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Biomedical subjects

P Collett

Publications and source records attributed to P Collett.

8 recordsLinked to original sources
PubMed1991

Diaphragmatic fatigue produced by constant or modulated electric currents.

In anesthetized rabbits the efficiency of phrenic nerve stimulation with trains of electric current was studied either when ventilation was effected entirely by bilateral nerve stimulation (electrophrenic ventilation) or during unilateral nerve stimulation when animals were ventilated with a pump and open chest. Trains of rectangular electric pulses (RPT) with constant amplitude and frequency or sine waves, both the amplitude and frequency of which were modulated and controlled by a computer (MSWT), were used with each animal. MSWT closely reproduced the physiological shape of transdiaphragmatic pressure waves. Diaphragm fatigue, as determined from the decrease in the maximal relaxation rate of twitches, occurred after 20 minutes of bilateral or unilateral nerve stimulation with RPT, but only after 60 min (unilateral stimulation) or 98 min (bilateral stimulation) with MSWT. These data show the importance of the motor signal pattern in long-lasting nerve stimulation.

Animals↗
PubMed1988

Relationship among EMG and contractile responses of the diaphragm elicited by hypotension.

In a canine model, we investigated the effects of severe hypotension on the indexes of diaphragmatic failure. We measured 1) the transdiaphragmatic pressure obtained in response to 20- and 100-Hz stimulation of phrenic nerves (Pdi20 and Pdi100), 2) the power spectrum of diaphragmatic electromyogram (EMG), 3) the ratio of integrated diaphragmatic EMG to Pdi (Edi/Pdi), and 4) the rate of relaxation of Pdi100 and Pdi20. Arterial blood pressure (Pa) was reduced to 40-50 mmHg by a balloon inflated in the inferior vena cava and was maintained at this level until Pdi100 declined to 75% of the control value (100% shock time, ST). A recovery period of 60 min at normal Pa was allowed. During hypotension, Pdi100 and Pdi20 declined only at 100% ST [95.0 +/- 13.0 (SE) min]; however, only Pdi100 recovered within 15 min. The power spectrum shifted to low frequencies early and progressively during shock period. Edi/Pdi rose significantly at 80 and 100% ST and recovered within 15 min. The relaxation rate of Pdi20 and Pdi100 increased significantly at 100% ST only. We conclude that 1) diaphragmatic contractility is depressed during severe hypotension, 2) changes in the power spectrum occurred first in the shock state, followed by alterations in Edi/Pdi, and subsequently both changes in the frequency-pressure curve and relaxation rate occurred last.

Animals↗
PubMed1985

Treatment of hemodialysis bone disease with 24,25-(OH)2D3 and 1,25-(OH)2D3 alone or in combination.

We studied the effects of vitamin D metabolites in 29 patients established on chronic hemodialysis. The patients were divided into four groups; one was treated with 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3] 0.5 microgram/day, one with 24R,25-dihydroxyvitamin D3 [24,25-(OH)2D3] 10 micrograms/day, and one with both metabolites. The control group was not given vitamin D. Plasma levels of both metabolites were low before treatment. 1,25-(OH)2D3 levels became normal, and 24,25-(OH)2D3 increased to supranormal levels after administration of the corresponding metabolite. Combined treatment produced still higher plasma levels of 24,25-(OH)2D3, suggesting an interaction between the two metabolites. Patients receiving 1,25-(OH)2D3 alone had a greater increase in plasma calcium than those receiving both metabolites. In control patients, hyperparathyroid bone disease worsened over the 10-month observation period. 1,25-(OH)2D3 improved hyperparathyroid bone disease in most patients, as reflected by a reduction in osteoclast and osteoblast numbers, but had no demonstrable effect on mild osteomalacia. 24,25-(OH)2D3 had no significant effect on plasma biochemistry or bone histology, and the effect of combined treatment on histology was similar to that of 1,25-(OH)2D3 alone. Stainable bone aluminum increased slightly in patients given 1,25-(OH)2D3, but aluminum did not affect the response to treatment. We conclude that 1,25-(OH)2D3 is a useful agent in the treatment of renal bone disease, but no therapeutic role is apparent for 24,25-(OH)2D3.

24,25-Dihydroxyvitamin D 3↗
PubMed1985

The pathogenesis of renal osteodystrophy: role of vitamin D, aluminium, parathyroid hormone, calcium and phosphorus.

Biochemical data and bone histology from 44 haemodialysis patients was compared using an histologic technique capable of evaluating separately the individual components of osteodystrophy. Hyperparathyroid bone disease was diagnosed by an elevated osteoclast count, and in advanced disease there was also fibrosis and woven bone. Osteomalacia, defined as an impairment in the rate of bone mineralisation, was present in two distinct forms: osteomalacia type I, characterised by wide osteoid seams, and osteomalacia type II, characterised by extensive thin, inactive osteoid. The histologic diagnoses were hyperparathyroid bone disease (15), osteomalacia type I (3), osteomalacia type II (6), hyperparathyroid bone disease and osteomalacia type I (12), hyperparathyroid bone disease and osteomalacia type II (6), normal (2). Aluminium was evident histochemically in 17 biopsies. Vitamin D metabolite levels were low in most patients and did not correlate with any biochemical or histological parameter. Parathyroid hormone levels were highly correlated with histological features of hyperparathyroid bone disease, and also correlated with plasma calcium, suggesting a degree of autonomy of parathyroid hormone secretion. Urea and creatinine were higher in the hyperparathyroid bone disease than the osteomalacia groups suggesting that poor dialysis contributes to the former. Statistical analysis showed that osteomalacia type I was associated with relatively low plasma calcium and phosphorus levels; osteomalacia type II was associated with increased bone aluminium and with the uraemic process itself, as reflected in the plasma creatinine level. This study shows relationships between renal osteodystrophy and plasma calcium and phosphorus levels, but no relationship with vitamin D metabolites. Aluminium appears to impair mineralisation even at relatively low levels of accumulation. However there are other unidentified factors associated with the uraemic process, contributing to all three components of renal osteodystrophy.

Adult↗
PubMed1979

Labetalol and bendrofluazide: comparison of their antihypertensive effects.

A randomized double-blind crossover trial of labetalol, bendrofluazide and placebo was carried out in 18 patients with mild to moderate hypertension. The reduction in blood pressure observed with labetalol and bendrofluazide was similar. The plasma levels of labetalol showed a significant correlation with changes in blood pressure (r = 0.07; P less than 0.021); and plasma level determinations of this drug may be of value in the management of patients who receive antihypertensive agents.

Adult↗