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Biomedical subjects

M Lye

Publications and source records attributed to M Lye.

At least 73 records · Page 4Linked to original sources
PubMed1984

Electrolyte disorders in the elderly.

Normal human ageing impairs homeostatic mechanisms in such a way as to exaggerate and prolong the effects of stress. Thus, an event--pathological or traumatic--which produces a trivial change in plasma electrolytes of young people may produce major oscillations of plasma levels in the elderly, which take much longer to return to 'normal levels'. This is especially apparent with perturbations in the plasma levels of sodium and potassium, mainly due to changes in renal function and neurohumeral mechanisms which occur with increasing age. Paradoxically this does not mean that the clinician should be over-enthusiastic in attempting to correct electrolyte imbalance because, for the same reasons, the danger of over-treatment producing the opposite and equally dangerous electrolyte imbalance is ever-present. Indeed, in clinical practice most electrolyte disturbances in old age are iatrogenic in origin. Cautious patience and vigilance should be the clinical approach with elderly patients. A high index of suspicion should lead to a careful appraisal of the drug (diuretic, intravenous fluid) and environmental (dehydration) aetiology of most electrolyte disturbances in old age.

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PubMed1984

Plasma arginine vasopressin in dehydrated elderly patients.

Plasma arginine vasopressin was assessed by radioimmunoassay in dehydrated elderly patients and healthy young and elderly control subjects. The elderly control subjects' AVP levels were higher than the young control subjects (Kruskal-Wallis rank sums z = 3.29; P less than 0.001). Despite similar plasma osmolalities, after correction for the osmotic contribution of urea, the patients' AVP levels were higher than the elderly controls (z = 4.16; P less than 0.001) and were in the range reported to evoke a maximal antidiuretic response. It is concluded that the dehydration which often accompanies acute illness in the elderly is not primarily a consequence of inadequate AVP release.

Adult↗
PubMed1984

The measurement of plasma noradrenaline before and after tilt in young and old healthy subjects.

Using a modified sensitive and specific radioenzymatic method we have determined the normal range for plasma noradrenaline in healthy, elderly individuals. The effects of tilt on the cardiovascular system and on plasma noradrenaline responses were found to be different compared with healthy young controls. The elderly had higher resting plasma noradrenaline concentrations with an exaggerated response to head-up tilt. In spite of this higher sympathetic drive, the cardiovascular responses in the elderly were attenuated.

Adult↗
PubMed1983

Patterns of urine flow and electrolyte excretion in healthy elderly people.

Twenty four young (mean age 29.2 years, range 25-35) and 21 elderly (mean age 66.5, range 60-80) healthy subjects collected their urine in timed aliquots over 24 hours. The elderly subjects had been selected for their fitness by clinical and laboratory examinations and all lived independently at home. Sodium and potassium excretions were reduced in the elderly subjects compared with the young subjects, potassium excretion considerably so. This was despite similar 24 hour urine volumes and total solute excretion by both groups. The ratios of rates of excretion of water, electrolytes, and solutes during the night to the rates of excretion during the day were found to be higher in the elderly than the young subjects. Reduced day to night ratios of urinary excretion may be partly responsible for complaints of nocturia and sleep disturbance in elderly people.

Adult↗
PubMed1983

Indican excretion in the elderly.

It has been suggested that up to a half of elderly hospitalized patients excrete an abnormally high concentration of indican compared with young individuals. Thus, the commonly used colorimetric qualitative test for urinary indican excess may be invalid in the aged. However, of 21 young control subjects, 18 healthy elderly subjects, and 23 disabled, elderly, long-stay patients, no individual had levels of indican detectable by the standard colorimetric qualitative test. The use of a quantitative assay demonstrated that urinary indican concentration is similar in young and elderly individuals. A diurnal variation in urinary indican concentration was discovered which may affect the interpretation of the qualitative test.

Adult↗
PubMed1983

A longitudinal study of the prognostic significance of ventricular ectopic beats in the elderly.

The prognostic significance of ventricular ectopic beats occurring in healthy, elderly individuals has only been assessed previously in short-term, longitudinal studies. 30 healthy, elderly people underwent 24-hour ambulatory electrocardiographic monitoring and approximately 2.5 years later subsequent morbidity and mortality was assessed. 1 individual could not be traced and 4 had died. Details of the cardiovascular health status of the remaining 25 were assessed by a questionnaire. There was no correlation between the numbers of ventricular ectopic beats and subsequent cardiovascular morbidity. Similarly, the results show no differences between ventricular ectopic beat activity and mortality 2.5 years later. On the basis of this study it is concluded that routine 24-hour ambulatory ECG monitoring does not provide clinically relevant predictive information in regard to cardiovascular morbidity or mortality.

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PubMed1982

Physiological responses to postural change in young and old healthy individuals.

The cardiovascular responses to 70 degrees head-up tilt were compared in 9 healthy young, mean age 31 +/- (S.D.) 3.2 years, and 8 healthy elderly subjects, mean age 71 +/- 5.1 years. After 10 minutes tilt, qualitatively similar responses were found in the two groups. Quantitatively, however, heart rate, stroke volume, cardiac output, and peripheral resistance showed smaller differences between the supine and tilt positions in the older group. Blood pressure and plasma volume changes were similar in both groups. There is an age-associated effect in the cardiovascular response to change in posture in healthy people that resembles that found in congestive cardiac failure.

Adult↗
PubMed1982

The prediction of body potassium in the elderly.

Whilst there are many regression formulae in the literature from which a predicted or expected value of body potassium can be calculated, different formulae give widely differing results. Several of these algorithms have been developed by estimating body potassium from exchangeable measurements which are not valid in most clinical situations. Those derived from studies of direct body-potassium measurement from whole-body counting have included few females or older persons--the very group likely to suffer disease-produced changes in potassium homeostasis. Eleven male and 11 female carefully screened healthy adults (mean agd 75, range 65-90 years) have been used to develop new formulae. It is shown that within this age range body potassium can be predicted from body weight to within +/- 20.4% in males and +/- 15.1% in females. These new relationships should be used in clinical practice for elderly patients.

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PubMed1982

Body potassium content and capacity of elderly individuals with and without cardiac failure.

Without some measure of potassium capacity it is impossible to determine whether an individual is potassium depleted or not. Whilst weight is a useful measure of capacity in some circumstances, it is less than adequate in elderly individuals wih chronic cardiac failure. Whole body potassium has been measured in 139 patients with oedema free cardiac failure, mean age 78 years, and the results compared with those obtained in 22 healthy age-matched subjects. The results show that male and female patients have lower (94 and 91% respectively) absolute whole body potassium levels than the healthy controls though the difference are only statistically significant in females. If the body potassium results are related simply to body weight the patients are 20 and 23% depleted whereas if height is used in a regression with weight they can be considered as being 12 and 16% depleted. When the body potassium results are related to fat-free mass then the cardiac patients results are only 1 and 2% less than the healthy controls. Thus, the "potassium depletion" of patients with cardiac failure reported by others may be more a reflection of weight change rather than true cation depletion. It is concluded that fat-free mass measured from skin fold thickness is a valuable measure of potassium capacity in oedema free elderly patients with cardiac failure. The results suggest that any potassium depletion in such patients is minimal and clinically irrelevant.

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PubMed1982

Can body potassium of old people be predicted from anthropometric data?

Body potassium was measured by whole body counting in a group of carefully screened healthy individuals, mean age 75 years. The results have been compared with values predicted by eight formulae in the literature derived using similar methods. The mean predicted results ranged from 87% to 102% of the mean observed level in male subjects and from 87% to 137% in female subjects. Individual male results range from 55% to 123% and in female subjects from 72% to 146% of the observed value. It is concluded that there are no published formulae which will adequately predict whole body potassium levels in old people--the very group likely by virtue of age-related disease, to need measurements of body potassium.

Age Factors↗
PubMed1981

Distribution of body potassium in healthy elderly subjects.

The whole body potassium content of a group of carefully screened, healthy, elderly subjects, mean age 73.5 years, has been accurately measured. The mean content was found to be approximately 10% lower than expected though there was a considerable range of individual values. Some of the interindividual variability could be reduced by taking into account body weight, height and in particular fat-free mass. The ratio of whole body potassium to fat-free mass (52.4 +/- 6.7 mmol/kg) was exceptionally low in this healthy group and showed no sex difference.

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PubMed1981

An analysis of impedance cardiography in the elderly.

Non-invasive impedance cardiography has been used to assess cardiac response to postural stress in old people but the results have been conflicting. We have statistically studied the responses of two groups of elderly people (healthy and with postural hypotension) and compared results with those obtained in a young group of controls. We conclude that with suitable precautions this inexpensive method is both reproducible and satisfactory in practice.

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PubMed1979

Whole body potassium and total exchangeable potassium in elderly patients with cardiac-failure.

Body potassium status of patients with cardiac failure may be estimated by a number of methods, but increasing reliance is being placed upon radioisotope dilution with 42K which measures the total exchangeable potassium. Total exchangeable potassium comprises between 86 per cent and 97 per cent of whole body potassium in healthy subjects. We have measured total exchangeable potassium in 22 oedema-free elderly patients with stable cardiac failure and compared the results with simultaneously determined measurements of whole body potassium obtained by whole body counting. The mean whole body potassium was 2360 +/- 640 mmol. The mean value of total exchangeable potassium measured at 24 hours was 1820 +/- 610 mmol (77% of whole body potassium) and increased further to 2000 +/- 600 mmol (84%) when measured after 48 hours. In patients with cardiac failure and, perhaps, also other patients with a history of fluid retention, the mixing of a tracer dose may be significantly delayed, which if not appreciated may lead to an overestimate of potassium depletion.

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