min. In the second phase (phase II), all gases showed a linear decrease in volume, which presumably represents a steady-state gas loss rate. However, the gas loss rate of -0.307 ± 0.170 µL min-1 for O2-filled MEs was significantly higher than the mean of -0.124 µL min-1 for all other gases. We used a previously established mathematical model to calculate the effective ME mucosal blood flow rate under steady-state (phase II) conditions. The blood flow results for O2-filled MEs differed greatly from those of the other gases (89.0 ± 49.28 vs. 26.5 µL min-1, on average), which suggest that the model used to calculate blood flow should be modified if used with O2-filled MEs. Further work should involve a comparison of our method with different methods to verify ME blood flow rate.

Perfusion and diffusion limitations in middle ear gas exchange: the exchange of CO2 as a test case.

A long standing debate on perfusion/diffusion limitations in the context of middle ear (ME) gas exchange was revisited using data obtained from previous iso-pressure gas-exchange measurements in different mammals. We tried to determine whether the exchange of CO(2) in the ME is limited by perfusion or by diffusion by comparing the mass specific cardiac output (msQ) and the mass specific initial CO(2) flow rate into air-washed MEs (msV(i) CO(2)) of rabbits and rats. Based on previously published allometry at rest, the msQ was 0.154 mL/(min g) in rabbits (mean body weight: 2800 g) and 0.259 mL/(min g) in rats (mean body weight: 179.1 g); msV(i) CO(2) (Delta t=0) was 0.109+/-0.047 microL/(h g) in rabbits (n=16) and 0.170+/-0.094 microL/(h g) in rats (n=9). Similar ratios were found when an allometric comparison was made between the ratio of msV(i) CO(2) (Delta t=0) (approximately 0.64), and the ratio of msQs (approximately 0.59) in rabbits and rats. If the active mucosal surface areas of MEs of rabbits and rats are directly proportional to their masses as are the masses of their hearts and if their msQs are proportional to the rates of blood flows in the ME mucosa, these results support the assumption that the exchange of CO(2) in the ME of mammals is mainly perfusion (and not diffusion) dependent.

Middle ear gas loss in inflammatory conditions: the role of mucosa thickness and blood flow.

Several middle ear (ME) pathologies are associated with ME gas deficit. These include in particular the chronic otitis media diseases that are associated with inflammation (hence, increased ME mucosal blood flow) and/or reduced Eustachian tube (ET) function. The present study models the trans-mucosal gas exchange in normal and inflamed middle ears of rats. The model evaluates the role of the gas diffusion path in the ME mucosa using mucosa thickness as its index and the role of the mucosal blood flow rate on ME gas economy in order to compare between normal and inflamed MEs. An experimental method employing ME gas volume changes at constant pressure due to trans-mucosal gas exchange, and blood gas values from the literature, was used in anaesthetized rats to corroborate the model. Mucosa thickness was measured as an index of the gas diffusion path between the ME space and the ME circulation. ME inner surface area was estimated from its measured gas volume. Inflammation was inflicted by applying lipopolysaccharide (LPS) into one ear. The contralateral ear served as control. ME gas volume decreased significantly faster with time (p=0.02) in inflamed ears (-0.107 microL min(-1) +/- 0.034 S.D., n=10) versus control ears (-0.067 microL min(-1) +/- 0.036 S.D., n=10). Mucosa thickness was significantly thicker in inflamed ears (48.4 microm +/- 11.0 S.D.) versus controls (20.5 microm +/- 10.1 S.D.). The mathematical model, the experimental results, and the blood gas values were used to estimate the relative effective mucosal blood flow rate. The model predicts that in spite of almost doubling mucosa thickness in LPS treated ears, the increased gas loss in inflamed ears may be explained by increased mucosal blood flow rate. We suggest that the ability to estimate ME blood flow as obtained by applying the model to the measurements, is relevant to medical management of inflamed ME.

Acute otitis media and mastoid growth.

CONCLUSIONS: This study implies that the hypothesis that acute otitis media (AOM) in infancy inhibits the growth of the mastoid system cannot be accepted. OBJECTIVE: To establish a relationship between AOM in children and their mastoid pneumatization development. PATIENTS AND METHODS: Lateral Schüller mastoid radiographs (LMRs) were measured in two groups of children at ages 2-11 years. Group A (n=116) had a history of recurrent AOM; group B (n=108) had no such history. Patients were treated in a private clinic. Data were analysed at Tel Aviv University. The patients had their LMR taken and measured planimetrically. LMR areas on left and right sides were compared in each group and age and were tested for possible differences using the paired Student's t test. When no left/right difference was detected, the values were averaged. Groups A and B were compared at different ages using two-tailed two-sample unequal variance and correlation coefficients. RESULTS: The analyses show that the LMR area became gradually and significantly larger with age in group A (R2=0.858; p<0.05). It did not develop significantly in group B.

Role of nitrogen in transmucosal gas exchange rate in the rat middle ear.

This study investigates the role of nitrogen (N2) in transmucosal gas exchange of the middle ear (ME). We used an experimental rat model to measure gas volume variations in the ME cavity at constant pressure. We disturbed the steady-state gas composition with either air or N2 to measure resulting changes in volume at ambient pressure. Changes in gas volume over time could be characterized by three phases: a primary transient increase with time (phase I), followed by a linear decrease (phase II), and then a gradual decrease (phase III). The mean slope of phase II was -0.128 microl/min (SD 0.023) in the air group (n = 10) and -0.105 microl/min (SD 0.032) in the N2 group (n = 10), but the difference was not significant (P = 0.13), which suggests that the rate of gas loss can be attributed mainly to the same steady-state partial pressure gradient of N2 reached in this phase. Furthermore, a mathematical model was developed analyzing the transmucosal N2 exchange in phase II. The model takes gas diffusion into account, predicting that, in the absence of change in mucosal blood flow rate, gas volume in the ME should show a linear decrease with time after steady-state conditions and gas composition are established. In accordance with the experimental results, the mathematical model also suggested that transmucosal gas absorption of the rat ME during steady-state conditions is governed mainly by diffusive N2 exchange between the ME gas and its mucosal blood circulation.

High-resolution measurements of middle ear gas volume changes in the rabbit enables estimation of its mucosal CO(2) conductance.

Transmucosal CO(2) exchange in the middle ear (ME) of the New Zealand White rabbit (Oryctolagus cuniculus) was studied using an accurate novel detecting and recording system for measuring gas volume changes at constant pressure, based on a principle that was previously used by Kania et al. (Acta Otolaryngol 124:408-410, 2004). After the ME cavity was washed with ambient air, the initial diffusion rate of CO(2) (V(.-)(i)CO(2)) from the blood perfusing the ME mucosa was calculated from gas volume change measurements. In nine cases, the (V(.-)(i)CO(2))calculated after normalization due to shifts in baseline was 314+/-112 microL x h(-1) (mean +/- SD). In two cases where normalization was not needed, (V(.-)(i)CO(2)) was 409 microL x h(-1) (276 and 543 microL x h(-1)). Normalization of (V(.-)(i)CO(2)) data was also made in five additional cases where secretion of fluids from the lining of the ear canal was observed. In these cases (V(.-)(i)CO(2)) was 245 +/- 142 microL x h(-1). No differences were found between results obtained in the three groups. Thus, an overall mean value of (V(.-)(i)CO(2)) of 305 +/- 131 microL x h(-1) (n = 16) was calculated. An effective coefficient of conductance of CO(2) (G(CO(2))) between the mucosal circulation and the ME gas cavity of the New Zealand White rabbit was estimated to be approximately 0.05 microL (h x Pa)(-1) and compared to the G(CO(2)) estimated for humans in a different study.

Temperature dependence of water loss rates in scorpions and its effect on the distribution of Buthotus judaicus (Buthidae) in Israel.

Scorpions of the family Buthidae have been shown to be more desiccation resistant in comparison with sympatric Scorpionidae species. This has been attributed to the surface-dwelling existence of the former, which unlike most other scorpion species do not avoid environmental extremes by burrowing. Still, within Buthidae, the mesic Buthotus judaicus showed better osmoregulatory capacities than the xeric Leiurus quinquestriatus, largely as a result of its high resistance to water loss. However, B. judaicus exhibited poor ability to regulate its haemolymph osmolarity at 37 degrees C. In this study we report a sharp increase in water loss rates of B. judaicus at the 30-35 degrees C temperature range compared to that measured for L. quinquestriatus, which could explain the poor osmoregulatory performance of the former at higher ambient temperatures. The increase in water loss rates of B. judaicus at high temperatures is not coupled with a similar increase in respiratory rate, suggesting an increase in cuticular permeability. We suggest that this increase in cuticular permeability, which may result from a relatively low critical transition temperature, contributes to limiting the distribution of B. judaicus to habitats of moderate environmental conditions.

In vivo demonstration of the absorptive function of the middle ear epithelium.

The present study investigated in vivo fluid and ion transport across the middle ear epithelium. The tympanic membrane of rats was punctured under general anesthesia. A capillary tube was fitted to the external auditory canal and the bulla filled with various solutions. Middle ear (ME) fluid volume variations were then measured at constant pressure. When saline was used, a linear decrease of fluid volume was apparent. Replacement of sodium with a non-permeable cation (N-methyl-D-glucamin) reduced the absorption rate from 0.065+/-0.008 to 0.019+/-0.003 microl/min (P<0.05, n=6). Similarly, amiloride (10(-3)M), a sodium channel antagonist, reduced the absorption rate to 0.027+/-0.006 microl/min (P<0.05, n=6). Net absorption was abolished when chloride was substituted with gluconate: -0.008+/-0.004 microl/min (P<0.02, n=6), which might have been related (i) to the role of chloride as a diffusible anion through the paracellular pathway, or (ii) to the secretion of chloride through apical channels. However in this condition, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, a chloride channel blocker, did not affect the rate of fluid exchange -0.008+/-0.007 microl/min (P=0.75, n=6). This model provides the first in vivo evidence for the absorptive function of the ME. Fluid introduced into the ME cavity disappears due to active transport through the mucosa. This process is sodium-dependent and can be hindered by high concentration of amiloride. The rate of absorption is high enough to allow total clearance of fluid from the cavity of the middle ear within 13 h. This process might play a role in the maintaining a fluid-free and gas-filled middle ear cavity.

Technical pitfalls in middle ear gas studies: errors introduced by the gas permeability of tubing and additional dead space.

CONCLUSIONS: We demonstrated errors introduced by the gas permeability of the tubing and additional dead space. Materials with practically no permeability, such as glass, must be used to overcome the loss or gain of gas through the walls of tubes used for studying ME gas variations. Experiments conducted at a constant volume (variable pressure) require the smallest possible tubing volume in order to obtain good sensitivity and improve the accuracy of the results. OBJECTIVES: Experimental studies that investigate middle ear (ME) gas exchanges, using either pressure measurements or volume changes, are conducted using various tubing connections between the ME and a measuring device. The aims of this study were to highlight experimental problems due to the errors introduced by (i) the gas permeability of the tubing used and (ii) additional dead space in experiments conducted at constant volume. MATERIAL AND METHODS: The problem of the gas permeability of the tubing was addressed by comparing three types of tube (silicone, polyethylene, PVC) with a glass tube. Horizontally placed tubes were connected to a syringe filled with pure CO2 via a gas-tight valve. The end of each tube tested was plunged into colored water (5% Coomassie Brilliant Blue R-250). The tube was washed out with CO2 until gas bubbles were seen leaving it. The valve was then closed and the movement of water in the tube was observed. The same experiments were repeated for pure O2. The problem of the error introduced by the additional dead space volume was addressed at a theoretical level using the well-known gas laws. Two conditions were studied: condition A, in which the experiment was conducted at constant pressure and the volume was measured; and condition B, in which the experiment was conducted at constant volume and the pressure was measured. The main outcome measure of each condition was the calculated variation in the final number of moles of gas involved. RESULTS: No water movement was observed in glass tubes. In contrast, plastic tubes exhibited significant gas permeability effects for both CO2 and O2. The colored solution advanced at a faster rate with CO2 than O2 but differently for each type of tubing. For condition A, gas transfer was independent of the volume of the external tubing and was accurately measured by the displacement of the droplet in the lumen. In contrast, for condition B, the pressure variations were influenced by the volume of the tubing.

Regional and developmental variations of blood vessel morphometry in the chick embryo chorioallantoic membrane.

Avian eggs contain all the necessary materials for embryonic development except for oxygen, which diffuses in from the environment via pores in the hard, calcified eggshell to the chorioallantoic membrane (CAM), the respiratory organ, which is rich in blood vessels. An air cell is formed at the blunt pole of the egg between the two membranes of the eggshell and enlarges during incubation due to water vapor loss. In this study of the CAM of chicken eggs, we compared blood vessel numerical density [N(A(v))], area fraction of blood vessels [A(A(v))], CAM thickness (D(CAM)), total length of blood vessels (L) and surface area of the CAM attached to the eggshell (CAMre) with those under the air cell (CAMac) during incubation. We found that N(A(v)), A(A(v)), D(CAM) and L of the CAM increase with embryonic age and development. The N(A(v)), A(A(v)) and L under the air cell were higher in relation to the rest of the CAM at all ages tested, while the D(CAM) under the air cell was always lower than around the rest of the egg. Since the eggshell over the air cell has a relatively greater porosity, and the respiratory gas exchange ratio there is higher than at other areas of the egg, there is a correlation between all the above morphometric data and the eggshell porosity. This suggests optimization of embryonic gas exchange in the chicken egg. We would like to propose that, during natural incubation, an increased gas diffusion under the air cell, together with increased blood vessel numerical density, may compensate for covering of the central part of the eggshell by the incubating parent.

Parasitoid wasp affects metabolism of cockroach host to favor food preservation for its offspring.

Unlike predators, which immediately consume their prey, parasitoid wasps incapacitate their prey to provide a food supply for their offspring. We have examined the effects of the venom of the parasitoid wasp Ampulex compressa on the metabolism of its cockroach prey. This wasp stings into the brain of the cockroach causing hypokinesia. We first established that larval development, from egg laying to pupation, lasts about 8 days. During this period, the metabolism of the stung cockroach slows down, as measured by a decrease in oxygen consumption. Similar decreases in oxygen consumption occurred after pharmacologically induced paralysis or after removing descending input from the head ganglia by severing the neck connectives. However, neither of these two groups of cockroaches survived more than six days, while 90% of stung cockroaches survived at least this long. In addition, cockroaches with severed neck connectives lost significantly more body mass, mainly due to dehydration. Hence, the sting of A. compressa not only renders the cockroach prey helplessly submissive, but also changes its metabolism to sustain more nutrients for the developing larva. This metabolic manipulation is subtler than the complete removal of descending input from the head ganglia, since it leaves some physiological processes, such as water retention, intact.

The effect of desiccation on water management and compartmentalisation in scorpions: the hepatopancreas as a water reservoir.

Scorpions of the Family Buthidae have lower water loss rates (WLR) and enhanced osmoregulatory capacities in comparison with sympatric species of F. Scorpionidae. In this study we followed changes in water content of different body compartments in four scorpion species under prolonged desiccation conditions. The high initial WLR previously reported for Scorpionidae result in rapid depletion of body water stores. A significant decrease in total body water content of Scorpionidae was recorded following loss of only 5% of initial mass, whereas no such decrease was recorded for Buthidae following severe desiccation. When desiccated, scorpions lose water primarily from the hepatopancreas, while haemolymph volume is more tightly regulated. However, the haemolymph volume of Scorpionidae decreases as a result of depletion of hepatopancreas water stores following severe desiccation. The increasing lipid fraction in the hepatopancreas of Scorpionidae during desiccation suggests that depletion of body water stores may induce enhanced catabolism of carbohydrates, which may contribute to volume regulation by making initially glycogen-bound water available to the desiccating scorpion.

Woodpecker cavity aeration: a predictive model.

We studied characteristics of the Syrian woodpecker (Dendrocopos syriacus) cavities in the field and a laboratory model, and rates of gas exchange in the laboratory. Night temperature of occupied cavities is 4.3 degrees C higher than empty ones, representing energy savings of approximately 24%. Oxygen conductance (GNO2) of an empty cavity is 7.1 ml[STPD] (Torr h)(-1), and is affected by winds at velocities up to 0.8 m/s. Day and night body temperatures were 42.0 and 40.1 degrees C, respectively. Steady-state O2 consumption rates (MO2) were 3.49 +/- 0.49 and 2.53 +/- 0.26 ml[STPD] (g h)(-1) during day and night respectively -- higher than predicted by allometry. A mathematical model describing PO2 in a cavity, taking into consideration MO2, GNO2, heat convection and wind speed, from the moment birds inhabit it, was developed. It shows that on the average, one woodpecker staying in its cavity at night does not encounter hypoxic conditions. However, in nest cavities with below the average GNO2, with more inhabitants (e.g. during the breeding season), hypoxia may become a problem.

Gas flow into and within the middle ear.

HYPOTHESIS: Both a normal and a narrowed eustachian tube (ET) are capable of equilibrating pressures between the middle ear (ME) and the atmosphere almost instantaneously. OBJECTIVES: The objective of this study was to assess experimentally the effect of narrowing a simulated ET isthmus on air passage into the ME. METHODS: A Perspex ME model (0.5 mL) was constructed in which a 1.5-mm long ET of 0.07- to 1.0-mm diameter and a "mastoid" of 0- to 10-mL volume were changeable. The ET could be opened and closed with a valve. A -5 mm H2O pressure difference between the system and the atmosphere was created by withdrawing gas from the system. The time required to equalize these pressures after opening the valve to the atmosphere were measured with a pressure transducer. RESULTS: A pressure difference of -5 mm H2O was created in the system when 1.3 to 6.5 microL of ME gas was removed. On ET valve opening, the pressure was equalized within 0.1 and 0.15 to 0.3 seconds for ET diameters of 1.00 and 0.07 mm, respectively, depending also on the "mastoid" volume. Similar results were obtained when the pressure was measured through the "tympanic isthmus" and "aditus ad antrum." CONCLUSIONS: Our model shows that under ordinary physiological conditions, the amount of gas that can pass through the ET during swallowing time (0.4 sec) is potentially higher than required to equalize a negative pressure. This is also the case when the ET is very narrow and open for a very short time. It is unlikely that any narrowing of the tube will, by itself, hamper gas transfer into or within the ME, as long as the ET is not totally obstructed.

Experimental model for investigating trans-mucosal gas exchanges in the middle ear of the rat.

OBJECTIVE: The total pressure in the middle ear depends on the air composition of this gas pocket, i.e. on gas exchanges occurring through either the Eustachian tube (ET) or mucosa. The aim of this study was to develop an experimental model to investigate the exclusive role of trans-mucosal gas exchanges in the middle ear (ME). MATERIAL AND METHODS: Both tympanic membranes of 20 Sprague-Dawley rats were punctured under general anesthesia. Rats were divided into two equal groups. Group 1 had no ET obstruction. In Group 2, the ET was blocked, after velar incision, by cauterization and application of cyanoacrylate glue into the lumen. One open transparent glass tube containing a droplet of colored water was placed horizontally and connected hermetically to each ear canal. The ME was then flushed with room air through the tube. Variations in ME gas volume were measured by reading the displacement of the liquid droplet in the horizontal tube. The kinetics of variations in gas volume between groups were displayed and statistically compared using a two-sided t-test. RESULTS: The pattern of variations in ME gas volume with time was similar in the two groups. Both were characterized by a decrease with three phases and an elimination rate of approximately 0.152 +/- 0.026 microl/min. There was no significant difference in the mean rate of ME volume changes between the two groups. CONCLUSION: This experimental model allows investigation of trans-mucosal gas exchanges. These exchanges exhibit an absorptive function resulting in a negative pressure that must be compensated, under physiological conditions, by air flow through the ET.

Comparative water relations of four species of scorpions in Israel: evidence for phylogenetic differences.

In an attempt to determine the nature of possible interspecific differences in osmotic responses to dehydration, the following species of two scorpion families were examined: Scorpio maurus fuscus (Scorpionidae) and Buthotus judaicus (Buthidae) from the mesic Lower Galilee (mean annual precipitation approximately 525 mm); and Scorpio maurus palmatus (Scorpionidae) and Leiurus quinquestriatus (Buthidae) from the xeric Negev Desert (mean annual precipitation approximately 100 mm). When sampled in the laboratory following their capture, B. judaicus (548+/-38 mOsm l(-1); mean +/- S.D.) and L. quinquestriatus (571+/-39 mOsm l(-1)) had higher and less variable haemolymph osmolarities than the scorpionids occupying the same habitats (511+/-56 and 493+/-53 mOsm l(-1) for S. m. fuscus and S. m. palmatus, respectively). In response to 10% mass loss when desiccated at 30 degrees C, the haemolymph osmolarity of the two buthids increased by 5-9%, compared to ca. 23% in the two scorpionids. Buthids had lower water loss rates than scorpionids. The similar oxygen consumption rates, when converted to metabolic water production, imply a higher relative contribution of metabolic water to the overall water budget of buthids. This could explain why the osmoregulative capabilities exhibited by buthids are better than those of scorpionids. We conclude that the observed interspecific differences in water and solute budgets are primarily phylogenetically derived, rather than an adaptation of the scorpions to environmental conditions in their natural habitat.

Barotrauma vis-a-vis the "chronic otitis media syndrome": two conditions with middle ear gas deficiency Is secretory otitis media a contraindication to air travel?

We compared 17 patients (29 ears) with barotrauma with 171 patients suffering from "chronic ears" (secretory otitis media, atelectasis, or previously operated cholesteatoma). The patients with "chronic ears" were followed up prospectively, and none were found to suffer from barotrauma after flying on a commercial airplane. The mastoid pneumatization (seen on lateral mastoid radiographs) was significantly larger in ears with barotrauma, averaging 16.85 cm2, versus 12.9 cm2 in normal controls, whereas in "chronic ears" it was only 3.6 cm2. During flight on a commercial airplane, the middle ear has to equalize about 20% of its gas volume with the ambient pressure. This equalization must happen within 15 to 20 minutes of ascent and descent in order to avoid barotrauma. This 20% is a fivefold greater task for ears with a large mastoid pneumatization than for ears with an undeveloped pneumatization; "chronic ears" usually have an undeveloped mastoid pneumatization. The smaller the middle ear (mastoid) volume, the smaller the volume of gas needed to pass through the eustachian tube in order to equalize pressure changes during flying. This factor may explain why "chronic ears" rarely suffer from barotrauma. It also implies that eustachian tubes of secretory otitis, atelectatic, and cholesteatomatous ears have little problem in equalizing large pressure differences (over 2,000 mm H2O) within 15 to 20 minutes of landing, in contrast to what has been traditionally believed. Individuals with "chronic ears" can be advised that they can fly safely.