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Biomedical subjects

G R Holt

Publications and source records attributed to G R Holt.

At least 19 recordsLinked to original sources
PubMed1999

Septorhinoplasty. Form versus function.

Septorhinoplasty is the most difficult and complicated procedure in facial plastic surgery. Because of the complex interdependency of the anatomical parts, alteration of one may have an impact on another. Three-dimensional relationships are important, as is the maintenance of a proper framework for the internal and external nose. Form and function are completely interwoven in septorhinoplasty.

Humans↗
PubMed1999

Biomechanics of nasal septal trauma.

Fractures of the nasal complex are the most common facial fracture. This is due to the fact that the nose is the most anteriorly projecting facial structure and is a composite structure of bone, cartilage, and soft tissue. Furthermore, the forces required to cause significant injury are less than that causing other facial fractures. Because of the wide range of activities and mishaps that cause nasal trauma, the instruments of injury range from bicycle handles to elbows. The causes, clinical anatomy, and future considerations regarding nasal septal trauma are discussed in this article.

Biomechanical Phenomena↗
PubMed1997

Shunting inhibition does not have a divisive effect on firing rates.

Shunting inhibition, a conductance increase with a reversal potential close to the resting potential of the cell, has been shown to have a divisive effect on subthreshold excitatory postsynaptic potential amplitudes. It has therefore been assumed to have the same divisive effect on firing rates. We show that shunting inhibition actually has a subtractive effect on the firing rate in most circumstances. Averaged over several interspike intervals, the spiking mechanism effectively clamps the somatic membrane potential to a value significantly above the resting potential, so that the current through the shunting conductance is approximately independent of the firing rate. This leads to a subtractive rather than a divisive effect. In addition, at distal synapses, shunting inhibition will also have an approximately subtractive effect if the excitatory conductance is not small compared to the inhibitory conductance. Therefore regulating a cell's passive membrane conductance-for instance, via massive feedback-is not an adequate mechanism for normalizing or scaling its output.

Animals↗
PubMed1997

Ulnar variance and age.

Ulnar variance was determined on 1,023 radiographs of normal wrists taken in standardized fashion. There were 468 women and 555 men. The age range was 13 to 109 years. In both sexes, ulnar negative variance decreased significantly with increasing age. Possible reasons for this are discussed.

Adolescent↗
PubMed1996

The interface of academic and community practice in medical and graduate medical education.

Historically, the interaction between academic departments of otolaryngology-head and neck surgery and the community practice of the specialty has been erratic, anecdotal, and often strained. A general sense of autonomy and isolationism that has characterized many university programs coupled with a paranoia on the part of many practitioners with respect to concerns about protecting their patient base have led to an uneasy relationship. Difficulties with managed care now threaten this relationship even more. It is clearly time to seek a solution that can enhance the educational opportunities for medical students and residents.

Academic Medical Centers↗
PubMed1996

Effects of air pollution on the upper aerodigestive tract.

The main route of contamination of the human body with airborne pollutants is through the upper air and food passages. Because of the delicate balance of the mucous membranes and special sensory organs of these passages with respect to mucociliary activity, local and recruited immune responses, rapid uptake of chemicals, and carcinogenic potential, the ingestion or inhalation of pollutants in the air can be harmful to these internal body barriers. The particular target organs for air pollution effects on the upper aerodigestive tract include the mucosa, olfactory epithelium, auditory receptor cells, glottic epithelium, and adjacent neural and muscular tissues. Hearing loss caused by noise exposure may be aggravated by the concomitant inhalation of solvents. The strongest evidence for the carcinogenic effect of occupational inhalants in the nasal cavity and paranasal sinuses is seen with exposure to hardwood dust, tobacco smoke, furniture making, and leather tanning. With the exception of tobacco smoke, which produces squamous cell carcinomas, the majority of the occupationally related cancers are adenocarcinomas, usually of the intestinal variety. Tobacco smoke, passive or active, may lead to end-artery obliteration at the level of the otic end organ, causing a progressive sensorineural hearing loss. Further environmental research in the upper aerodigestive tract should aim at developing biologic markers to determine early, premalignant tissue changes; identifying the effects of chronic, low-dose toxic exposure on mucous membranes and neurosensory organs; providing field-tested tools for the standardized screening of large at-risk populations.

Adenocarcinoma↗
PubMed1996

Comparison of discharge variability in vitro and in vivo in cat visual cortex neurons.

1. In neocortical slices, the majority of neurons fire quite regularly in response to constant current injections. But neurons in the intact animal fire irregularly in response to constant current injection as well as to visual stimuli. 2. To quantify this observation, we developed a new measure of variability, which compares only adjacent interspike intervals and is therefore less sensitive to rate variations than existing measures such as the coefficient of variation of interspike intervals. 3. We find that the variability of firing is much higher in cells of primary visual cortex in the anesthetized cat than in slice. The response to current injected from an intracellular electrode in vivo is also variable, but slightly more regular and less bursty than in response to visual stimuli. 4. Using a new technique for analyzing the variability of integrate-and-fire neurons, we prove that this behavior is consistent with a simple integrate-and-fire model receiving a large amount of synaptic background activity, but not with a noisy spiking mechanism.

Animals↗
PubMed1995

Compensation, work status, and disability in low back pain patients.

STUDY DESIGN: A prospectively designed study was performed to assess the influence of employment status and a compensation claim on patients experiencing low back pain. OBJECTIVES: To determine the factor that most influences disability arising from low back pain, unemployment or a compensation claim. SUMMARY OF BACKGROUND DATA: Two hundred sixty-nine consecutive patients were assessed from a low back pain clinic. METHODS: Disability was assessed using the Oswestry Disability Score, and employment, and compensation status were recorded. RESULTS: Both unemployment and patients involved in compensation had higher disability scores. However, by controlling the data for employment and assessing only the compensation group it was found that those claiming compensation, but still working had significantly less disability than those claiming compensation who were unemployed. CONCLUSIONS: Both unemployment and compensation claims influence disability, but employment status is the most important factor.

Adult↗
PubMed1994

The future of wound healing in otolaryngology-head and neck surgery.

The future of wound healing progress lies in the support of research being performed at this very moment. In basic science and clinical laboratories all across the nation, there are investigative studies underway, which have as their purpose, the ultimate improvement of wound healing capabilities of the human body in both soft and hard tissues.

Debridement↗
PubMed1994

Talocalcaneal coalition in patients who have fibular hemimelia or proximal femoral focal deficiency. A comparison of the radiographic and pathological findings.

The prevalence of congenital anomalies of the foot was studied in ninety-nine children (105 limbs) who had fibular hemimelia or proximal femoral focal deficiency, or both. Twenty-six of these patients had had a Syme amputation at our institution and the specimens were analyzed anatomically; they were found to include fourteen talocalcaneal coalitions (54 per cent). The preoperative radiographs of these same patients, however, revealed only four such coalitions (15 per cent). Thirty-seven of the ninety-nine patients had had a Syme amputation previously at another facility (with subsequent follow-up at our institution), and ten of them (ten feet) had radiographs that were adequate for analysis of congenital anomalies. Forty-two feet that had not yet been amputated were also analyzed radiographically. Nine of these fifty-two feet included in the radiographic analysis had a talocalcaneal coalition, a radiographic prevalence similar to that found on the preoperative radiographs of the twenty-six patients included in the anatomical analysis. The true prevalence of talocalcaneal coalition remains to be determined; however, this can be done only at the time of skeletal maturity. Examination of the twenty-six amputation specimens revealed only one talocalcaneal coalition in the nine patients who had proximal femoral focal deficiency alone, six such coalitions in the eight patients who had only fibular hemimelia, and seven coalitions in the nine patients who had both proximal femoral focal deficiency and fibular hemimelia. These findings should be useful in the evaluation of the radiographic anatomy of the feet in children who have proximal femoral focal deficiency or fibular hemimelia, or both, particularly if limb-lengthening is considered as a treatment option.

Calcaneus↗