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Biomedical subjects

K S Konrádsson

Publications and source records attributed to K S Konrádsson.

9 recordsLinked to original sources
PubMed2000

Pressure transfer between intracranial and cochlear fluids in patients with Meniere's disease.

OBJECTIVES: To elucidate the pressure transfer between intracranial and labyrinthine fluids in patients with well-defined unilateral Meniere's disease. STUDY DESIGN: Eleven patients previously exposed to hypobaric pressure agreed to be investigated further with the tympanic membrane displacement (TMD) technique. TMD was used to indirectly analyze perilymph pressure changes as the result of changes in body position. METHODS: Repeated measurements for both the diseased and the healthy ears were made with the patients supine and then in a sitting position. The TMD parameters for the maximum inward displacement, the Vi, and the mean volume displacement, the Vm, were calculated and compared. RESULTS: The paired comparison showed statistically significant larger Vi values for both ears in the supine position. A similar tendency was observed for the Vm value. This difference of the Vi was significantly larger for the diseased ear compared with the currently healthy ear. The results were compared to the audiometric and electrocochleographic results previously obtained on the same patients when they were subjected to hypobaric pressure. Patients who experienced the largest differences in hearing level thresholds in the lower frequencies also showed the greatest differences in TMD values as the result of postural changes. CONCLUSIONS: Despite the limited number, the statistically supported results suggest a relation between the efficiency of the routes of pressure transfer and the observed effect of hypobaric exposure. The results also indicate that for the patients tested, the routes of communication are more effective in the diseased ear than in the healthy ear--a condition that may relate to the pathogeneses of Meniere's disease.

Adult↗
PubMed1999

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 Meniere's 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.

Adult↗
PubMed1997

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.

Animals↗
PubMed1994

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.

Animals↗
PubMed1992

Pressure transfer between the perilymph and the cerebrospinal fluid compartments in cats.

This is a review of our studies of the labyrinthine fluid pressure in cats subjected to pressure changes in the middle ear (implosive routes) and the cerebrospinal fluid compartment (explosive routes) as well as to changes in vascular and ambient pressures. The perilymph, cerebrospinal fluid (CSF), middle ear, venous and arterial pressures were measured with the cochlear aqueduct (CA) patent as well as surgically blocked. Experiments on explosive pressure changes revealed that the perilymph pressure was regulated by the CSF in case of CA patency. The CSF influence was dominant enough to obscure any direct effect on the labyrinth from other sources. With the CA obstructed the CSF influence on the labyrinth was apparently mainly via the endolymphatic sac and duct although limited and much delayed. Systemic arterial pressure changes had a pronounced influence on the perilymph pressure, but this effect was revealed only when the CSF influence was reduced by CA obstruction. Experiments on implosive and ambient pressure changes suggested that there was no fundamental difference in the perilymph response to equivalent levels of implosive versus hypobaric pressure. Three factors determined the effect of implosive and hypobaric pressure: the patency of the CA, the rate of the pressure change, and the eustachian tube function.

Air Pressure↗
PubMed1988

Three-dimensional laser Doppler interferometric display of human tympanic membrane vibrations at two different frequencies and sound pressure levels.

The vibrational movements of the tympanic membrane of human in vitro specimens were studied by computerized laser Doppler interferometry. The entire surface of the vibrating tympanic membrane was scanned with the laser beam and all information was stored digitally making it possible to recreate the movements as in slow motion on the oscilloscope. Single phases of interest from the vibrational cycle were plotted as shown. The resonance patterns at 0.58 kHz and 3.11 kHz are compared and the effect of different sound pressure levels on the vibrational movement of the tympanic membrane demonstrated.

Doppler Effect↗
PubMed1987

Computerized laser Doppler interferometric scanning of the vibrating tympanic membrane.

The vibrational movements of the tympanic membrane (TM) of in vitro human specimens were studied by computerized laser Doppler interferometry. The versatility of the method for measuring the velocity of the vibrating TM was demonstrated by point measurements, horizontal sweeps, and three-dimensional scans of the entire TM. Single phases of the TM vibration were examined and plotted three-dimensionally. All information was stored digitally, making it possible to recreate the movements as in slow motion on the oscilloscope. The effect of coating the TM with a thin layer of magnesium oxide was studied. The repeatability of the method was demonstrated. TM vibrational patterns at different sound pressure levels and frequencies are displayed and discussed as also are the results of scanning the specimen in different positions.

Computers↗
PubMedDate not supplied

Bilaterally preserved otoacoustic emissions in four children with profound idiopathic unilateral sensorineural hearing loss.

Severe to profound unilateral sensorineural hearing loss of the left ear was discovered by screening in four healthy children without any family history of hearing loss. Three of the children were four years old and one child was seven years old at the time of discovery. The PTA0.5-2 was 66-75 dB HL for three of the children and one child was without any hearing reactions on the affected ear. The hearing of the right ear was normal in all four cases. The hearing thresholds have been stable during an observation period of 3-12 years. No certain auditory-evoked brainstem responses were recorded with stimulation of the affected ear. Electronystagmography was normal in all cases and magnetic resonance imaging gave no explanation of the hearing loss. Repeated recordings of the transiently evoked otoacoustic emissions (TEOAE) have shown clear bilateral responses using different instrumentation systems. Recently the hearing levels were unchanged and the TEOAE responses of the affected ears were 6.7-19.9 dB SPL (waveform reproducibility: 88-98 per cent) recorded on the ILO88 OAE Analyser (stimulus: 82.2-83.4 dB peak). The collected results suggest that the children suffer from a similar disorder with a unilateral affection of the cochlea, involving the inner hair cells and/or the first neuron. The TEOAE recordings indicate substantially preserved outer hair cell function independent of the profound hearing loss.

Auditory Threshold↗