A triaxial accelerometer and portable data processing unit for the assessment of daily physical activity.

The present study describes the development of a triaxial accelerometer (TA) and a portable data processing unit for the assessment of daily physical activity. The TA is composed of three orthogonally mounted uniaxial piezoresistive accelerometers and can be used to register accelerations covering the amplitude and frequency ranges of human body acceleration. Interinstrument and test-retest experiments showed that the offset and the sensitivity of the TA were equal for each measurement direction and remained constant on two measurement days. Transverse sensitivity was significantly different for each measurement direction, but did not influence accelerometer output (< 3% of the sensitivity along the main axis). The data unit enables the on-line processing of accelerometer output to a reliable estimator of physical activity over eight-day periods. Preliminary evaluation of the system in 13 male subjects during standardized activities in the laboratory demonstrated a significant relationship between accelerometer output and energy expenditure due to physical activity, the standard reference for physical activity (r = 0.89). Shortcomings of the system are its low sensitivity to sedentary activities and the inability to register static exercise. The validity of the system for the assessment of normal daily physical activity and specific activities outside the laboratory should be studied in free-living subjects.

Daily physical activity assessment: comparison between movement registration and doubly labeled water.

The use of movement registration for daily physical activity assessment was evaluated during a 7-day period in 30 free-living subjects. Body movement was registered with a Tracmor motion sensor consisting of a triaxial accelerometer and a data unit for on-line processing of accelerometer output over 1-min intervals. Average Tracmor output was correlated against four different energy estimates: 1) average daily metabolic rate (ADMR), determined with doubly labeled water; 2) ADMR-sleeping metabolic rate (SMR; determined in a respiration chamber); 3) (ADMR-SMR) per kilogram of body mass; and 4) the overall physical activity level (PAL = ADMR/SMR). The highest correlation was found for the relationship between Tracmor output and PAL (r = 0.58). After correction for Tracmor values arising from vibrations produced by transportation means, this correlation was improved to 0.73. There was no difference between Tracmor output and PAL in discriminating between overall activity levels with "low" (PAL < 1.60), "moderate" (1.60 < or = PAL < or = 1.85), and "high" (PAL > 1.85) intensity. It is concluded that the Tracmor can be used in free-living subjects to distinguish among interindividual as well as intraindividual levels of daily physical activity.

Assessment of energy expenditure for physical activity using a triaxial accelerometer.

A triaxial accelerometer was used to evaluate the relationship between energy expenditure due to physical activity (EEact) and body acceleration during different types of activity. In a laboratory experiment, 11 male subjects performed sedentary activities and walked on a motor driven treadmill (3-7 km.h-1). EEact was calculated from total energy expenditure (EEtot), as measured by indirect calorimetry, and sleeping metabolic rate (SMR): EEact = EEtot--SMR. Body accelerations were measured with a triaxial accelerometer at the low back. Special attention was paid to the analysis of unidirectional and three-directional accelerometer output. During sedentary activities a linear relationship between EEact and the sum of the integrals of the absolute value of accelerometer output from all three measurement directions (IAAtot) was found (r = 0.82, P < 0.001, Sy,x = 0.22 W.kg-1). During walking EEact was highly correlated with the integral of absolute accelerometer output in antero-posterior direction (IAAx; r = 0.96, P < 0.001, Sy,x = 0.53 W.kg-1). When all examined activities were included in a regression analysis, a strong linear relationship between EEact and IAAtot was found (r = 0.95, P < 0.001, Sy,x = 0.70 W.kg-1). Using this relationship, EEact during sedentary activities as well as EEact during walking could be estimated with an accuracy of about 15%. Although sedentary activities and walking represent a large part of normal daily physical activity, the validity and usefulness of the triaxial accelerometer--measuring IAAtot--to predict EEact in daily life must be studied under free-living conditions.

Percutaneous implantation of a new intracoronary stent in pigs.

Sixty-two self-expanding parallel wire stainless steel stents were implanted in normal coronary arteries of 31 young pigs using a newly developed delivery system. In 57 of 62 procedures, the percutaneous coronary implant of the stent was successful; five stents were released in side branches. Implants remained in place for a few hours to 6 months. In spite of correct sizing, two stents migrated out of the coronary arteries. Seven pigs died prematurely; in six of them death might be stent-related. Although no anticoagulant and antiplatelet aggregation drugs were administered during the follow-up period, at autopsy thrombi were observed in only seven arteries (nonobstructive in four of seven arteries). All arteries except for three were patent; these three vessels occluded probably due to oversizing of the stent. Complete neointimal coverage was found within 3 weeks. Important hyperplasia was not seen. It was concluded that coronary implantation of this stent usually was easy. Obstructive thrombus formation was rather uncommon despite the absence of chronic anticoagulant and antiplatelet aggregation therapy. Hyperplasia was rare.

Oxidative phosphorylation in human muscle in patients with ocular myopathy and after general anaesthesia.

The fuel preference of human muscle mitochondria has been given. Substrates which are oxidized with low velocity cannot be used to detect defects in oxidative phosphorylation. After general anaesthesia, the oxygen uptake with the different substrates is much lower than after local analgesia. The latter was therefore used in the subsequent study. In 15 out of 18 patients with ocular myopathy, defects in oxidative phosphorylation could be detected in isolated muscle mitochondria prepared from freshly biopsied tissue. Measurement of the activity of segments of the respiratory chain in homogenate from frozen muscle showed no, or minor defects. In two of these patients showing exercise intolerance, decreased oxidation of NAD(+)-linked substrates and apparently normal mitochondrial DNA, further study revealed deficiency of pyruvate dehydrogenase in a girl with ptosis and a high Km of complex I for NADH in a man. Both patients responded to vitamin therapy.

Primary carnitine deficiency.

Carnitine deficiency can be defined as a decrease of intracellular carnitine, leading to an accumulation of acyl-CoA esters and an inhibition of acyl-transport via the mitochondrial inner membrane. This may cause disease by the following processes. A. Inhibition of the mitochondrial oxidation of long-chain fatty acids during fasting causes heart or liver failure. The latter may cause encephalopathy by hypoketonaemia, hypoglycaemia and hyperammonaemia. B. Increased acyl-CoA esters inhibit many enzymes and carriers. Long-chain acyl-CoA affects mitochondrial oxidative phosphorylation at the adenine nucleotide carrier, and also inhibits other mitochondrial enzymes such as glutamate dehydrogenase, carnitine acetyltransferase and NAD(P) transhydrogenase. C. Accumulation of triacylglycerols in organs increases stress susceptibility by an exaggerated response to hormonal stimuli. D. Decreased mitochondrial acetyl-export lowers acetylcholine synthesis in the nervous system. Primary carnitine deficiency can be defined as a genetic defect in the transport or biosynthesis of carnitine. Until now only defects at the level of carnitine transport have been discovered. The most severe form of primary carnitine deficiency is the consequence of a lesion of the carnitine transport protein in the brush border membrane of the renal tubules. This defect causes cardiomyopathy or hepatic encephalopathy usually in combination with skeletal myopathy. In a patient with cardiomyopathy and without myopathy, we found that carnitine transport at the level of the small intestinal epithelial brush border was also inhibited. The patient was cured by carnitine supplementation. Muscle carnitine increased, but remained too low. This suggests that carnitine transport in muscle is also inhibited. Carnitine transport in fibroblasts was normal, which disagrees with literature reports for similar patients.

Muscle carnitine level in endurance training and running a marathon.

Twenty sedentary volunteers (13 men and 7 women) who were subjected to an 18- to 20-month training program aimed at completing a marathon after the onset of training participated in this study. In the course of the training and after running a marathon, the content of total carnitine in the m. vastus lateralis did not change. The content of muscle total carnitine was not sex related. However, significant correlations were demonstrated between muscle total carnitine content and plasma urea and creatinine concentrations. Also a negative significant correlation was found between the content of muscle total carnitine and the plasma activity of CK before running a marathon.

Carnitine deficiency, mitochondrial dysfunction and the heart. Identical defect of oxidative phosphorylation in muscle mitochondria in cardiomyopathy due to carnitine loss and in Duchenne muscular dystrophy.

Cardiomyopathies are often caused by a metabolic defect. Carnitine deficiency and mitochondrial defects in the metabolism of acyl-CoA, including defects in oxidative phosphorylation, start the same circular mechanism of mitochondrial doom. Patients with cardiomyopathy due to carnitine loss are cured by carnitine supplementation. In such a patient we found defective oxidative phosphorylation in isolated muscle mitochondria. The stimulation of the respiratory rate with all substrates by ADP was decreased, probably the cause of inhibition of the adenine nucleotide translocator by accumulating long-chain acyl-CoA. The same condition was encountered in patients with Duchenne muscular dystrophy, who often get cardiomyopathy in the course of the disease process.

Cardiomyopathy associated with carnitine loss in kidneys and small intestine.

A boy was first seen at the age of 1 year on account of congestive cardiomyopathy. Growth and development had been normal. Total plasma carnitine was extremely low (1.8 mumol/l; normal range: 25-64 mumol/l). No hypoglycaemia, lactic acidaemia or dicarboxylic aciduria were found. Other laboratory findings were unremarkable except for a slight deficiency in iron, vitamin D and vitamin E. Total muscle carnitine was 1.5% of normal; however, no signs or symptoms of myopathy could be detected. After carnitine loading, liver carnitine increased to 24% of normal. Isolated muscle mitochondria showed decreased oxidative capacity with all substrates tested. Stimulation of O2 uptake by adenosine diphosphate (ADP) was decreased. After loading with both intravenous and oral carnitine, there was a rise in plasma carnitine and a rapid loss in the urine and the faeces. These findings suggest a defect in the brush border carnitine transport system of the kidneys and of the small intestine. Renal clearance of carnitine was abnormally high. Therapy with 1 g oral L-carnitine/kg per day was instituted without any problems and the cardiac disease resolved within 3 months. The parents and the patient's five sibs also had low plasma carnitine but displayed no cardiomyopathy.

The role of the carnitine system in myocardial fatty acid oxidation: carnitine deficiency, failing mitochondria and cardiomyopathy.

The carnitine system functions in the transport of activated acyl groups over the mitochondrial inner membrane, and is needed for oxidation of long-chain fatty acids by all mitochondria. The rate of cardiac fatty acid oxidation is determined by availability of fatty acids, oxygen and the activity of carnitine palmitoyltransferase I, which is regulated by a variety of factors. It is inhibited by malonyl-CoA, which in rat heart was found to be synthesized by acetyl-CoA carboxylase. It is also inhibited by long-chain acylcarnitine. Linoleoylcarnitine was found to be a better inhibitor than palmitoylcarnitine. The concentration of carnitine in human heart, muscle and other tissues is much higher than is needed for the optimal beta-oxidation rate. In contrast to controls, we found in several myopathic patients that extra carnitine (from 1/2 to 5 mM) caused a considerable increase in beta-oxidation rate of isolated muscle mitochondria. In some of these patients we detected medium-chain acyl-CoA dehydrogenase deficiency. Patients with primary carnitine deficiency caused by a renal carnitine leak often show cardiomyopathy, which completely disappears under carnitine therapy. Cardiomyopathy may also be the cause of secondary carnitine deficiency resulting from a mitochondrial defect in acyl-CoA metabolism, or by the mitochondrial defect itself, which may be induced by drugs or viral attack, or be the result of a genetic error. In cardiomyopathic patients with a (subclinical) myopathy, study of isolated mitochondria and homogenate from skeletal muscle may reveal a mitochondrial dysfunction, which, in some patients, is treatable by dietary measures and supplementation with vitamins, CoQ and/or carnitine. When the cause of cardiomyopathy is not known, determination of plasma carnitine and carnitine supplementation of hypocarnitinemic patients is of great therapeutic value.

Defects in oxidative phosphorylation. Biochemical investigations in skeletal muscle and expression of the lesion in other cells.

Mitochondria are very vulnerable to genetic and environmental damage. If a patient is suspected of having a mitochondrial disease, elevated blood lactate, lowered blood free carnitine, abnormal urinary organic acids and carnitine esters and tissue histopathology may help with the diagnosis. For biochemical assessment of the defect, muscle is the tissue of choice even when involvement of other organs like heart or brain is more prominent. We have studied isolated muscle mitochondria and homogenates from muscle biopsies in 250 patients, and have detected in more than one third mitochondrial defects in oxidative phosphorylation, dehydrogenases, non-redox enzymes catalyzing synthesis of fuel molecules and in the carnitine system. Several patients showed more than one defect. We have selected eight patients to illustrate how a relatively simple series of investigations in both isolated mitochondria and homogenate can be used for the identification of defects in oxidative phosphorylation in a small amount of muscle (200 mg or more). Identification of the defect(s) is important since it may provide the basis for rational treatment. A minority of the patients recovered partly or completely, which is unique in treatment of inborn errors of subcellular organelles. An important aspect of mitochondrial dysfunction is the tissue specificity. The defect may be systemic but is often clinically expressed in only one or a few tissues. Rarely, tissue-specific defects can be understood on the basis of tissue-specificity of mitochondrial (iso-)enzymes. Mitochondrial deficiencies of all biotin enzymes and most CoA-linked enzymes are expressed in fibroblasts; most respiratory chain defects are not. When mitochondrial ATP synthesis has been compromised by a mitochondrial defect, secondary lesions may be generated by changes in mitochondrial protein synthesis, activated proteases and phospholipases, increased matrix CoA and resulting carnitine deficiency, decrease in Krebs cycle intermediates and increased free radical formation and lipid peroxidation.

Riboflavin-responsive lipid-storage myopathy and glutaric aciduria type II of early adult onset.

A 17-year-old girl with progressive lipid-storage myopathy for 2 years had low muscle carnitine levels. There was no therapeutic response to prednisone and DL-carnitine-HCl. Chemical findings indicated glutaric aciduria type II. Riboflavin therapy and a fat-restricted, carbohydrate-enriched diet resulted in dramatic improvement. Low carnitine concentrations in plasma and muscle were observed in three asymptomatic sisters who had normal urinary excretion patterns. There was impaired mitochondrial beta-oxidation in cultured skin fibroblasts from the index patient and all three siblings.