Björn Carlborg

Transmission of Low Frequency Pressure Steps to the Perilymphatic Fluid

The perilymphatic pressure was investigated in response to low frequency pressure changes in the ear canal and in the middle ear in the cat. the pressure transmission to the inner ear showed nonlinear characteristics with an asymmetry in the perilymphatic response to positive and negative pressure stimulation, respectively. a positive pressure stimulus in the ear canal and middle ear, respectively, caused a larger change in perilymphatic pressure than did a corresponding negative one. When the tympanic cavity was opened there was a substantial reduction in the amount of pressure transmitted to the inner ear from the ear canal. a shift in asymmetry was often also seen towards a greater change in perilymphatic pressure in response to a negative pressure stimulation than in response to a positive one. the stabilization process of the perilymphatic pressure in response to different input levels contained two different time constants indicating the pressure regulating mechanisms of the inner ear. the possibili...

On Physiological and Experimental Variation of the Perilymphatic Pressure in the Cat

The closeness of the hydrodynamic relationship between the perilymph and the cerebrospinal fluid (CSF) in different animal species and man is still debatable. the effect of variation of some basic physiological conditions on the perilymphatic pressure (Pp) was investigated in cats during simultaneous recording of the CSF, venous and arterial pressures. the perilymphatic pressure proved very sensitive to even moderate hypoxia and hypercapnia, both causing a rapid rise in the perilymphatic pressure. the therapeutic use of CO2 breathing in cases of sudden sensorineural hearing loss was thus questioned. Changes in position of the body caused a similar change in the Pp. and Pcsf- During a prolonged change in body position a pressure gradient was established between the Pp and Pcsf because the Pp fell slightly more than Pcsf. Blood pressure changes induced by neck vein compression, overhydration and exsanguination had a marked influence on the Pp and /CSF. the experiments showed that any change in the CSF press...

Continuous Long-term Measurements of the Middle Ear Pressure in Subjects without a History of Ear Disease

A new method was used for continuous measurement of the middle ear (ME) pressure during a 24-h period. In 10 subjects without a history of ear disease a small perforation was made through the tympanic membrane. A tight rubber stopper containing a small polyethylene tube was fitted into the external ear canal. Conventional tubal function tests were performed. The equipment was then carried by the subjects for 24 h of normal activity to monitor any slow or rapid dynamic pressure change in the ME. Body position was found to be the most important factor affecting ME pressure variation, during the 24-h continuous pressure measurements. A significant pressure rise occurred in the recumbent position in all but one subject. Few rapid pressure equilibrations were seen during the recordings, indicating few tubal openings. This implies that the pressure changes in the ME seen in this study were mainly the result of gas exchange over the mucosa. The investigation might be a base for reference when investigating different kinds of pathologic conditions in the ear.

Continuous 24-hour Measurement of Middle Ear Pressure

A new method was developed for continuous measurement of the middle ear pressure during a 24-h period. The equipment consisted of a piezo-electric pressure device and a digital memory. To allow continuous pressure recordings during normal every-day activities the equipment was made light and portable. The measurement accuracy of the equipment as well as the base-line and temperature stability were tested and found to meet to our requirements satisfactorily. In 4 volunteers with different middle ear conditions, a small perforation was made through the tympanic membrane. A rubber stopper containing a small polyethylene tube was fitted into the external ear canal. Tubal function tests were made to establish the equipments ability to monitor fast pressure changes. The tests were well in accordance with other methods of direct pressure measurements. The equipment was carried by the volunteers for 24 h to monitor any slow or rapid dynamic pressure changes in the middle ear. Four continuous 24-h measurements are presented. The method was found to be suitable for valid measurements of dynamic pressure changes in the middle ear during normal every-day activities. It may become a useful instrument in the search for a better understanding of the development of chronic middle ear disease.

Perilymphatic pressure in the cat. Description of a new method for study of inner ear hydrodynamics.

Continuous recordings of the perilymphatic (Pp), cerebrospinal fluid (PCSF), central venous (PCV) and arterial (PA) pressures have been performed on anesthetized cats. The perilymphatic space was reached by an extraural approach that leaves the ear canal and middle ear intact. A conical canal was drilled into the temporal bone down to the vestibule. The position of the canal was later confirmed histologically. A small, threaded, metallic cannula was screwed into the bone. For pressure measurements Millar microtip transducers were used, thus giving minimum measurement volume displacement. The mean PP and PCSF were found to be equal, whereas the maximum pressure during expiration was significantly higher in the CSF. not affected by the given anesthetics. Ligation of the external jugular veins had a minor and temporary effect on the PP and PCSF. The method is considered to be suitable for studies on the inner ear hydrodynamics as well as for audiophysiological measurements with an intact middle ear transmission system.

Tympanic pressure gradients and otoacoustic emissions

OBJECTIVE The purpose of this study was to investigate the immediate effects of tympanic over- and under-pressure, induced by variations in ambient pressure on click-evoked otoacoustic emissions (CEOAEs) in healthy individuals. It was of particular interest to elucidate whether changes in the CEOAE response in both spectral and time domains could be attributed not only to tympanic, but also to cochlear influence. DESIGN Nine healthy subjects with normal hearing and middle ear pressure were exposed to ambient pressure changes in a pressure chamber. The pressure was progressively changed in 100 daPa steps to accomplish an increase and a decrease in tympanic pressure. Pressure equilibration of the middle ear was avoided. The relative tympanic over- and under-pressure (+/- 320daPa) was monitored by tympanometry and the CEOAEs recorded at every step of tympanic pressure change. RESULTS There was a statistically significant reduction of the otoacoustic emission (OAE) response levels and reproducibility already at 100 daPa of ambient pressure change. The OAE response was progressively reduced by increased pressure gradients. The CEOAEs recorded during progressive tympanic over- and under-pressure also had increasingly shorter latencies. These changes of the OAE response characteristics were most pronounced in the 750 to 3000 Hz frequency bands. CONCLUSIONS The progressive attenuation of the OAE response and the concomitant shortening of the OAE response latencies were observed during a combination of altered middle and inner ear pressure. Although the middle and inner ear influence cannot be separated we suggest, based on our findings, that the shortening of latencies may partly be caused by inner ear pressure changes and stiffening of the labyrinthine membranes. Further studies are needed to more specifically clarify the relative contribution of the tympanic and labyrinthine influence, respectively, for the various aspects of pressure influence on the OAE response.

Pressure Gradients Affecting the Labyrinth during Hypobaric Pressure Experimental Study

Hypobaric effects on the perilymph pressure were investigated in 18 cats. The perilymph, tympanic cavity, cerebrospinal fluid, and systemic and ambient pressure changes were continuously recorded relative to the atmospheric pressure. The pressure equilibration of the eustachian tube and the cochlear aqueduct was studied, as well as the effects of blocking these channels. During ascent, the physiologic opening of the eustachian tube reduced the pressure gradients across the tympanic membrane. The patent cochlear aqueduct equilibrated perilymph pressure to cerebrospinal fluid compartment levels with a considerable pressure gradient across the oval and round windows. With the aqueduct blocked, the pressure decrease within the labyrinth and tympanic cavities was limited, resulting in large pressure gradients toward the chamber and the cerebrospinal fluid compartments, respectively. We conclude that closed cavities with limited pressure release capacities are the cause of the pressure gradients. The strain exerted by these pressure gradients is potentially harmful to the ear.

Perilymph pressure during hypobaric conditions : cochlear aqueduct obstructed

Nine cats with the cochlear aqueduct surgically blocked were anaesthetised, put in a pressure chamber, and stepwise exposed to hypobaric pressure, each of the two steps lasting 5 min. The chamber pressure was reduced to -5 and -7 kPa. Concluding the experiment the cats were observed for 5 min after restoration of atmospheric pressure. The perilymph, tympanic cavity, cerebrospinal fluid, central venous, arterial and surrounding chamber pressures were continuously recorded. Reduced chamber pressure caused relative overpressure within the tympanic cavity, thereby inducing pressure gradients between the chamber, the tympanic cavity, the labyrinth and the cerebrospinal fluid and vascular pressures respectively. Our results demonstrate that hypobaric effects on the labyrinth are mediated via pressure changes in the tympanic cavity and not by systemic, vascular or cerebrospinal fluid influence. Substantial perilymph overpressure lasted throughout the hypobaric conditions. The magnitude and the duration of this overpressure were influenced by the patency of the Eustachian tube whereas the rate of the pressure change in the chamber was of little importance. As atmospheric pressure was restored in the chamber the overpressure in the labyrinth was reversed to underpressure--relative to pre-experimental conditions.

Electrocochleographic and audiometric evaluation of hypobaric effect in Meniere's disease

Objectives: To elucidate the effects of hypobaric pressure on cochlear hydrodynamics in patents with well‐defined Menieres disease. Design: Sixteen patients were consecutively selected. Elevated hearing threshold levels and pathological transtympanal electrocochleography (tt‐ECOG) were confirmed at the day of trial. The patients were exposed to repeated episodes of hypobaric pressure in a pressure chamber. The rate (20 daPa/s) and magnitude (‐285 daPa) of chamber pressure change were low. The induced tympanic overpressure (+185 daPa) was continuously monitored and any tympanic equilibration was avoided. Methods: The results of Bekesy and speech audiometry as well as tt‐ECOG performed immediately before and after exposure were compared. The importance of chamber pressure change, number of hypobaric episodes, duration of exposure, and the induced relative tympanic overpressure was tested. Results: It is shown that the relative tympanic overpressure is the most important factor to affect the cochlear hydrodynamics. Higher relative overpressure was associated with improvement of hearing threshold levels, while the ECOG results tended to improve with lower induced tympanic overpressure. Conclusion: The importance of tympanic overpressure shown in this study is in agreement with previous findings from hypobaric animal experiments. The inverse relation of psychoacoustic and ECOG tests suggests that the two methods evaluate different parameters, perhaps contributing differently to the physiology of hearing.

Continuous Long-term Measurements of the Middle Ear Pressure in Subjects with Symptoms of Patulous Eustachian Tube

Direct middle ear (ME) pressure measurements during 24 h and tubal function tests were performed on 11 subjects with the clinical diagnosis patulous Eustachian tube (PET). The pressure was recorded from the ME via a perforation in the tympanic membrane. The method used has previously been reported in a study on subjects with normal ME function and no symptoms of PET: a normal group. Results from tubal function tests correlated well with the clinical diagnosis of PET and the sniff test was positive in most subjects. Continuous ME pressure measurements during normal everyday and night-time activities showed no indications of pressure changes induced by sniffing. Subjects with the clinical diagnosis PET did not have a static state of an open ET. The ME pressure varied during the day and night, indicating that the function of the ET changed over time from a closed to an open state. Subjects with PET had a long-term pressure pattern significantly different from that of a normal group, a difference seen in the erect as well as in the recumbent position during the night. The subjects demonstrated a negative mean pressure level in the recumbent position during the night, whereas the normal group had a slight positive mean pressure. The difference was statistically significant. Many subjects demonstrated frequent slow rate negative pressure trends during normal day-time and night-time activities. Long-term continuous pressure measurements seem to add valuable information to that of conventional tubal function tests.