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Biomedical subjects

R H Kay

Publications and source records attributed to R H Kay.

At least 19 recordsLinked to original sources
PubMed1990

Postoperative evaluation of ascending aortic prosthetic conduits by magnetic resonance imaging.

Operative repair of ascending thoracic aortic dissection and aneurysm often involves the placement of prosthetic aortic conduits and stents with wrapping of the native aorta around the prosthetic device. Postoperative assessment has been clinical because of the absence of an adequate noninvasive imaging modality and a reluctance to perform invasive contrast aortography. Magnetic resonance imaging was performed on ten patients after operative placement of a prosthetic ascending aortic graft. The MR images were reviewed and a grading system was devised based on appearance of the operative site. An increase in MR signal was noted in some patients between the graft and wrapped native vessel. In 20 percent of patients vascular lumen compromise was noted. Magnetic resonance imaging offers a noninvasive technique to assess postoperative complications and offers a viable alternative to invasive contrast aortography.

Adult↗
PubMed1989

Polymorphic ventricular tachycardia.

The case of a patient with torsade de pointes in the setting of congenital complete heart block is described. Lack of recognition of this polymorphic ventricular tachycardia resulted in therapy that potentiated the dysrhythmia. After correct recognition, and directed therapy, the patient responded appropriately. The clinical settings, recognition, and management options available for torsade de pointes are discussed to familiarize the emergency physician with this important and unique dysrhythmia.

Adult↗
PubMed1986

Echocardiographic and hemodynamic features of severe aortic regurgitation with diastolic opening of the aortic valve.

Severe aortic regurgitation may be associated with premature aortic valve opening. Several possible etiologies for this diastolic opening have been suggested. We present a patient with hemodynamic data, M-mode and 2-D echocardiography in the setting of severe aortic regurgitation and diastolic aortic valve opening. Our data lead us to conclude that aortic valve opening in this situation is neither from passive flotation nor dependent on atrial systole. We believe that active ventricular recoil mechanisms can facilitate increases in diastolic ventricular pressure which then can transiently exceed aortic pressure in the setting of severe aortic regurgitation. This hemodynamic observation suggests that the valve opening is an active process.

Adult↗
PubMed1986

Steady-state evoked responses to sinusoidally amplitude-modulated sounds recorded in man.

Steady-state potentials evoked in response to binaural, sinusoidally amplitude-modulated (AM) pure tones and broadband noise signals were recorded differentially from position F4 and the ipsilateral mastoid on the human scalp. The responses elicited by the AM stimuli were approximately periodic waveforms whose energy was predominantly at the modulation frequency of the stimulus. The magnitude of responses was between 0.1 and 4 microV for modulation frequencies between 2 and 400 Hz imposed on a 1-kHz carrier signal. The magnitude of the responses increased linearly with log modulation depth for low (4 Hz) and high (80 Hz) modulation rates. The response magnitude also increased linearly with the mean intensity of the sound for intensities up to 60 dB above the subject's pure tone threshold; at higher levels the response saturated. The relationship between response magnitude and modulation frequency (the modulation transfer function) was a lowpass function for both pure tone and broadband noise carrier signals. The modulation transfer functions were similar to those obtained from human psychophysical measurements where spectral cues are either unavailable or not used by the subject. The responses also contained a significant component at the second harmonic of the modulation frequency. The magnitude of this component was greatest at modulation rates between 5 and 20 Hz. The responses elicited by ipsilateral and contralateral monaural stimulation were approximately equal in magnitude, and binaural stimulation produced a potential 30% greater than the individual monaural responses. It is suggested that the evoked response represents the entrained neural activity to temporal amplitude fluctuations, and reflects the psychophysically measured performance of the auditory system for the detection and analysis of amplitude modulation.

Adult↗
PubMed1985

Delineation of FM rate channels in man by detectability of a three-component modulation waveform.

Adaptation studies have provided evidence for auditory mechanisms which operate on the modulation waveform of frequency-modulated sounds, and that these mechanisms behave like a series of channels selectively tuned to a limited range of modulation rates. In the present experiments, measurements of the modulation detectability threshold of a frequency-modulated tone, which had a modulation waveform spectrum consisting of three components: one component at the modulation rate and two sidebands which could be set to different frequency positions on either side of it, revealed that when the two sidebands were located within a limited bandwidth around the central component they contributed to the detection of the modulation. However, when the sidebands were more widely separated from the central component, the modulation detection threshold was dependent only on the magnitude of the central component. Within the area of sideband interaction, there was an inversely proportional relationship between the magnitude of the sidebands and the modulation threshold. Differences in the time-integrated sound spectra for the FM signals, although very complex, do not contain changes which adequately explain the data on the basis of critical band mechanisms, or a peak-to-peak detection model. The data provide further evidence in support of the hypothesis derived from adaptation studies that channels selectively sensitive to the rate of frequency modulation in frequency-modulated tones are concerned in the processing of frequency-modulated signals.

Auditory Threshold↗
PubMed1974

A study of single axons in the cat's medial lemniscus.

1. A method was developed for locating the rostral part of the medial lemniscus in anaesthetized cats and then exploring it with a micro-electrode selective for single axons. Records were made from 165 axons, all shown histologically to lie in the lemniscus.2. Almost all lemniscal axons responded at short latency to a shock through surface electrodes over the dorsal columns at C2. The great majority probably belonged to the dorsal column-lemniscal system, though some may have belonged to other (e.g. spinocervicothalamic) systems.3. Resting discharge was seen in almost all axons in the absence of any stimulation, and must have been generated almost entirely in the relevant relay nuclei, particularly since in many axons it was easily depressed or totally inhibited by appropriately placed mechanical stimulation of skin or a shock to the dorsal columns.4. For each fibre held for an adequate length of time, the receptive field, if accessible, was classified as accurately as possible. Fifty-two axons were precisely categorized in this way: many more were studied for long enough to yield useful information.5. One half (twenty-six) of the best categorized axons had receptive fields suggesting excitation by only one type of receptor: fifteen by tylotrich hairs, four by rapidly adapting tactile foot pad receptors, two by claw movement, two by cutaneous touch corpuscles and three by Type II cutaneous receptors. Rigidly held probes driven by electromechanical transducers were used to establish stimulus/response relations. Adjacent or surround inhibition was seen in nearly all these fields, except for the Type II category.6. The other half (twenty-six) of the best categorized axons showed various degrees of inter-receptive excitatory convergence. Five responded to all types of hair, twelve to hair movement and foot-pad displacement, and nine to hair movement combined with inputs from a variety of slowly adapting receptors in skin or deep tissues, thresholds for the latter ranging from light contact to noxious pressure.7. Forty axons responded with a slowly adapting discharge to joint movement, some with properties suggesting that their receptors did not lie in the joint capsule itself. The high threshold of most of these axons to dorsal column stimulation suggested that the relevant primary axons lay either deep in the dorsal column or in some other tract.8. Of axons whose receptive fields were accurately located, 88% lay in forelimb or upper trunk - the remainder in lower trunk, hind limb or tail. The forepaw accounted for 41% of the former group. Axons with receptively ;pure' properties tended to lie in central or deep parts of the main lemniscal mass at the level studied. Axons responding to joint movement tended to lie deep in the main mass and in the ventromedial lemniscal bundle. There was some clustering of axons with identical receptive properties.

Action Potentials↗