Effects of time,temperature and blood cell counts on levels of lactate in heparinized whole blood gas samples

OBJECTIVE: To investigate whether lactate levels may vary in relation to time, substrate concentration and blood cells counts. METHODS: In this study 110 samples from the daily clinical routine blood samples were collected. Determinations of lactate were made at different times where the samples had not been left for more than 120 min at room temperature (24 degrees C) or in the fridge (4 degrees C). The influence of glucose and blood cells on lactate production was also estimated. The rate in change of concentration (slope) and the increase expected at the beginning (intercept) were estimated through linear regression using a longitudinal marginal method. RESULTS: The time-related change in lactate was significantly higher at room temperature (0.012 mmol L(-1) min(-1)) than at 4 degrees C (0.0035 mmol L(-1) min(-1)) (p<0.0001). There was a significantly positive relationship between blood cells (mainly leucocytes) and the rate of reaction at room temperature. CONCLUSIONS: A delay in the processing of a whole blood sample of more than 15 min at room temperature or an hour in the fridge entails an important overestimation of the initial lactate levels. Pronounced leucocytosis (higher than 6 x 10(10)/L) meaningfully cut down the stability period (10 min).     

Effect of glibenclamide on insulin release at moderate and high blood glucose levels in normal man

Insulin release occurs in two phases; sulphonylurea derivatives may have different potencies in stimulating first- and second-phase insulin release. We studied the effect of glibenclamide on insulin secretion at submaximally and maximally stimulating blood glucose levels with a primed hyperglycaemic glucose clamp. Twelve healthy male subjects, age (mean ± SEM) 22.5 ± 0.5 years, body mass index (BMI) 21.7 ± 0.6 kg m^?2, were studied in a randomized, double-blind study design. Glibenclamide 10 mg or placebo was taken before a 4-h hyperglycaemic clamp (blood glucose 8 mmol L^?1 during the first 2 h and 32 mmol L^?1 during the next 2 h). During hyperglycaemic clamp at 8 mmol L^?1, the areas under the Δinsulin curve (AUC_Δinsulin , mean ± SEM) from 0 to 10 min (first phase) were not different: 1007 ± 235 vs. 1059 ± 261 pmol L^?1 × 10 min (with and without glibenclamide, P = 0.81). However, glibenclamide led to a significantly larger increase in AUC_Δinsulin from 30 to 120 min (second phase): 16 087 ± 4489 vs. 7107 ± 1533 pmol L^?1 × 90 min (with and without glibenclamide respectively, P < 0.03). The same was true for AUC_ΔC-peptide: no difference from 0 to 10 min but a significantly higher AUC_ΔC-peptide from 30 to 120 min on the glibenclamide day (P < 0.01). The M/I ratio (mean glucose infusion rate divided by mean plasma insulin concentration) from 60 to 120 min, a measure of insulin sensitivity, did not change: 0.26 ± 0.05 vs. 0.22 ± 0.03 μmol kg^?1 min^?1 pmol L^?1 (with and without glibenclamide, P = 0.64). During hyperglycaemic clamp at 32 mmol L^?1, the AUC_Δinsulin from 120 to 130 min (first phase) was not different on both study days: 2411 ± 640 vs. 3193 ± 866 pmol L^?1 × 10 min (with and without glibenclamide, P = 0.29). AUC_Δinsulin from 150 to 240 min (second phase) also showed no difference: 59 623 ± 8735 vs. 77389 ± 15161 pmol L^?1 × 90 min (with and without glibenclamide, P = 0.24). AUC_ΔC-peptide from 120 to 130 min and from 150 to 240 min were slightly lower on the glibenclamide study day (both P < 0.04). The M/I ratio from 180 to 240 min did not change: 0.24 ± 0.04 vs. 0.30 ± 0.07 μmol kg^?1 min^?1 pmol L^?1 (with and without glibenclamide, P = 0.25). In conclusion, glibenclamide increases second-phase insulin secretion only at a submaximally stimulating blood glucose level without enhancement of first-phase insulin release and has no additive effect on insulin secretion at maximally stimulating blood glucose levels. Glibenclamide did not change insulin sensitivity in this acute experiment.     

Effects of caffeine and high ambient temperature on haemodynamic and body temperature responses to dynamic exercise

Caffeine can enhance mean arterial blood pressure (MAP) and attenuate forearm blood flow (FBF) and forearm vascular conductance (FVC) during exercise in thermal neutral conditions without altering body temperature. During exercise at higher ambient temperatures, where a greater transfer of heat from the body core to skin would be expected, caffeine‐induced attenuation of FBF (i.e. cutaneous blood flow) could attenuate heat dissipation and increase body temperature (T_re). We hypothesized that during exercise at an ambient temperature of 38°C, caffeine increases MAP, and attenuates FBF and FVC such that T_re is increased. Eleven caffeine‐naive, active men, were studied at rest and during exercise after ingestion of a placebo or 6 mg kg^–1 of caffeine. MAP, heart rate (HR), FBF, FVC, T_re skin temperature (T_sk) and venous lactate concentrations (lactate) were assessed sequentially during rest at room temperature, after 45 min of exposure to an ambient temperature of 38°C, and during 35 min of submaximal cycling. Heat exposure caused increases in MAP, FBF, FVC and T_sk that were not altered by caffeine. HR, T_re, and lactate were unaffected. During exercise, only MAP (95 ± 2 vs. 102 ± 2 mmHg), HR (155 ± 10 vs. 165 ± 10 beats min^–1), and lactate (2·0 ± 0·4 vs. 2·3 ± 0·4 mmol l^–1) were increased by caffeine. These data indicate that increases in cutaneous blood flow during exercise in the heat are not reduced by caffeine. This may be because of activation of thermal reflexes that cause cutaneous vasodilation capable of offsetting caffeine‐induced reductions in blood flow. Caffeine‐induced increases in lactate, MAP and HR during exercise suggest that this drug and high ambient temperatures increase production of muscle metabolites that cause reflex cardiovascular responses.     

Direct vasodilator effects of physiological hyperinsulin-aemia in human skeletal muscle

Systemic hyperinsulinaemia induces vasodilatation in human skeletal muscle. This effect is gradual in onset, and at low insulin levels not maximal until at least 3 h. To investigate whether the vasodilator response to insulin results from a direct vascular effect, we infused insulin directly into the cannulated brachial artery (perfused forearm technique) in a total of 30 experiments in 20 healthy, lean, normotensive volunteers. Local, intra-arterial, infusion of insulin (180 min, 0.3 mU dL^?1 forearm volume min^?1, n = 15, forearm venous insulin concentration approximately 540 pmol L^?1) induced a gradual increase in forearm blood flow (FBF; venous occlusion plethysmography) from 1.86 ± 0.17 to 3.64 ± 0.64 mL dL^?1 min^?1 after 180 min (anova P < 0.001). Percentage increases in FBF after 60, 120 and 180 min averaged 14.4 ± 5.9, 59.4 ± 25.5 and 124.6 ± 51.2% respectively. Forearm glucose uptake increased from 0.24 ± 0.05 to a maximum of 1.98 ± 0.28 μmol dL^?1 min (P < 0.001). Furthermore, insulin infusion increased forearm lactate release and potassium uptake. In 10 out of these 15 individuals, the forearm glucose uptake was further increased in a second, separate, repeat experiment with concomitant intra-arterial infusion of glucose 5% (0.2 mL dL^?1 min^?1), resulting in forearm venous glucose concentrations of approximately 15 mmol L^?1. This combined infusion achieved a similar vasodilator response to the infusion of insulin alone. The individual vascular responses of the two paired experiments showed a strong correlation (r = 0.87, P < 0.01). In five subjects time and vehicle control experiments were performed, showing no changes in FBF or metabolism during the 180 min. We conclude that the slow vasodilator response to insulin (as observed during systemic infusion) can, at least partly, be explained by a direct vascular effect of insulin. Insulin-mediated skeletal muscle glucose uptake precedes this effect, but seems not to be an important determinant of the vasodilator response to insulin.     

Evaluation of a new, rapid lactate analyzer in critical care

Objective: To determine the reliability, precision and clinical usefulness of a newly developed substrate-specific lactate/blood gas analyzer (Chiron M865). Setting: A university hospital 31-bed mixed medical/surgical intensive care unit (ICU). Patients: Seventeen critically ill patients with sepsis (n = 4), post-cardiac surgery (n = 8), hepatic failure (n = 2) or acute respiratory failure (n = 3). Measurements and results: Lactate levels were measured in 17 critically ill patients on whole blood using the new Chiron M865, and on plasma by a stat lactate/glucose analyzer (Yellow Spring Instrument, YSI mode 2300) and a reference lactate/glucose/electrolyte/enzyme analyzer (Hitachi 911). The influences of temperature and storage on blood lactate levels were then evaluated. Mean lactate values obtained were 3.73 ± 2.84 mmol/l with the Chiron, 3.03 ± 2.60 mmol/l with the YSI, and 3.59 ± 2.92 mmol/l with the Hitachi. There was a strong correlation between the three analyzers (Chiron vs YSI r = 0.99; Chiron vs Hitachi 911 r = 0.98), and good agreement between the Chiron and the two other methods (Chiron/YSI bias was –0.65, SD 0.50 mmol/l; Chiron/Hitachi bias was 0.12, SD 0.55 mmol/l). The variability coefficients were 3.7 % for the Chiron and 3.0 % for the YSI. During short term storage, a continuous increase in lactate levels was observed at room temperature (2.36 ± 1.68 mmol/l to 2.53 ± 1.74 mmol/l, p < 0.05), but when the samples were kept on ice there was just a small statistically significant, but not clinically significant, increase after 8 min (2.37 ± 1.62 mmol/l to 2.39 ± 1.63 mmol/l, p < 0.05). For longer storage times, samples on ice showed a small increase in lactate levels after 15 min (3.73 ± 2.90 mmol/l to 4.01 ± 3.00 mmol/l, p < 0.05) but no further increase during the subsequent 45 min. Conclusions: The new Chiron lactate analyzer is reliable for serial whole blood lactate measurements in an intensive care stat laboratory. Samples should be kept on ice immediately after sampling to minimize in vitro erythrocyte production of lactate. Received: 25 September 1998 Final revision received: 4 January 1999 Accepted: 3 February 1999     

Efficiency of acidemia correction on intermittent versus continuous hemodialysis in acute methanol poisoning

Context: Acidemia is a marker of prognosis in methanol poisoning, as well as compounding formate-induced cytotoxicity. Prompt correction of acidemia is a key treatment of methanol toxicity and methods to optimize this are poorly defined.

Objective: We studied the efficiency of acidemia correction by intermittent hemodialysis (IHD) and continuous renal replacement therapy (CRRT) in a mass outbreak of methanol poisoning.

Methods: The study was designed as observational cohort study. The mean time for an increase of 1?mmol/L HCO₃^–, 0.01 unit arterial blood pH, and the total time for correction of HCO₃^– were determined in IHD- and CRRT-treated patients.

Results: Data were obtained from 18 patients treated with IHD and 13 patients treated with CRRT. At baseline, CRRT group was more acidemic than IHD group (mean arterial pH 6.79?±?0.10 versus 7.05?±?0.10; p?=?0.001). No association was found between the rate of acidemia correction and age, weight, serum methanol, lactate, formate, and glucose on admission. The time to HCO₃^– correction correlated with arterial blood pH (r=??0.511; p?=?0.003) and creatinine (r?=?0.415; p?=?0.020). There was association between the time to HCO₃^– correction and dialysate/effluent and blood flow rates (r=??0.738; p?r=??0.602; p?The mean time for HCO₃^– to increase by 1?mmol/L was 12?±?2?min for IHD versus 34?±?8?min for CRRT (p?p?=?0.024). The mean increase in HCO₃^– was 5.67?±?0.90?mmol/L/h for IHD versus 2.17?±?0.74?mmol/L/h for CRRT (p?Conclusions: Our study supports the superiority of IHD over CRRT in terms of the rate of acidemia correction.     

Is the effect of acute hyperglycaemia on interdigestive antroduodenal motility and small-bowel transit mediated by insulin?

Acute hyperglycaemia inhibits antroduodenal motility. In non-diabetic subjects this inhibitory effect may result from reactive endogenous hyperinsulinaemia. Therefore, we investigated the effects of hyperinsulinaemia during both hyperglycaemia and euglycaemia on interdigestive antroduodenal motility (perfusion manometry) and duodenocaecal transit time (DCTT; lactulose breath-H₂ test). Six healthy volunteers (age 20–26 years) were studied for 240 min on three separate occasions in random order during: (a) i.v. saline (control); (b) acute hyperglycaemic hyperinsulinaemia (HG) with plasma glucose at 15 mmol L^?1; and (c) euglycaemic hyperinsulinaemia (HI) with plasma insulin at 80 mU L^?1 and glucose at 4–5 mmol L^?1. Results: DCTT was significantly (P < 0.05) prolonged during HG (158 ± 23 min) compared with control (95 ± 25 min), whereas HI had no effect (100 ± 17 min). Mean duration of complete migrating motor complex (MMC) cycles was significantly (P < 0.05) reduced during HG (63 ± 9 min) compared with control (103 ± 15 min) and HI (105 ± 16 min), which resulted from a significantly (P < 0.05) shorter duration of phase II. Antral motility was significantly (P < 0.05) reduced during both HI (20 ± 8 contractions 240 min^?1) and HG (9 ± 5) compared with control (43 ± 7). It is concluded that in healthy subjects hyperglycaemia prolongs DCTT, increases duodenal MMC cycle frequency and inhibits antral motility. Hyperinsulinaemia reduces antral motor activity but has no effect on interdigestive duodenal motility or DCTT. Thus, other factors, apart from insulin, mediate the inhibitory effect of hyperglycaemia on interdigestive intestinal motility and transit.     

Acute saline infusion induces extracellular acidification and activation of the Na+/H+ exchanger in man

The effect of acute expansion of the extracellular fluid volume (ECV) with isotonic (0.9%) saline on the activity of the lymphocyte Na⁺/H⁺ antiport (NHE) was studied in a total of 18 healthy volunteers. Saline was infused at a constant rate so that 4 mmol kg^?1 b.w. was administered over 2 h. NHE activity was measured by quantifying cytosolic pH (pH_i) recovery following acidification of the cells with propionic acid and by pH clamping at various pH_i values between 7.2 and 5.8 using nigericin. Both methods demonstrate NHE activation associated with intravenous saline infusion, the kinetic difference being a marked decrease in the Hill coefficient n from 3.28 ± 0.21 (SEM) to 2.22 ± 0.11 in the absence of changes in baseline pH_i (7.14 ± 0.02 vs. 7.08 ± 0.02; P = 0.15), V_max (42.8 ± 2.7 vs. 48.1 ± 2.8 mmol L^?1 min^?1; P = 0.08) and pK (6.32 ± 0.04 vs. 6.35 ± 0.02). NHE activation was associated with significant decreases in serum chloride (P = 0.016), calcium (P = 0.008), total cholesterol (P = 0.008), low-density lipoproteins (P = 0.016) and high-density lipoproteins (P = 0.008). Moreover, saline infusion induced extracellular acidification with a decrease in pH from 7.39 ± 0.01 to 7.37 ± 0.01 (P = 0.016), HCO₃^? from 23.3 ± 0.43 mmol L^?1 to 21.3 ± 0.25 mmol L^?1 (P = 0.008) and base excess from ?1.03 ± 0.38 mmol L^?1 to ?3.00 ± 0.31 mmol L^?1 (P = 0.008). Our results show for the first time that acute ECV expansion with isotonic saline is followed by an activation of the lymphocyte NHE. The underlying mechanism(s) remain to be investigated. However, the demonstration in our study of marked changes in acid–base balance induced by acute saline points to a possible inter-relationship of antiporter activation and extracellular acidification.     

Effect of Temperature on the Size Distribution,Shell Properties,and Stability of Definity®

Physical characterization of an ultrasound contrast agent (UCA) aids in its safe and effective use in diagnostic and therapeutic applications. The goal of this study was to investigate the impact of temperature on the size distribution, shell properties, and stability of Definity^®, a U.S. Food and Drug Administration-approved UCA used for left ventricular opacification. A Coulter counter was modified to enable particle size measurements at physiologic temperatures. The broadband acoustic attenuation spectrum and size distribution of Definity^® were measured at room temperature (25 °C) and physiologic temperature (37 °C) and were used to estimate the viscoelastic shell properties of the agent at both temperatures. Attenuation and size distribution was measured over time to assess the effect of temperature on the temporal stability of Definity^®. The attenuation coefficient of Definity^® at 37 °C was as much as 5?dB higher than the attenuation coefficient measured at 25 °C. However, the size distributions of Definity^® at 25 °C and 37 °C were similar. The estimated shell stiffness and viscosity decreased from 1.76?±?0.18 N/m and 0.21?×?10^–6?±?0.07?×?10^–6 kg/s at 25 °C to 1.01?±?0.07 N/m and 0.04?×?10^–6?±?0.04?×?10^–6 kg/s at 37 °C, respectively. Size-dependent differences in dissolution rates were observed within the UCA population at both 25 °C and 37 °C. Additionally, cooling the diluted UCA suspension from 37 °C to 25 °C accelerated the dissolution rate. These results indicate that although temperature affects the shell properties of Definity^® and can influence the stability of Definity^®, the size distribution of this agent is not affected by a temperature increase from 25 °C to 37 °C.     

Interstitial lactate levels in human skin at rest and during an oral glucose load: a microdialysis study

In vitro data have suggested that the skin is a significant lactate source. The purpose of the present study was to measure lactate and glucose concentrations in intact human skin in vivo using the microdialysis technique. Microdialysis fibres of 216 μm were inserted intradermally and perfused at a rate of 3 μl min^–1. In the first experimental protocol, dialysis fibres were calibrated by the method of no net flux in eight subjects. Skin lactate concentrations of 2·48 ± 0·17 mmol l^–1 were significantly greater than lactate concentrations of 0·84 ± 0·15 mmol l^–1 in venous plasma (P<0·01). Glucose concentrations in skin and venous plasma were similar (5·49 ± 0·18 vs. 5·26 ± 0·24 mmol l^–1). In the second experimental protocol, changes in lactate and glucose levels were studied in 10 subjects after an oral glucose tolerance test (OGTT). After the OGTT, plasma glucose and lactate levels increased by 54% and 39% to peak levels at 30 and 60 min respectively. In comparison, skin glucose and lactate increased by 41% and 18% at 60 and 90 min. No changes in skin blood flow were observed during the OGTT. The data suggest that resting skin is a significant lactate source with no significant lactate production during OGTT. The cellular source of lactate in the skin remains undetermined to date.     

Cardiovascular,plasma norepinephrine,and thermal adjustments to prolonged exercise in young and older healthy humans

Summary. We tested the hypothesis that the whole body energy expenditure, plasma norepinephrine, cardiovascular, and internal body temperature adjustments to prolonged submaximal exercise (i.e., ‘cardiovascular drift’) performed at the same per cent of peak oxygen uptake (per cent VO₂peak) under thermoneutral ambient conditions would be smaller in older compared to young non-physically trained men. Healthy young (25±1 years; VO₂max = 49.3±1.6 ml kg^-1 min^-1; n=6) and older (66±2 years; VO₂max = 31.5±2.3 ml kg^-1 min^-1; n=6) untrained men with similar levels of chronic physical activity were studied during pre-exercise standing rest and serially during 45 min of constant load treadmill walking at ?65%VO₂peak (Ta=?23±C; ?40 RH). There were no group differences at rest. From rest to 5 min of exercise, the increases in heart rate were less (P<0–05), the changes in arterial blood pressure and per cent δ blood volume were not different, and the rise in plasma norepinephrine concentration was greater (P<0–05) in the older men vs. young controls. Consistent with our hypothesis, the increases in rectal temperature and plasma norepinephrine concentrations from 5 to 45 min of exercise were smaller in the older men (1.06–0.18 vs. 1.46±0.16±C and 110±132 vs. 443±189%, respectively, P<0.05). In contrast, the progressive increases in KO2, heart rate, and perceived effort, as well as the time-dependent reductions in systolic, mean and diastolic arterial blood pressure and per cent δ blood volume, were not different in the two groups. Thus, the whole body energy expenditure and selected cardiovascular adjustments to prolonged submaximal treadmill exercise performed at the same per cent VO₂peak under comfortable ambient conditions are not different in healthy, physical activity-matched young and older men, despite a smaller elevation in internal body temperature in the latter.     

Moderate hyperthyroidism reduces liver amino nitrogen conversion,muscle nitrogen contents and overall nitrogen balance in rats

There are conflicting data on the effect of thyroid hormones on nitrogen metabolism. We determined the basal blood amino nitrogen (amino-N) concentrations, the urea nitrogen (urea-N) synthesis rate and the maximum hepatic capacity of urea nitrogen synthesis during saturating infusion of alanine, in moderately acutely (24 h) and chronically (7 days) hyperthyroid rats and compared this with changes in organ nitrogen contents in muscles and kidney, nitrogen excretion and nitrogen balance. Forty-three rats were made acutely hyperthyroid through administration of 5 μg 100 g^?1 triiodothyronine twice daily (T₃: 2.2 ± 0.7 vs. 0.87 ± 0.04 nmol L^?1, P < 0.01). Fifty-one rats were made chronically hyperthyroid through administration of 12.5 μg 100 g^?1 thyroxine twice daily (T₃: 2.63 ± 0.18 vs. 0.87 ± 0.04 nmol L^?1, P < 0.01). Weight gain was halved in this group. Both acute and chronic hyperthyroidism increased basal blood amino-N concentration in both groups by 16% (4.5 ± 0.15 vs. 3.9 ± 0.13 mmol L^?1 and 4.7 ± 0.12 vs. 3.9 ± 0.13 mmol L^?1, respectively, P < 0.01), and decreased basal urea-N synthesis rate in both groups by 30% [2.7 ± 03 vs. 4.1 ± 0.3 μmol (min ×100 g)^?1 and 3.1 ± 0.3 vs. 4.1 ± 0.3μmol (min ×100 g g)^?1, respectively, P < 0.01]. The capacity of urea-N synthesis during saturation fell in both groups by 35% compared with controls [6.5 ± 0.4 vs. 9.3 ± 0.5 μmol (min ×100 g)^?1 and 5.7 ± 0 .5 vs. 9.3 ± 0.6 μmol (min ×100 g)^?1, respectively, P < 0.01]. Nitrogen contents in the muscles, soleus and extensor digitorum longus, of chronically hyperthyroid rats decreased by 22% and 11%, respectively, whereas kidney N-content increased by 12% (P < 0.05). N-balance and urinary urea-N excretion fell by 30%, whereas faeces-N excretion increased by 80% in hyperthyroid rats. Overall liver function assessed by galactose elimination capacity did not differ among groups. Both acute and chronic moderate hyperthyroidism increase blood amino-N and decrease basal and maximum rate of urea formation. Furthermore, chronic hyperthyroidism reduces N-contents of muscles, urinary urea-N excretion and N-balance. Thyroid hormones thus mobilize muscle-N, whereas amino-N in the liver is spared from irretrievable conversion into urea.     

Acute hyperinsulinaemia decreases cholesterol synthesis less in subjects with non-insulin-dependent diabetes mellitus than in non-diabetic subjects

To investigate the effect of insulin on cholesterol synthesis in vivo we measured plasma mevalonic acid (MVA) concentrations using gas chromatography–mass spectrometry in six non-obese patients with non-insulin-dependent diabetes mellitus (NIDDM) [four men, two women; age 57.5±2.2 years (mean±SEM); glycated haemoglobin (HbA1) 8.5±0.5%; total cholesterol (TC) 5.7±0.5 mmol L^?1, triglyceride (TG) 3.8±0.9 mmol L^?1] and six non-diabetic, sex- and age-matched control subjects (age 55.7±2.8 years; HbA1 6.5±0.1%; TC 5.4±0.3 mmol L^?1, TG 1.2±0.1 mmol L^?1). Subjects were studied twice: during 13-h hyperinsulinaemic (1 mu kg^?1 min^?1), euglycaemic (5 mmol L^?1) clamp and during a saline infusion. Baseline MVA concentration was significantly higher in diabetic patients than in control subjects (9.8±0.7 ng mL^?1 vs. 5.6±0.9 ng mL^?1P=0.004). At the end of each study, MVA concentration, expressed as a percentage of baseline, was significantly lower during the hyperinsulinaemic, euglycaemic clamp than during the saline study in both the diabetic (54.4±5.3% vs. 69.6±6.3%, P=0.036) and control subjects (30.5±3.4% vs. 61.7±6.0%, P=0.01). However, the decrease in MVA during the hyperinsulinaemic clamp study was more marked in the control subjects than in the diabetic subjects (P=0.03). A significant positive correlation was found between percentage decrease of MVA and non-esterified fatty acids following the insulin clamp in NIDDM (r=0.83, P=0.04). We conclude that acute hyperinsulinaemia decreases cholesterol synthesis less in subjects with NIDDM than in non-diabetic subjects and that this phenomenon, together with increased basal cholesterol synthesis in NIDDM, may in part be due to insulin resistance.     

Examination of blood haemoglobin concentration measured using the OSM2

Blood haemoglobin concentration is regularly measured automatically by instruments reporting the value in around 1?min. The OSM2 from Radiometer is an example. Results from this instrument have been compared with those of a reference method using the hemiglobincyanide principle. Four healthy, moderately trained, young men (non‐smokers) cycled for 2?min to exhaustion. Blood samples were drawn from indwelling catheters in the femoral artery and vein before exercise, during exercise and in the 1?h recovery. Blood haemoglobin concentration was analysed using both methods. The results of the OSM2 were linearly related to those of the control method, with a random variation of 0.14?mmol?L^?1 (1.5?%). For arterial blood, the OSM2 showed a systematic bias of ?0.36?mmol L^?1 (?4?%). For femoral venous samples the bias varied depending on the haemoglobin concentration, being negative at low concentrations and positive at high values (?3 to +2?%). Consequently, the arteriovenous (a‐v) difference differed systematically between the two methods. The varying bias in the results of the OSM2 for femoral‐venous samples correlated with pH, pCO₂, O₂ saturation of haemoglobin (sO₂) and with the haemoglobin concentration itself (cHb). Partial correlation analyses suggest that only the latter two correlations were independent, while correlations of the bias with pH and pCO₂ were removed when correcting for the effect of sO₂ and cHb. In conclusion, the OSM2 measures the blood haemoglobin concentration fairly precisely, but there is a variable bias of up to 4?% in absolute value. Finally, the instrument does not report a‐v differences reliably.     

Glucose metabolism in chronic diabetic foot ulcers measured in vivo using microdialysis

Ten subjects with diabetes mellitus and unilateral chronic foot ulcer were investigated. Local tissue concentrations of glucose and lactate were measured using the microdialysis method at a distance of 0·5–1 cm from the edge of the ulcer and in normal skin in the contralateral foot. Subcutaneous blood flow in the area investigated was measured using the ¹³³Xe-washout technique. The interstitial glucose concentration in the ulcer was found to be lower than in intact skin (8·0 ± 1·0 mmol l^?1 vs. 8·5 ± 1·1 mmol l^?1) (P<0·02), and the interstitial lactate concentration was higher in the ulcer than in intact skin (3·2 ± 0·2 mmol l^?1 vs. 2·1 ± 0·3 mmol l^?1) (P<0·01). The subcutaneous blood flow was on average 40% higher in the ulcer than in the intact skin. The calculated local glucose uptake and lactate outputs were twofold higher in the ulcer than in the intact skin. However, the molar ratio between lactate output and glucose uptake was approximately two, both in the ulcer and in the intact skin, indicating that the glucose metabolism was qualitatively the same in the two regions.     

Impairment of mitochondrial respiration following ex vivo cyanide exposure in peripheral blood mononuclear cells

Objectives: The objective of this study is to measure mitochondrial respiration using intact cells from whole blood exposed to cyanide as a new biomarker for mitochondrial inhibition. Methods: A single nontourniqueted venous blood sample was collected from 10 healthy volunteers after informed consent. Venous lactate was measured immediately following blood collection. Half of the remaining blood sample was then incubated with 100 mM of potassium cyanide (KCN) for 5 min, and half of the sample remained unexposed. Repeat lactate measurements were performed from blood exposed and not exposed to KCN. Measurement of mitochondrial respiration: intact PBMCs were placed in a 2-mL chamber at a final concentration of 2–3?×?10⁶ cells/mL. Measurements of oxygen consumption were performed at 37°C in a high-resolution oxygraph (Oxygraph-2k Oroboros Instruments, Innsbruck, Austria). Oxygen flux (in pmol O₂/s/10⁶ cells), which is directly proportional to oxygen consumption, was recorded continuously using DatLab software 6 (Oroboros Instruments). Results: There were significance differences in the relevant key parameters of mitochondrial respiration: Of the parameters measuring mitochondrial respiration, four of the six demonstrated a statistically significant mean difference between control and cyanide: for routine respiration (mean difference [control-cyanide]: 8.9 pmol O₂/s/10⁶ cells; 95% CI: 5.6–12.2, p?<?0.0001); Proton Leak (mean difference: 0.73 pmol O₂/s/10⁶ cells; 95% CI:??0.33–1.79, p?=?0.157); Maximal respiration (mean difference: 21.7 pmol O₂/s/10⁶ cells; 95% CI: 16.0–27.6, p?<?0.0001); Residual oxygen consumption (mean difference 0.25 pmol O₂/s/10⁶ cells; 95% CI:??0.68–1.18, p?=?0.557). There was a significant difference in spare respiratory capacity (SRC) and adenosine triphosphate (ATP)-linked respiration with the control samples demonstrating a higher SRC and ATP-linked respiration. Finally, there is a statistically significant difference in lactate (mean difference??0.32, 95% CI:??0.41 to??0.23, p?<?0.0001), though clinically similar level, with a higher lactate concentration in the cyanide samples. Conclusions: In this ex vivo model, the measurements of key parameters in mitochondrial respiration may be a more sensitive measure of cellular function when compared to lactate.     

Red cell concentrate storage and transport temperature

Background and Objectives: This study investigated the current UK guidelines for storage and transport of red cell concentrates (RCC) in saline, adenine, glucose and mannitol (SAGM). The guidelines stipulate storage at 2–6 °C but allow exposure to between 1–10 °C core temperature in a single occurrence of less than 5 h and a surface temperature of 2–10 °C for no more than 12 h during transportation. Methods and Materials: Twenty RCC units in SAGM were selected on the day of blood collection (day 0) and in vitro quality was tested pre‐ and post‐temperature deviation at 10 °C and up to day 42 of storage. Each group of 10 RCC units was incubated for either 12 h or for both 5 and 12 h. Results: Haemolysis was below the 0·8% UK limit at day 42 in all units, although there was an unexpected trend towards lower haemolysis in packs incubated for 5 and 12 h rather than just 12 h alone. Supernatant potassium was significantly higher than reference data on day 35 (P < 0·05) with a maximum of 58 mmol L^?1 and day 42 (P < 0·001). All units incubated at 10 °C had comparable levels of adenosine triphosphate and, 2,3‐diphosphoglycerate to reference data from previous studies, throughout storage. Conclusion: These results suggest that exposure to 10 °C for 12 h or for 5 and 12 h did not adversely affect in vitro red cell quality for the remainder of the components shelf life.     

Accuracy and responsiveness of the stepwatch activity monitor and ActivPAL in patients with COPD when walking with and without a rollator

Purpose: To evaluate the measurement properties of the StepWatch^? Activity Monitor (SAM) and ActivPAL in COPD. Method: Whilst wearing both monitors, participants performed walking tasks at two self-selected speeds, with and without a rollator. Steps obtained using the monitors were compared with that measured by direct observation. Results: Twenty participants aged 73?±?9 years (FEV₁?=?35?±?13% pred; 8 males) completed the study. Average speeds for the slow and normal walking tasks were 34?±?7 m·min^?1and 46?±?10 m·min^?1, respectively. Agreement between steps recorded by the SAM with steps counted was similar irrespective of speed or rollator use (p?=?0.63) with a mean difference and limit of agreement (LOA) of 2 steps·min^?1 and 6 steps·min^?1, respectively. Agreement for the ActivPAL was worse at slow speeds (mean difference 7 steps·min^?1; LOA 10 steps·min^?1) compared with normal speeds (mean difference 4 steps·min^?1; LOA 5 steps·min^?1) (p?=?0.03), but was unaffected by rollator use. The change in step rate between slow and normal walking via direct observation was 12?±?7 steps·min^?1 which was similar to that detected by the SAM (12?±?6 steps·min^?1) and ActivPAL (14?±?7 steps·min^?1). Conclusions: The SAM can be used to detect steps in people who walk very slowly including those who use a rollator. Both devices were sensitive to small changes.

Implications for Rehabilitation

• The evaluation of physical activity (PA) before and after pulmonary rehabilitation in people with chronic obstructive pulmonary disease (COPD) has evolved to be an important outcome measure.

• Selecting an appropriate device to obtain valid measures of PA remains a challenge, especially for those individuals who walk slowly or use a rollator to assist with ambulation.

• The StepWatchTM Activity Monitor and the ActivPAL have been shown in this study to be sensitive to small changes in step rate, thus these devices can be used to assess changes in physical activity in individuals with COPD such as following pulmonary rehabilitation, including those who walk slowly or use a walking aid such as a rollator.

     

The Quick and Owren prothrombin time methods for oral anticoagulant therapy do not agree well using the International Normalized Ratio (INR) units

Abstract

Natriuretic peptides are a laboratory tool with significant implications for the diagnosis and prognosis of heart failure (HF). The International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) recommended that assays must be examined for sample stability because there appears to be assay dependent. We aimed to evaluate the in vitro stability of B-type natriuretic peptide (BNP) under different handling conditions and using a BNP assay from Fujirebio Diagnostics (Tokyo, Japan). BNP concentrations were measured in plasma EDTA samples from 11 subjects to evaluate the in vitro stability at room temperature and at 4?°C and in 10 subjects to check the in vitro stability of samples stored at –20?°C during 1 and 3 months. Stability limit was defined according to Spanish Society of Laboratory Medicine (SEQC-ML) recommendations. At room temperature and 4?°C, BNP concentrations decreased progressively in samples collected in both groups, remaining stable within four hours from collection. BNP concentrations also were stable within four hours from collection in whole blood at room temperature. Finally, at –20?°C, BNP concentrations remained stable in both groups at 1 and 3 months, respectively. According to our results, BNP, stored at room temperature or at 4?°C, should be assayed in the first four hours after collection. Besides, BNP was shown to be stable in whole blood for at least four hours at room temperature. If the testing cannot be performed within the first four hours, the plasma should be frozen and kept at –20?°C for up to 3 months.     

Forearm metabolism during infusion of adrenaline: comparison of the dominant and non‐dominant arm

Human skeletal muscle metabolism is often investigated by measurements of substrate fluxes across the forearm. To evaluate whether the two forearms give the same metabolic information, nine healthy subjects were studied in the fasted state and during infusion of adrenaline. Both arms were catheterized in a cubital vein in the retrograde direction. A femoral artery was catheterized for blood sampling, and a femoral vein for infusion of adrenaline. Forearm blood flow was measured by venous occlusion strain‐gauge plethysmography. Forearm subcutaneous adipose tissue blood flow was measured by the local ¹³³Xe washout method. Metabolic fluxes were calculated as the product of forearm blood flow and a‐v differences of metabolite concentrations. After baseline measurements, adrenaline was infused at a rate of 0·3 nmol kg^?1 min^?1. No difference in the metabolic information obtained in the fasting state could be demonstrated. During infusion of adrenaline, blood flow and lactate output increased significantly more in the non‐dominant arm (8·12 ± 1·24 versus 6·45 ± 1·19 ml 100 g^?1 min^?1) and (2·99 ± 0·60 versus 1·83 ± 0·43 μmol 100 g^?1 min^?1). Adrenaline induced a significant increase in oxygen uptake in the non‐dominant forearm (baseline period: 4·98 ± 0·72 μmol 100 g^?1 min^?1; adrenaline period: 6·63 ± 0·62 μmol 100 g^?1 min^?1) while there was no increase in the dominant forearm (baseline period: 5·69 ± 1·03 μmol 100 g^?1 min^?1; adrenaline period: 4·94 ± 0·84 μmol 100 g^?1 min^?1). It is concluded that the two forearms do not respond equally to adrenaline stimulation. Thus, when comparing results from different studies, it is necessary to know which arm was examined.