Denis Simard

Angiotensin inhibition and coronary autoregulation in a canine model of LV hypertrophy

Abstract. In humans with hypertension and LV hypertrophy, beneficial effects of angiotensin inhibition may be associated with preserved autoregulatory capacity. We studied the effect of acute angiotensin converting enzyme (ACE) inhibition on coronary autoregulatory pressure-flow relations and transmural distribution of blood flow in sham and LV hypertrophy dogs. Heart/body weight ratio increased (p = 0.001) from 5.5 ± 0.7 in sham to 6.9 ± 0.5 in LV hypertrophy dogs. The lower coronary pressure limit (LPL) on the pressure-flow relation was 47 ± 2 mmHg in sham and 57 ± 6 mmHg (p = 0.001) in LV hypertrophy dogs; after acute ACE-inhibition the LPL was reduced to 40 ± 5 mmHg and 49 ± 6 mmHg (p = 0.001), respectively. Transmural distribution of blood flow was preserved at the LPL in both groups before and after acute ACE-inhibition. Concomitant blockade of prostaglandin and nitric oxide release and bradykinin catabolism had no additional effects on the LPL and distribution of blood flow. After acute ACE-inhibition in LV hypertrophy dogs, distribution of blood flow across the LV wall was preserved and subendocardial vascular reserve was maintained even though the LPL was significantly lower. Preservation of autoregulatory capacity by ACE inhibitors contributes to beneficial outcome in patients with hypertension and LV hypertrophy.

Myocardial blood flow after chronic cardiac decentralization in anesthetized dogs: effects of ACE-inhibition

Coronary blood flow regulation was studied in dogs with an intact or chronically decentralized intrinsic cardiac nervous system. We also examined the effect of angiotensin-converting enzyme inhibition (ACEI) on coronary autoregulatory pressure-flow relations and distribution of blood flow since the renin-angiotensin system may play a critical role in vasoregulation. Myocardial oxygen demand was reduced in the chronic decentralized dogs compared to the control dogs. The lower pressure limit of the autoregulatory pressure-flow relation was similar for the control and chronic decentralized dogs (47+/-2 and 44+/-7 mm Hg, respectively; p = NS). After ACEI, the lower pressure limit shifted leftward to 40 mm Hg (p=0.001) in both groups. Concomitant blockade of cyclooxygenase, bradykinin catabolism and nitric oxide synthase had no further effect on the lower pressure limit. Total myocardial blood flow was lower (p=0.001) in the chronic decentralized dogs compared to the control dogs, while transmural distribution of blood flow was preserved in both groups. The results show that even though myocardial oxygen requirements are lower in the chronically decentralized heart compared to controls, coronary autoregulation is maintained at levels observed in normally innervated hearts. The present findings indicate that intrinsic cardiac neurons contribute to coronary autoregulatory control and myocardial blood flow distribution even in the absence of cardiac connections to the central nervous system. In addition, in the chronic decentralized dog, ACEI allows the heart to work at lower coronary perfusion pressures while myocardial blood flow distribution is preserved.

RAPPORT À LA CULTURE ET APPROCHE CULTURELLE DE L’ENSEIGNEMENT

Cet article presente les resultats d’une recherche exploratoire qui visait a comprendre la relation entre le rapport a la culture d’etudiants en formation initiale a l’enseignement et la mise en œuvre d’une approche culturelle de l’enseignement dans la discipline « francais », ainsi qu’a preciser le cadre theorique du rapport a la culture. Nous avons analyse les textes de trente ‐ cinq etudiants (n=35), dans lesquels ils devaient definir ce que signifie pour eux la culture ainsi que leur conception du role de l’enseignant dans le developpement culturel de leurs futurs eleves. L’analyse de contenu et de discours, realisee dans chacun de ces textes, combinee a plusieurs travaux sur le rapport au savoir − notamment ceux de l’equipe ESCOL − nous a permis dans un premier temps de circonscrire quatre types de rapport a la culture : desimplique, instrumentaliste, scolaire et integratif/evolutif. De plus, comme il s’agit de futurs enseignants, nous avons degage deux plans de leur rapport a la culture, soit les plans individuel et pedagogique − ce dernier etant compris comme l’accompagnement de l’eleve dans son appropriation de la culture. Enfin, l’analyse montre que le rapport a la culture de type integratif ‐ evolutif sur le plan individuel semble etre un prealable a la mise en œuvre d’une approche culturelle de l’enseignement. Mots cles : Culture, rapport a la culture, approche culturelle de l’enseignement, formation initiale a l’enseignement In this article, we present the results of an exploratory research which aimed at understanding the relationship between the relation to culture of students in a teacher education program and the undertaking of a cultural approach to French teaching, and at specifying the relation to culture’s theoretical framework. We have analyzed texts written by thirty ‐ five aspiring teachers (n=35), who had to tell how they define culture and how they conceive the teacher’s role in students’ cultural development. The combination of content and discourse analysis of each of these texts and of writings on the relation to culture – especially those of the ESCOL team – led us at first to circumscribe four types of relation to culture: the non ‐ implicated type, the instrumentalist type, the schooled type and the integrative ‐ evolutive type. Furthermore, since the research’s participants are prospective teachers, we have identified two sides of their relation to culture, the individual side and the pedagogical one – the latter being understood as the accompanying of the learner in his or her appropriation of culture. Finally, the analysis shows that an integrative ‐ evolutive type of relation to culture on the individual side seems to be a prerequisite to the undertaking of a cultural approach to teaching. Key words: Culture, relation to culture, cultural approach to teaching, teacher education program

Blood flow to the heart from noncoronary arteries: an intriguing but challenging research field.

INTRODUCTION It has been proven that blood supply to the heart can include blood from noncoronary collateral circulation. Whether this network can somehow be augmented to provide an alternative therapy for ischemic patients is an intriguing hypothesis with no clear answer yet due to the challenging nature of this research field. In an attempt to enhance noncoronary collateral blood flow, we experimented with left internal thoracic artery ligature and angiogenic growth factors in a canine model. MATERIALS AND METHODS Eight dogs weighing between 20 and 29 kg were scheduled for three operations each. Neutron-activated microspheres were used for blood flow measurement throughout the study. The first operation was a left thoracotomy for ameroid constrictor positioning at the proximal segment of the circumflex coronary artery. Three weeks later the left internal thoracic artery was ligatured distally. A micro-pump was positioned in the mediastinum, connected with a small catheter inserted in the proximal segment of the left internal thoracic artery for slow delivery of vascular endothelial growth factor. The protocol called for a coronary angiography 4 weeks later, sacrifice of the animals, and explantation of the heart for microsphere analysis. RESULTS Four of the dogs failed to tolerate ameroid constrictor positioning by thoracotomy and died after the first operation. The remaining four dogs underwent a second operation to ligate their left internal thoracic arteries and implant micro-pumps with catheters. The implant was a success, but only one dog survived in the postoperative period. When the last dog was voluntarily sacrificed after a third operation, coronary angiography showed no neovascularization, nor did heart slice analysis reveal microspheres. CONCLUSIONS Despite the technical challenge of building research protocols to exactly quantify blood from noncoronary arteries, there are many historical, anatomical, physiopathological, clinical, radiological, and surgical indications suggesting that blood flow from extracardiac structures may play an important role in ischemic heart disease. Our preliminary investigation combining internal thoracic artery occlusion and angiogenic growth factors was unsuccessful for several reasons, the main one being it was too heavy a protocol for the dogs. Despite this, we think that noncoronary collateral blood flow represents an intriguing research field worthy of debate and further study.