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Biomedical subjects

J A Davis

Publications and source records attributed to J A Davis.

At least 19 recordsLinked to original sources
PubMed1979

Case report 84.

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Aged↗
PubMed1979

Mechanism of the isoproterenol hyperpnea in the cat.

To clarify the role of peripheral chemoreceptors in the abrupt hyperpnea induced by isoproterenol injection, we measured, in anesthetized cats, the time course of VE, PETCO2, H.R. and B.P. following i.v. bolus injection of 0.5--2 microgram isoproterenol before and after bilateral section of the carotid sinus (csx), aortic (ax) and vagus (vx) nerves. We compared the hyperpneic response of isoproterenol to that of 100 microgram injections of NaCN (CN), a drug known to stimulate peripheral chemoreceptors, during air and 100% O2 breathing. The ventilatory response to isoproterenol persisted for over 90 s, whereas the CN response lasted only 30 s. Also 100% O2 markedly attenuated the CN hyperpnea but had little effect on the ventilatory response to isoproterenol. The maximum increase in ventilation in response to isoproterenol was reduced by approximately 1/3 by csx, 1/2 by combined csx and ax, and 2/3 by combined csx, ax and vx. The residual hyperpnea after csx, ax, and vs is delayed in time and lagged behind the increase in PETCO2. It is concluded that the peripheral chemoreceptors and possibly vagal afferents play a major role in the hyperpnea caused by isoproterenol, but in their absence central chemoreceptors respond to the increased PaCO2 induced by the elevated cardiac output to stimulate ventilation.

Animals↗
PubMed1979

Anaerobic threshold alterations caused by endurance training in middle-aged men.

Nine previously sedentary middle-aged males underwent cycle endurance training 45 min/day for 9 wk with an average attendance of 4.1 days/wk. Seven males served as controls. Before and after the training period, the subjects performed three cycle ergometer tests. Work rate was incremented by 15 W/min, to the limit of the subjects' tolerance, in the first two tests; the third test consisted of contant-load cycling at an O2 uptake (VO2) just below the pretraining anaerobic threshold (AT). After training, the AT increased significantly by 44%, expressed as absolute VO2, and by 15%, expressed relative to VO2 max. Significant increases were also noted in VO2max (25%), maximal minute ventilation (19%), and maximal work rate (28%). The test-retest correlation coefficients for the AT (%VO2max) were 0.91, pre- and posttraining. Training did not alter steady-state VO2 during the submaximal exercise test whereas significant decreases occurred in CO2 output, VE, respiratory quotient, and VE/VO2. No changes occurred in the control subjects during this period. These results demonstrate that the AT is profoundly influenced by endurance training in previously sedentary middle-aged males.

Adult↗
PubMed1979

Peripheral chemoreceptors and exercise hyperpnea.

The carotid bodies appear to be the only peripheral chemoreceptors mediating ventilatory control during exercise in man. While little is known about the mechanism of stimulation, much is known about the effects of carotid body stimulation upon pulmonary ventilation (VE). These effects have been produced by hypercapnia, hypoxia, metabolic acidosis, arterial blood pressure, temperature, and catecholamines. A signal from CO2 flow is attractive because of the strong correlation between CO2 output and VE during exercise. The carotid body's role in the hyperpnea depends on the intensity of exercise. During heavy exercise, pH falls and hyperventilation ensues. The carotid bodies appear to be the exclusive mediators of the ventilatory compensation for the acidosis at this exercise intensity. For moderate exercise, mean arterial PCO2 does not change. Therefore, how is the CO2 signal transmitted to the respiratory center? Two current theories are: (1) since arterial PCO2 and pH oscillate with each breath, the amplitude and period of these oscillations may change during exercise and may be of sufficient magnitude to stimulate the carotid bodies, and (2) there exists a disequilibrium between hydrogen ion activity within the red blood cell and in the plasma because carbonic anhydrase is found in the former but not the latter. This theory assumes that the enzyme is not accessible to the plasma.

Aortic Bodies↗
PubMed1979

Validation of a bench stepping test for cardiorespiratory fitness classification of emergency service personnel.

Field tests are used in many occupations to screen and classify personnel for cardiorespiratory fitness. Presumably these tests yield predictive results which correlate well with maximal oxygen uptake (VO2 max), the most widely-accepted criterion of cardiorespiratory fitness. The purpose of this study was to validate one of the most popular field tests, the modified Kasch Pulse Recovery Step Test (KPRST), used by several emergency service agencies in Southern California. One hundred fourteen male state traffic officers from the California Highway Patrol, ranging in age from 24 to 56 years, performed treadmill VO2 max tests to volitional fatigue and the modified KPRST. Heart rates taken during the first and last 10 seconds of the one-minute recovery period for the modified KPRST compared against treadmill VO2 max values yielded correlations of --0.25 and --0.27, respectively, indicating that the modified KPRST is a poor predictor of cardiorespiratory fitness for the population studied. These results suggest that agencies should carefully validate any predictive measure of cardiorespiratory health and performance before adopting that measure for screening purposes and cardiorespiratory classification.

Adult↗
PubMed1978

Vascular disease in infective endocarditis. Report of immune-mediated events in skin and brain.

A patient with subacute bacterial endocarditis, who had a prosthetic mitral valve, exhibited hypocomplementemia, mixed (IgG, IgM) cryoglobulinemia, and widespread dermal vasculitis with IgM deposited at the dermoepidermal junction. Postmortem findings included immune-complex glomerulonephritis and deposits of IgG in the choroid plexus. These findings are consistent with a generalized vasculitis, which may be mediated by circulating immune complexes; basement membrane localization of immune complexes to the skin and choroid plexus appears not to be specific for systemic lupus erythematosus, as has been previously thought, but may represent the general phenomenon of immune-mediated pathogenesis.

Adolescent↗
PubMed1978

Infantile spasms in Down syndrome: a report of 5 cases and review of the literature.

Five patients with Down syndrome (DS) and infantile spasms were examined in a four-year interval. Previous reports of this association have been infrequent except during experimental treatment with 5-hydroxytryptophan, a precursor of serotonin. Malformations of the brain in DS are associated with an increased incidence of epilepsy, and both gross and cytoarchitectural anomalies have been described. The severity and distribution of these central nervous system anomalies presumably predispose to the infantile spasms. The contribution of altered serotonin metabolism is uncertain.

5-Hydroxytryptophan↗