Barotraumatic edema

Very good work on this topic wasis presented on the website of the Federation of freediving of the Russian Federation. the abstract was called "The structure and functions of the ear in the context of freediving" (author Alexander Zhuravlev), there is a lot of biology and terminology in the work, so I selected the most "vital" and present it to your attention.

Effect of pressure on the ears

When immersed under water, the pressure in the outerthe auditory passage becomes equal to the pressure of the water, regardless of whether there is air in the passageway or the passage is filled with water - the air remaining in the passage is compressed until its pressure is equal to the water pressure. Under pressure, the tympanic membrane flexes inward.
With a strong bending of the tympanic membranethere is pain, and further bending can lead to its stretching or rupture. To prevent this, it is necessary to equalize the pressure in the tympanum with pressure from the outside. To do this, using a special maneuver into the tympanum, air is pumped through the auditory tube. This is called "blowing". The nasopharyngeal orifice of the tube and its membranous cartilaginous part, when immersed under water, are pressurized, which makes it difficult to blow. Therefore, it is necessary to blow it out often enough not to overstrain the tympanic membrane and to prevent strong pinching of the auditory tube, which can make the purge completely impossible or requiring the injection of large pressure into the nasopharynx. There are two main ways of blowing: the Valsalva maneuver and the Frenzel maneuver.

In this blowing method, the pressure in the cavitieshead (and podmasschnom space) is increased by exhalation with closed nasal and oral openings. Increased pressure is created in the lungs due to the tension of the diaphragm and intercostal muscles. This maneuver is simple in execution, but has drawbacks. From the energy point of view, to increase the pressure in the head cavities, it is ineffective to use lungs whose volume is tens of times larger than the volume of the head cavities - when the tension of the respiratory muscles is used, unnecessarily much oxygen is consumed. In addition, the creation of excessive pressure in the lungs complicates blood circulation in them and increases blood pressure in the body, which further compresses the lumen of the auditory tube. If the purge is not performed in time, then an increase in blood pressure with an overly tense attempt to blow through the Valsalva maneuver can cause a round window membrane injury. This is due to the fact that when the blood pressure rises, the pressure of the perilymphatic fluid increases, as a result of which the membrane of the round window arches outward. If there was already a decreased pressure in the tympanic cavity in comparison with the pressure in the tissues and the membrane of the round window was bent outward, then because of straining it can bend even more and tear. In addition, the displacement of the perilymphatic fluid stimulates the body of equilibrium, which causes dizziness.

In this method of blowing, fill the oral cavityair (before the dive or under water exhalation from the lungs), close the vocal cavity (i.e., the entrance to the trachea) and then use the tongue or lower jaw to increase the pressure in the nasopharynx, leaving the muscles of the trunk relaxed and the pressure in the lungs unchanged. It is not difficult to perform purging using the Frenzel method, it is more difficult to explain how to do this. If the language is used to increase pressure (Frenzel's language maneuver), it is tightly pressed against the teeth and its middle part is used as a piston to push air into the nose. If jaws are used to increase the pressure (Frenzel's jaw maneuver), the mouth is first filled with air, while the lower jaw is pulled down. Then, avoiding the leakage of air through the mouth, the jaws close. As a result, air pressure in the nasopharynx increases and the ears are blown. The tongue should not be hermetically sealed to the teeth, otherwise the air will not enter the nasopharynx. The language maneuver makes it possible to obtain a high compression ratio, but because of the small volume of the compressed air it ensures only a purge. The jaw maneuver gives less compression (it is limited by the ability of the lips to not let out air), but due to a significantly larger volume of compressed air can provide several blows.

The Frenzel maneuver requires periodic injectionair in the mouth. The filled mouth suffices from one to several purges, after which the mouth is filled again with an exhalation from the lungs. To fill the mouth requires less tension of the lungs than when blowing the ears, so you save effort in comparison with the maneuver Valsalva. To increase the volume of air collected in the oral cavity, along with the lowering of the lower jaw inflate cheeks. In this position, the oral cavity accommodates more than 100 ml of air. Inflammation of the cheeks should be performed at the time of injection of air into the mouth, and not after the closure of the glottis; otherwise it turns into a useless grimace. Strictly speaking, the installation immediately becomes inflated with light cheeks, and the mouth at the same time is filled by itself.

Care must be taken in the jaw maneuver,taking care not to drive air into the salivary glands, which can lead to their barotrauma. In order for air to open the auditory tube before it opens the ducts of the salivary glands, the first must be easily blown. Therefore, beginners, until they develop an auditory tube, should not make great efforts in the jaw maneuver of Frenzel.
In the purging of the Frenzel maneuver, three phases can be distinguished:

  1. Filling the mouth with air. Immediately after the maximal filling of the mouth and cheeks, it is difficult to perform purging, but as the depth increases, the air in the oral cavity contracts and its volume becomes suitable for maneuvering. The higher the skill of the plunger, the greater the amount of air in the mouth at which it can start blowing.

Inflation of the auditory tube by pressure increaseair in the mouth due to the jaw closure (jaw maneuver). To the air did not come out through the compressed lips you have to strain your cheeks, and creates the feeling that the blowing is carried out at the expense of the cheeks.

When the volume of air in the mouth decreasesto such an extent that the jaws join, a further decrease in volume and increase in pressure is due to the movement of the tongue and throat inside (Figure 7) (language maneuver). After the third phase, the throat remains in the concave position and a low pressure is created in the nasopharynx. This creates discomfort and makes it difficult to open the voice gap to fill the mouth with air - to open it you need to return the throat to an uncrowned position, but this lowers the pressure in the nasopharynx. When diving in a mask at this point, you can feel the suction of the mask to the face. Therefore, the third phase is best performed during the dive only once - for the last blowing before turning.

All three phases can be trained on land, simulatingdecrease in volume under the influence of pressure by slow release of air through the nose. Training in water and on land increases the volume of maximum filling of the mouth and the volume at which it is possible to perform purging.

Purging the ears takes a lot of effort from the divers. It is interesting to consider what determines the depth interval between blowdowns (blowdown step). The larger the blowdown step, the fewer blows must be made during the dive, and the more the diver saves.

First, for simplicity, we consider the case whenthe middle ear does not change its volume with changes in external pressure, i.e. We neglect changes in volume due to tying the tympanic membrane inside the tympanum. In this case, the pressure in the tympanum cavity will remain unchanged until air enters it. The pressure p outside the tympanic membrane is determined by the depth d of the immersion: p = 0.1d + patm (hereinafter the pressure is measured in the atmospheres, and the depth in meters, the density of water is assumed equal to 1 kg / l). After each purge, the pressure on both sides of the tympanic membrane becomes the same, and with a subsequent increase in depth by a value of h, the pressure difference becomes 0.1h. When this pressure difference reaches a certain maximum value Δpmax, which is capable of sustaining the tympanic membrane without pain, a desire arises to blow through. The blowdown step h, thus, does not depend on the immersion depth and is determined by the formula:

In novice divers, the blowdown step is often notTherefore, they have to be blown very often. This may be due to the weakness of the tympanic membrane, a slight inflammation of the eardrum (and perhaps also low mobility of the joints of the auditory ossicles, weakness of the stenosis muscle). As the training increases, the blowdown step quickly reaches 3-4 m. If this does not happen, you should consult a doctor to check the eardrum and middle ear. At highly trained divers, the blowdown step reaches 6 m or more.

It is known from experience that during the diveincreasing the depth of immersion, the interval between blowdowns increases, and does not remain constant, as follows from formula (1). This can be explained if we take into account that as the external pressure increases, the tympanic membrane is pressed inward, and consequently the volume of the middle ear cavity decreases. As the volume decreases, the pressure in the middle ear increases, and thus some pressure compensation due to the elasticity of the air is achieved. The magnitude of this compensation increases with increasing depth, since with increasing pressure the air becomes more elastic. As a result, the interval between blowdowns increases. For numerical estimates, we find the formula for the step of the n-th purge taking into account the decrease in the volume of the middle ear under the action of water pressure. We will assume that after each purging the tympanic membrane occupies the same position (on the average, so it is).

Suppose that the nth blowing is performed at a depth dn. Pressure p on both sides of the eardrum became equal to 0.1dn + patm. After increasing the depth by an amount h, the pressure outside will increase by 0.1h, and inside, according to the law pV = const, by pΔV / (V0 - ΔV), where V0 is the total volume of the cavity of the middle ear (equal to the sum of the volumes of the drum cavity and airborne cavities of the temporal bone), ΔV - change of this volume due to the difference in pressure. When the difference between the external and internal pressures reaches the value of Δpmax, a desire to blow through will appear. We denote by

α = ΔVmax / (V0 - ΔVmax).

The coefficient α characterizes the maximum contractionmiddle ear, which the diver can withstand without pain, ΔVmax - the amount of decrease in the volume of the cavity of the middle ear with the difference in pressure Δpmax. With the notation introduced, we obtain the equation for the blowdown step: Δpmax = 0.1h-αp. Hence the blowdown step is

h = 10Δpmax + 10αp. (3)

We see that in comparison with (1) the blowdown step has increased by a value of 10αp, which grows directly in proportion to the pressure.

To find the explicit expression for the nth purge step, substitute in (3) the pressure value at the depth of the nth purge p = 0.1dn + patm and taking into account that according to (3) the first purge step is equal to

h1 = 10Δpmax + 10αpatm, (4)

Since hn + 1 is hn = α (dn-dn-1) = αhn, it is not difficult to find the desired expression for the n-th blowing step:

Now, using this formula, we makenumerical estimates. Assuming that for a maximum tolerated pressure difference, the eardrum displacement does not exceed 0.5 cm, then taking into account the area of ​​the tympanic membrane is no more than 1 cm2. The change in the volume of the middle ear ΔVmax will not exceed 0.2 cm3 (we assume that the displaced eardrum has the form of a cone). Really, it will be noticeably smaller, so this is an estimate from above. Since the total volume of the middle ear V0 is about 10 cm3, then α does not exceed 0.02. Therefore, between the fifth and sixth purges, the interval will not exceed (1 + α) 5 = (1,02) 5,1,1 from the depth of the first purge, and between the tenth and eleventh - 1,22. According to (5), the increase in the purging step at a depth d in comparison with the incompressible ear is αd, which at a depth of 20 m will give no more than 0.4 m, and at a depth of 50 m - no more than 1 m.

In practice, the trained diversdepth, the blowing step is increased by several meters, and the relative increase is 1.5 and more times. For example, if the first step was 3 m, then at a depth of 20 m the step could well reach 5 m, which corresponds to α

0.1. Thus, it is not possible to fully explain the observed data only by the displacement of the tympanic membrane. Apparently, there are other ways to reduce the volume of the middle ear.

Here, a hypothesis is posed about a possible mechanismsuch reduction. Let us turn to the anatomy of the mastoid cells. The surface area of ​​the mucosa of these cells is quite large - 75-330 cm 2, which is achieved due to their large number and small size. The thickness of the mucosa is of the order of 0.05 mm. Thus, the volume of the mucosa is of the order of 1 cm 3. It seems plausible that a change in the blood filling of the mucous in the case of pressure changes can change its volume by a factor of 2. If we take into account the decrease in the volume of the middle ear caused by this, then α can become of the order of 0.1. This is quite sufficient to obtain the observed increase in the purge step, since (1.1) 5≈1.6.

This explanation requires an experimentalverification. As a result of searching in the available literature, references to the compensation of the pressure of the mucocutaneous mast cells were not found for humans, but were found for diving mammals. Observations from satellites on hooded people showed that they are able to dive to a depth of more than 1 km and stay there for up to 1 hour. A study of the structure of their ears revealed that in the middle ear there is a cavernous tissue that, when immersed, is filled with blood and reduces the volume of gas in the middle ear to almost zero! - There is no need to blow the hoodlums. Application of formula (2) in the case of hooded animals gives α → ∞, and therefore according to (4) the depth of the first purge is h1 → ∞.

It is likely that a person along with othersdiving reflexes of mammals are this, although, of course, not in such a pronounced form as in seals. It can be assumed that the change in the blood filling of mucocutaneous mast cells occurs not only passively due to the difference in pressures, but also with the active change in the lumen of the vessels of the mucosa.

In the tympanic membrane in the region of the baseHandles of the malleus there is a small, unstretched part (pars flaccida, figure 2), which is devoid of the fibrous layer and is easily displaced by the difference in pressure. It has been suggested that this part serves as a pressure sensor. If this is the case, then we can also assume that there is a reflex change in the blood filling of the mucous mastoid cells with the participation of pars flaccida. When the pars flaccida is displaced, the blood filling increases, and when it is displaced outwards, it decreases, so that the pressure in the middle ear is compensated.

If there is a nervous regulation of blood fillingvessels of the mucous mastoid cells, it is obvious that it will be affected by the mental state, just as it happens with the nasal mucosa. In this case, the degree of increase in the interval between blowdowns will also depend on the psychological mood. Since it is easier to dive to a greater depth with an increased interval between purges, then (in case of confirmation of the hypotheses) new factors influencing the productivity in freediving are revealed.

In this context, in a new lightvasoconstrictor. Their use helps to eliminate the obstruction of the auditory tubes, but at the same time reduces the compensating expansion of the mucosa in the middle ear, i.e. reduces the coefficient α. It is easier to bloat, but it is necessary to do it more often. Therefore, for deep immersion, the use of vasoconstrictor is undesirable. This is all the more true, given that their effect partly extends to the vessels of the lungs, which reduces the compensatory flow of blood to the lungs and thereby increases the probability of barotrauma of the latter.

The degree of decrease in the volume of the middle ear depends on the maximum tolerant pressure difference Δp max. This difference, apparently, is limited mainly by the tympanic membrane, since it is usually she who is injured when the Δp max. but obviously this question requires statistical research, since it can not be ruled out that in some individuals the other parts of the ear are the limiting (ie, weak points).

So, we see that the increase in the interval between blowdowns is achieved due to two factors: 1) increasing the maximum tolerant pressure difference Δp max and 2) increasing the compressibility of the middle ear α. This is described by formula (3). The first factor increases as the training of ear tissues, especially the tympanic membrane, is strengthened. The second factor is little investigated. It is not yet clear to what extent it gives in to training, but it is possible that it depends on the mental state (through the regulation of the vascular tone in the mucosa of the middle ear).

By measuring the actual intervals between the blowdowns and their depths, it is possible to calculate Δp max and α, for which formulas (4) and (5) best correspond to actual values. In this way, you can collect statistics on freedivers and continue to investigate this issue.

The blowing of the ears takes some time and effort. During the dive, the first purging usually takes from 0.5 to 2 s. [10]

Duration of blowdown (pumping timeair in the middle ear) is determined by the air volume ΔV, which should be injected into the middle ear, the shape of the auditory tube, the difference in pressure Δp in the nasopharynx and the middle ear before purging and the viscosity η of air.

In the first approximation, we shall assume that the formauditory tube and pressure difference Δp are the same in each act of blowing. The viscosity of air with increasing pressure increases insignificantly: about 1% per 100 m depth, so its changes can also be neglected. With regard to the volume of the blown air ΔV, it is easy to estimate on the basis that the total number n of air molecules in the middle ear is equal to n = pV / kT, where p is the average ear pressure, V is the volume of the middle ear cavity, k is the constant Boltzmann, T - temperature in the middle ear. Hence, to equalize the pressure difference Δp, Δn = ΔpV / kT of air molecules must be injected. Since the pressure difference Δp is approximately the same in all purge acts, the number of injected molecules Δn is also the same. The volume ΔV occupied by molecules Δn is equal to ΔV = ΔnkT / p = ΔpV / p.

Thus, the volume ΔV blown into the middle earair, decreases with increasing depth inversely proportional to the pressure p of water. Consequently, the time spent for purging decreases with increasing depth. For example, if a purge at a depth of 3 m required 1 s, then at a depth of 30 m it can take 1/3 c, and at a depth of 70 m - only 1/6 c.

In practice, however, it may happen that whenan increase in the depth of immersion accumulates barotraumatic swelling of the auditory tube due to incomplete purging, the lumen of the auditory tube narrows and the purging time does not decrease or even increases. On the other hand, at depths of more than 30-40 m (and when diving in exhalation at shallower depths), a significant outflow of blood to the lungs takes place, as a result of which the blood supply to the auditory tube decreases. Therefore, in the absence of barotraumatic edema, the lumen of the tube increases and its opening is facilitated, which leads to an additional reduction in the purge time. Thus, for deep dives, it is important to thoroughly and timely blow your ears, not allowing incomplete purging. Then with increasing depth, it will be easier to blow it (of course, while there is enough air), and the purge itself will require less time.

The impact of pressure on the external ear canal (dive into the helmet)

When diving without a helmet, water can freely flow inin the external auditory meatus and reduce the volume of air remaining in the ear canal until its pressure spontaneously aligns with the water pressure. When the helmet is attached to the head and the auricle is closed, the situation changes. Under pressure, the helmet is pressed against the auricle and prevents water from flowing into the external auditory meatus. As a result, the pressure in it is leveled mainly due to the deflection of the helmet inside the auricle. However, the deflection of the helmet is limited by the shape of the outer ear, and the volume of air can decrease in this way only 2-4 times. Hence, starting from a certain depth (of the order of 10-30 m), compensation will not be enough. When blown, the tympanic membrane will bend outward and may be injured. If the blowing is not done, then under the load is the membrane of the round window, because the pressure of the perilymph is equal to the pressure of the water, and the pressure in the tympanum is slightly more than the atmospheric pressure. The thicker the material of the helmet, the greater the force required to deflect it, and the greater the difference between the pressures from different sides of the helmet, that is, in the outer ear canal and water. Therefore, with a thick helmet, spontaneous equalization of pressure in the outer ear is worse than with a thin helmet.

To facilitate the equalization of pressure in the externalear let out air from under the helmet (especially from the space between the helmet and the auricle) at a shallow depth. In this case, to change the volume of the remaining air several times, only a small deflection of the helmet will be required, which will allow diving to substantially greater depths. Sometimes they make small holes in the helmet opposite the auricles - this radically solves the problem of equalizing the pressure in the outer ear. However, if water is cold such a method is undesirable - there is a risk of chilling your ears. In this case, it is better to use a helmet without holes and pour warm water into it. However, if the holes are made small, for example, with a diameter of 1 mm, this will be enough to equalize the pressure, but the water circulation will be small.

To prevent ear barotrauma when divingthe baro function of the auditory tube should be normal. If it is disturbed, as well as with a cold, angina, inflammation or swelling of the nasopharyngeal mucosa, it is better to refrain from diving.

Apparently, the simplest and most effective way to increase the patency of the auditory tubes and train the tubular muscles is to regularly purge the ears.

Beginner divers are recommended sparingincrease the load on the ears, not allowing pain, so as not to injure the miniature joints of the auditory ossicles. Injury of these joints is fraught with a decrease in their mobility, which will cause a decrease in tolerance to pressure and loud sounds, as well as a decrease in severity of hearing.

Some novice divers who do not haveexperience diving at sea, salty sea water, getting into the mouth or nose causes swelling of the nasopharyngeal mucosa. It can take several days to get used to salt water. Since leaving to the sea is usually limited in time, novice divers often seek to force the development of depth despite difficulties with blowing. This increases the risk of barotrauma. Barotrauma further violate the baro function. Therefore, the desire for accelerated development of depth can give the opposite result. Addiction to salt water is facilitated by rinsing the throat with sea water. For 1-2 weeks before going to the sea, you can start gargling with a hypertonic salt solution (2 teaspoons without top 250 ml - about the same concentration of salt in the Red Sea). Washing the nose with sea water can also be helpful, but to reduce the risk of infection, it is better to use a solution of salt in pure water or boil seawater, and then pass it through a paper filter. It is better to rinse the nose in the first days with a normotonic solution (0.9 g salt per 100 ml) and gradually move to higher concentrations. However, it is hardly advisable to use more concentrated solutions than 2 g per 100 ml. Too frequent and long rinsing (daily for months) is hardly useful for mucous nasopharynx and sinuses. In particular, it is not clear whether this can lead to its hypertrophy or atrophy of the ciliated epithelium.

Swelling of the nasopharyngeal mucosa can be causedpsychosomatic factors, including mental anxiety. The excitement decreases with the accumulation of experience, increasing knowledge of the theory of diving and in a friendly atmosphere.

Edema of the nasal mucosa occurs reflexively when the body is cooling, especially the feet, so using a good wet suit reduces the risk of ear barotrauma.

When diving in a helmet to a depth of more than 20 m in a thin suit and more than 10 m in a thick one, one should not forget about the need to equalize the pressure in the external auditory canal (see above).

The strength of the tympanic membrane is determinedstrength of collagen fibers of its fibrous layer. To produce collagen, the body needs protein and vitamin C. [13] Therefore, to prevent barotrauma, adequate nutrition is needed. Changes in the tissues become noticeable 1-2 weeks after the change in the diet.

With a weakened hearing associated with a violationconductivity in the middle ear, large loads on the tympanic membrane should be avoided, since abnormalities in the auditory ossicles, the annular bunch of the stapes and the round window membrane can make them intolerant to static loads. On the other hand, moderate loads on the tympanic membrane can probably have a positive effect on the state of the sound-conducting system of the middle ear, increasing the mobility of its elements.

Assisting with ear barotrauma

First of all, it is necessary to reduce the riskinfection, provide comfort and rest to the injured (because stress weakens immunity), as well as good nutrition. If dusty or windy around, a sterile bandage should be applied to the ear. Without examining the tympanic membrane it is difficult to be sure whether its rupture or only stretching occurred, so one should not wash anything with the ear, cleanse the external ear canal from the blood by itself. You can not blow your nose, loudly talk and blast. To diagnose and prescribe treatment, you need to contact an otolaryngologist. In the field, the presence of perforation can be established by blowing underwater - when the membrane bursts from the ear, air bubbles will escape.

Treatment consists mainly in preventinginfection, accelerate resorption of hematomas and removal of exudate from the ear. In the presence of headaches, painkillers are used. To prevent the development of pathological processes in the middle ear, it is necessary to ensure the normal patency of the auditory tube, if it is broken. To this end, in the nose (in the position on the back), vasoconstrictive agents are instilled (for example 2-3% solution of ephedrine 3-5 drops per each nasal opening, 3-4 times a day). If the tube is not passable, the lowering (due to the dissolution of the gases) the pressure in the middle ear will constantly equalize with the atmospheric through the place of rupture in the membrane, and the regular opening of the wound will prevent it from becoming infected.

If there is no infection with a stretching drummembranes and small ruptures usually heal independently in 1-3 weeks. Strong breaks may require restoration of the tympanic membrane (myringoplasty). In this area of ​​surgery, significant advances have been made - even missing membranes and auditory ossicles can be restored through the use of allografts. Damage to the windows of the cochlea can be manifested by a sense of instability and a slight staggering when walking. In the absence of infection, perforations in the windows of the cochlea often heal independently, but if this did not happen within a month, then surgical intervention is necessary, since with the further postponement of the operation the probability of deafness development is high. With the timely operation, the windows heal successfully.