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NEW TRANSDUCER FOR DETECTING FETAL HEART SOUNDS
907 NEW TRANSDUCER FOR DETECTING FETAL HEART SOUNDS
SIR,—The device described by Dr Talbert and colleagues (Feb 25, p
426)
is
not new.
A fetal
pulse-rate monitor with
a
tuned reed
principle was described by Simpson and Leask in 1959.1 The only difference is that the vibrations were detected photoelectrically instead of with a piezoelectric bar, which was not so readily available in those
days.
Uxbndge Road, Rickmansworth WD3 2DQ
93
B. M. WRIGHT
*t*This letter has been shown to Dr Talbert and Dr Southall, whose reply follows.-ED. L. SIR,—We thank Dr Wright for drawing our attention to the ingenious device described by Simpson and Leask and to a misunderstanding that others may share. The Simpson and Leask device was not compliance matched. Wright describes that device as a vibrating reed. Like the reed in a mouth organ, it is narrowly tuned. Simpson and Leask tuned it to 60 Hz because they knew that a large proportion of the fetal heart sound energy lay around that frequency. If average heart rate is all that is required narrowly tuned devices, with their high rejection of noise signals at other frequencies, may work well. It is clear from the way Simpson and Leask distorted their signal to make it more audible that this is all they were attempting to do. We have tried to reproduce their signal (though not their noise) by feeding a tape-recorded Tapho signal through an electrical analogue of the mechanical and circuit details provided. This is shown in the top trace of the accompanying figure. When automatic rate monitoring was attempted in the late 1960s it was realised that better accuracy was to be attained by selecting frequencies between 70 and 110 Hz, which represented valve closure events (see centre trace). The lowest trace (c) is a direct write-out of the signals obtained from the Tapho transducer and is the signals used to make the other two traces. Unlike the other two systems Tapho is a non-tuned, wide-band "hi-fi" system. It relies, not on filtering, but on the high sound coupling efficiency resulting from mechanical matching of compliance to the mother to give good signal-to-noise ratio. Simpson and Leask made no attempt to produce a phonocardiograph, and had no interest in the signal, apart from obtaining a clear indication of rate. Tapho, on the other hand, enables details of cardiac function to be seen. For instance, during the illustrated systole Sz the fetus was observed to take a shallow breath on a real time ultrasonic scanner. In the lower trace the mitral/tricuspid closure signal can be seen to 1.
Simpson DC, Leask E. A foetal pulse-rate monitor. Lancet 1959; i:
1977.
be reduced at this time and a systolic murmur occurred. On the other hand the ejection recoil signal changed little, although the aortic/pulmonary closure signal was reduced in size. The murmur signal passed through the simulated Simpson and Leask system and would have been heard by them, but the changes in valve closure signal would have been lost. On the other hand the 1970 system rejects murmurs but reveals changes in valve signal strength. We believe that our suggestion, of matching the compliance of the transducing element to the softness of the mother’s skin, can improve the performance offetal phonocardiographic equipment in a similar way to that in which impedance matching of transducers has improved ultrasonic imaging. D. G. TALBERT Cardiothoracic Institute, London SW3 6HP D. P. SOUTHALL
GLYCOPHORIN C AND THE INVASION OF RED CELLS BY PLASMODIUM FALCIPARUM
SIR,—Human red cells deficient
on
the
major red cell
erythrocytes.7
Since invasion is a complex process, with initial attachment to surface receptors followed by deformation of the red cell, such a link between membrane and cytoskeleton might be important for deformation of the red cell to occur. On a patient7 1. Miller
LH, Haynes JD, McAuliff FM, Shiroishi T, Durocher JR, McGinniss MH. Evidence for differences in erythrocyte surface receptors for the malarial parasites Plasmodium falciparum and Plasmodium knowlesi. J Exp Med 1977; 146: 277-81. 2. Pasvol G, Wainscoat JS, Weatherall DJ. Erythrocytes deficient in glycophorin resist invasion by the malarial parasite Plasmodium falciparum. Nature 1982; 297: 64-66. 3. Pasvol G, Jungery M, Weatherall DJ, et al. Gycophorin as a possible receptor for Plasmodium falciparum. Lancet 1982; ii: 947-50. 4. Howard RJ, Haynes JD, McGuinniss MH, Miller LH. Studies on the role of red blood cell glycoproteins as receptors for invasion by Plasmodium falciparum merezoites. Mol Biochem Parasit 1982; 6: 303-15. 5. Facer CA. Erythrocyte sialoglycoproteins and Plasmodium falciparum invasion. Trans Roy Soc Trap Med Hyg 1983; 77: 524-30. 6. Mueller TJ, Morrison M. In: Erythrocyte membranes 2: Recent clinical and experimental advances. New York: Alan R. Liss, 1981: 95-112. 7. Anstee DJ, Parsons SF, Ridgwell K, et al. Two individuals with elliptocytic red cells J apparently lack three minor erythrocyte membrane sialoglycoproteins. Biochem 1984; 218: 615-19.
fidelity of reproduction of fetal heart sounds. Playback of tape-recorded fetal heart sound signals from a Tapho transducer (c) direct, (b) through a filter typical of heart valve selective filter used in the 1970s, and (a) through a filter and amplifier simulating a mechanically tuned device developed in the late 1950s by Simpson and Leask. To the right of each trace are shown the filter characteristics of the different systems. =mitral/tricuspid closure complex; X=aortic/pulmonary closure complex; Ej = ejection recoil complex; S = systolic period (approximate). Effect of system band width
in
sialoglycoproteins glycophorin A(&agr;)1,2and glycophorin B(&dgr;)3-5 show relative resistance to invasion by the malarial parasite Plasmodium falciparum. Although glycophorin C (used here as a collective term for sialoglycoproteins &bgr;, &bgr;1 and y6,7) constitutes ’ <10% of these surface molecules, it has been suggested that is one of the transmembrane components which is directly linked to the underlying cytoskeleton, and it has been named glycoconnectin.6 &bgr;1 and y are also associated with the cytoskeleton of normal
Frequency
Hz
SIR,—The device described by Dr Talbert and colleagues (Feb 25, p
426)
is
not new.
A fetal
pulse-rate monitor with
a
tuned reed
principle was described by Simpson and Leask in 1959.1 The only difference is that the vibrations were detected photoelectrically instead of with a piezoelectric bar, which was not so readily available in those
days.
Uxbndge Road, Rickmansworth WD3 2DQ
93
B. M. WRIGHT
*t*This letter has been shown to Dr Talbert and Dr Southall, whose reply follows.-ED. L. SIR,—We thank Dr Wright for drawing our attention to the ingenious device described by Simpson and Leask and to a misunderstanding that others may share. The Simpson and Leask device was not compliance matched. Wright describes that device as a vibrating reed. Like the reed in a mouth organ, it is narrowly tuned. Simpson and Leask tuned it to 60 Hz because they knew that a large proportion of the fetal heart sound energy lay around that frequency. If average heart rate is all that is required narrowly tuned devices, with their high rejection of noise signals at other frequencies, may work well. It is clear from the way Simpson and Leask distorted their signal to make it more audible that this is all they were attempting to do. We have tried to reproduce their signal (though not their noise) by feeding a tape-recorded Tapho signal through an electrical analogue of the mechanical and circuit details provided. This is shown in the top trace of the accompanying figure. When automatic rate monitoring was attempted in the late 1960s it was realised that better accuracy was to be attained by selecting frequencies between 70 and 110 Hz, which represented valve closure events (see centre trace). The lowest trace (c) is a direct write-out of the signals obtained from the Tapho transducer and is the signals used to make the other two traces. Unlike the other two systems Tapho is a non-tuned, wide-band "hi-fi" system. It relies, not on filtering, but on the high sound coupling efficiency resulting from mechanical matching of compliance to the mother to give good signal-to-noise ratio. Simpson and Leask made no attempt to produce a phonocardiograph, and had no interest in the signal, apart from obtaining a clear indication of rate. Tapho, on the other hand, enables details of cardiac function to be seen. For instance, during the illustrated systole Sz the fetus was observed to take a shallow breath on a real time ultrasonic scanner. In the lower trace the mitral/tricuspid closure signal can be seen to 1.
Simpson DC, Leask E. A foetal pulse-rate monitor. Lancet 1959; i:
1977.
be reduced at this time and a systolic murmur occurred. On the other hand the ejection recoil signal changed little, although the aortic/pulmonary closure signal was reduced in size. The murmur signal passed through the simulated Simpson and Leask system and would have been heard by them, but the changes in valve closure signal would have been lost. On the other hand the 1970 system rejects murmurs but reveals changes in valve signal strength. We believe that our suggestion, of matching the compliance of the transducing element to the softness of the mother’s skin, can improve the performance offetal phonocardiographic equipment in a similar way to that in which impedance matching of transducers has improved ultrasonic imaging. D. G. TALBERT Cardiothoracic Institute, London SW3 6HP D. P. SOUTHALL
GLYCOPHORIN C AND THE INVASION OF RED CELLS BY PLASMODIUM FALCIPARUM
SIR,—Human red cells deficient
on
the
major red cell
erythrocytes.7
Since invasion is a complex process, with initial attachment to surface receptors followed by deformation of the red cell, such a link between membrane and cytoskeleton might be important for deformation of the red cell to occur. On a patient7 1. Miller
LH, Haynes JD, McAuliff FM, Shiroishi T, Durocher JR, McGinniss MH. Evidence for differences in erythrocyte surface receptors for the malarial parasites Plasmodium falciparum and Plasmodium knowlesi. J Exp Med 1977; 146: 277-81. 2. Pasvol G, Wainscoat JS, Weatherall DJ. Erythrocytes deficient in glycophorin resist invasion by the malarial parasite Plasmodium falciparum. Nature 1982; 297: 64-66. 3. Pasvol G, Jungery M, Weatherall DJ, et al. Gycophorin as a possible receptor for Plasmodium falciparum. Lancet 1982; ii: 947-50. 4. Howard RJ, Haynes JD, McGuinniss MH, Miller LH. Studies on the role of red blood cell glycoproteins as receptors for invasion by Plasmodium falciparum merezoites. Mol Biochem Parasit 1982; 6: 303-15. 5. Facer CA. Erythrocyte sialoglycoproteins and Plasmodium falciparum invasion. Trans Roy Soc Trap Med Hyg 1983; 77: 524-30. 6. Mueller TJ, Morrison M. In: Erythrocyte membranes 2: Recent clinical and experimental advances. New York: Alan R. Liss, 1981: 95-112. 7. Anstee DJ, Parsons SF, Ridgwell K, et al. Two individuals with elliptocytic red cells J apparently lack three minor erythrocyte membrane sialoglycoproteins. Biochem 1984; 218: 615-19.
fidelity of reproduction of fetal heart sounds. Playback of tape-recorded fetal heart sound signals from a Tapho transducer (c) direct, (b) through a filter typical of heart valve selective filter used in the 1970s, and (a) through a filter and amplifier simulating a mechanically tuned device developed in the late 1950s by Simpson and Leask. To the right of each trace are shown the filter characteristics of the different systems. =mitral/tricuspid closure complex; X=aortic/pulmonary closure complex; Ej = ejection recoil complex; S = systolic period (approximate). Effect of system band width
in
sialoglycoproteins glycophorin A(&agr;)1,2and glycophorin B(&dgr;)3-5 show relative resistance to invasion by the malarial parasite Plasmodium falciparum. Although glycophorin C (used here as a collective term for sialoglycoproteins &bgr;, &bgr;1 and y6,7) constitutes ’ <10% of these surface molecules, it has been suggested that is one of the transmembrane components which is directly linked to the underlying cytoskeleton, and it has been named glycoconnectin.6 &bgr;1 and y are also associated with the cytoskeleton of normal
Frequency
Hz