Advantages of contralateral acoustic reflex pathway
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Acoustic reflex assessment involved the presentation of the tonal and/or noise stimuli to elicitate reflex response from the stapadious muscle. The resulting change in the impedance is measured using same instrument as for tympanometry.
Although several methods has been used for measurement of the acoustic reflex but the measurement of change in acoustic admittance is widely used.
As the stimulus level decreases there is a change in the magnitude of the acoustic admittance until no response is obtained.
The lowest stimuli level at which that produce a change in the acoustic admittance is the acoustic reflex threshold (ART).
Probe ear : The ear with probe assembly is called probe ear.
Stimulus ear : The ear receiving the stimulus sound is called stimulus ear.
Ipsilateral : stimulus & probe in the same ear.
Right Contralateral : stimulus in the in the right ear and probe in the left ear.
The diagnostic power of the acoustic reflex is maximized with the use of both ipsilateral and contra lateral reflexes.
Advantages of contralateral test over ipsilateral :
1. It is sensitive to disorder of involving crossed reflex pathway.(RCP)
2. Less susceptible to artifact ( in ipsilateral as both stimulus and probe tone given to same ear)
3. Amount of stimulus intensity is higher as compare to ipsilateral mode.
4. More extensive normative available for contralataral modes
Advantages of ipsilatral mode.
1. Very sensitive to middle ear pathology.
2. Each ear is tested independently
3. Not influenced by disorder of opposite ear.
4. Easy in child & special difficult population.
5. False conductive hearing component is found in contra mode from opposite ear, but is not found in ipsilateral mode as use of insert ear phone prevents ear canal collapse.
Hermetic seal And Ear canal Pressure :
Whenever possible the acoustic reflex should be measured at the point of tympanometric peak pressure.
It is possible to obtain acoustic reflex in the ear canals of normal ear or sensorineural cases but with or without seal because tympanic peak pressures close to atmospheric pressure.
But in cases of resolving conductive disorder as reflexes could be absent without a seal.
Generally The ART get elevated as the pressure in the ear canal deviates from the tynpanometric peak pressure range of ± 240daPa.This effect is rather small (10dB or less) but in some ceses acoustic reflex become absent with large pressure variation.
Monophasic Responses
The acoustic reflex is generally conceptualized as an increase in impendence or decrease in the admittance over its entire duration in the monopahsic response
Biphasic response :
In many normal reflex responses it is found that a brief drop in the impendence at the onset of the response, followed by increase in the impendence for the remainder duration. This is due to cochlear fluid: A reduction in the resistance occur at onset as the muscle contraction momentary changes the coupling between stapediuos footplate and the cochlear fluid.
Sometimes in earlier stages of otoscerosis biphasic pattern found but in both onset and off set of reflex. Also found in Cogan’s syndrome , congenital stapes fixation and osteogenesis imperfect.
In normal ear with high frequency probe tone (eg 600 or 700Hz) produce biphasic reflexes but in otoscletosis it produces biphasic response both low and high frequencies probe tones.
Non Acoustic Reflex
The detail pathway of non acoustic reflexogenic was given by Djupesland (1964, 1967). The reflexogenic skin zone is supplied by touch impulse mediated by four cranial nerves ( V, VII, IX,X). The sensory input terminate within the reticular formation in the area of solitary tracks nucleus, further more the input supply area of the dorsolateral portion of the reticular formation thought to be an associated nexus receiving impulse from the spinal cord and higher brainstem level. The nexus is actually a reflex centre transmitting various impulses to cranial nerve motor nuclei.
The pathway is associated the following component……….
1. Portion of reflexogenic skin zone
2. Sensory portion of the nerve V, VII, IX, X.
3. Solitary track nucleus
4. A reflex centre ( dorsolateral portion of the reticular formation.
5. Facial motor nuclei
6. Motor portion of the nerve VII
7. Stapedial muscle and sptapes
Impendence associated with coetaneous stimulation
Luscher Slight blowing against outer ear and introduction of a glass olive into the EAC results in small contraction of stapedious, moreover amplitude of the contraction diminished if the cutaneous stimuli were applied in rapid succession. Generally there is a binaural contraction of stapedious muscle for monaural stimulation is found.
Although several methods has been used for measurement of the acoustic reflex but the measurement of change in acoustic admittance is widely used.
As the stimulus level decreases there is a change in the magnitude of the acoustic admittance until no response is obtained.
The lowest stimuli level at which that produce a change in the acoustic admittance is the acoustic reflex threshold (ART).
Probe ear : The ear with probe assembly is called probe ear.
Stimulus ear : The ear receiving the stimulus sound is called stimulus ear.
Ipsilateral : stimulus & probe in the same ear.
Right Contralateral : stimulus in the in the right ear and probe in the left ear.
The diagnostic power of the acoustic reflex is maximized with the use of both ipsilateral and contra lateral reflexes.
Advantages of contralateral test over ipsilateral :
1. It is sensitive to disorder of involving crossed reflex pathway.(RCP)
2. Less susceptible to artifact ( in ipsilateral as both stimulus and probe tone given to same ear)
3. Amount of stimulus intensity is higher as compare to ipsilateral mode.
4. More extensive normative available for contralataral modes
Advantages of ipsilatral mode.
1. Very sensitive to middle ear pathology.
2. Each ear is tested independently
3. Not influenced by disorder of opposite ear.
4. Easy in child & special difficult population.
5. False conductive hearing component is found in contra mode from opposite ear, but is not found in ipsilateral mode as use of insert ear phone prevents ear canal collapse.
Hermetic seal And Ear canal Pressure :
Whenever possible the acoustic reflex should be measured at the point of tympanometric peak pressure.
It is possible to obtain acoustic reflex in the ear canals of normal ear or sensorineural cases but with or without seal because tympanic peak pressures close to atmospheric pressure.
But in cases of resolving conductive disorder as reflexes could be absent without a seal.
Generally The ART get elevated as the pressure in the ear canal deviates from the tynpanometric peak pressure range of ± 240daPa.This effect is rather small (10dB or less) but in some ceses acoustic reflex become absent with large pressure variation.
Monophasic Responses
The acoustic reflex is generally conceptualized as an increase in impendence or decrease in the admittance over its entire duration in the monopahsic response
Biphasic response :
In many normal reflex responses it is found that a brief drop in the impendence at the onset of the response, followed by increase in the impendence for the remainder duration. This is due to cochlear fluid: A reduction in the resistance occur at onset as the muscle contraction momentary changes the coupling between stapediuos footplate and the cochlear fluid.
Sometimes in earlier stages of otoscerosis biphasic pattern found but in both onset and off set of reflex. Also found in Cogan’s syndrome , congenital stapes fixation and osteogenesis imperfect.
In normal ear with high frequency probe tone (eg 600 or 700Hz) produce biphasic reflexes but in otoscletosis it produces biphasic response both low and high frequencies probe tones.
Non Acoustic Reflex
The detail pathway of non acoustic reflexogenic was given by Djupesland (1964, 1967). The reflexogenic skin zone is supplied by touch impulse mediated by four cranial nerves ( V, VII, IX,X). The sensory input terminate within the reticular formation in the area of solitary tracks nucleus, further more the input supply area of the dorsolateral portion of the reticular formation thought to be an associated nexus receiving impulse from the spinal cord and higher brainstem level. The nexus is actually a reflex centre transmitting various impulses to cranial nerve motor nuclei.
The pathway is associated the following component……….
1. Portion of reflexogenic skin zone
2. Sensory portion of the nerve V, VII, IX, X.
3. Solitary track nucleus
4. A reflex centre ( dorsolateral portion of the reticular formation.
5. Facial motor nuclei
6. Motor portion of the nerve VII
7. Stapedial muscle and sptapes
Impendence associated with coetaneous stimulation
Luscher Slight blowing against outer ear and introduction of a glass olive into the EAC results in small contraction of stapedious, moreover amplitude of the contraction diminished if the cutaneous stimuli were applied in rapid succession. Generally there is a binaural contraction of stapedious muscle for monaural stimulation is found.
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