SEARCH

SEARCH BY CITATION

Thumbnail image of

For many days after the surprising news that I was selected for the 2005 Ian Donald Gold Medal Award, I could not help but turn the same question over and over in my mind: ‘What was the likelihood of a graduate from the poorest country of the Americas being selected as recipient of the highest award from this prestigious international society?’ In anybody's opinion, the answer to this question would be very simple: his chances would be very slim indeed! The first reaction might be that this individual must be very lucky; he must have been at the right place at the right time by chance. Another explanation could be that this selection was the result of hard work, plain hard work. In my case, I'm happy to acknowledge that sometimes I have been lucky in my life. As for being a hard worker, I must confess to having some reservations, since my relationship with work has been constantly tinted by a certain relativity of things, sometimes referred to as ‘the Caribbean approach to work’.

There is, however, a third dimension that could explain my presence on this podium, a dimension which, I hope, is the most influential. I am referring to my profound conviction that I am an extremely privileged member of the human community. I can only hope that this awareness was and will remain a basic motivation in my professional life, because, in my case, the list of privileges is long indeed. It started way back on my native island when I had the privilege of having access to school in a society in which 60–70% of the population was then illiterate. In the following years, the list kept getting longer and longer: the privileges of being among the happy few to attend medical school at the State University of Haïti; of completing my pediatric training in Montreal, among remarkable and devoted pediatricians at the Sainte-Justine Hospital; of moving to the United States for my pediatric cardiology training and working 2 years with two outstanding scientists—Professor Abraham Rudolph, the father of fetal cardiovascular physiology and Julian Hoffman, an authentic humanist; of starting my fetal cardiology career with a sabbatical leave during which I had the privilege of meeting world leaders in the field, such as Joshua Copel and Charles Kleinman at Yale University in New Haven, David Sahn in San Diego, Lindsey Allan and Gurleen Sharland in London, and finally in Malmö, Sweden, someone I consider as one of the warmest, brightest and certainly most honest and rigorous researchers that I have ever met, Professor Karel Marsal.

All these privileges carry with them a rigorous obligation: to transmit to others the accumulated knowledge received from generous predecessors. In other words, to consider teaching as a moral duty. But this is not enough. Considering the enormous number of unresolved health problems on this planet, to sit back and wait for other less privileged citizens to find solutions to these problems would be, to say the least, irresponsible. Research, therefore, must also be considered as a moral obligation.

I am always amazed to see how the enthusiasm, the curiosity, the genuine desire to change the world generally observed among first-year medical students frequently fade away as they progress on their journey in medicine. This metamorphosis puzzles me. Could it be possible that we, the teachers, are doing something wrong? Are we failing in our responsibility to transmit to the younger generations the vision that teaching and research are not only academic requirements for nominations and promotions, but also moral issues? Let us remember that we are all privileged members of society for the simple reason that all of us have been well educated, while 785 million adults in the world are still illiterate, deprived of the fundamental tools with which to gather knowledge. Are we giving to the younger generations real opportunities to answer their questions, however simple they might seem to be? Simple questions frequently lead to valid research projects and, more importantly, sometimes to surprising results that were not the primary goal of the so-called simple studies. We have a proverb in the islands, which expresses this concept very well: ‘Deyè môn, gan môn’, literally ‘behind a mountain, there is always another hidden mountain’. If I had to choose one sentence, characterizing any research program, this is the sentence I would put forward: ‘Deyè môn, gan môn’.

I would like to illustrate my point by sharing with you a personal experience. In 1992, we started to study in fetal lambs the hemodynamic impact of an increased placental vascular resistance, as observed in intrauterine growth restriction (IUGR). At that time, I could not find a satisfactory explanation for the appearance of diastolic retrograde flow in the umbilical arteries of severe IUGR fetuses. After all, in postnatal life, an increase in pulmonary vascular resistance does not cause reversed diastolic flow in the pulmonary arteries. With elevated placental resistance to flow created experimentally in fetal lambs, we noted that reversed diastolic flow in the umbilical artery was associated with reversed flow not only in the descending aorta but also in the aortic isthmus. This finding opened my eyes and those of all my colleagues and fellows then working with me in the laboratory, namely Amanda Skoll now in Vancouver, Sven-Erik Sonesson, presently in Stockholm and Philippe Bonnin and Georges Teyssier, now working in Paris and St-Etienne, respectively. We were all suddenly struck by a fundamental incoherence in the physiological role assigned to the ductus arteriosus in the fetal circulation.

Indeed, for you and me, with our two ventricles disposed in series, not in parallel, the presence of a patent ductus arteriosus would divert blood from its original destination, shunting either from right-to-left or left-to-right, depending on the balance between the downstream resistances of the systemic and pulmonary vascular networks. In the fetus, the ductus arteriosus does not divert any blood ejected by the right ventricle from its normal destination, which is the systemic circulation. If, in the fetus, we keep using the term right-to-left shunting through the ductus arteriosus, we must then rationally conclude that in prenatal life as in postnatal life, the two ventricles are disposed in series.

The acceptance that the two fetal ventricles perfuse the same circulation, which is the systemic circulation, in parallel fashion, carries with it a number of implications, among them the difference in ventricular outputs, the similarities in arterial pressures and the detour concept in the presence of malfunction of one ventricle. To these typical features, we must logically add the special status of the aortic isthmus. If we believe that the two fetal ventricles are disposed in parallel, we have to admit that there is only one vascular segment, which does not belong to either the left or the right ventricular outlet, namely the isthmus. In systole, the two ventricles will have an opposite influence on the flow through the isthmus: forward from the left ventricle, retrograde from the right. In diastole, when the two semilunar valves are closed, flow through the fetal isthmus will depend on the balance between the two downstream resistances of the upper and lower (subdiaphragmatic) systemic vascular networks (Figure 1). Normally, the systolic and diastolic shunt will be from the upper to the lower body because of the very low vascular placental resistance. In the presence of IUGR, however, the increase in placental resistance will first cause a reduction in the diastolic shunt and in severe cases, reversed diastolic flow will be observed.

thumbnail image

Figure 1. Illustration of the fetal aortic isthmus situated between the parallel configuration of the aortic and pulmonary arches. In diastole, the amount and direction of the shunt through the isthmus will be influenced mainly by the balance between the two downstream vascular resistances.

Download figure to PowerPoint

So, what started out as a very simple research project kept us very busy for many years. Behind the mountain of reversed flow in the umbilical arteries, we found another mountain called the isthmus. The highlights of this journey can be summarized in the following concepts: I - the aortic isthmus, not the ductus arteriosus, is the only arterial shunt in the fetal circulation; II - Doppler flow recording in the aortic isthmus is a reliable indicator of fetal individual ventricular performance; III - since the fetal aortic isthmus is the sole link between the two parallel arterial systems, namely the aortic arch perfusing the upper body and the pulmonary arch perfusing the subdiaphragmatic circulation, any change of flow or resistance affecting one of these arterial networks should influence the flow pattern within the isthmus.

I cannot finish this lecture without acknowledging the two most important privileges of my life. First, the privilege of living for more than 40 years with a wife who has been an inspiration for me and an intellectual challenge. After all these years, she knows me very well and I can confirm that this common saying is true: ‘Behind a successful man, there is frequently a surprised woman’. I have also referred frequently to duties in my lecture. My last but not least privilege was to have a father who repeatedly reminded me throughout my university years that: ‘Duty is the first degree of virtue; below it is zero!’.