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Biomedical subjects

G C Bond

Publications and source records attributed to G C Bond.

At least 19 recordsLinked to original sources
PubMed1988

Effect of arteriovenous shunting on plasma vasopressin levels in the anesthetized dog.

Studies were performed in dogs anesthetized with chloralose to establish the plasma arginine vasopressin (AVP) response to 30-minute periods of femoral arteriovenous (AV) shunting at levels of either 10%, 30%, or 50% of control cardiac output. Significant increases in cardiac output, heart rate, and total body peripheral resistance (shunt resistance excluded), suggesting decreased sinoaortic baroreceptor activity, occurred at shunt fractions greater than 10%. There were no significant changes in plasma concentrations of AVP at any level of AV shunting. In separate studies, significant elevations in plasma AVP levels were observed in vagotomized dogs during AV shunting of 50% of control cardiac output. These results indicate that AV shunting less than or equal to 50% of cardiac output does not acutely alter plasma AVP levels in the intact dog and that cardiopulmonary receptors with vagal afferents suppress AVP release that might otherwise occur in this canine model of AV shunting.

Anesthesia↗
PubMed1983

Role of renal nerves in mediating the increased renin secretion during continuous positive-pressure ventilation.

The effect of renal denervation on the increase in plasma renin levels during continuous positive-pressure ventilation (CPPV) was studied in anesthetized dogs. Renin secretion was measured in a group of dogs with intact renal nerves and a group which had previously undergone bilateral renal denervation. Renal perfusion pressure was maintained constant throughout the experiment. Renin secretion increased significantly during application of CPPV with a positive and expiratory pressure of 10 cm water in the dogs of the intact group but was not altered in dogs of the denervated group. These results support the conclusion that CPPV increases renin secretion by reflexly altering renal nerve activity.

Animals↗
PubMed1980

Role of sinoaortic baroreceptors in initiating the renal response to continuous positive-pressure ventilation in the dog.

Experiments were conducted to determine the role of cardiopulmonary receptors with vagal afferents and sinoaortic baroreceptors in initiating the reflex antidiuresis and antinatriuresis during continuous positive-pressure ventilation (CPPV). CPPV was applied to 18 dogs: seven control, five that underwent bilateral vagotomy; and six that underwent sinoaortic baroreceptor denervation. The dogs were anesthetized with pentobarbital, paralyzed with succinylcholine, and their lungs were mechanically ventilated with a volume ventilator. Renal function and systemic hemodynamics were monitored by clearance methods and pressures, respectively. After two 30-min control periods of intermittent positive-pressure ventilation (IPPV), CPPV using 10 cm H2O positive end-expiratory pressure was applied for two 30-min experimental periods. Three 30-min recovery periods of IPPV followed. In dogs of the control group and vagotomy group, CPPV caused statistically significant decreases from control levels in urinary flow, sodium excretion, and glomerular filtration rate. However, in the dogs of the sinoaortic baroreceptor denervation group, CPPV did not produce any significant change in these variables. Therefore, the results do not support the hypothesis that cardiopulmonary receptors mediate the renal response to CPPV. Rather, the data indicate that the aortic arch and carotid sinus baroreceptors participate in initiating the reflex antidiuresis and antinatriuresis during CPPV.

Animals↗
PubMed1975

Integration of chemoreceptor stimuli by rostral brainstem respiratory areas.

Ventilatory regulation by brainstem sites rostral to the midpontile level was assessed in decerebrate cats by comparing the effects of punctate pneumotaxic center lesions with those of midpontile transection. After either procedure, PACO2 was significantly elevated. Moreover an equal suppression of hypercapnia-induced minute volumes and maintenance, at some PACO2 levels, of minute volume responses to hypoxia was observed. Tidal volume elevations accounted for the maintenance of hypoxia-induced minute volumes. Following pneumotaxic center lesions, hypercapnia-induced tidal volumes were higher than those exhibited subsequent to midpontile transection. After carotid sinus nerve section, PACO2 was elevated and hypoxia-induced alterations were abolished. Bilateral vagotomy resulted in apneusis. These data demonstrate that, in the brainstem area examined, only the pneumotaxic center influences the PACO2 level or set point for respiratory activity. A locus of tidal volume generation is ascribed to rostral brainstem sites outside this pneumotaxic center. Data obtained support the hypothesis of a differential brainstem integration of peripheral and central chemoreceptor afferent stimuli.

Animals↗
PubMed1975

Atrial receptors and renal function.

The hypothesis that receptors in the heart or pulmonary vasculature initiate a reflex that influences urine flow was derived from experiments designed to evaluate the effect of mechanical ventilation on renal function. These experiments indicated that urine flow usually decreases during positive-pressure breathing and usually increases during negative-pressure breathing. It was surmised that impulses from certain cardiopulmonary receptors affect the secretion of ADH, which in turn influences urine flow. A subsequent investigation appeared to localize the pertinent receptors to the left atrium, but the results of this particular investigation were influenced by several complication factors that have not been widely appreciated. The apparent localization of volume-regulating recpetors to the left atrium and the accumulating evidence that atrial receptors do respond to changes in atrial pressure or atrial volume triggered a myriad of further studies on the function of left receptors. Nearly all these studies employed indirect techniques that produced changes in systemic and pulmonary hemodynamics in addition to changes in left atrial pressure. Nevertheless, it often was assumed that if changes in left pressure were produced, any concomitant changes in circulating ADH or in urine flow were attributable to a reflex elicited from atrial receptors. Mush of the data obtained were interpreted as being compatible with the elft atrial volume-receptor hypothesis, but very liggle of the data pertained to left atrial receptors specifically.

Animals↗
PubMed1970

Suspended matter in surface waters of the Atlantic continental margin from Cape Cod to the Florida Keys.

Appreciable Amounts Of suspended matter (> 1.0 milligram per liter) in surface waters are restricted to within a few kilometers of the Atlantic coast. Particles that escape estuaries or are discharged by rivers into the shelf region tend to travel longshoreward rather than seaward. Suspended matter farther offshore, chiefly amorphous organic particles, totals 0.1 milligram per liter or less. Soot, fly ash, processed cellulose, and other pollutants are widespread.

Filtration↗