Temporary threshold shifts from prolonged exposure to noise

Eight monaural chinchillas were trained to respond to tones, and their auditory thresholds were measured behaviorally. The animals were then exposed to octaveband noise centered at either 0.5 or 4.0 k Hz for periods of two to 21 days. Octaveband levels (OBL) between 65 and 105 dB SPL were used. The growth of temporary threshold shift (TTS) was measured during brief interruptions in the exposure. TTS increased for the first 24 to 48 hours of an exposure and then reached an asymptote and remained constant for as long as the exposure continued. At asymptote the relation between the TTS and the level of the octave band centered at 0.5 k Hz was TTS 4 ∞ = 1.6 (OBL-65), where TTS 4 ∞ was measured with a test tone of 0.715 k Hz at four minutes after an interruption of the noise. Decay of TTS after termination of the exposure was slow and approximately exponential with a time constant of about 29 hours. Empirically, the time for TTS to decay to near-zero values ranged from three to six days. The course of decay of TTS was independent of the duration of the exposure once asymptote had been reached.

Infection after depressed fracture of skull. Implications for management of nonmissile injuries

✓ The authors analyze and discuss the 10% infection rate among 359 civilians with compound skull fractures. Infection results from incomplete debridement, for which antibiotics are no substitute. Inadequate treatment usually derives from missing the diagnosis of depressed fracture completely, but sometimes from underestimating the seriousness of the individual injury. Many patients with this injury never lose consciousness, do not have immediate x-ray studies, and are not admitted to hospital; infection is a serious risk in this group. Complete removal of all bone fragments, as recommended for missile injuries, is not necessary. If bone is replaced, the incidence of infection (and of epilepsy) is not greater, and the need for cranioplasty avoided; bone can be safely replaced even when surgery is delayed for 24 hours and when the dura is torn.

Classification of community hospitals by scope of service: four indexes

Four indexes are presented for classifying short-term nonfederal general hospitals by the scope of service they provide. The indexes, constructed by the application of Guttman scaling to data from 5439 hospitals, are tested for cohesiveness and unidimensionality and their relation to hospital expenses and staffing is examined. The usefulness of the indexes for classifying hospitals and as stratification variables is discussed.

Relationship between volume flow and velocity in the cerebral circulation

The relationship between the velocity of the cerebral circulation and the cerebral blood flow was explored at varying levels of PaCO(2), systemic arterial pressure, intracranial pressure, and perfusion pressure, using radioisotope techniques in baboons. Only at low flow rates did velocity increase with flow, and then non-linearly; at high rates velocity increased progressively less. Changes in flow are reflected by changes in velocity in such restricted circumstances that mean circulation time is a very unreliable indication of cerebral blood flow.

Effects of hyperbaric oxygen on intracranial pressure and cerebral blood flow in experimental cerebral oedema

Increased intracranial pressure was induced in anaesthetized dogs by application of liquid nitrogen to the dura mater. Intracranial pressure and cerebral blood flow were measured, together with arterial blood pressure and arterial and cerebral venous blood gases.Carbon dioxide was administered intermittently to test the responsiveness of the cerebral circulation, and hyperbaric oxygen was delivered at intervals in a walk-in hyperbaric chamber, pressurized to two atmospheres absolute.Hyperbaric oxygen caused a 30% reduction of intracranial pressure and a 19% reduction of cerebral blood flow in the absence of changes in arterial PCO(2) or blood pressure, but only as long as administration of carbon dioxide caused an increase in both intracranial pressure and cerebral blood flow. When carbon dioxide failed to influence intracranial pressure or cerebral blood flow then hyperbaric oxygen had no effect. This unresponsive state was reached at high levels of intracranial pressure.

Value of osteopathy

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The effect of hyperbaric oxygen on experimentally increased intracranial pressure

✓ The effect of breathing high partial pressures of oxygen on intracranial pressure (ICP) was assessed in 10 anesthetized, ventilated dogs in which ICP had been increased by slow inflation of extradural balloons. Cerebrovascular responsiveness was tested by the addition of carbon dioxide (CO2) to the inspired gases. Inhalation of 100% oxygen reduced ICP by 23% when delivered at normal atmospheric pressure (arterial pO2, 585 mm Hg) and by 37% when delivered at 2 atmospheres absolute (ATA) in a hyperbaric chamber (arterial pO2, 1076 mm Hg). This reduction in ICP, which was present only during oxygen administration, was not associated with any change in arterial blood pressure or pCO2. Hyperbaric oxygen (OHP) reduced ICP only at the stage when the cerebral circulation was still responsive to CO2, as manifested by a rise in ICP; at high levels of ICP, responsiveness to both CO2 and OHP was lost. When the ipsilateral pupil became dilated following balloon inflation, a reduction in size was observed during administration of OHP in 11 out of 13 instances. During the responsive phase, when OHP reduced ICP, cerebral venous PO2 which was 41.7 ± 2.3 mm Hg (S.E.M.) on air breathing was modestly increased by OHP to 58.3 ± 2.5 mm Hg; when ICP no longer responded to OHP, cerebral venous PO2 was higher, on both air breathing (52.0 ± 4.1 mm Hg) and OHP (161.4 ± 14.7 mm Hg).

Persistent proatlantal artery

A case of persistent proatlantal artery is described and the developmental anatomy reviewed. This vessel, arising from the internal carotid artery in the neck, is liable to be confused with the hypoglossal artery, but unlike the latter it forms the vertebral artery outside the skull and enters through the foramen magnum.

Value of angiography in acute conditions affecting the thoracic aorta

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Antagonism of some smooth muscle actions of prostaglandins by polyphloretin phosphate

1. The antagonism of the smooth muscle stimulating actions of PGF(2a) and PGE(2) by polyphloretin phosphate (PPP) was studied on several isolated smooth muscle preparations and on the blood pressure of the anaesthetized rabbit.2. PPP (2.5-20 mug/ml) reversibly inhibited contractions of the jird colon produced by PGE(2) or PGF(2a); PGF(2a) was more readily antagonized than PGE(2).3. PPP (2.5-30 mug/ml) reversibly antagonized contractions produced by PGE(2) and PGF(2a) on the isolated rabbit jejunum and uterus. In these preparations PPP antagonized PGE(2) as readily as PGF(2a).4. It is concluded that PPP is a selective antagonist to the prostaglandins on these tissues, for contractions produced by other agonists, such as acetylcholine, angiotensin, 5-hydroxytryptamine and bradykinin were not reduced by concentrations of PPP which markedly antagonized responses to the prostaglandins.5. Intravenous injections of PPP (25-200 mg/kg) resulted in a variable antagonism to the fall in blood pressure produced by intravenous injections of PGF(2a) in the anaesthetized rabbit; vasodepressor responses produced by PGE(2) and acetylcholine were not antagonized.6. The mechanism of this antagonism by PPP is not clear and must await further investigation.