Effects of a modified Q-switched Nd-YAG laser on human vascular tissue: an ex vivo study.

RATIONALE AND OBJECTIVES: Relatively disappointing results with continuous-wave lasers stimulated us to evaluate pulsed lasers for interventional radiology. In this article, we describe our efforts to assess the effects of this technology ex vivo. METHODS: We modified a Q-switched yttrium aluminum garnet (Nd-YAG) laser to emit pulses of 300 mJ maximum with a 20-Hz repetition rate, at 1064 nm, and with a duration that ranged from 300 ns to 2.3 microseconds. The lengthening of the pulse duration by a factor of 100 (compared with the conventional nanosecond Q-switched Nd-YAG laser) and the ability to define it exactly were obtained by controlling the opening and closing of the Pockels cell electronically. Lengthening the pulse duration made it possible to reduce peak power while conserving the same total energy. In this way, high energy was transmitted through thin optical fibers. RESULTS: One hundred fifty millijoules with 2-microsecond pulses, 140 mJ with 1-microsecond pulses, and 100 mJ with 500-ns pulses were transmitted through a 300-micron silica-polymer fiber. The transmission coefficient was identical for the three pulse durations. Ex vivo irradiation experiments were performed on human atheromatous arteries in saline solution using a 300-micron diameter optical fiber. Craters were easily obtained. Their depth and width were related to maximum energy transmission and irradiation time. No carbonization occurred and no destruction of the optical fiber was observed. CONCLUSION: A modified Q-switched Nd-YAG laser can transmit high-energy pulses through thin optical fibers without damaging them and can destroy human atheroma in an ex vivo setting.

Ventral hernia repair with simultaneous panniculectomy.

The repair of a ventral hernia in an obese patient presents an interesting clinical challenge. We retrospectively reviewed the charts of 55 patients who, over a 12-year period from 1983 to 1995, concomitantly underwent both ventral herniorrhaphy and panniculectomy or abdominoplasty. In six of 55 patients, the hernia was recurrent. Forty-six patients had primary abdominal wall hernias or diastasis recti. Nineteen of 55 patients had weight greater than 200 lbs. This last subset of patients had a significantly higher incidence of complications, such as seroma, cellulitis, and persistent wound drainage. In our 55 patients, we experienced only two hernia recurrences (3.6%) during an average patient follow-up of 53 weeks. From this experience, we believe that simultaneous ventral hernia repair and panniculectomy is a safe and efficacious approach to these two problems so commonly found in the obese patient. Patients with a preoperative weight greater than 200 lbs can be expected to have a greater risk of wound complications. In all cases, the wounds eventually healed with no long-term sequelae.

[Cardiac relaxation in experimental chronic myocardial hypertrophy: role of the sarcoplasmic reticulum]. / La relaxation cardiaque au cours de l'hypertrophie myocardique chronique expérimentale: le rôle du réticulum sarcoplasmique.

The relaxation phase was studied in normal rat hearts submitted to chronic myocardial pressure and/or volume overload (stenosis of the abdominal aorta, aortic regurgitation, aorto-caval fistula) and in spontaneously hypertensive rats, some of which also had aorto-caval fistulae. Four indices were chosen to quantify the relaxation phase: maximal velocity of relaxation during contraction with preload alone, the negative peak of the derivative of isometric tension, and two other indices testing the sensitivity of the relaxation phase to other conditions of load. The first two indices were found to be depressed during chronic myocardial overload, especially with aorto-caval fistulae and mixed overload. On the other hand, the other two indices of the degree of sensitivity to the relaxation load by two different methods showed no significant difference between chronically overloaded and control hearts, though changes were observed after acute hypoxia. These two indices are related to morphological development and to the functional state of the sarcoplasmic reticulum. These results suggest that the rate of calcium uptake by the sarcoplasmic reticulum is reduced during chronic myocardial overload but that the myocardium retains its ability to regulate the relaxation phase with respect to time and the degree of total load. This property disappears temporarily after hypoxia when the heart behaves like frog myocardium which has practically no sarcoplasmic reticulum.

[In vitro opening of human atheromatous coronary arteries using a pulsed laser]. / Désobstruction in vitro des artères coronaires humaines athéromateuses par laser impulsionnel.

This study was undertaken to assess the respective values of pulsed and continuous laser emission for in vitro recanalisation of very stenosed atheromatous human coronary arteries. The Nd-YAG laser used emitted a 10 Hz 10 ns burst in the infrared band (1 064 microns). Previous spectroscopic studies had shown no specific band of absorption in the spectral field of emission of the usual lasers. The laser beam was focused in the axis of the segment of coronary artery irradiated. The crater or neo lumen obtained usually had irregular walls. No perforation of the arterial wall or macroscopic debris were observed. Histological studies showed minimal burn lesions with sparse coagulation necrosis limited to a few tens of micron thickness. The percentage recanalisation obtained with pulses of 200 mJ attained 50% for a total energy of 450 J delivered in 2 mn. This study confirmed the feasibility of disobliteration of atheromatous coronary arteries by pulsed laser. Our results suggest that ultra short pulsed laser acts more by a mechanical than by a thermal mechanism which may lead to less side effects than observed in vivo with continuous laser emission.

[The use of lasers in the study of cardiac mechanics]. / Apport du laser à l'étude de la mécanique cardiaque.

Cardiac and skeletal muscles exhibit regularly spaced light and dark transverse striations (the I and A bands respectively). Consequently, when they are illuminated by a laser beam, they behave like diffraction gratings. The diffraction line spacing varies inversely with the sarcomere length. Real-time kinetics of sarcomere can be measured with a high accuracy. The analysis of the diffraction pattern indicates a high degree of synchronization of sarcomere movements (contraction and relaxation). This technique represents a powerful method to analyse the mechanical behaviour of heart muscle at subcellular level.