Real ear SPL (RE/SSPL90) produced by four different hearing aids was compared to the standard SSPL90 measurements for the same hearing aids on a 2-cc coupler. The effects of venting, location, and reliability for RE/SSPL90 were also studied. As expected, the real ear output level was greater than the coupler level. No systematic influence of earmold venting was found. An earmold that occludes an ear canal decreases the output in the high-frequency range so that only a small difference remains between RE/SSPL90 and 2-cc coupler levels above 2000 Hz. The difference seems to be affected slightly by the output impedance of the hearing aid receiver system. Individual variation for the RE/SSPL90 is as much as 10 dB. Finally, the saturated output levels measured were found to be insensitive to changes in actual microphone input levels caused by different procedures for calibrating ambient SPL. The RE/SSPL90 method is easy to use and reliability seems quite adequate for the typical clinical setting.

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Audiometric earphone discomfort level and hearing aid saturation sound pressure level for a 90 decibel input signal (SSPL90) as measured in the human ear canal.

The acoustical problems involved in matching the saturation sound pressure level for a 90 dB input signal (SSPL90) of a hearing aid to individual discomfort level were investigated. The real ear SPL (RE/SSPL90) produced by a supra-aural earphone used when measuring uncomfortable loudness (UCL), and RE/SSPL90 produced by three different hearing aids at 90 dB SPL input, were measured for nine subjects, using a miniature microphone technique, and compared to the corresponding coupler levels used when matching hearing aid maximum output to UCL. It was found that a hearing aid often gives about 5 dB, and sometimes 10 dB, higher RE/SPLs than the earphone, if the hearing aid output levels, as measured in a 2-cc coupler (IEC126), are equal to the earphone output levels as measured in a 6-cc coupler (NBS9A). It is recommended that a safety margin of at least 5 dB be used in the preliminary fitting when matching hearing aid SSPL90 to the patient's UCL, converted to dB SPL.

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Venous and volume factors in women during and after normotensive pregnancy.

1. Venous compliance and plasma volume were measured in thirty-one continuously normotensive women early (11-20 weeks) and late (31-40 weeks) in pregnancy and following delivery. 2. Mathematically fitted pressure/volume curves, obtained by venous occlusion plethysmography, were analysed according to two describing functions (i) the peak of the first derivative dv/dp max and (ii) a work index, integral of 25 (10) p dv. 3. The relationship between venous/volume factors seen after delivery, was disturbed during pregnancy, at which time the work index provided evidence for decreased venous compliance. 4. Pregnancy could be regarded as a potentially hypertensive state, brought about by a vascular/volume mismatch.

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Automatic tympanometry in clinical practice.

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