J. Carlsten

Long-term in vivo experience of an electrochemical sensor using the potential step technique for measurement of mixed venous oxygen pressure

An implantable amperometric blood oxygen sensor was developed to improve rate adaptation of heart pacemakers. Two different working electrode materials in direct contact with the blood were tested, smooth glassy carbon and gold. Reference electrodes of Ag/AgCl and porous pyrolytic carbon were evaluated. A counter electrode being the titanium housing of the pulse generator was partly coated with carbon. An implantable pacemaker system with chronocoulometric oxygen detection was developed. Heart synchronous potential steps were periodically applied to the 7.5 mm2 working electrode in the atrium. Both single and double potential step techniques were evaluated. The oxygen diffusion limited current was used to calculate the stimulation rate. Bench tests and studies on 31 animals were performed to evaluate long-term stability and biocompatibility. In five dogs, the AV node was destroyed by RF ablation to create a realistic animal model of a pacemaker patient. Sensor stability and response to exercise was followed up to a maximum implantation time of 4 years. Post-mortem examinations of the electrode surfaces and tissue response were performed. The results show that a gold electrode is more stable than glassy carbon. The Ag/AgCl reference was found not to be biocompatible, but activated carbon was stable enough for use as reference for the potentiostat. Double potential steps stabilize the sensor response in comparison to single steps. Blood protein adsorption on the gold surface decreased the oxygen transport but not the reaction efficacy. No adverse tissue reactions were observed.

Risk factors associated with hindlimb lameness and degenerative joint disease in the distal tarsus of Icelandic horses.

The aim of this study was to evaluate potential risk factors associated with hindlimb lameness and radiographic signs of degenerative joint disease (DJD) in the distal tarsus in Icelandic horses. The material consisted of riding horses (n = 420) age 6-12 years sired by 17 selected sires representing all major breeding lines, and of riding horses (n = 194) in the same age range sired by other sires. The examination protocol included the following: interview with owners/trainers, assessment of conformation, motion evaluation and radiographic examination. At the interview, data related to factors outside the horse (environmental variables) and data associated directly with the horse (intrinsic variables) were obtained. Data analysis was performed in 2 steps: screening using bivariate analysis, followed by testing with a multivariate logistic regression model. In the multivariate analysis, the factors of sire, age when broken to saddle and stud show participation were strongly associated with the prevalence of lameness. Height at the croup and ability to perform different gaits were also associated with the prevalence of lameness, but to a lesser degree. The risk factors of age, tarsal angle and birthplace were significantly associated with radiographic signs of DJD in the distal tarsus. Neither the variation in applied training intensity, the use of a professional or amateur trainer nor the temperament or front limb action of the individual horse was significantly associated with the prevalence of hindlimb lameness and/or radiographic signs of DJD in the distal tarsus in the Icelandic horse.

Radiographic and clinical survey of degenerative joint disease in the distal tarsal joints in Icelandic horses

The prevalence of degenerative joint disease (DJD) in the distal tarsal joints and the relation between radiographic and clinical signs compatible with the disease were estimated in a population of Icelandic horses used for riding. The material consisted of 614 horses age 6-12 years (mean age = 7.9 years). Radiographs with 3 projections of each tarsus were made and a clinical examination, including palpation of the medial aspect of the distal tarsus and motion evaluation of the hindlimbs before and after a flexion test of the tarsus, was performed. Radiographic signs of DJD in the distal tarsal joints were found in 30.3% of the horses and the prevalence was strongly correlated with age. Hindlimb lameness before and after flexion test and palpation abnormalities were significantly associated with the radiographic findings. The lameness was usually mild and, in most cases, detectable only after the flexion test. The prevalence of lameness was not significantly correlated with age. Lameness could not be predicted by details of the radiographic findings.

The role of sympathetic activity in initiating malignant hyperthermia

The role of sympathetic activity in triggering malignant hyperthermia (MH) is controversial. Increased sympathetic activity has been considered by some to be the causal factor, whilst others believe this activity to be secondary to metabolic events in the MH syndrome. In this study, a number of parameters, including the blood levels of noradrenaline and adrenaline, were followed in pigs susceptible to MH during exposure to halothane. Seven pigs, crossbreeds of Swedish Landrace and Yorkshire, females and castrated males, aged about 9 months were used. Results are presented for individual pigs. One of the pigs was a nonresponder. The time of onset for different signs of MH varied greatly, as judged by ten independent observers. Onset of changes in heart rate, muscle temperature, blood Pco2 and pH, plasma adrenaline and noradrenaline could be scored. The metabolic events (increased Pco2 and decreased pH in blood) significantly preceded the signs of increased sympathetic activity (increased heart rate and elevated levels of catecholamines in blood). Our results support the view that increased sympathetic activity does not initiate MH. The sympathetic activity, however, strongly contributes to the fulminant MH syndrome.

The heritability of degenerative joint disease in the distal tarsal joints in Icelandic horses

The heritability of radiographic signs of degenerative joint disease (DJD) in the distal tarsal joints and hind limb lameness after flexion test of the tarsus was estimated in a population of Icelandic horses being used for riding. Furthermore, the genetic and phenotypic correlation between the radiographic signs and lameness was estimated. Of the 614 examined horses, aged 6–12 years, 420 belonged to progeny groups from 17 selected stallions and 194 were sired by unselected stallions. The heritability was analyzed by two statistical models based on the threshold liability concept, a non-linear sire model and a linear animal model. The heritability of radiographic signs of DJD in the distal tarsal joints was not found to be significantly different from zero. The h2 estimate for lameness was higher and in the order of 0.4. A positive genetic and phenotypic correlation was identified between radiographic signs of DJD in the distal tarsal joints and lameness. The results indicate that the prevalence of DJD in the distal tarsal joints could be reduced in Icelandic riding horses by breeding selection based on flexion test of the tarsus followed by radiographic examination.

A new dual chamber single lead system.

A DDD pacing system normally requires the introduction and positioning of two separate electrode leads. A VDD system may use a single lead with a ventricular electrode at the tip and at least one atrial ring electrode. The disadvantage of VDD systems is that the full range of DDD stimulation and detection alternatives is not available. The present animal study was made to evaluate a new single lead design with the distal electrode placed in the atrium and the proximal ring electrode in the right ventricle. This design permits the full range of DDD options including atriai stimulation. Acute stimulation thresholds and sensing amplitudes were stable and comparable to conventional DDD systems. Long‐term studies are on‐going.

Oxygen Pressure as Biosensor for Rate Adaptive Cardiac Pacing

A new carbon based oxygen sensor for rate adaptive cardiac pacing has been developed. It measures oxygen partial pressure In mixed venous blood. The system was implanted in six sheep with a mean follow‐up time of 261 days after implant. The sensor reacted in a physiological manner when the animals were at rest as well as during exercise. Long‐term sensor stability and sensitivity were satisfactory, and we found excellent correlation with spontaneous heart rate variations and with oxygen saturation measurements. The sensor shows great promise although our experience is still limited and further development on the concept is on‐going.