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Biomedical subjects

H Suga

Publications and source records attributed to H Suga.

At least 325 records · Page 18Linked to original sources
PubMed1977

Effects of stroke volume and velocity of ejection on end-systolic pressure of canine left ventricle. End-systolic volume clamping.

To study the effects of contraction mode on ventricular end-systolic pressure-volume relationship, we compared the end-systolic pressure of isovolumic contraction with that of ejecting contraction at an identical end-systolic volume. The left ventricle of excised cross-circulated canine hearts was fitted with a water-filled balloon. The balloon was connected to a hydraulic pump that allowed the ventricle to contract to a preset constant end-systolic volume (19-37 ml) from a variable end-diastolic volume. At each of control, enhanced, and depressed levels of contractility, differences of end-systolic pressures of steady state isovolumic and ejecting contractions were evaluated while stroke volume and velocity of ejection were widely varied. The end-systolic pressure in the ejecting contraction tended to decrease by 5-15% from that of the isovolumic beat with increases in either stroke volume to 20-25 ml or peak velocity of ejection to about 800 ml/sec. There was no obvious difference in the results at different levels of contractility. The magnitude of the end-systolic pressure depression due to ejection was, however, relatively small as compared to 4-fold changes in end-systolic pressure due to the changes in contracility. We, therefore, conclude that the ventricular end-systolic pressure-volume relationship is affected slightly by ejection, and that this effect is much smaller than the maximal effect of changing contractility on the end-systolic pressure-volume relationship.

Animals↗
PubMed1976

Lightning eye movements.

Physiologic studies were performed on a patient who demonstrated lightning eye movements, palatal myoclonus and myoclonic jerks of the left platysma and sternocleidomastoid muscles. The myoclonus and lightning eye movements were separate phenomena with no defined relationship to each other. Analysis of this ocular dyskinesia identified strictly horizontal saccadic oscillations, 2 to 5 Hz in frequency, with amplitudes varying greatly but often reaching 25 degrees. A brief stationary period between each saccadic oscillation was frequently observed. They were particularly induced by vertical or horizontal ocular pursuit as well as sustained upward or downward ocular deviation. Caloric nystagmus abolished the oscillations but they persisted, irregularly, during optokinetic nystagmus. Thus a faulty visual fixation mechanism is postulated to precipitate lightning eye movements. Constrast studies revealed a mass lesion arising from the right dorsolateral portion of the medulla. These results indicate that lightning eye movements occur with caudal as well as rostral brain-stem lesions. From the clinical findings cerebellar pathway involvement is likely.

Adult↗
PubMed1976

Controls of ventricular contractility assessed by pressure-volume ration, Emax.

The present study on canine left ventricles showed that Emax which we previously proposed as a good index of both ventricular contractility and its pumping capability, decreased from 2.06 to 1.38 kPa/ml (15.5 to 10.4 mmHg/ml) via the sino-aortic baroreceptor reflex. Cerebral ischaemic response increased Emax to 3.83 kPa/ml (28.8 mmHg/ml). Emax decreased to 1.17 kPa/ml (8.8 mmHg/ml) after cardiac denervation.

Animals↗
PubMed1976

Influence of heart rate and age on Q-Korotkoff sound intervals.

The Korotkoff sound appearance time (QK intervals) was measured in 224 normal subjects of both sexes between the age of 6 and 79 years. The sex difference was not obvious except for the diastolic values of the intervals (QKd) in the sixth decade. Although the QK intervals remained almost unchanged between the third and the fifth decade, both the systolic (QKs) and the diastolic values were significantly smaller in the young subjects under the age of 20. On the other hand, QKs was significantly decreased and QKd and the difference between the systolic and diastolic values (QKs-d) were significantly increased in the elderly subjects. The short QK interval in the young subjects was considered to be mainly attributable to the short preejection period, while the increased pulse wave velocity was postulated to be the main responsible factor for the shortening of QKd in the elderly subjects. A statistically significant negative correlation was demonstrated between QKd and the heart rate in both sexes, while QKs and QKs-d were not significantly correlated with the heart rate.

Adolescent↗
PubMed1976

Correlative changes in total vascular capacity and resistance in carotid sinus reflex.

To attain a quantitative understanding of carotid sinus reflex control of circulation, we studied the correlation between changes in total vascular capacity (V) and total peripheral resistance (R). We used a newly devised, accurate and simple method to measure changes in V while both mean central venous and arterial pressures being kept constant. In 7 open chest dogs (7-11 Kg, mean 8.9 Kg), bilateral carotid occlusion after vagotomy reduced V by as much as 58 +/- 9 (SE) ml or approximately 8% of total blood volume while R increased by 36 +/- 5% from 0.08 +/- 0.01 mmHg-min/ml. Similar responses were obtained either in the reflex before vagotomy or with infusion of norepinephrine. Mathematical analysis with Poiseuille's law suggested that internal radius of an average resistance vessel decreased approximately 1.5 to 3 times as much as that of an average capacitance vessel. The wall to lumen ratio of the average resistance vessel estimated from the correlation was 0.3 to 0.6, being within physiological range. Therefore, the difference in vascular sensitivity may be partly owing to the wall to lumen ratio of resistance vessels. Moreover, the correlative changes in the capacitance and resistance vessels were elucidated to be significantly responsible for the characteristic hemodynamic changes in carotid sinus reflex.

Animals↗
PubMed1976

Positive feedback hypothesis on development of essential hypertension.

A hypothesis is presented on a possible mechanism of development of the essential hypertension. The present theoretical consideration with Laplace's law and Poiseuille's law indicates that arteriolar constriction increases, unless the blood flow is reduced, both arterial blood pressure and vascular circumferential wall tension which is considered a trigger of medial hypertrophy of the constricted arteriole. If the medial hypertrophy aggravates the vascular constriction, it all the more increases arterial pressure and wall tension. Therefore, the initial arteriolar constriction, however slight, may progressively produce hypertension and augment medial hypertrophy by such a positive feedback mechanism.

Arteries↗
PubMed1976

Principle of adaptation of heart size to volume load. A theoretical approach.

A hypothesis of a principle of the adaptation of heart size to volume load was generalized from some experimental findings in literature on hearts of a few mammalian species. The hypothesis was that the heart adapts its size and weight so that both myocardial force per unit cross sectional area and extent of shortening per unit length be kept constant. From these 2 conditions, mathematical relationships of heart weight and enddiastolic volume to stroke volume were derived by the aid of a thick wall sphere model of the left ventricle. The calculated result was in good agreement with comparative physiology data in literature on normal hearts from rats to cows. The present hypothesis was therefore suggested to be a basic principle of heart adaptation to the natrual volume load in a wide variety of mammalian species.

Adaptation, Physiological↗
PubMed1976

Hemodynamics of experimentally hypertensive rats in conscious and anesthetized states.

Cardiac output was measured by a pulse contour method in reno-vascular hypertensive rats, deoxycorticosterone (DOC) hypertensive rats and normotensive control Wistar rats in the conscious state. All rats were male in sex and 12-13 weeks of age (2-3 weeks after operation in the hypertensive rats). Cardiac output per body weight was not significantly different among the groups. Therefore, the hypertension in the experimentally hypertensive rats in the conscious state was ascribable to an increased total peripheral resistance. After anesthesia with pentobarbital and thoracotomy, the DOC rats were no longer hypertensive. However, in the renovascular hypertensive rats, the hypertensive state due to an increase in vascular resistance persisted after anesthesia, thoracotomy, and even ganglion blockade with hexamethonium bromide, indicating the importance of non-neural factors in the renovascular hypertension. Aortic compliance measured in vivo under anesthesia was smaller in either the renovascular or DOC hypertensive rats than in the control rats before and after ganglion blockade, which suggests a non-neural hardening of elastic vessels in the experimental hypertensions.

Animals↗
PubMed1976

Left ventricle as a compression pump.

Pressure-volume relationship of the left ventricle at endsystole was studied in three different series of experiment on the dog. Intraventricular pressure was measured with a miniature gauge at the apex. Intraventricular volume was accurately measured by three different methods: (1) plethysmographically with a cardiometer cup, (2) with an intraventricular balloon and a volumetric cylinder, and (3) with the same balloon and areciprocal pump which could clamp the endsystolic volume. We found consistently that as long as the contractile state was stable the endayatolic pressure-volume relationship curve was largely independent of the loading conditions such as enddiastolic volume and ventricular afterload pressure and also of whether the mode of contraction was isovolumic, auxobaric or physiologically ejecting. When the endsystolic pressure was kept unchanged in the ventricle with a stable contractile state, the intraventricular volume decreased to the same volume as given by the endsystolic pressure-volume relationship and the afterload pressure. When the endsystolic volume was maintained constant, the ventricle developed at the end of systole almost the same pressure as that predicted from the same endsystolic pressure-volume relationship. The endsystolic pressure-volume relationship, therefore, uniquely characterizes the degree of ventricular compression under a given contractile state.

Animals↗
PubMed1975

New technique of measurement of effective capacity changes of total vascular bed.

A simple device was developed which can accurately measure effective changes in total vascular capacity as viewed from the site of the heart. The device consists of a funnel and a suction bottle. It is connected via a single large-bore cannula to the right atrium of an open-chest animal without opening the closed loop of the circulation. It serves to clamp the steady-state level of mean central venous pressure precisely at any desired value and to measure the volume of any displacement of blood out of or into the total vascular bed caused by changes in total vascular capacity. The device was tested in mock and animal experiments and proved to function accurately, except during a short transient phase of less than 1 min following an intervention on the total vascular capacity. Errors in clamp pressure in the steady state, which are theoretically zero, were found to be less than 0.2 mm Hg, and were practically insignificant. Errors in the volume measurement were less than 5 ml.

Animals↗
PubMed1975

Effect of increasing age on hemodynamics of spontaneously hypertensive rats.

Arterial pressure, cardiac output, and total peripheral resistance were compared between spontaneously hypertensive rats (SHR) and normotensive control rats (NCR) at 4, 7, and 12 months of age. The rats were anesthetized with pentobarbital sodium, thoracotomized and kept under positive pressure respiration. Cardiac output was measured with an electromagnetic flowmeter probe placed at the ascending aorta. On all the age groups, arterial pressure and total peripheral resistance were significantly higher in SHR than in NCR, while cardiac output per body weight was not different. However, the significant differences in pressure and resistance at each age disappeared after ganglion blockade with hexamethonium bromide. Total peripheral resistance was not higher in SHR than in NCR even after cardiac output, which had once been diminished by blockade, was restored to the pre-blockade level by dextran infusion. Phenoxybenzamine, an alpha adrenergic receptor blocker, also equalized arterial pressure and total peripheral resistance between SHR and NCR, both aged about 10 months, without decrease in cardiac output. It is concluded that, in both young and old SHR's, the hypertensive state is maintained by an increase in total peripheral resistance ascribable to sympathetic activity.

Aging↗