Biomedical subjects

N Hedin

Publications and source records attributed to N Hedin.

5 recordsLinked to original sources

PubMed2001

Mortality after carotid body denervation in rats.

Carotid body denervation (CBD) in neonatal goats and piglets results in minimal irregular breathing and no fatalities. Redundancy and/or plasticity of peripheral chemosensitivity and a relatively mature ventilatory control system at birth may contribute to the paucity of CBD effects in these species. In the present study, we tested the hypothesis that CBD mortality would be greater in neonates of a less mature species such as the rat. We found that the mortality in rats denervated at 2-3 and 7-8 days of age was significantly higher (P < 0.05) than in sham-CBD rats. In all surviving rats, pulmonary ventilation during hypoxia was lower in CBD than in sham operated rats 2 days after denervation. In surviving rats denervated during the 7th and 8th postnatal days, there was also reduced weight gain and pulmonary ventilation during eupnea, including apneas up to 20 s in duration. However, the effects of CBD were compensated within 3 wk after denervation. Local injections of NaCN indicated that aortic chemoreceptors might have been one of the sites of recovery of peripheral chemosensitivity. We concluded that CBD has higher mortality in newborn rats than in other mammals, possibly because of the relative immaturity of these animals at birth. Nonetheless, in survivors there was enough redundancy and plasticity in the control of breathing to eventually compensate for the consequences of CBD.

Age Factors↗

PubMed2000

Accurate intensities of broad NMR lines from composite pulse experiments.

Accurate determination of integral intensities of broad lines is difficult when spin relaxation during the applied pulses cannot be neglected and/or when ringing of the tank circuit interferes with the signal. Here we present an extension of the analytical solution of the generalized Bloch equations (G. A. Morris and P. B. Chilvers, J. Magn. Reson. A 107, 236 (1994)), which is then used to evaluate the signal intensity obtained in a composite pulse experiment designed to cancel ringing effects. Comparing intensities of broad and narrow (81)Br spectral lines tests and proves the accuracy of this approach.

Bromine↗

PubMed1998

Temperature imaging by 1H NMR and suppression of convection in NMR probes

A simple arrangement for suppressing convection in NMR probes is tested experimentally. Diffusion experiments are used to determine the onset of convection and 1H temperature imaging helps to rationalize the somewhat surprising results. A convenient new 1H NMR thermometer, CH2Br2 dissolved in a nematic thermotropic liquid crystal, is presented. Copyright 1998 Academic Press.

Journal Article↗

PubMed1992

Lead extraction. Indications and techniques.

Each of the extraction techniques and their ancillary tools was reported as used successfully; however, until now, no technique has been successful when used in more than a few isolated instances. The technique for intravascular countertraction and the associated tools described in this paper were devised and selected in an attempt to develop one technique to be used on all patients, with all types of leads, and with a very low complication rate. Its versatility permitted single or multiple lead extractions combined with the precision of selecting and extracting a specific lead. In our experience, as well as the experience of others, the techniques described in this paper have proved to be superior by minimizing the inherent risk and morbidity, allowing us to expand the indications for lead removal beyond septicemia and free-floating leads, to include infection, abandonment of pockets, and replacement of malfunctioning or fractured leads. Intravascular countertraction was a consistently safe and efficacious method of removing transvenous pacemaker leads regardless of the duration of the implant, thus permitting extractions in patients not considered candidates for a more extensive surgical procedure. Intravascular countertraction encompasses surgical and fluoroscopic techniques possessed by most physicians experienced in pacemaker and automatic implantable cardioverter defibrillator implants. However, there is a learning curve, predicating caution for the inexperienced physician. In addition, advanced surgical skills may be needed in handling associated conditions such as debridement and primary closure of chronically inflamed tissues, especially in submuscular pockets and sinus tracts in the neck. Although the potential for a cardiovascular complication is small, it does exist, and cardiovascular surgical backup is a recommended precaution.

Cardiopulmonary Bypass↗

PubMed1991

Intravascular techniques for extraction of permanent pacemaker leads.

Intravascular techniques were used to extract 226 leads from 124 patients. Indications for lead extraction were life-threatening septicemia (30%), complications of free-floating leads (2%), abandonment of pockets (40%), and replacement of malfunctioning leads (28%). Extraction tools included flexible, telescoping sheaths advanced over the lead to dilate scar tissue and apply countertraction, deflection catheters, and wire basket snares. Countertraction is defined as the direct force of traction on the lead countered by the circumference of an extraction sheath. One hundred sixty-four leads were extracted through the superior vena cava by advancing the sheaths over the lead to the myocardial wall. Most of these leads passed through the subclavian vein. An approach through the inferior vena cava was used for the remaining 62 leads. The countertraction sheaths were passed from the femoral vein into the right atrium. A maneuvering catheter and an extracting snare were placed inside the sheaths. The lead was positioned by the maneuvering catheter, entangled in the extracting snare, and the sheaths advanced over the snare and lead to the myocardium. An atriotomy by means of a limited surgical approach was required to free one lead. One infected lead broke 5 cm from the electrode and was removed through a median sternotomy, ventriculotomy, and retrograde extraction. All patients had unremarkable recoveries. Intravascular countertraction techniques proved to be a viable alternative, minimizing the risks and morbidity of lead removal.

Adolescent↗