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Biomedical subjects

M Sugimachi

Publications and source records attributed to M Sugimachi.

At least 91 records · Page 5Linked to original sources
PubMed1994

Transfer function analysis from arterial baroreceptor afferent activity to renal nerve activity in rabbits.

In vagotomized and anesthetized rabbits, aortic pressure (AP), aortic depressor nerve activity (ANA), and renal sympathetic nerve activity (RNA) were simultaneously measured while perturbing AP randomly. To quantitatively characterize the role of the arterial baroreflex system in generating RNA, we determined the transfer function (TF) of the central baroreflex arc from ANA to RNA in the frequency domain (0.02-5 Hz). The magnitude of squared coherence was > 0.5, the phase was close to -180 degrees, and the gain of TF was flat over 0.02-0.3 Hz, indicating that changes in RNA were linearly and instantaneously but inversely related to changes in ANA over this frequency range. Above 0.3 Hz, the coherence was low, suggesting that RNA unrelated to ANA existed in the frequency range. In animals without AP perturbations, power spectrum of RNA resided over 0.2-5 Hz with a broad peak at 1 Hz, which may represent central activity. Our results suggest that over 0.02-0.3 Hz the relationship between arterial baroreceptor afferent nerve activity and RNA is linear and instantaneous but above 0.3 Hz it is not linear possibly due to an interaction between central activity and arterial baroreflex.

Afferent Pathways↗
PubMed1994

Reduction in serum cholesterol with pravastatin improves endothelium-dependent coronary vasomotion in patients with hypercholesterolemia.

BACKGROUND: This study aimed to determine if cholesterol-lowering therapy improves endothelium-dependent coronary vasomotion in patients with hypercholesterolemia. METHODS AND RESULTS: Nine patients with hypercholesterolemia were studied before and after cholesterol-lowering therapy with pravastatin (an inhibitor of HMG-CoA reductase) for 6 +/- 3 months, which lowered serum cholesterol from 272 +/- 8 to 187 +/- 16 mg/dL (P < .01). Control patients with serum cholesterol of 218 +/- 23 mg/dL also were studied twice in a similar interval (8 +/- 2 months) with no cholesterol-lowering drugs. Acetylcholine (the endothelium-dependent vasodilator) and papaverine and nitrate (endothelium-independent vasodilators) were infused into the study coronary artery. Changes in the diameter of the epicardial coronary artery and coronary blood flow were assessed by quantitative coronary arteriography and an intracoronary Doppler catheter. In patients with hypercholesterolemia, acetylcholine-induced vasoconstriction of the epicardial artery was less (P < .05) and the acetylcholine-induced increases in coronary blood flow were greater (P < .001) after than before pravastatin. In control patients, responses of the epicardial coronary artery and coronary blood flow to acetylcholine did not change over the follow-up period. The vasomotor responses to papaverine or nitrate were similar between the two groups, and no interval changes in their responses were noted in either group. CONCLUSIONS: These results suggest that cholesterol-lowering therapy with pravastatin may improve endothelium-dependent coronary vasomotion, which may possibly contribute to the improvement of myocardial perfusion as well as the regression of coronary atherosclerosis.

Adult↗
PubMed1993

Contribution of wall mechanics to the dynamic properties of aortic baroreceptors.

To examine the contribution of wall mechanics to dynamic properties of baroreceptors, we subdivided the transfer function of baroreceptors into two subsystems [aortic pressure to diameter and diameter to aortic depressor nerve activity (ANA)]. In six alpha-chloralose-anesthetized rabbits, we measured pressure, diameter, and ANA while randomly perturbing pressure. We obtained transfer functions (pressure to ANA, diameter to ANA, and pressure to diameter) by taking the ratio of crosspower spectrum to the input power spectrum (0.005-5 Hz). Below 3 Hz, the transfer function from pressure to ANA was nearly identical to that from diameter to ANA, whereas that from pressure to diameter was flat. Using transfer functions we could reproduce adaptation and hysteresis that were quantitatively similar between pressure-ANA transduction and diameter-ANA transduction. The pressure-diameter relationship was almost instantaneous and thus showed no hysteresis. In a second group of rabbits, the ratio of the shift of the hysteresis loop was unchanged by ouabain (40 micrograms/kg iv, n = 7). We conclude that the dynamic properties of baroreceptors may not be related to the wall mechanics or the Na(+)-K(+)-adenosinetriphosphatase activity.

Animals↗
PubMed1993

Effects of age on endothelium-dependent vasodilation of resistance coronary artery by acetylcholine in humans.

BACKGROUND: It has been suggested that endothelium-related vasomotion is important in the control of coronary circulation. Our goal was to determine if endothelium-dependent dilation of the coronary vasculature was altered with aging in 18 patients with atypical chest pain (age, 23-70 years) who had angiographically normal coronary arteries and no coronary risk factors. METHODS AND RESULTS: We infused an endothelium-dependent vasodilator acetylcholine (1, 3, 10, and 30 micrograms/min) and an endothelium-independent vasodilator papaverine (10 mg) into the left coronary artery. The large coronary diameter was assessed by arteriography, and the increase in coronary blood flow was measured using the intracoronary Doppler catheter technique. Acetylcholine increased coronary blood flow in a dose-dependent manner with no changes in arterial pressure and heart rate. The maximum increase in coronary blood flow evoked by acetylcholine varied widely among patients (increase in coronary blood flow ranged from 200% to 560%) and was correlated significantly with aging (r = -.86, P < .001), whereas the peak coronary blood flow response to papaverine was affected slightly by aging (r = -.44, P = .07). The percent increase in blood flow response to acetylcholine to the response to papaverine correlated with aging (r = -.87, P < .001). The slope of the coronary blood flow response to acetylcholine also correlated significantly with aging. The large epicardial coronary artery response to the low doses of acetylcholine (< or = 10 micrograms/min) correlated inversely with aging. CONCLUSIONS: The results of this study suggest that endothelium-dependent dilation of coronary arteries evoked by acetylcholine may be decreased with aging in humans.

Acetylcholine↗
PubMed1993

Differentiation between aberrant ventricular conduction and ventricular ectopy in atrial fibrillation using RR interval scattergram.

BACKGROUND: Differentiation between aberrant ventricular conduction and ventricular ectopy during atrial fibrillation (AF) is of etiologic, prognostic, and therapeutic importance. We developed a noninvasive technique to diagnose aberrant ventricular conduction and ventricular ectopy in AF. METHODS AND RESULTS: We studied the Holter ECGs of 34 patients with paroxysmal AF and 62 patients with chronic AF. In all the patients, frequent wide QRS complexes were observed, and 32 patients were shown by electrophysiological examination to have ventricular ectopies or aberrant ventricular conductions. We obtained the RR interval scattergrams by plotting sequential pairs of RR intervals. Each point has the (n)th RR interval as its x value and the (n + 1)th RR interval as its y value. The irregularity of the RR intervals in AF resulted in widely scattered points delineated by the envelope along the axes. The y value of the envelope along the x axis indicates the shortest coupling interval to the preceding RR interval. Therefore, this curve defines the functional refractory period of atrioventricular conduction. The scattergram of the RR interval pairs immediately preceding the aberrant conduction (coupling points of aberrant conduction) specifically distributed along the envelope. In contrast, the coupling points of ventricular ectopies showed different distributions that had no relation to the envelope. That is, it included three typical patterns, ie, linear distribution below the envelope, linear distribution partially overlapped in the area of normal AF conduction, and chaotic distribution in the AF area. None of the scattergrams of ventricular ectopies showed curvilinear distribution along the envelope as aberrant conduction did. The specific distribution of the aberrant conduction on the RR interval scattergram suggested that aberrant conduction in AF could result from the difference of refractory periods between the AV node and bundle branch block. CONCLUSIONS: We conclude that the RR interval scattergram makes it possible to differentiate between aberrant ventricular conduction and ventricular ectopy in atrial fibrillation, and thus, it is a useful noninvasive clinical tool.

Atrial Fibrillation↗
PubMed1993

Impaired coronary blood flow response to acetylcholine in patients with coronary risk factors and proximal atherosclerotic lesions.

We examined whether coronary risk factors and atherosclerotic lesions in the study artery were associated with impaired endothelium-dependent dilation of coronary resistance arteries. Acetylcholine (ACH) at graded doses (1, 3, 10 and 30 micrograms/min) and papaverine (10 mg) were selectively infused into the left anterior descending coronary artery of 28 patients, in whom the study artery was angiographically normal (n = 16) or with mild stenosis < or = 40% (n = 12). Coronary blood flow (CBF) was estimated from the product of mean CBF velocity measured by an intracoronary Doppler catheter and the arterial cross-sectional area of the study artery determined by quantitative arteriography. ACH increased CBF in a dose-dependent manner. However, the maximum CBF response to ACH varied widely among patients (from 50% to 660%). By multivariate analysis, the presence of atherosclerotic lesions in the study artery was an independent predictor for impaired CBF response to ACH (P < 0.01). Hypertension (P < 0.001), hypercholesterolemia (r = -0.52, P < 0.005), age > or = 50 yr (P < 0.01) and total number of coronary risk factors (r = -0.62, P < 0.001) were associated with the impaired increase in CBF with ACH by univariate analysis. The percent increase in CBF evoked with papaverine did not correlate with these risk factors. The results suggest that mild atherosclerotic lesions in the study artery and coronary risk factors are accompanied by impaired endothelium-dependent dilation of coronary resistance arteries evoked with ACH. Endothelial dysfunction of coronary resistance arteries may result in altered regulation of myocardial perfusion in patients with mild coronary atherosclerosis and coronary risk factors.

Acetylcholine↗
PubMed1993

Optimal coupling of the left ventricle with the arterial system.

In the human the heart contracts more than 2.0 billion times during the lifetime. The total amount of energy required in this period is equivalent to lift a huge tanker (more than 200 thousand tons) above your head. Thus there is no question that the heart requires a huge amount of energy. Since minimization of energy requirements would be one of the major design goals of the cardiovascular system, we investigated energy efficiency of ventriculo-arterial coupling under various conditions. In normal conscious dogs, the arterial system extracted maximal work from the left ventricle during exercise as well as at rest. At the same time, the energy consumption of the left ventricle to support the peripheral demand was minimum. This optimal coupling condition was well maintained despite changes in blood volume. The baroreflex system appeared to play a crucial role in this optimization. In the presence of left ventricular dysfunction, however, this optimality was no longer maintained. We conclude that the efficiency of cardiac contraction is fairly well maintained under various stresses as long as left ventricular function is normal.

Animals↗
PubMed1992

Evaluation of the severity of mitral regurgitation by transesophageal Doppler flow echocardiography.

The severity of mitral regurgitation (MR) was assessed by transesophageal Doppler flow echocardiography (TEE) using new criteria in 87 patients. The severity of MR assessed by TEE (TEE-MR) was compared with that obtained by left ventriculography (LVG-MR). Although the severity of TEE-MR has been evaluated by MR jet area, it is often difficult because the MR jet extends beyond a single frame image in severe MR. We found that (1) when the MR area was larger than 3 cm2, the severity of MR was more than second-degree by LVG; (2) there was systolic turning flow (STF) of the MR jet within the left atrial cavity in 27 of 30 patients with third- and fourth-degree LVG-MR; and (3) there was late systolic backward flow (SBF) in the pulmonary veins in 9 of 10 patients with fourth-degree LVG-MR. A new grading of the severity of MR by TEE was proposed, which combined the findings of STF, SBF, and the MR area. These new criteria of the severity of TEE-MR excellently correlated with that by LVG (y = 0.94x + 0.08; r = 0.95, p less than 0.01). The criteria for MR by TEE were also useful for assessment of MR in patients with prosthetic mitral valve dysfunction (y = 0.96x + 0.04; r = 0.97, p less than 0.01). We conclude from this study that the severity of MR can be accurately assessed with TEE by measuring the MR area and the specific flow patterns in the left atrium and pulmonary veins.

Adolescent↗
PubMed1992

Mechanisms involved in aortic baroreceptor excitation during drug-induced aortic pressure elevation in intact rabbits.

Aortic baroreceptor activity during drug-induced elevation of arterial pressure in intact animals is determined not only by the magnitudes of arterial pressure elevation but also by other mechanisms such as the direct effects of drugs on aortic wall property and on baroreceptors per se. This study aimed to determine the relative contribution of arterial pressure elevation and other mechanisms on aortic baroreceptor activity during intravenous infusion of norepinephrine (NE), phenylephrine (PE) or angiotensin II (Ang II) in intact anesthetized rabbits, all of which were used to assess arterial baroreflex function in vivo. We simultaneously recorded aortic pressure (AP), afferent aortic nerve activity (ANA) and the aortic diameter (AD) during elevation of AP induced by intra-aortic balloon inflation or intravenous infusions of NE, PE, and Ang II. During Ang II-infusion or balloon inflation, AD progressively increased with increases in AP. The relationships among changes in AP, ANA, and AD were similar during balloon inflation and during Ang II infusion which indicated that increases in ANA during Ang II infusion were caused by increases in AD or strain of baroreceptors. In contrast, during NE or PE infusion, ANA increased with no changes or decreases in AD, respectively. The latter results suggest that in intact rabbits increases in ANA during NE or PE infusion resulted from mechanisms other than an increase in strain of baroreceptors, such as the direct excitatory effect on baroreceptors. Thus, different mechanisms were involved in aortic baroreceptor excitation in intact rabbits during elevation of AP caused by the vasopressor drugs, which are commonly used to assess arterial baroreflex function in vivo.

Angiotensin II↗
PubMed1992

Dynamic effects of carotid sinus baroreflex on ventriculoarterial coupling studied in anesthetized dogs.

We evaluated dynamic effects of the carotid sinus baroreflex on ventriculoarterial coupling. In seven anesthetized, vagotomized dogs, we bilaterally isolated carotid sinuses and randomly changed carotid sinus pressure while measuring aortic pressure, aortic flow, and left ventricular pressure. Estimating left ventricular end-systolic elastance (Ees) and effective arterial elastance (Ea) on a beat-to-beat basis, we determined transfer functions from the carotid sinus pressure to Ees (HEes) and from the carotid sinus pressure to Ea (HEa) over the frequency range spanning 0.002-0.25 Hz. Both HEes and HEa exhibited characteristics of a second-order low-pass filter. The gains of HEes and HEa were 0.085 +/- 0.065 (mean +/- SD) and 0.081 +/- 0.049 mm Hg/ml/mm Hg, respectively. There were no significant differences in natural frequencies (0.039 +/- 0.013 versus 0.039 +/- 0.007 Hz) or damping ratios (0.65 +/- 0.11 versus 0.64 +/- 0.24). The results indicated that the carotid sinus baroreflex dynamically altered Ees and Ea to the same extent in the process of stabilizing arterial pressure. Because the arterial system extracts maximal external work from a given heart when Ea equals Ees, the carotid sinus baroreflex appeared to be designed to regulate the ventricular and arterial properties to optimize the energy transmission from the left ventricle to the arterial system in anesthetized, vagotomized dogs.

Anesthesia↗
PubMed1992

Mechanical matching of the left ventricle with the arterial system in exercising dogs.

We investigated how changes in ventricular contractility and arterial properties associated with exercise influence the energy transmission from the left ventricle to the arterial system. On six chronically instrumented dogs preconditioned to run on a treadmill, we imposed exercise loads of various degrees by altering the speed and slope of the treadmill (up to 7 km/hr and 20% slope). We evaluated ventricular contractility by end-systolic elastance (Ees) and arterial properties in terms of the effective arterial elastance (Ea). Ea was estimated by the ratio of mean aortic pressure to stroke volume. With exercise, Ees significantly increased from 7.6 +/- 1.7 to 10.9 +/- 2.6 mm Hg/ml (p less than 0.005), and Ea tended to increase from 4.9 +/- 1.4 to 6.7 +/- 1.8 mm Hg/ml (p = 0.068), whereas the ratio of Ea to Ees remained fairly constant (from 0.69 +/- 0.26 to 0.63 +/- 0.21, NS). The mechanical optimality index, defined as the ratio of stroke work to its theoretically derived maximal value, was 0.93 +/- 0.07 at rest and 0.92 +/- 0.08 at peak exercise. Similarly, the metabolic optimality index, defined as the ratio of cardiac oxygen consumption to stroke work conversion efficiency and its theoretical maximal value, was 0.98 +/- 0.02 at rest and 0.99 +/- 0.01 at peak exercise (NS). We conclude that external work of the left ventricle of these dogs was at a near maximal level for a given preload during exercise as well as at rest without compromising the conversion efficiency of metabolic energy to stroke work.

Animals↗
PubMed1991

Identification of the rate-dependent functional refractory period of the atrioventricular node in simulated atrial fibrillation.

We continuously observed successive pairs of R-R intervals during atrial fibrillation and hypothesized that the shortest R-R interval for a given preceding R-R interval in a pair represents the functional refractory period of the atrioventricular node at that preceding interval. To test this hypothesis we simulated atrial fibrillation in 28 isolated cross-perfused canine hearts and obtained an R-R interval scatterplot by plotting the R-R intervals as a function of the immediately preceding R-R interval. This scatterplot enabled us to detect a series of the shortest R-R intervals for a wide range of preceding R-R intervals, and this allowed us to estimate the rate-dependent functional refractory period of the atrioventricular node in simulated atrial fibrillation. The estimated functional refractory periods correlated well with those measured by the conventional method (r = 0.93). We conclude that the proposed method makes it possible to estimate the rate-dependent functional refractory periods of the atrioventricular node in atrial fibrillation.

Animals↗
PubMed1991

Autoregressive analysis of aortic input impedance: comparison with Fourier transform.

We evaluated the advantages of the autoregressive (AR) model over the conventional Fourier transform in estimating aortic input impedance. In 10 anesthetized open-chest dogs, we digitized aortic pressure and flow at 200 Hz for 51.20 s under random ventricular pacing and subdivided them into five segments. We obtained aortic input impedance over the frequency range of 0.1-20 Hz both by AR model and by Fourier transform for various lengths of data, i.e., from one to four consecutive segments. For any given data length, the impedance spectrum estimated by the AR model was smoother than that obtained by the Fourier transform. To evaluate the accuracy of the estimated impedance, we predicted instantaneous aortic pressure of the fifth segment by convolving corresponding aortic flow with the impulse response of aortic input impedance. The prediction error was less with the AR model than that resulting from Fourier transform as long as the number of the segments was less than four. We conclude that the AR model provides a more accurate estimate of aortic input impedance than does the Fourier transform when data length is limited.

Animals↗
PubMed1991

Effects of the new cardiotonic phosphodiesterase inhibitor 1,2-dihydro-5- imidazo[1,2-a]pyridin-6-yl-6-methyl-2-oxo-3-pyridine-carbonitrile hydrochloride monohydrate on aortic input impedance.

Beneficial effects of cardiotonic phosphodiesterase inhibitors on congestive heart failure are possibly mediated in part by a reduction of afterload. 1,2-Dihydro-5-imidazo[1,2-a]pyridin-6-yl-6-methyl-2-oxo-3- pyridinecarbonitrile hydrochloride monohydrate (E-1020, CAS 119615-63-3), a new cardiotonic phosphodiesterase inhibitor was evaluated for its effect on aortic input impedance in eight anesthetized open-chest dogs. First instantaneous aortic pressure and flow under random ventricular pacing before and after E-1020 infusions (10, 30, and 100 micrograms/kg i.v.) were measured. Then aortic input impedance over the frequency range of 0.024 to 20 Hz was estimated using a multichannel autoregressive model. With the infusion of E-1020, aortic input impedance was decreased in the low frequency range (below 0.1 Hz) and shifted leftward in the transitional frequency range (from 0.1 to 2 Hz), while it remained unchanged in the high frequency range (above 2 Hz). Parameterization of the aortic input impedance using a three-element Windkessel model indicated that E-1020 (at a dose of 100 micrograms/kg i.v.) decreased arterial resistance by 35% (p less than 0.01) and increased arterial compliance by 12% (p less than 0.01). It is concluded that E-1020 improves cardiac performance by unloading static and dynamic afterload in addition to its cardiotonic effect.

Animals↗
PubMed1990

A new method to identify dynamic transduction properties of aortic baroreceptors.

We identified, in 17 alpha-chloralose-anesthetized rabbits, the dynamic transduction characteristics of the aortic arch baroreceptors using a "white-noise technique." We recorded aortic pressure and aortic depressor nerve activity while perturbing pressure by rapid, intermittent ventricular pacing (400 beats/min). Dividing the cross-power spectrum between nerve activity and pressure by the power spectrum of pressure yielded the transfer function. The gain of the transfer function increased threefold as the frequency increased from 0.005 to 5 Hz, suggesting that the baroreceptors responded primarily to dynamic rather than to static changes in pressure. To quantify the nonlinear properties of baroreceptor transduction, we compared measured instantaneous nerve activity with that linearly predicted. We demonstrated that the major nonlinearity was attributable to "threshold". The overall baroreceptor transduction properties could be represented by a cascade connection of a linear subsystem followed by a nonlinear subsystem with threshold. The white-noise technique made it possible to identify the unbiased linear properties in a nonlinear system, and thus was very useful in identifying complex biological systems.

Animals↗
PubMed1988

Random exercise stress test in diagnosing effort angina.

To improve the performance of exercise stress testing in the diagnosis of effort angina while minimizing risks of serious complications, we evaluated an impulse response of ST changes, which is a transient ST response resulting from a hypothetical, strenuous-impulselike exercise, without actually imposing the strenuous load. To obtain the impulse response, subjects walked intermittently according to a computer-generated random binary sequence on a treadmill for 20 minutes (with a constant speed of 1.7 mph and a slope of 10%). We used Fourier transform for beat-to-beat changes in ST level and the binary sequence of exercise. We then determined the transfer function by taking the ratio of Fourier transformed ST level to exercise over the frequency range of 0.5 through 5.0 cycles/min. Converting the transfer function to the time domain yielded the impulse response of ST change. The subjects consisted of 49 patients (60 +/- 9 years) with effort angina, 13 patients with atypical chest pain (56 +/- 9 years), and 30 healthy, male volunteers (23 +/- 7 years). In 82 subjects (89%), the ST impulse response showed an initial depression followed by a smooth, gradual restoration toward the preexercise ST level (type I response). The average duration of the initial depression was 8 +/- 3 seconds in the healthy volunteers, whereas it was significantly prolonged to 23 +/- 14 seconds in effort angina (p less than 0.05). The depression in patients with atypical chest pain was not significantly different from that in the healthy volunteers.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗