Delay in centrifugation and measurement of serum constituents in normal subjects

It is a fairly common practice to issue biochemical results of multichannel analysers containing many analytes, irrespective of the number of tests requested by the physician. Abnormal results in such profiles may occur from presentation of artefacted blood samples; it is sometimes not possible to differentiate the abnormality arising as a result of pathological process from that due to a poor sample quality. In this study normal volunteers were studied to examine changes occurring when centrifugation was delayed for a few hours to a few days. Analyses on stored serum samples over the same period were also studied. If haemolysis is present, lactate dehydrogenase (hydroxybutyrate dehydrogenase), aspartate transaminase, potassium, chloride, bicarbonate, phosphate and creatinine estimations are not valid. Accurate data, however, can be obtained on sodium, urea, proteins, albumin, alkaline phosphatase and gammaglutamyl transferase. The very concept of efficient and cost-effective testing by multichannel profiles may generate further unnecessary investigations with a consequent waste of health service resources if pre-analytical factors are not taken into consideration.     

Plasma ammonia is the principal source of ammonia in sweat

Sweat contains ammonia. However, neither its source nor factors affecting its concentration in the sweat are known. The aim of this study was to examine the effect of plasma concentrations of ammonia and urea on the concentration of ammonia in the sweat. Four groups of male volunteers were examined: one control, two after ingestion of ammonium chloride, three cirrhotic, hyperammonaemic, four uraemic. Sweat was collected from each subject from the palmar side of the forearm using gauze pads, after previous iontophoresis of pilocarpine. Ammonia and urea concentrations were determined in the sweat and in the plasma. It was found that elevated plasma ammonia concentration in healthy subjects after ingestion of ammonium chloride as well in the cirrhotic patients resulted in an increase of ammonia concentration in the sweat. High plasma and sweat urea concentration in the uraemic subjects did not affect the concentration of ammonia in the sweat. It was concluded that plasma ammonia was the principal source of ammonia in the sweat.     

Heart rate analysis in normal subjects of various age groups

Background  

Analysis of heart rate variation (HRV) has become a popular noninvasive tool for assessing the activities of the autonomic nervous system (ANS). HRV analysis is based on the concept that fast fluctuations may specifically reflect changes of sympathetic and vagal activity. It shows that the structure generating the signal is not simply linear, but also involves nonlinear contributions. Linear parameters, Power spectral indice (LF/HF) is calculated with nonlinear indices Poincare plot geometry(SD1,SD2), Approximate Entropy (ApEn), Largest Lyapunov Exponent (LLE) and Detrended Fluctuation Analysis(DFA). The results show that, with aging the heart rate variability decreases. In this work, the ranges of all linear and nonlinear parameters for four age group normal subjects are presented with an accuracy of more than 89%.     

Parameters of somatosensory evoked potentials in normal subjects in relation to age and height

Cortical SEPs by stimulation of median nerve at wrist (159 measurements; 144 subjects, 63 M - 81 F; mean age 39.7, range 11-70; mean height 162.5, range 134-190) and cortical SEPs by stimulation of posterior tibial nerve at ankle (100 measurements; 81 subjects, 37 M - 44 F; mean age 34.7, range 11-60; mean height 161.1, range 134-180 cm) have been performed. The latencies of N1 of median SEPs and of N1 and P1 of tibial SEPs significantly increase with the height of subjects. The statistical evaluation of latency values of each subject normalized at a height of 165 cm show a little increase of latency according to the age of the subjects; this increase is quite evident for the latency of P1 of tibial SEP.     

Total fasting and postprandial serum bile acids determination by 3 alpha-hydroxysteroid dehydrogenase in normal subjects

Total serum bile acids (SBA) have been evaluated in 28 healthy subjects by an enzymatic-fluorimetric method using the enzyme 3 alpha-hydroxysteroid dehydrogenase. The healthy subjects showed a value of 2.78 +/- 1.84 microM/1 (mean +/- SD), ranging 0.5 to 4.7 microM/1. In addition, two hours postprandial evaluation of SBA was carried out in five of the above subjects. The mean value of SBA before and after the meal was 2.58 +/- 1.4 and 8.73 +/- 1.7 microM/1 respectively and the postprandial increase was found statistically significant (P less than 0.001). The present method for quantitative determination of SBA seems to be sensitive, reliable and useful as a routine clinical aid.     

Effects of short-term exercise in the heat on thermoregulation, blood parameters, sweat secretion and sweat composition of tropic-dwelling subjects

This study investigates the effects of a short-term aerobic training program in a hot environment on thermoregulation, blood parameters, sweat secretion and composition in tropic-dwellers who have been exposed to passive heat. Sixteen healthy Malaysian-Malay male volunteers underwent heat acclimation (HA) by exercising on a bicycle ergometer at 60% of VO2max for 60 min each day in a hot environment (Ta: 31.1+/-0.1 degrees C, rh: 70.0+/-4.4%) for 14 days. All parameters mentioned above were recorded on Day 1 and at the end of HA (Day 16). On these two days, subjects rested for 10 min, then cycled at 60% of VO2max for 60 min and rested again for 20 min (recovery) in an improvised heat chamber. Rectal temperature (Tre), mean skin temperature (Tsk) heart rate (HR), ratings of perceived exertion (RPE), thermal sensation (TS), local sweat rate and percent dehydration were recorded during the test. Sweat concentration was analysed for sodium [Na+]sweat and potassium. Blood samples were analysed for biochemical changes, electrolytes and hematologic indices. Urine samples were collected before and after each test and analysed for electrolytes.After the period of acclimation the percent dehydration during exercise significantly increased from 1.77+/-0.09% (Day 1) to 2.14+/-0.07% (Day 16). Resting levels of hemoglobin, hematocrit and red blood cells decreased significantly while [Na+]sweat increased significantly. For Tre and Tsk there were no differences at rest. Tre, HR, RPE, TS, plasma lactate concentration, hemoglobin and hematocrit at the 40th min of exercise were significantly lower after the period of acclimation but mean corpuscular hemoglobin and serum osmolality were significantly higher while no difference was seen in [Na+]sweat and Tsk. It can be concluded that tropic-dwelling subjects, although exposed to prolonged passive heat exposure, were not fully heat acclimatized. To achieve further HA, they should gradually expose themselves to exercise-heat stress in a hot environment.     

Thermal sweat lactate in cystic fibrosis and in normal children

We attempt to determine whether the decrease in Na+ reabsorption and the increase in K+ secretion in sweat of cystic fibrosis patients (CF) were associated with changes in glandular anaerobic metabolism evaluated by forehead sweat lactate excretion rate. 6 CF and 11 normal (C) children, 5 months to 14 years old, were exposed to external thermal load (45 degrees C). The data showed that: 1) Na+, K+ and Cl- concentrations in CF are constant at any flow rate (Qsw); 2) In both groups the excretion rates of Na+, K+ and Cl- increased linearly with Qsw but the slopes in CF were significantly higher than in C (p less than 0.001); 3) Lactate excretion rate increased with Qsw as in CF and C with the same slope. We suggest that an increase in energy expenditure of Na+ - K+ exchange and an active secretion of K+ by the duct could explain the normal energy metabolism that we observed in CF sweat glands.