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Biomedical subjects

C G Newstead

Publications and source records attributed to C G Newstead.

53 records · Page 3Linked to original sources
PubMed1992

The influence of increased age and age matching on graft survival after first cadaveric renal transplantation.

We examined the influence of donor and recipient age as well as close donor and recipient age matching by analysis of the actuarial survival of 397 consecutive first cadaveric renal transplants carried out in the years 1987 to 1990. Graft failure was defined as return to dialysis, transplant nephrectomy, or death of the recipient from any cause. Overall 1-, 2-, and 3-year actuarial graft survival was 87, 84, and 79%. No effect on graft survival in adult patients was seen of advanced age of either donor or recipient. The source of the donor whether from within or outside the North Western Regional Health Authority did not influence outcome whatever the donor age. Results from patients in whom the donor was within 5 years of the recipient's age were no different from those obtained when the age difference was greater than 5 years. These data do not support the hypothesis that close age matching influences graft survival. Age matching need not be used as a recipient selection criterion. As neither recipient nor donor age influenced early graft survival, consideration should be given to increasing the average age of both donors and recipients.

Adolescent↗
PubMed1990

Potassium as a respiratory signal in humans.

Six renal transplant recipients underwent a series of incremental exercise experiments. Minute ventilation (VE), carbon dioxide production rate (VCO2), and arterial blood chemistry were measured at rest and while subjects exercised on a stationary bicycle. Four of the subjects performed a similar experiment while exercising on a static rowing machine. Within each subject, arterial potassium concentration ([K+]a) was linearly related to VCO2 and VE during exercise. The slope of the relationship between [K+]a and VCO2 was similar in the cycling and rowing experiments. This implies that the absorption of potassium by resting muscle does not significantly limit the arterial hyperkalemia seen during exercise. When VE, VCO2, and [K+]a were measured 1 and 5 min after the end of cycling there was no correlation, whereas VE continued to be closely correlated with VCO2. The relationship demonstrated between change in [K+]a and VCO2 in these experiments is compatible with change of [K+]a acting as a respiratory signal during exercise but not during recovery from exercise in humans.

Adult↗
PubMed1989

Jejunal dialysis in man using mannitol as the perfusate.

In four normal subjects a 50-cm segment of the jejunum was perfused through a multilumen tube with either hypertonic (1300 mOsm/kg) or isotonic mixtures of mannitol and water at rates between 18 and 70 ml/min. There was no difference in the solute clearances produced by the two solutions. Mean clearances (ml/min) were urea 23, creatinine 8, urate 4. Ninety-five mmol of sodium and 3.8 mmol of potassium were removed during a 1-h perfusion period. Clearances of glucose, calcium, phosphate and protein were negligible. Mean free water clearance was 0.5 ml/min during isotonic perfusion and 22.4 ml/min during hypertonic perfusion. These clearances of urea and creatinine are similar to those previously reported during perfusion of the whole bowel in uraemic patients with isotonic mannitol and during segmental jejunal perfusion with glucose/sodium mixtures. Over the range of flow rates studied there was a positive linear relationship between perfusate flow rates might achieve clinically useful solute clearance. However, the efficacy of the method in prolonged perfusion of uraemic patients may be different from that seen in normal subjects.

Acute Kidney Injury↗
PubMed1987

The relationship between ventilation and oxygen consumption in man is the same during both moderate exercise and shivering.

1. Four naïve subjects clothed in protective suits were immersed up to the neck in water on twenty-two occasions, the minimum skin temperature was 20 degrees C and the average skin temperature 26 degrees C. Subjects at first rested, initially demonstrating an increase in thermal muscular tone which did not lead to perceptible limb movements. Later, while resting, visible shivering with small unco-ordinated limb movements supervened. The subjects then exercised while still immersed by stationary cycling. 2. Steady-state minute oxygen consumption (VO2) and minute ventilation (VE) were measured on 152 occasions by timed collection of expired air. 3. The first collection was made at least 5 min after initial immersion. Hyperventilation due to recent immersion in cold water was not demonstrated. 4. The same linear relationship between VE and VO2 was demonstrated whether the increased oxygen consumption was due to shivering alone or to a combination of shivering and exercise. 5. VE was matched to VO2 in spite of an increase in the work of breathing as well as any ventilation-perfusion mismatching as a consequence of head-out water immersion. 6. Minute ventilation was not influenced by the large co-ordinated limb movements which only occurred during exercise. These results reinforce previous findings which have shown that in conscious man VE can be closely matched to VO2 below the anaerobic threshold despite large variations in the type and intensity of limb movements. 7. When VO2 is increased by thermal muscular tone VE is increased in direct proportion in a situation when the limbs are not perceptibly moving at all.

Adult↗
PubMed1986

Effects of fluctuating skin temperature on thermoregulatory responses in man.

Fluctuations in the skin temperature of volunteers in water, of up to +/- 1.5 degrees C, were induced by circulating water through a tube suit at a fluctuating temperature for 80 min. Fluctuations with a cycle length of 2.5, 5.0 or 10.0 min all slowed the fall in core temperature that otherwise occurred in water at 29 degrees C, and reduced thermal comfort. Metabolic rate increased. Symmetrical fluctuations, or ramp fluctuations with either slow cooling and rapid warming phases or slow warming and rapid cooling phases, were all effective. Similar but less clear effects on core temperature were usually produced by fluctuating skin temperature in water at 25 and 33 degrees C; metabolic rate tended to increase during fluctuation in the 25 degrees C experiments, but not in the 33 degrees C experiments. Stability of the temperature of cutaneous receptors appears to be factor in insidious hypothermia produced by immersion in mildly cool water.

Adult↗
PubMed1985

Heat exchanges in wet suits.

Flow of water under foam neoprene wet suits could halve insulation that the suits provided, even at rest in cold water. On the trunk conductance of this flow was approximately 6.6 at rest and 11.4 W . m-2 . C-1 exercising; on the limbs, it was only 3.4 at rest and 5.8 W . m-2 . degrees C-1 exercising; but during vasoconstriction in the cold, skin temperatures on distal parts of limbs were lower than were those of the trunk, allowing adequate metabolic responses. In warm water, minor postural changes and movement made flow under suits much higher, approximately 60 on trunk and 30 W . m-2 . degrees C-1 on limbs, both at rest and at work. These changes in flow allowed for a wide range of water temperatures at which people could stabilize body temperature in any given suit, neither overheating when exercising nor cooling below 35 degrees C when still. Even thin people with 4- or 7- mm suits covering the whole body could stabilize their body temperatures in water near 10 degrees C in spite of cold vasodilatation. Equations to predict limits of water temperature for stability with various suits and fat thicknesses are given.

Adult↗
PubMed1983

The effect of increased lung volume on the expiratory rate of rise of alveolar carbon dioxide tension in normal man.

The rate at which alveolar PCO2 (PA, CO2) rises during expiration has been measured in seven healthy medical students. PA, CO2 rate of rise [delta PA, CO2/delta t] was measured by a method utilizing constant expiratory flow rates in individual breaths in two subjects, and was calculated from airway PCO2 and expiratory tidal volume in the remaining five subjects. Steady-state runs were recorded at two or more metabolic rates with the subject making no special effort to control mean lung volume. This was done to establish the relationship between delta PA, CO2/delta t and the rate of CO2 production (VCO2) at normal lung volume in individual subjects. Steady-state runs were also recorded at high lung volume. In each subject delta PA, CO2/delta t was less than would have been obtained at normal lung volume. Inversion of a hypothetical relation between delta PA, CO2/delta t, VCO2 and average lung volume (VLa; DuBois, Britt & Fenn, 1952) yielded calculated values of VLa for both the normal and the high lung volume states. Lung gas volume was measured in a whole body plethysmograph, ('box volume') both for the normal and high lung volume states, in each subject. Mean VLa and 'box volume' estimates showed only moderately good agreement, whereas the estimated differences between normal and high lung volume obtained by the two methods were virtually identical. These experiments suggest that the expiratory PA, CO2 rate of rise is determined, in the steady state, partly by the rate of CO2 production (a directly proportional relationship) and partly by the mean lung volume (an inversely proportional relationship).

Carbon Dioxide↗
PubMed1982

The rate of rise of alveolar carbon dioxide pressure during expiration in man.

1. The purpose of the study was to see whether the rate of rise of alveolar PCO2 (PA, CO2) in expiration was directly proportional to the rate of pulmonary elimination of CO2 (VCO2) in man in the steady state. 2. Alveolar ventilation at rest and during exercise in man was calculated from the difference between total ventilation and dead space ventilation, and from the ratio of the rate of pulmonary CO2 elimination to the mean expired alveolar CO2 (total) fraction. The results were indistinguishable. In agreement with other workers' findings alveolar ventilation changed in direct proportion to the rate of carbon dioxide elimination, confirming the isocapnia of exercise ventilation in man. 3. The rate of rise of expiratory alveolar PCO2 in individual breaths has been obtained by two methods. In the first, a pattern of respiration with constant expiratory flow in each breath brought expiratory alveolar profiles to the outermost end of the airway. In the second method, the early part of the alveolar PCO2 during normal expiration was calculated from airway PCO2 and expired volume. 4. The data obtained with both methods show that, in the steady state, expiratory alveolar PCO2 rises at a rate which is directly proportional to the rate of CO2 production.

Carbon Dioxide↗
PubMedDate not supplied

Estimation of total daily creatinine clearance in CAPD from serum creatinine concentration.

OBJECTIVE: To establish whether estimation of creatinine clearance (CrCl) from serum creatinine, gender, age, and weight might reduce the number of 24-hour urine and dialysate collections required to monitor adequacy of delivered dialysis on continuous ambulatory peritoneal dialysis (CAPD). DESIGN: Retrospective single-center study. SETTING: University Hospital. PATIENTS: Creatinine excretion and CrCl were measured in 187 24-hour urine and dialysate collections from 99 CAPD patients (55 male, 44 female). Multiple regression analysis was used to estimate creatinine excretion from age and weight in males and females. CrCl was derived and also calculated using the Cockcroft-Gault and Mitch-Walser formulas. Positive and negative predictive values for indicating adequacy of dialysis were determined. RESULTS: Measured and derived CrCl were correlated (males: r = 0.85; females: r = 0.83; p < 0.001), but agreement was poor (95% limits of agreement: males, 26.05 to -25.75 L/wk; females, 37.47 to -19.49 L/wk). Taking the minimum acceptable CrCl as 60 L/week, the respective positive predictive values of the derived, Cockcroft, and Mitch methods in predicting underdialysis were 88%, 100%, and 100% in males and 88%, 88%, and 89% in females. Negative predictive values were 83%, 57%, and 53% in males and 53%, 48%, and 45% in females. CONCLUSION: A derived CrCl > 60 was not predictive of adequate dialysis. Because the detection of underdialysis is our objective, formal clearance studies should be performed in this group. A derived CrCl < 60 L/wk was predictive of underdialysis in males and females and an increase in dialysis dose without formal clearance measurements could be suggested in these patients. The use of this approach could allow an important reduction in the number of clearance studies required to monitor CAPD adequacy.

Adult↗