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Biomedical subjects

J A Davis

Publications and source records attributed to J A Davis.

At least 199 records · Page 11Linked to original sources
PubMed1985

Anaerobic threshold: review of the concept and directions for future research.

Although the term anaerobic threshold was introduced 20 years ago, the concept that an exercise-induced lactic acidosis occurs at a particular oxygen uptake which varies among subjects is over 50 years old. The surge of new interest in the parameter relates to its strong relationship to prolonged exercise performance. The average marathon running speed has been shown to be closely related to the running speed at the anaerobic threshold. Numerous studies have shown that the parameter can be validly measured during incremental exercise from the gas exchange consequences of the increased carbon dioxide and hydrogen ion levels in blood resulting from bicarbonate buffering of lactic acid. Refinement of the noninvasive detection scheme has made the parameter attractive to investigators in preventative, rehabilitative, and occupational medicine and to researchers in the exercise sciences. Controversy exists regarding the specific cause for the onset of exercise-induced metabolic acidosis. As experimentation continues to unravel the mechanisms of lactate production and ventilatory control during exercise, the anaerobic threshold concept can be further evaluated.

Acidosis↗
PubMed1984

Racquet ear.

Explore the source record for details and available documents.

Athletic Injuries↗
PubMed1984

Pancuronium prevents pneumothoraces in ventilated premature babies who actively expire against positive pressure inflation.

Preterm infants who were making expiratory efforts against ventilator inflation were randomised to be paralysed with pancuronium or to receive no paralysing agent during ventilation. Pneumothoraces developed in all 11 unparalysed babies but in only 1 of 11 (p less than 0.0004) of those managed with pancuronium, which had no serious side-effects. In 34 infants excluded from the trial because they were not breathing against the ventilator, no pneumothoraces developed.

Clinical Trials as Topic↗
PubMed1984

Provoked augmented inspirations in ventilated premature babies.

The stimulating and moderating factors of augmented inspirations provoked by artificial ventilation have been studied in 40 preterm babies on 182 different occasions. Provoked augmented inspirations were demonstrated by recording spontaneous respiratory activity during artificial ventilation by means of an oesophageal balloon and a pneumotachograph. Augmented inspirations were only seen during 18% of the study occasions. The frequency of this reflex was inversely related to the lung compliance as was the ventilator pressure necessary to provoke the augmented inspiration. The inflating volume which stimulated the reflex, when related to body weight, was similar in all the babies. Augmented inspirations were always provoked during the rapid rise in ventilator pressure at the onset of each inflation. Neonates who were recovering from paralysis by pancuronium and others being treated with theophylline both showed an increased frequency of augmented inspirations. It is possible that theophylline could be used to harness this advantageous reflex for the benefit of the ventilated preterm neonate.

Humans↗
PubMed1984

Altered auditory brainstem evoked responses in the ferret model for Reye's syndrome.

The effects of influenza B, aspirin and hyperammonemia on the functional integrity of the cochlea were examined using the ferret model for Reye's syndrome. Auditory brainstem evoked responses (ABR) were recorded from treated ferrets and compared to those recorded from controls. Delayed latencies of all waves, as well as increased I-IV Interwave latencies were observed in recordings from treated ferrets. Importantly, the latencies of Wave I, nerve generator potential from the eighth nerve, and Wave IV, response potential from the brainstem nuclei, increased on Days 3 and 5 of the study. However, recorded ABR from treated ferrets on Day 10 showed that while the latencies of Wave IV were approximate to those of controls, Wave I remained delayed. These results suggest that systemic effects of influenza B, aspirin and hyperammonemia may lead acutely to both peripheral and central auditory dysfunction, and that the functional integrity of the central auditory system may recover more quickly than that of the peripheral system. Furthermore, these results suggest that such effects may lead to acute transient hearing impairment in patients with Reye's syndrome.

Ammonia↗
PubMed1984

Alpha-adrenoreceptor reagents. 2. Effects of modification of the 1,4-benzodioxan ring system on alpha-adrenoreceptor activity.

Modification of the 1,4-benzodioxan ring present in RX 781094 has not previously been considered. This paper describes a number of analogues of this ring system, including compounds in which one of the oxygen atoms has been replaced by a methylene group and also those in which the ring size has been changed to give, for example, furan and thiophene derivatives. The dihydrobenzofuranylimidazoline compound 7 is the only analogue possessing presynaptic antagonist potency potency and selectivity comparable to that of 1. In view of this result, a number of derivatives was prepared to determine the structure-activity relationships within this series. Many derivatives, as well as the parent compound 7, were found to possess presynaptic alpha 2-adrenoreceptor antagonist and postsynaptic alpha 1-adrenoreceptor partial agonist properties. Two of the selective presynaptic antagonists, 13 and 14 possess greater potency and selectivity than that possessed by 1. The 5-chloro derivative 25 is twice as potent as after oral administration but only about half as potent when given intravenously.

Adrenergic alpha-Antagonists↗
PubMed1984

The ventilatory stress of exercise in obesity.

The effect of obesity as a factor limiting exercise tolerance is described and can be attributed to three mechanisms: (a) the increased metabolic and therefore ventilatory requirement to perform a given work task; (b) the increased metabolic cost of breathing because of interfering chest wall and abdominal obesity and high breathing frequency; and (c) pulmonary insufficiency in response to the high breathing work and lung atelectasis. The role of support and posture minimizing the effect of obesity should be considered when attempting to improve the work tolerance of obese patients. One cannot predict accurately the O2 cost of exercise in the obese patient from the ergometer load because of uncertainties of distribution of the adipose tissue, the uncertain effects on breathing work, and often reduced motor efficiency or skill. The metabolic cost of exercise in the obese patient, therefore, needs to be directly measured; only then can one establish the degree of normality of the physiologic responses to exercise, e.g., heart rate, blood pressure, cardiac output, and minute ventilation.

Humans↗
PubMed1984

Ototoxic and nephrotoxic effects of combined treatment with cis-diamminedichloroplatinum and kanamycin in the guinea pig.

Ototoxic and nephrotoxic potentiation with concomitant cis-diamminedichloroplatinum, or cis-platinum II (CSP), and aminoglycoside therapy was investigated in the guinea pig. We evaluated possible potentiation of the toxic effects of CSP and kanamycin compared with CSP alone in the inner ear and kidney and quantitatively localized CSP in the cochlea with gamma emission analysis of 195mPt. Kanamycin-treated animals demonstrated cytocochleograms and ABR waveforms, absolute latencies, and interwave latencies for waves I, II, and III similar to control animals at our maximum level of acoustic stimulation. CSP treatment produced 60% to 70% mean outer hair cell (OHC) loss in the basal turn of the cochlea, a reduction in ABR waveform and amplitude, and an increase in latencies of ABR waves I, II, and III. Combined CSP and kanamycin treatment produced 90% to 100% mean OHC loss in all rows of the basal turn of the cochlea, with no discernible ABR waveform corresponding to the region stimulated by a 4500 to 7000 Hz acoustic click. Combined treatment produced the most significant cortical medullary tubular necrosis and interstitial nephritis. Furthermore, this study reports for the first time localization of platinum in the inner ear.

Acute Kidney Injury↗
PubMed1983

Increased choline acetyltransferase activity in pressure-overloaded right ventricles of guinea pigs.

Choline acetyltransferase activity, a biochemical indication of parasympathetic innervation, is increased in the hypertrophied right ventricle of guinea pigs after pulmonary artery constriction (PAC). The increase appears to be dependent on the severity and the duration of hypertrophy. This change in choline acetyltransferase activity suggests compensatory changes occur in the parasympathetic innervation of PAC guinea pigs which allows the right ventricle to maintain its level of parasympathetic innervation despite marked hypertrophy. Unlike the right ventricle, the SA node of PAC guinea pigs does not have detectable changes in choline acetyltransferase activity. This model of right ventricular hypertrophy also does not have detectable changes in baroreflex control of heart rate.

Animals↗
PubMed1983

Respiratory reflexes in ventilated premature babies.

The respiratory response to therapeutic lung inflation by artificial ventilation in premature babies has been studied. Both the Hering-Breuer and an augmented inspiratory reflex could be provoked by ventilator inflation in neonates as premature as 25 weeks gestational age. No chemo-receptor control was demonstrated on the presence of these reflexes. Augmented inspirations were only seen in the first five postnatal days regardless of gestational age, but the Hering-Breuer reflex persisted throughout the period of study of 11 days. The frequency of elicitation of augmented inspirations was shown to be inversely related to the dynamic compliance. The relative stimulation of these two respiratory reflexes may explain why some infants are easy to ventilate and others difficult.

Humans↗
PubMed1983

Inner ear pathology associated with Reye's syndrome.

Severe pathological changes were observed in the inner ear tissues of a 2-month-old patient who died of Reye's syndrome after 5 days of hospitalization. In the organ of Corti, the inner hair cells appeared to be more severely damaged than the outer hair cells. Various degrees of degeneration were observed in all non-sensory epithelial cells lining the cochlear duct. In most turns of the cochlear duct, Reissner's membrane was ruptured and/or collapsed onto the organ of Corti. Likewise, both sensory and non-sensory cells of the vestibular end organs were markedly degenerated. These observations suggest that the inner ear tissues are acutely affected in patients with Reye's syndrome, and that the changes may cause impairment of hearing and/or equilibrium in patients who recover.

Acoustic Maculae↗
PubMed1983

Does the gas exchange anaerobic threshold occur at a fixed blood lactate concentration of 2 or 4 mM?

The anaerobic threshold (theta an) is defined as the VO2 at which blood lactate concentration [lactate] begins to systematically increase (lactate "break point") during incremental exercise. Numerous studies have shown that gas exchange break points at the anaerobic threshold correlate highly (r congruent to 0.90) with the lactate break point. Recently, it has been suggested that the anaerobic threshold occurs at a fixed [lactate] of 2 mM or 4 mM. We therefore compared the gas exchange theta an to the three lactate criteria (break point, 2 mM, and 4 mM) for theta an estimation. Fourteen subjects performed an incremental cycle ergometer test. Ventilation and gas exchange were computed every 30 s. During the same 30-s intervals, venous blood was sampled for [lactate]. Four criteria were used for theta an determination: (1) systematic increase in VE/VO2, without a concomitant increase in VE/VCO2; (2) lactate break point; (3) 2 mM [lactate]; and (4) 4 mM [lactate]. Relative to the gas exchange criterion (i.e., #1), theta an was higher by 44, 280, and 1028 ml X min-1 for the three lactate criteria, respectively; the last two being significantly different (P less than 0.05). Thus, the anaerobic threshold discerned from gas exchange or the lactate break point does not correspond with a fixed, absolute [lactate] of 2 mM or 4 mM.

Adult↗
PubMed1983

Effects of beta-adrenergic blockade on ventilation and gas exchange during exercise in humans.

The effects of beta-adrenergic blockade induced by intravenous propranolol hydrochloride (0.2 mg/kg) on ventilatory and gas exchange responses to exercise were studied during tests in which the work rate was either increased progressively or maintained at a constant load in six healthy young male subjects. Heart rate during exercise decreased by about 20% and cardiac output, as estimated by a modification of the method of Kim et al. (J. Appl. Physiol. 21: 1338-1344, 1966), by about 15%. The relation between work rate and O2 uptake (VO2) was unaffected by propranolol, whereas maximal O2 uptake (VO2max) decreased by 5% and the anaerobic threshold, estimated noninvasively, was lowered by 23%. The relations between CO2 output (VCO2) and end-tidal CO2 partial pressure (PCO2) and between VCO2 and minute ventilation (VE) were both unaffected. The time constants for changes of VO2, VCO2, and VE during on-transients from unloaded pedaling to either a moderate (ca. 50% VO2max) or a heavy (ca. 67% VO2max) work rate in the control studies were in agreement with previously reported values, i.e., 42, 60, and 69 s, respectively. beta-Blockade was associated with a significantly increased time constant for VO2 of 61 s but with less consistent and insignificant changes for VCO2 and VE. There was a small but significant increase of the time constant for heart rate from 40 to 45 s. It is concluded that propranolol exerts its primary influence during exercise on the cardiovascular system without any discernible effect on ventilatory control.

Adult↗