| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| ||||||||||||||||||||||||||||||||||||||||||||||||||||
Short communication |
Cardiology Department, Rambam Medical Center, Haifa 31096, Israel
 |
Introduction |
|---|
 Top Introduction References |
|---|
The Doppler effect is an integral part of modern theories on the beginning of the universe (the Big Bang and the red shift). It is used today for weather forecasting, in radar and modern navigation, in studying the motion of stars and is widely used in the diagnosis of cardiovascular diseases. The effect takes its name from the Austrian physicist Christian Johann Doppler. Who was this man who gave us the tools to explore these divergent and different subjects?
Christian Johann Doppler was born 29 November 1803 in Salzburg, Austria [2–5] (Figure 1
). He came from a family of master stonemasons who had had a successful business in Salzburg since 1674 [6]. Naturally, the family tradition would have had him grow up to take over the stonemasonry business. However, Doppler's health was never very good and he was quite frail, so he could not follow in the family tradition. Because of Doppler's poor health, his father considered him suitable for the book-keeping function of the family business.
|
The Polytechnic Institute had only been founded in 1815, so it was still a new establishment when Doppler began his studies there in 1822 [2]. He excelled in his mathematical and other studies and graduated in 1825. After this, at the age of 21, he returned to his native Salzburg and finished his education (philosophy lectures at the Salzburg Lyceum) while supporting himself by giving classes in mathematics and physics. Then, for the next 4 years, he went to the University of Vienna where he studied higher mathematics, mechanics and astronomy.
At the end of his studies at the University of Vienna in 1829, Doppler was appointed as assistant to Professor Burg, the professor of higher mathematics and mechanics at the University. During his 4 years as Burg's assistant, Doppler published four mathematics papers, his first being A contribution to the theory of parallels [6]. This assistantship was only a temporary appointment and Doppler, rather older than most assistants, began to seek permanent employment at the age of 30. He applied to schools in Linz, Salzburg, Gorizia, Ljubljana, Vienna, Zurich and Prague [5, 6]. Like other great scientists, including Einstein, Doppler received many rejections in response to applications for positions.
During this time Doppler had to earn his living and spent 18 months as a book keeper at a cotton spinning factory. This was a period of sadness and great difficulty for Doppler. Discouraged, he set his eye on America and even discussed with the American consul in Munich the possibilities of emigrating and finding a teaching position in America. Indeed, he sold his possessions to finance his journey. But while in Munich Doppler received two offers to teach in highschools in Switzerland and Prague, which was then part of the Austrian Empire. Doppler chose the position in the secondary Technical School in Prague. It took a long time for the process of appointment to be concluded and Doppler commenced his position in March 1835, almost 2 years after entering the competition for the post.
However, Doppler did not like teaching elementary mathematics at the Technical School. He became frustrated, making him anxious to leave Prague. He applied for positions of professor of higher mathematics at the Polytechnic Institute in Vienna and at the Polytechnic in Prague without success. However, during the period of 1836–1838 he was able to teach higher mathematics for 4 hours a week at the Polytechnic.
Doppler married Mathild Sturm, a native of Strasburg, in 1836. At the end of 1837 the professorship in practical geometry and elementary mathematics became vacant. Doppler assumed the duties of the position but things were not that straightforward. Despite the fact that he was carrying out the duties of the position, a competition for this office was held on October 1839. Doppler did not have to take part in the competition but was hurt by the fact that it was held at all. He was formally appointed full Professor in March 1841.
Christian Doppler presented the idea that immortalized his name at a meeting of the Natural Sciences Section of the Royal Bohemian Society in Prague [7–9]. On 25 May 1842 Doppler, then 38 years old and Professor of Mathematics and Practical Geometry at the Technical Institute of Prague, presented the paper Über das farbige Licht der Doppelsterne (Concerning the coloured light of the double stars and certain other stars of the heavens).
Like many physicists before and after him, Doppler derived his inspiration for his principle from observations of natural phenomena. He wrote, "We know from general experience that a ship of moderately deep draught which is steering toward the oncoming waves has to receive, in the same period of time, more waves and with a greater impact than one which is not moving or is even moving along in the direction. If this is valid for the waves of water, then why should it not also be applied with necessary modification to air and ether waves?" [4]. Doppler applied his principle first to astronomy. The paper presented for the first time the Doppler principle, which relates the frequency of a source to its velocity relative to an observer. He theorized that, since the pitch of sound from a moving source varies for a stationary observer, the colour of the light from a star should alter according to the star's velocity relative to Earth. He stated that all stars emitted white light and that the color of some of the stars was owing to their motion toward or away from us. Although Doppler was correct in saying that his principle would change the colours of double stars, depending on which star was approaching or receding from the Earth, the effect is too small to be significant. But the principle is correct; an apparent shift in the frequency of waves received by an observer depends on the relative motion between the observer and the source of the waves. Doppler does, however, make a remarkable prediction in his paper; "It is almost to be accepted with certainty that this will in the not too distant future offer astronomers a welcome means to determine the movements and distances of such stars which, because of their unmeasurable distances from us and the consequent smallness of the parallactic angles, until this moment hardly presented the hope of such measurements and determinations". Although changes in colours were impossible to observe with the instruments of the time, the situation with sound was rather different. He theorized that sound waves from a moving source would be compressed or expanded, or that the frequency would change. This theory was not tested until 1845 [7].
Doppler did not have an easy time teaching at the Polytechnic. In 1844 his health, always less than good, failed under the strain. He had to give up teaching and requested sick leave. The situation was made worse by Doppler's students complaining that he was too harsh in his examining. Doppler was investigated and reprimanded while the students were allowed to retake their examinations. Doppler considered himself totally innocent and demanded that the reprimand be withdrawn. Eventually the reprimand was reluctantly withdrawn at the end of 1844 but Doppler was not well enough to return to his duties until 1846.
In June 1845, a Dutch meteorologist from Utrecht, Christoph Hendrik Diederik Buys Ballot (1817–1890), confirmed Doppler's principle on the railway between Utrecht and Amsterdam. Using a locomotive capable of attaining the, at that time, incredible speed of 40 mph, to pull an open cart in which horn players were riding, Ballot observed changes in the apparent pitch of the notes played by the musicians as they approached or receded [7]. In the same year Doppler set up an experiment using two groups of trumpeters, all of whom had perfect pitch. One group set up at a train station while the other set up on a train car that was to be pulled past the station. Both groups were to play the same note and Doppler's theory stated that the notes would be dissonant (that the frequencies would be different). This turned out to be true; the notes were audibly different, even though both groups of musicians were playing the same note. In 1846 Doppler published a revised version of his principle where he considered both the motion of the source and the motion of the observer [4]. Later, a French physicist, Armand Hippolyte Louis Fizeau (1818–1896), who made one of the first measurements of the velocity of light, generalized Doppler's work by applying his theory not only to sound but also to light [1, 10].
With such a difficult time in Prague, in spite of his advancements, it is no surprise that Doppler wanted to move. When he was offered the professorship of mathematics, physics and mechanics at the Academy of Mines and Forests in Banska Stiavnica, a small Czechoslovakian town, he did not hesitate. When Doppler left Prague, he did not suspect that his stay in Banska Stiavnica would be so short. The stormy year 1848 shook all parts of the monarchy and revolution broke out in Prague, Vienna and Budapest. Due to political unrest the situation in Banska Stiavnica became complicated and Doppler was once again seeking refuge. By now he was famous. He was elected to the Royal Bohemian Society in 1843 and in 1847 he was elected deputy secretary of the Society. Other honours which came Doppler's way in 1848 were election to ordinary membership of the Imperial Academy of Sciences in Vienna and an honorary doctorate from the University of Prague.
In 1849 Doppler was appointed professor at the Vienna Polytechnic, the place where he began his studies 27 years earlier. On 17 January 1850 he was appointed as the first director of the new Institute of Physics at the Imperial University in Vienna. He had reached the high point of his career. Among the candidates Doppler examined at the Imperial University, was a 20-year-old Augustinian monk, Johann Gregor Mendel. Professor Doppler was not very impressed by his mathematical ability and Mendel was refused admission to the university. Mendel was finally admitted and later laid the foundation of genetics as an abbot in a monastery.
Doppler's time as the first Director of the Institute of Physics at the Imperial University was a short one. He suffered from tuberculosis, which had spread to the larynx and made speaking increasingly difficult. By November 1852 his health had so deteriorated that he took a 6 month period of convalescence in Venice in the hope that the warmer climate would bring about some improvement. It was not to be. Doppler's wife, who had given him stable and firm support throughout their marriage, had remained in Vienna with their three sons and two daughters, awaiting his return. On realizing that his end was near, she made the journey to Venice and was with him when he died, at the age of 50, on 17 March 1853. Doppler was buried in Venice. The city of Venice honored Doppler with a "grave of honour" and the physicsts of the city erected a plaque in the colonnades of the cemetery.
No other work by Doppler came anywhere close in matching the importance of his publications on the Doppler principle. He did publish on electricity and magnetism, the variation of magnetic declination with time, as well as several publications on optics and astronomical topics. His mind would continually come up with new ideas and so he was led to invent many instruments, particularly optical instruments, and improve existing ones. Many of his ideas were quite revolutionary and he was certainly a very original thinker. Although most of the ideas just would not work in practice, one can often see the germ of some important future discovery there, even though the idea as presented by Doppler was basically incorrect.
In medicine the Doppler principle was first utilized to detect cardiac motion and the opening and closing times of the cardiac valves [3]. Satomura [11] used a continuous ultrasound beam transmitted through the chest wall to the heart. The beam reflected from the heart structures underwent a frequency shift, or Doppler shift; its magnitude and direction were based on the speed and direction of movements of the heart. The frequency of the reflected sound was proportional to the component of the velocity of the target along the line of the ultrasound beam. Initially, a simple continuous wave was used, and one had to rely on recognizing the pattern of flow in the vessels under investigation rather than actually identifying the vessel by imaging it and then looking at the flow.
In 1964, Callagan et al [12] applied the Doppler principle to the investigation of fetal blood flow and enabled fetal circulation to be studied in detail. Strandness et al [13], from the University of Washington, used continuous wave ultrasound to study flow in the peripheral vessels. Pourcelot [14], from France, contributed to much of the work on blood flow in the 1960s. He and his colleagues were involved with the development of the first Doppler equipment for the surveillance of the cardiovascular system of astronauts in space.
Technological developments with Doppler equipment brought improvements in parallel with those seen in imaging systems. Pulsed Doppler combined with real-time images to give duplex scanners expanded possibilities [15–17]. The development of real-time two-dimensional images overlaid with colour Doppler flow imaging (first developed by the Aloka Company Ltd, Japan in 1982 [18]) to indicate blood or tissue velocity, not only allowed observation and recognition of flow patterns but also allowed recognition of anatomy and pathology. More recent development of power Doppler identifies regions of tissue perfusion without being dependent on flow velocity or direction.
The introduction of pulse wave Doppler allowed localization of flow velocity measurements to specific valves and chambers [19, 20]. This way it is possible to localize murmur, determine orifice size from jet diameter and measure pulmonary flow and pulmonary artery pressure. Doppler's principle has made it possible to determine the ejection fraction of the heart, one of the most valuable measurements in cardiology. It has, to a large extent, together with echocardiography, replaced cardiac catheterization, particularly in children with congenital heart disease. The correlation between measured Doppler flow velocities and pressure gradients form the basis for assessment of valvular and vascular stenosis, prosthetic valves and permitted estimation of chamber pressure [3]. It allows determination of intracardiac shunts (atrial and ventricular septal defects) carotid and peripheral arterial stenoses and deep venous thromboses. Doppler's principle is also applicable to the diagnosis of congenital malformations of the heart in utero [3].
Doppler's discovery had no practical applicability in his own lifetime. It took more than 100 years to make an impact on cosmology, meteorology and medicine. In medicine, the Doppler concept provides blood flow and tissue movement information by non-invasive techniques. The ease of performance and its accuracy allows serial measurements to be made without subjecting the patient to risk or discomfort.
|
|
References |
|---|
|
TopIntroductionReferences |
|---|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| BJR | DMFR | IMAGING | ALL BIR JOURNALS |
