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Biomedical subjects

D Henderson

Publications and source records attributed to D Henderson.

At least 217 records · Page 12Linked to original sources
PubMed1985

10B

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Journal Article↗
PubMed1985

Impact noise and the equal energy hypothesis.

The equal energy hypothesis (EEH) was evaluated over a limited range of conditions by exposing four groups of chinchillas to impact noise (200-ms B duration) presented at a fixed rate of four impacts per second. The intensity of the impacts (107-125 dB peak SPL) and the duration (120-1.87 h) of the four exposure conditions were counterbalanced so that the four groups received the same total energy. The traumatic power of the exposures was assessed by measuring the threshold shift of the auditory evoked response and the amount of hair cell loss. Exposure between 107 and 119 dB were consistent with the EEH in that they produced roughly the same amount of permanent threshold shift (less than 20 dB) and hair cell loss (less than 20%). However, the 125-dB exposure produced substantially more threshold shift and hair cell loss than the three lower intensities. Thus, the EEH may be applicable only at lower impact intensities; above a "critical intensity" the amount of damage increases significantly.

Animals↗
PubMed1985

Morphological differences in cutaneous and skeletal muscle vasculature during compensatory and decompensatory hemorrhagic hypotension.

PURPOSE: to determine if morphological differences exist between vasculature shown to decompensate, ie, skeletal muscle (SM) and vasculature that maintains the compensatory effort, ie, cutaneous (C). METHODS: dogs were anesthetized and subjected to a Wiggers hemorrhagic shock protocol. SM and C flows were monitored using electromagnetic flowmeters. Gracilis (SM) and saphenous (C) arterial segments were removed during: prehemorrhage control, compensation, and decompensation. Segments were fixed at in vivo intraluminal pressures. Both light and EM sections were made from each sample. RESULTS: During the compensatory phase, both SM and C showed signs of strong vasoconstriction. Even though the amount of endothelial folding was comparable, the C did and the SM did not sustain the vasoconstriction. Vascular diameters of the SM but not C increased during decompensation. Ultrastructural changes consisted of extreme folding of the internal elastic lamina (IEL) during compensation and subsequent flattening out of the IEL during decompensation in the SM but not the C tissues. Cell deformation, damage, and exfoliation were seen in both SM and C tissues. CONCLUSION: The data are consistent with the theory that SM vasculature, specifically endothelium, synthesizes an inhibitor of NE release, probably prostaglandins.

Animals↗
PubMed1984

Control of sheep scab and other sheep ectoparasites with propetamphos.

Propetamphos is a new organophosphorous compound with broad spectrum acaricidal and insecticidal activity. Dip wash concentrations of 100 to 200 ppm protect sheep against field challenge for approximately 10 weeks for blowflies, 16 weeks for lice and keds and six weeks for ticks. During laboratory and field trial studies a wash concentration of 125 ppm propetamphos eradicated sheep scab and protected from reinfestation for over four weeks.

Animals↗
PubMed1984

Anatomical correlates of impulse noise-induced mechanical damage in the cochlea.

Changes in the surface morphology of the organ of Corti in the chinchilla were studied following exposure to blast waves at 160 dB peak SPL. The generation and development of a mechanically induced lesion on the organ of Corti was followed over a period of 30 days using scanning electron microscopy. The most prominent feature of the lesion was the complete separation of a 5-7 mm strip of the sensory epithelia consisting of outer hair cells, Deiter cells and Hensen cells from the reticular lamina and the basilar membrane. The inner hair cells in this same area survived for several days in a remarkably normal condition. A spectrum of ciliary changes was observed on the inner and outer hair cells that differ somewhat from those commonly reported following continuous noise exposure. Some of the observed changes in morphology can be related to a variety of inferred mechanical events on the basilar membrane.

Animals↗
PubMed1984

Amplitude modulation thresholds in chinchillas with high-frequency hearing loss.

Estimates of auditory temporal resolution were obtained from normal chinchillas using sinusoidally amplitude modulated noise. Afterwards, the animals were exposed to noise whose bandwidth was progressively increased toward the low frequencies in octave steps. The first exposure was to an octave band of noise centered at 8 kHz. Three additional octave bands of noise were subsequently added to the original exposure in order to progressively increase the extent of the high-frequency hearing loss. The first exposure produced a temporary hearing loss of 50 to 60 dB near 8 kHz and elevated the amplitude modulation thresholds primarily at intermediate (128 Hz) modulation frequencies. Successive noise exposures extended the temporary hearing loss toward lower frequencies, but there was little further deterioration in the amplitude modulation function until the last exposure when the hearing loss spread to 1 kHz. The degradation in the amplitude modulation function observed after the last exposure, however, was due to a reduction in the sensation level of the test signal rather than to a decrease in the hearing bandwidth. The results of this study suggest that the high-frequency regions of the cochlea may be important for temporal resolution.

Animals↗
PubMed1983

Cypermethrin pour-on for control of the sheep body louse (Damalinia ovis).

The sheep body louse Damalinia ovis is a potentially serious problem affecting the value of the fleece and possibly causing reduced weight gains. Control has been based on the dipping or showering of sheep using insecticidal oil in water emulsions. The results using a pour-on formulation of the synthetic pyrethroid cypermethrin to control louse infestation are reported. Application rates of 5 mg/kg or more gave 99 to 100 per cent control.

Administration, Topical↗
PubMed1983

Response patterns of auditory nerve fibers during temporary threshold shift.

Temporary threshold shifts were studied in chinchillas exposed to noise (octave-band noise centered at 500 Hz, 95 dB SPL, 5 days duration) and the response properties of their auditory nerve fibers were measured. The threshold shifts of the fibers were approximately 35 to 65 dB; these values were equal to or slightly greater than those measured behaviorally. Most units had broad V-shaped tuning curves due to a greater loss in sensitivity near the characteristic frequency (CF) than in the low-frequency tail. In 17% of the units, the thresholds were actually lower in the tail than at CF, so that the tuning curves were W-shaped. The latencies of the fibers were within normal limits in terms of absolute intensity, but shorter than normal in terms of intensity relative to threshold. Other measures such as the spontaneous discharge rate, the discharge rate-intensity functions, and the firing patterns to tone bursts at CF appeared normal. These results indicate that neural response patterns during noise-induced temporary threshold shift are similar to those measured during permanent threshold shift.

Action Potentials↗
PubMed1983

Herpes simplex chorioretinitis in a healthy adult.

A previously healthy 20-year-old man developed bilateral chorioretinitis that included mild anterior uveitis, vitreous cells, multifocal chorioretinitis, and optic nerve swelling that progressed to severe optic neuropathy in one eye. Chorioretinal biopsy specimens cultured herpes simplex type 1 from separate chorioretinal and vitreous samples. Although the visual acuity of one eye remained at light perception, sight in the second eye was saved when treatment with systemic acyclovir and corticosteroids led to resolution of the inflammation. A recurrence was successfully treated with acyclovir alone and the patient shows no evidence of active disease.

Acyclovir↗
PubMed1983

Comparison of auditory-evoked potentials and behavioral thresholds in the normal and noise-exposed chinchilla.

Auditory sensitivity was tested in three monaural chinchillas using standard techniques and the auditory-evoked potential technique (AEP). Hearing was measured at octave steps from 500 to 8000 Hz before, 1 day after, and 30 days after exposure to a simultaneous combination of 50 impulses (A duration = 30 microseconds) presented at a rate of of 1/min and at 158 dB pe SPL and continuous noise (1 h of 95 dB 2-4 kHz octave band of noise). The two independent assessments of auditory sensitivity showed good agreement and the results support the use of AEP testing in experimental animals.

Animals↗