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Cause of the disappearance of the auscultatory sound in indirect blood pressure measurements
Cause of the disappearance of the ausculta-tory indirect blood pressure measurements
sound
in
Hiroshi Irisawa, M.D.* Hiroshi Goki, M.D.** Masato Yukutake, M.D.** Hiroshima, Japan
T
he presence of an auscultatory gap in the indirect measurement of human blood pressure has been observed frequently among patients, especially those suffering from arterial hypertension. Practically, this source of error can be eliminated by simultaneous palpation of the arterial pulse, which persists throughout an inaudible range of systolic pressure. However, the cause of this auditory gap is still unknown.7 According to a standard textbook of physiology, the respiratory variation of blood pressure may cause a rhythmic disappearance of the sound, if the systolic level is closely approximated and the decompression is slow.’ The present experimental design consists of a direct recording of the auscultatory sound, for verification of this rhythmical disappearance of the sound, and for the purpose of obtaining a more precise knowledge of the turbulent flow in systolic pressure. Methods
Fig. 1 illustrates schematically the method used during this experimental design. A small contact microphone was sutured inside the pressure cuff so that the Aided
Korotkoff sounds could be recorded through the convenient low-level RC-coupling amplifier. The time constant of this amplifier was 0.3 second; no special high-cut filter was used for the vibration recording. The vibration tracing was displayed on pen 1 of the four-channel direct-ink-writing recorder. According to Geddes, Spencer and H~ff,~ the frequencies of the Korotkoff sounds range from 2.5 to 250 cycles per second. Although the frequency response of the direct-writing pen recorder reduced greatly beyond 70 cycles per second, loss of higher frequency components appeared to be practically negligible. The continuous recording of the linger volume was displayed on pen 2. The volume recorder consisted of a small pilot lamp and a Claire crystal photocell (CL-3). The intensity of the light transmitted through the finger altered the output voltage of the photocell, which was amplified by the direct-coupled amplifier and recorded by the ink-writing recorder. From this tracing, both the peripheral arterial pulsation and the change in volume of the finger can be monitored. Ko attempts have been made to calibrate the curve in terms of the
by Research Grant H-6968 iron the National Heart Institute, National Institutes Public Health Service. Received for publication Jan. 23. 1962. *Department of Physmlogy, School of Medicine. Hiroshima University, Hiroshima. Japan. **Department of Internal Medicine, School of Medicine, Hiroshima University. Hiroshima.
308
of Health,
Japan.
United
States
Sound recording in blood $ressure measurements
absolute change in volume of the finger. The digital volume curve does not necessarily represent the flow of blood through more proximal tissues. In the present communication, it is assumed that the digital volume and the blood flow in the forearm have a rough correlation. The sph~~gmo~llano~neter cuff was inflated manLldly, although the inflation bulb is not shown in the illustration. The pressure inside the sphygmomanometer cuff was recorded continuously by the electrical pressure manometer (MI’-4T, Nihon Koden, functionally equivalent to the Statham gauge P-23) and was displayed on pen 3 of the recorder. The pressure was also measured subjectively by means of the mercury manometer, and recorded as a dot on the time scale at the top of the illustration.
309
In the fourth channel, the thoracic movement was recorded as an indication of the respiratory movement. The movement of the thoracic wall was recorded by means of a strain gauge fixed directly on the thoracic wall. In Fig. 2, a small thermistor was placed in the mouthpiece so that the respiration could be registered in terms of the variation in electrical resistance. Here again, the tracing illustrates only the relative movement, and no attempts have been made to measure the absolute change in volume of respiration. The downward deflection indicates the act of inspiration. In Fig. 3, instead of the respiratory tracing, the phasic change in the cuff pressure was amplified and recorded, in the bottom tracing. More than 40 healthy medical students participated in this experiment. 0ne of
..
FINGER i
:
VOLUME-L i.L_t.
!
iA.:
,
_i
.Jb.“LL..i
Fig. 1. LejL: Experimental setup of indirect blood pressure measurement. IKIC.: Crystal microphone sutured inside the sphygmomanometer cuff. CR.AMP: CR-coupled amplifier, time constant 1 second. P.T.: Pressure transducer (MP-1’f’). Right: Typical esperimental tracings: Top, The time interval of 1 second. Pen 1, The vibration tracing picked up from the contact microphone; the two arrow-s indicate where the slight reduction in the amplitude of vibration occurred. Pen 2, The finger volume curve; the upward tracing indicates the increase in the blood volume of the finger. Pen 3, The pressure inside the sphygmomanometer cuff. Pen 4, The respiration curye; the upward deflection indicates the expiration.
310
Irisawa,
Goki, and
Firr. 2. A, Rhythmical variation of vibratjon due to the temporal in A and B.
Yukutake
of vibration tracing due to the deep respiration. B, Reduction arrest of respiration. The amplification of the respiration
them had a blood pressure reading over 140 mm. Hg: the other readings ranged frotn 120 to 100 mtn. Hg. Results A typical vibration recording during measurement of pressure can be seen in the tracings on the right-hand side of Fig. 1. The top markings are the time scale of 1 per second. The vibration tracing is shown in the second row. Since the vibration tracing correlates fairly well with the sound heard by the auscultatory method, we may refer this tracing to the sound tracing. The initial dark triangular deflection indicates the inflation artifact. The duration of this artifact is about 5 seconds, and indicates the time the pressure cuff is inflated. The audible sound begins at about 90 mm. Hg in this particular instance. The amplitude of this sound is about 64 mv., and the deflection gradually increases up through the next
in the amplitude curve is different
four cycles. At the fifth cycle, .however, the deflection decreases, as is indicated by the first arrow. In the sixth cycle, the deflection again increases, and at the eleventh cycle the reappearance of the reduction in amplitude is observed. The two arrows on the vibration tracing show where the reduction in the vibration occurred. One can also notice that these points clearly correlate with the onset phase of inspiration. The rapid sweep of the paper indicates the change in wave pattern during this reduction in amplitude. It is suggested, therefore, that these points are related to the clinical manifestation of the pressure measurements. The fingervolume tracing indicates that the flow of blood to the finger does not increase until 70 mm. Hg, where the sound becomes progressively greater. Since we noticed that a slight decrease in vibration correlated with the respirator) movement, we designed another experi-
Sound recording in blood $ressure measurements
ment in which the grade of respiration was intentionally changed. This was accomplished by having the subject breathe deeply. Fig. 2,A shows a tracing similar to that in Fig. 1, but obtained from another subject. The repeated deep respiration, which begins shortly after the beginning of the deflation of the sphygmomanometer cuff, is demonstrated in the bottom tracing. The dot mark superimposed on the time scale coincides with the pressure reading which begins from 170 mm. Hg and ends at 50 mm. Hg. The interval of the two markings indicates a fall of 10 mm. Hg in cuff pressure. It is noted that the definite audible sound is recorded at 140 mm. Hg in this particular
instance. Here again, the region of reduction in the vibration tracing can be noticed between 130 and 120 mm. Hg. The reduction in the amplitude of vibration is so remarkable compared to the preceding experiment in Fig. 1, that by auscultation the definite auscultatory gap coincides with the reduced region. It is noted that the reduction in the amplitude of the vibration tracing coincides with the temporal decrease in the upward deflection of finger volume, and also with the onset of inspiration. The decrement in vibration around 100 mm. Hg is also correlated with the onset of deep inspiration, but the large amplitude of vibration indicates that it is an audible sound.
Fig. 3. Effect of the increased peripheral resistance on the Korotkoff sounds. Through an application of the lower pressure cuff (CU$ 2) the blood flow in the lower arm is occluded in B and D. Note that the rhythmical variation of Korotkoff sounds decreases in A, which suggests that the primary cause of this reduction in amplitude is the change
in blood
flow.
311
312
Irisawa,
Goki, and Yukutake
When the pressure cuff is deflated slowly, the rhythmical variation in the amplitude of the vibration tracing is recorded. In such instances, several inaudible zones have appeared in the vibration record, and it can be demonstrated that the inaudible zone is definitely correlated with the onset of inspiration. Although the reduction in the amplitude of the vibration could be seen in the tracing each time the inspiration began, at the first and second places it was inaudible and at the third gap it was definitely audible, although the sound was muffled. The temporal reduction in the finger-volume tracing also coincides with the inaudible zone. In Fig. 2,B the cuff pressure begins to deflate at about 170 mm. Hg, where the initial dot mark on the time scale is recorded. The following dots on the time scale indicate reductions of 10 mm. Hg of cuff pressure, as is given in the illustration. In this instance, the respiration was intentionally changed by asking the subject to stop his breathing temporarily. Because of this procedure, the blood pressure rose slightly, and during this temporal arrest of the respiration the marked reduction in vibration was recorded. The reduction lasts fairly long and it resembles the clinical auscultatory gap. Next, the flow of blood in the forearm was intentionally occluded by application of the second pressure tourniquet on the forearm (see Fig. 3), in order to see how the flow of blood in the forearm is related to the inaudible gap. Fig. 3,A shows the control tracing before the second tourniquet was applied to the forearm. As was mentioned before, instead of recording the respiratory movement, the small phasic pressure fluctuation in the cuff was amplified, and it is shown in the bottom tracing. Fig. 3,B illustrates the results, where the lower cuff is inflated prior to measurement of pressure. ;2yo remarkable difference in the vibration tracing is observed between A and B, except for a slight reduction in amplitude in the vibration. The fact that the systolic blood pressure is slightly elevated appears to be due to spontaneous fluctuation in the blood pressure. The finger-volume tracing is altered remarkably in B, which suggests the continuous increment of finger volume through deep
arterial supply. Fig. 3,C illustrates the effect of deep respiration in the same subject; this tracing was obtained a short while after the previous one, without application of the second tourniquet on the forearm; the remarkable disappearance of the vibration tracing, which coincides with the inaudible zone of the auscultatory method, is noted. It can be seen that the remarkable reduction in finger volume coincides with the inaudible gap, which indicates a decrease in the flow of blood in the finger. Fig. 3,D illustrates the effects of the combination of both the deep respiration and the compression of the lower tourniquet. linder this condition, the variation in the sound tracing is remarkably depressed, which indicates that the change in blood flow is the principal factor in the formation of this inaudible gap. Discussion
Many investigators have made graphic recordings of the Korotkoff sounds.2*5s6 Geddes, Spencer and Hoff4 recently recorded the Korotkoff sounds in a normotensive subject, and stated that the auscultatory gap occurs in Phase II, wherein the murmur-like sounds can be heard with the auscultatory method. They did not discuss the mechanism of formatiorr of this gap. The present experiment shows that the auscultatory gap produced by deep inspiration is caused by a decrease in blood
now. The fact that the volume of the finger did not increase until 90 mm. Hg was reached, and that it then rapidly increased from 90 to 70 mm. Hg, suggests that the flow in an occluded artery follows the formula, pressure equalsflow multiplied by the resistance. During occlusion of the artery, the resistance may be at its greatest value, and the pressure and the flow both at their minimum. At the time the blood flow resumes in the slightest degree, the pressure in the forearm is lower than that in the upper arm because the resistance to the artery is still considerable. The flow begins to increase slightly, and the resistance decreases slightly, in the next moment. As a result, the pressure under the cuff increases slightly. ‘Therefore, the relationship between the flow and the pressure should not be linear, but hyper-
Sound recording in blood pressure
bolic. This may explain the cause of the nonlinear increase in finger volume although the pressure falls linearly. The tracing shows that the inaudible zone clearly coincides with the region of high cuff pressure, where the blood flow in the lower part of the cuff appears to be small and below the control level. The decrease in the flow of blood through the artery tends to decrease the acceleration of the column of blood in the peripheral arterial tree, so that turbulence would temporarily be stopped. On the other hand, the arterial pulse may be palpable, since the cuff pressure is below the systolic pressure. The immediate application of these discussions to auscultatory gaps which are frequently observed in patients must be deferred until more precise observations in patients are available. Erlanger3 found that the occlusion of the peripheral artery with the second cuff did not affect the auscultatory sound. The statement is true, as can be seen in tracings A and B of Fig. 3, and this result indicates that the increase in peripheral arterial resistance does not cause any qualitative change in the auscultatory sound. Under the condition of the combination of deep breathing and application of a tourniquet, the periodic variation in the auscultatory sound disappeared, although the respiratory rhythm remained slightly because of the change in systemic blood pressure. It appears to be reasonable to conclude th:lt the auscultatory gap produced by deep inspiration is due to the decrease in blood How and not to the rhythmic change in the s!-stemic arterial pressure.
measurements
313
Summary The correlation between Korotkoff sounds and respiration was studied. The Korotkoff sounds, the finger volume, the sphygmomanometer cuff pressure, and the respiratory movements were recorded on the four-channel direct-writing recorder. The slight reduction in the vibration superimposed on the Korotkoff sounds was reinforced when the subject intentionally continued deep respiration, and the reproducible auscultatory gap was recorded. The cause of this auscultatory gap due to inspiration was suggested to be a decrease in the flow of the blood in the arm. IVe are grateful to Professor Sunao Wada encouragement throughout the course of this
for his work.
REFERENCES 1. Bazett, H. C., and Bard, P.: Indirect measurement of arterial blood pressure in man, in Bard, P., editor: Medical physiology, St. Louis, 1956,The C. V. Mosby Company, p. 124. 2. Currens, J. H., Brownell, G. L., and Aronow, S.: An automatic blood pressure recording machine, New England J. Med. 256:780. 19.57. 3. Erlanger, J.: Studies in blood pressure estimation by indirect methods, Am. J, Physiol. 40:82, 1916. 4. Geddes, L. A., Spencer, W. A., and Hoff, H. E.: Graphic recording of the Korotkoff sounds, AM. HEART J. 57:361, 1959. 5. Gilson, W. E., Goldberg, H., and Slocum, H.: An automatic device for periodically determining and recording both systolic and diastolic BP in man, Science 94:194, 1941. 6. Rose, J. C., Gilford, S. R., Broida, H. P., Solar, A., Partenope, E. A., and Freis, E. D.: Clinical and investigative application of a new instrument for continuous recording of BP and heart rate, New England J. Med. 249:615, 1953. 7. Rushmer, R. F. : Pressure measurements, itt Cardiovascular dynamics, Philadelphia, 1961, W. B. Saunders Company, p. 137.
sound
in
Hiroshi Irisawa, M.D.* Hiroshi Goki, M.D.** Masato Yukutake, M.D.** Hiroshima, Japan
T
he presence of an auscultatory gap in the indirect measurement of human blood pressure has been observed frequently among patients, especially those suffering from arterial hypertension. Practically, this source of error can be eliminated by simultaneous palpation of the arterial pulse, which persists throughout an inaudible range of systolic pressure. However, the cause of this auditory gap is still unknown.7 According to a standard textbook of physiology, the respiratory variation of blood pressure may cause a rhythmic disappearance of the sound, if the systolic level is closely approximated and the decompression is slow.’ The present experimental design consists of a direct recording of the auscultatory sound, for verification of this rhythmical disappearance of the sound, and for the purpose of obtaining a more precise knowledge of the turbulent flow in systolic pressure. Methods
Fig. 1 illustrates schematically the method used during this experimental design. A small contact microphone was sutured inside the pressure cuff so that the Aided
Korotkoff sounds could be recorded through the convenient low-level RC-coupling amplifier. The time constant of this amplifier was 0.3 second; no special high-cut filter was used for the vibration recording. The vibration tracing was displayed on pen 1 of the four-channel direct-ink-writing recorder. According to Geddes, Spencer and H~ff,~ the frequencies of the Korotkoff sounds range from 2.5 to 250 cycles per second. Although the frequency response of the direct-writing pen recorder reduced greatly beyond 70 cycles per second, loss of higher frequency components appeared to be practically negligible. The continuous recording of the linger volume was displayed on pen 2. The volume recorder consisted of a small pilot lamp and a Claire crystal photocell (CL-3). The intensity of the light transmitted through the finger altered the output voltage of the photocell, which was amplified by the direct-coupled amplifier and recorded by the ink-writing recorder. From this tracing, both the peripheral arterial pulsation and the change in volume of the finger can be monitored. Ko attempts have been made to calibrate the curve in terms of the
by Research Grant H-6968 iron the National Heart Institute, National Institutes Public Health Service. Received for publication Jan. 23. 1962. *Department of Physmlogy, School of Medicine. Hiroshima University, Hiroshima. Japan. **Department of Internal Medicine, School of Medicine, Hiroshima University. Hiroshima.
308
of Health,
Japan.
United
States
Sound recording in blood $ressure measurements
absolute change in volume of the finger. The digital volume curve does not necessarily represent the flow of blood through more proximal tissues. In the present communication, it is assumed that the digital volume and the blood flow in the forearm have a rough correlation. The sph~~gmo~llano~neter cuff was inflated manLldly, although the inflation bulb is not shown in the illustration. The pressure inside the sphygmomanometer cuff was recorded continuously by the electrical pressure manometer (MI’-4T, Nihon Koden, functionally equivalent to the Statham gauge P-23) and was displayed on pen 3 of the recorder. The pressure was also measured subjectively by means of the mercury manometer, and recorded as a dot on the time scale at the top of the illustration.
309
In the fourth channel, the thoracic movement was recorded as an indication of the respiratory movement. The movement of the thoracic wall was recorded by means of a strain gauge fixed directly on the thoracic wall. In Fig. 2, a small thermistor was placed in the mouthpiece so that the respiration could be registered in terms of the variation in electrical resistance. Here again, the tracing illustrates only the relative movement, and no attempts have been made to measure the absolute change in volume of respiration. The downward deflection indicates the act of inspiration. In Fig. 3, instead of the respiratory tracing, the phasic change in the cuff pressure was amplified and recorded, in the bottom tracing. More than 40 healthy medical students participated in this experiment. 0ne of
..
FINGER i
:
VOLUME-L i.L_t.
!
iA.:
,
_i
.Jb.“LL..i
Fig. 1. LejL: Experimental setup of indirect blood pressure measurement. IKIC.: Crystal microphone sutured inside the sphygmomanometer cuff. CR.AMP: CR-coupled amplifier, time constant 1 second. P.T.: Pressure transducer (MP-1’f’). Right: Typical esperimental tracings: Top, The time interval of 1 second. Pen 1, The vibration tracing picked up from the contact microphone; the two arrow-s indicate where the slight reduction in the amplitude of vibration occurred. Pen 2, The finger volume curve; the upward tracing indicates the increase in the blood volume of the finger. Pen 3, The pressure inside the sphygmomanometer cuff. Pen 4, The respiration curye; the upward deflection indicates the expiration.
310
Irisawa,
Goki, and
Firr. 2. A, Rhythmical variation of vibratjon due to the temporal in A and B.
Yukutake
of vibration tracing due to the deep respiration. B, Reduction arrest of respiration. The amplification of the respiration
them had a blood pressure reading over 140 mm. Hg: the other readings ranged frotn 120 to 100 mtn. Hg. Results A typical vibration recording during measurement of pressure can be seen in the tracings on the right-hand side of Fig. 1. The top markings are the time scale of 1 per second. The vibration tracing is shown in the second row. Since the vibration tracing correlates fairly well with the sound heard by the auscultatory method, we may refer this tracing to the sound tracing. The initial dark triangular deflection indicates the inflation artifact. The duration of this artifact is about 5 seconds, and indicates the time the pressure cuff is inflated. The audible sound begins at about 90 mm. Hg in this particular instance. The amplitude of this sound is about 64 mv., and the deflection gradually increases up through the next
in the amplitude curve is different
four cycles. At the fifth cycle, .however, the deflection decreases, as is indicated by the first arrow. In the sixth cycle, the deflection again increases, and at the eleventh cycle the reappearance of the reduction in amplitude is observed. The two arrows on the vibration tracing show where the reduction in the vibration occurred. One can also notice that these points clearly correlate with the onset phase of inspiration. The rapid sweep of the paper indicates the change in wave pattern during this reduction in amplitude. It is suggested, therefore, that these points are related to the clinical manifestation of the pressure measurements. The fingervolume tracing indicates that the flow of blood to the finger does not increase until 70 mm. Hg, where the sound becomes progressively greater. Since we noticed that a slight decrease in vibration correlated with the respirator) movement, we designed another experi-
Sound recording in blood $ressure measurements
ment in which the grade of respiration was intentionally changed. This was accomplished by having the subject breathe deeply. Fig. 2,A shows a tracing similar to that in Fig. 1, but obtained from another subject. The repeated deep respiration, which begins shortly after the beginning of the deflation of the sphygmomanometer cuff, is demonstrated in the bottom tracing. The dot mark superimposed on the time scale coincides with the pressure reading which begins from 170 mm. Hg and ends at 50 mm. Hg. The interval of the two markings indicates a fall of 10 mm. Hg in cuff pressure. It is noted that the definite audible sound is recorded at 140 mm. Hg in this particular
instance. Here again, the region of reduction in the vibration tracing can be noticed between 130 and 120 mm. Hg. The reduction in the amplitude of vibration is so remarkable compared to the preceding experiment in Fig. 1, that by auscultation the definite auscultatory gap coincides with the reduced region. It is noted that the reduction in the amplitude of the vibration tracing coincides with the temporal decrease in the upward deflection of finger volume, and also with the onset of inspiration. The decrement in vibration around 100 mm. Hg is also correlated with the onset of deep inspiration, but the large amplitude of vibration indicates that it is an audible sound.
Fig. 3. Effect of the increased peripheral resistance on the Korotkoff sounds. Through an application of the lower pressure cuff (CU$ 2) the blood flow in the lower arm is occluded in B and D. Note that the rhythmical variation of Korotkoff sounds decreases in A, which suggests that the primary cause of this reduction in amplitude is the change
in blood
flow.
311
312
Irisawa,
Goki, and Yukutake
When the pressure cuff is deflated slowly, the rhythmical variation in the amplitude of the vibration tracing is recorded. In such instances, several inaudible zones have appeared in the vibration record, and it can be demonstrated that the inaudible zone is definitely correlated with the onset of inspiration. Although the reduction in the amplitude of the vibration could be seen in the tracing each time the inspiration began, at the first and second places it was inaudible and at the third gap it was definitely audible, although the sound was muffled. The temporal reduction in the finger-volume tracing also coincides with the inaudible zone. In Fig. 2,B the cuff pressure begins to deflate at about 170 mm. Hg, where the initial dot mark on the time scale is recorded. The following dots on the time scale indicate reductions of 10 mm. Hg of cuff pressure, as is given in the illustration. In this instance, the respiration was intentionally changed by asking the subject to stop his breathing temporarily. Because of this procedure, the blood pressure rose slightly, and during this temporal arrest of the respiration the marked reduction in vibration was recorded. The reduction lasts fairly long and it resembles the clinical auscultatory gap. Next, the flow of blood in the forearm was intentionally occluded by application of the second pressure tourniquet on the forearm (see Fig. 3), in order to see how the flow of blood in the forearm is related to the inaudible gap. Fig. 3,A shows the control tracing before the second tourniquet was applied to the forearm. As was mentioned before, instead of recording the respiratory movement, the small phasic pressure fluctuation in the cuff was amplified, and it is shown in the bottom tracing. Fig. 3,B illustrates the results, where the lower cuff is inflated prior to measurement of pressure. ;2yo remarkable difference in the vibration tracing is observed between A and B, except for a slight reduction in amplitude in the vibration. The fact that the systolic blood pressure is slightly elevated appears to be due to spontaneous fluctuation in the blood pressure. The finger-volume tracing is altered remarkably in B, which suggests the continuous increment of finger volume through deep
arterial supply. Fig. 3,C illustrates the effect of deep respiration in the same subject; this tracing was obtained a short while after the previous one, without application of the second tourniquet on the forearm; the remarkable disappearance of the vibration tracing, which coincides with the inaudible zone of the auscultatory method, is noted. It can be seen that the remarkable reduction in finger volume coincides with the inaudible gap, which indicates a decrease in the flow of blood in the finger. Fig. 3,D illustrates the effects of the combination of both the deep respiration and the compression of the lower tourniquet. linder this condition, the variation in the sound tracing is remarkably depressed, which indicates that the change in blood flow is the principal factor in the formation of this inaudible gap. Discussion
Many investigators have made graphic recordings of the Korotkoff sounds.2*5s6 Geddes, Spencer and Hoff4 recently recorded the Korotkoff sounds in a normotensive subject, and stated that the auscultatory gap occurs in Phase II, wherein the murmur-like sounds can be heard with the auscultatory method. They did not discuss the mechanism of formatiorr of this gap. The present experiment shows that the auscultatory gap produced by deep inspiration is caused by a decrease in blood
now. The fact that the volume of the finger did not increase until 90 mm. Hg was reached, and that it then rapidly increased from 90 to 70 mm. Hg, suggests that the flow in an occluded artery follows the formula, pressure equalsflow multiplied by the resistance. During occlusion of the artery, the resistance may be at its greatest value, and the pressure and the flow both at their minimum. At the time the blood flow resumes in the slightest degree, the pressure in the forearm is lower than that in the upper arm because the resistance to the artery is still considerable. The flow begins to increase slightly, and the resistance decreases slightly, in the next moment. As a result, the pressure under the cuff increases slightly. ‘Therefore, the relationship between the flow and the pressure should not be linear, but hyper-
Sound recording in blood pressure
bolic. This may explain the cause of the nonlinear increase in finger volume although the pressure falls linearly. The tracing shows that the inaudible zone clearly coincides with the region of high cuff pressure, where the blood flow in the lower part of the cuff appears to be small and below the control level. The decrease in the flow of blood through the artery tends to decrease the acceleration of the column of blood in the peripheral arterial tree, so that turbulence would temporarily be stopped. On the other hand, the arterial pulse may be palpable, since the cuff pressure is below the systolic pressure. The immediate application of these discussions to auscultatory gaps which are frequently observed in patients must be deferred until more precise observations in patients are available. Erlanger3 found that the occlusion of the peripheral artery with the second cuff did not affect the auscultatory sound. The statement is true, as can be seen in tracings A and B of Fig. 3, and this result indicates that the increase in peripheral arterial resistance does not cause any qualitative change in the auscultatory sound. Under the condition of the combination of deep breathing and application of a tourniquet, the periodic variation in the auscultatory sound disappeared, although the respiratory rhythm remained slightly because of the change in systemic blood pressure. It appears to be reasonable to conclude th:lt the auscultatory gap produced by deep inspiration is due to the decrease in blood How and not to the rhythmic change in the s!-stemic arterial pressure.
measurements
313
Summary The correlation between Korotkoff sounds and respiration was studied. The Korotkoff sounds, the finger volume, the sphygmomanometer cuff pressure, and the respiratory movements were recorded on the four-channel direct-writing recorder. The slight reduction in the vibration superimposed on the Korotkoff sounds was reinforced when the subject intentionally continued deep respiration, and the reproducible auscultatory gap was recorded. The cause of this auscultatory gap due to inspiration was suggested to be a decrease in the flow of the blood in the arm. IVe are grateful to Professor Sunao Wada encouragement throughout the course of this
for his work.
REFERENCES 1. Bazett, H. C., and Bard, P.: Indirect measurement of arterial blood pressure in man, in Bard, P., editor: Medical physiology, St. Louis, 1956,The C. V. Mosby Company, p. 124. 2. Currens, J. H., Brownell, G. L., and Aronow, S.: An automatic blood pressure recording machine, New England J. Med. 256:780. 19.57. 3. Erlanger, J.: Studies in blood pressure estimation by indirect methods, Am. J, Physiol. 40:82, 1916. 4. Geddes, L. A., Spencer, W. A., and Hoff, H. E.: Graphic recording of the Korotkoff sounds, AM. HEART J. 57:361, 1959. 5. Gilson, W. E., Goldberg, H., and Slocum, H.: An automatic device for periodically determining and recording both systolic and diastolic BP in man, Science 94:194, 1941. 6. Rose, J. C., Gilford, S. R., Broida, H. P., Solar, A., Partenope, E. A., and Freis, E. D.: Clinical and investigative application of a new instrument for continuous recording of BP and heart rate, New England J. Med. 249:615, 1953. 7. Rushmer, R. F. : Pressure measurements, itt Cardiovascular dynamics, Philadelphia, 1961, W. B. Saunders Company, p. 137.