Search PubMed⌕ Search

Biomedical subjects

K Shirato

Publications and source records attributed to K Shirato.

283 records · Page 16Linked to original sources
PubMed1977

Effects of pacing location on coronary circulation in dogs.

In 13 open chest dogs, the right atrium and various ventricular sites (i.e. the inflow and outflow tracts and apex of the right ventricle, apex and lateral wall of the left ventricle) were stimulated electrically at a given rate, ranging from 140 to 210 per min. Coronary circulation and cardiodynamics in response to ventricular pacing were compared with those to right atrial pacing at equivalent heart rate. Stimulation of the ventricle except lateral wall of the left ventricle produced no significant changes in coronary sinus blood flow and myocardial oxygen consumption despite decreased blood pressure and cardiac output. The minor change of coronary sinus blood flow was related to the decrease in coronary vascular resistance. Oxygen content of coronary sinus blood decreased during ventricular pacing, while arterial oxygen saturation remained constant. The response of coronary circulation to ventricular pacing did not differ essentially at faster and slower heart rates. It was considered that when stimuli were applied to the ventricular surface, the relatively constant myocardial oxygen consumption in the presence of lowered cardiac performance was attributed to the asynchrony of fractionate contractions of the ventricular muscle.

Animals↗
PubMed1977

Effects of isometric handgrip exercise on coronary sinus blood flow in idiopathic cardiomyopathy.

Coronary sinus blood flow (CSBF) was measured by the dye dilution method in 18 patients with idiopathic cardiomyopathy including 13 with hypertrophic type and 5 with congestive type, and the capacity for increasing CSBF in response to handgrip exercise was studied in 14 patients. CSBF at rest ranged from 41 to 236 ml/min/M2. Average CSBF of 114 +/- 12 ml/min/M2 (112 +/- 14 in hypertrophic type and 119 +/- 25 in congestive type) was significantly larger than control value of 77 +/- 6 presented previously (p less than 0.01). Handgrip exercise at 30% maximal effort for 3 min resulted in the increase in CSBF, averaging 23 +/- 8 ml/min/M2 (22 +/- 8%). However, in about one-half of cases, the percent increase in CSBF was much smaller than the percent increase in effort index which represents myocardial oxygen demand. The change of CSBF was not correlated with the changes of left ventricular systolic pressure, cardiac output, and stroke work. The diminished response of CSBF to isometric handgrip exercise was ascribed to the decreased coronary vascular reserve in this disorder.

Adolescent↗
PubMed1977

Regional contraction patterns of the left ventricle during ventricular pacing.

Ten mongrel dogs were used to assess regional myocardial function in response to electrical pacing form the inflow (RVI), outflow tracts (RVO), and apex (RVA) of the right ventricle and apex (LVA) and lateral wall (LVL) of the left ventricle. Strainguauge arches were sutured to the epicardial segments of the apical and lateral walls of the left ventricle and their mechanical shortening was measured during right artial (RA) and during ventricular pacing. The onset of shortening of two segment did not differ significantly in RA and RVI pacing, while the stimulation of RVA and LVA caused the initial contraction of the apical segment, and RVO and LVL pacing caused that of the lateral segment; i.e. RVA and RVO pacing resulted in left ventricular asynchrony of contraction similar to LVA and LVL pacing, respectively. Asynchrony of contraction was not accompanied by a uniform change in peak tension of regional myocardial segments, but prejection tension rose and ejection tension fell at the pacing site. The reduction in mean aortic pressure inversely correlated with the prolongation of the time interval between the onset of shortening of two segments during left ventricular pacing. The decrease in cardiac performance observed during ventricular pacing was related to the severity of asynchrony rather than the direction of the ventricular depolarization or change in regional myocardial tension.

Animals↗
PubMed1977

Pulmonary arterial pressure-flow characteristics in atrial septal defect: comparative study with ventricular septal defect and patent ductus arteriosus.

Pulmonary arterial pressure-flow relation was studied in 142 patients with artrial septal defect (ASD) and was compared with that of 139 patients with ventricular septal defect (VSD) and was compared with that of ductus arteriosus (PDA). The incidence of pulmonary arterial mean pressure (PAm) over 25 mmHg was 21 percent in ASD, 36 percent in VSD and 43 percent in PDA, and that over 40 mmHg was 3 percent, 23 percent and 19 percent, respectively. Large left to right shunt over 50 percent was found more frequently in ASD (58 percent) than in VSD (22 percent) and PDA (30 percent). When patients were separated into 2 groups at a PAm of 40 mmHg, lower pressure group showed a positive correlation between PAm and left-to-right shunt in each disease, although the correlation was poor in ASD (r equals 0.23) as compared with VSD (r equals 0.49) and PDA (r equals 0.47). The slope of the regression line was less steep in ASD (0.08) than in VSD (0.17) and PDA (0.14). It is considered that pulmonary hypertension in ASD develops on the basis of pulmonary vascular changes caused by prolonged hyperkinetic circulation.

Adolescent↗
PubMed1976

Plasma catecholamine levels in the coronary sinus, aorta and femoral vein of subjects undergoing cardiac catheterization at rest and during exercise.

Plasma catecholamine (CA) levels in the coronary sinus (CS), aorta (Ao) and femoral vein (fv) were simultaneously measured in 22 patients with various heart diseases at rest and during handgrip exercise (IHG). The mean resting levels of plasma norepinephine (NE) in CS, Ao and FV were 359 +/- 49 (SEM) pg/ml, 290 +/- 27 and 234 +/- 24, respectively. The corresponding values of epinephrine (E) were 127 +/- 18 pg/ml, 186+/- 30 and 97 +/- 11, respectively. The E values in Ao were significantly greater than those in CS and in FV (p less than 0.05). IHG exercise induced an obvious elevation of plasma CA levels in every portion of the circulation studied. The mean increments of NE concentration were 81%, 54% and 67% of the resting levels at CS, Ao and FV, respectively, while IHG induced elevation of E were 70% of the resting values at each portion studied. Significant correlations were observed between individual CA concentrations in CS and in Ao, and also between those in Ao and in FV at rest. Under raised sympathoadrenal conditions, however, individual values of NE in CS failed to correlate signficantly to those in Ao and in FV, respectively. The NE output from CS was limited to only 3% and 5% of those in Ao at rest and during IHG, respectively. An actual mean increment of NE on its passing through the coronary circulation was only 2% or less of NE output in ao at both stages. It appears, thus, to be untenable that the cardiac tissue is one of the major source of circulating CA at physiological condition. From these reasons, the direct measurement of NE levels in CS may be mandatory, when plasma CA assay is designed for the purpose of studying the role of the sympathetic nerve activity in the regulation of cardiac function.

Adolescent↗
PubMed1976

Coronary blood flow and lactate metabolism during isometric handgrip exercise in heart disease.

Twenty-one patients with various heart diseases undergoing the coronary sinus catheterization had myocardial blood flow studies before and during isometric handgrip exercise. At 30% of the maximal voluntary contraction (MVC), handgrip increased both coronary sinus blood flow by 19.8% and myocardial O2 consumption by 21.0% on the average as compared to those at rest. At 20% of MVC, the increase of the both was slight except for 1 case. The increase in coronary sinus blood flow significantly correlated to the increase of myocardial O2 consumption. Lactate extraction ratio decreased to less than 10% during handgrip in 4 of 19 cases studied despite of normal values at rest. Lactate extraction ratio had significantly positive correlations with coronary sinus blood flow and myocardial O2 consumption during handgrip, while there were not significant ones at rest. It is suggested that isometric handgrip exercise is useful as a stress test for detection of myocardial ischemia in the heart of coronary artery disease.

Adolescent↗
PubMed1976

Effects of varying pacemaker sites on left ventricular performance.

The hemodynamic effects of the site of the artificial cardiac stimulation were studied in 17 open chest dogs. The right atrium and five ventricular sites (the inflow and outflow tracts and apex of the right ventricle, apex and lateral wall of the left ventricle) were stimulated electronically at a given rate, ranging from 130 to 190 per min. When cardiac performance during ventricular pacing was compared with those during right atrial pacing, the former uniformly caused a diminution of cardiac output and systemic blood pressure, without reduction of left ventricular end-diastolic pressure. Ventricular function curves, in which left ventricular stroke work was related to left ventricular end-diastolic pressure, shifted downwards and to the right during ventricular pacing. Stimulation frequency did not alter these variables. It was considered that the left ventricular dysfunction in ventricular pacing resulted from the absence of atrial contribution to ventricular filling, mitral regurgitation present and asynchronous ventricular contraction. No significant difference of cardiac performance was demonstrated by changing the site of ventricular pacing, suggesting that the mode of ventricular depolarization itself was not relevant to a decrease in cardiac performance.

Animals↗
PubMedDate not supplied

CO2 response for the brain stem artery blood flow velocity in man.

We examined changes in the blood flow velocity of brain stem artery (BSA) and middle cerebral artery (MCA) in response to hypercapnic, normocapnic and hypocapnic hyperventilation in seven awake subjects with a transcranial Doppler to determine if there are differences in blood flow control in regional brain perfused by these respective arteries, and to separate the effects of CO2 and ventilation itself on blood flow velocity during CO2 loading. During hypercapnic hyperventilation, BSA flow velocity increased linearly with an increase in end-tidal partial pressure of CO2 (PETCO2). During hypocapnic hyperventilation, BSA flow velocity decreased linearly with decrease in PETCO2, but did not change during normocapnic hyperventilation. The mean CO2 reactivity of BSA was 2.8%/mmHg. The responses of MCA to these hyperventilations and CO2 reactivity were similar to those of BSA. These findings suggest that CO2 rather than ventilation per se is the important stimulus to changes in brain blood flow velocity and that the CO2 responses of brain arteries are not affected by differences in vascular beds.

Adult↗
PubMedDate not supplied

Interaction between sarcomere and mitochondrial length in normoxic and hypoxic rat ventricular papillary muscles.

We hypothesized that the mitochondrial length may be altered according to changes in the sarcomere length, and that this relationship may be affected by exposure to hypoxia. Rat ventricular papillary muscles were isolated and immersed in normoxic or hypoxic solutions for 10 min. Sarcomeres of various lengths were obtained by fixing the papillary muscles in a slack or stretched state, or after exposure to a contracture solution containing saponin and CaCl(2). The mitochondrial length measured using electron microscopy significantly correlated to the length of the adjacent sarcomere in both the normoxic (n=767) and hypoxic (n=1145) groups (P<.0001). The slope of the regression line, however, was significantly less steep, and its intercept was significantly larger in the hypoxic group than in the normoxic group (analysis of covariance). When we analyzed the mitochondrial lengths among the three sarcomere-length subgroups (<1.5, 1.5-2.0, and >2.0 microm), the mitochondrial length was significantly shorter in the hypoxic condition than in the normoxic condition at sarcomere lengths greater than 2.0 microm. Staining for desmin, the major muscle-type intermediate filament, the longitudinal system of which connects the mitochondria with the Z bands of sarcomeres, showed a clear cross-striation pattern in both papillary muscles with and without the exposure to hypoxia, suggesting that desmin was preserved after the exposure to hypoxia. These data indicate that the mitochondrial length changes according to changes in the sarcomere length, suggesting the possible role of mitochondria as an internal load against myocyte contraction. It is also suggested that mitochondria exposed to hypoxia may be more resistive to both compression and stretch in a longitudinal direction than those in the normoxic condition.

Animals↗
PubMedDate not supplied

Immunohistochemical analysis of platelet-derived growth factor-B expression in myocardial tissues in hypertrophic cardiomyopathy.

Intimal and/or medial hyperplasia of intramyocardial small vessels is thought to be one of the causes of myocardial ischemia in hypertrophic cardiomyopathy (HCM). However, the pathogenesis of such vascular lesions in HCM is not yet known. To evaluate the pathogenic role of platelet-derived growth factor (PDGF-B) and basic fibroblast growth factor (b-FGF), which have a potential to induce cellular and molecular changes observed in the vessels in HCM, we examined the expression of these molecules and PDGF receptors in cardiac tissues from six patients with HCM and seven controls using immunohistochemistry. The percentage of PDGF-B positive cells in the myocyte population in HCM was significantly higher than that in controls (52.6 +/- 16.2 (mean +/- SD) vs. 21.6 +/- 9.6, p < 0.01). PDGF-B was also observed in vascular regions in HCM (61.1 +/- 25.5% of arterioles) but not in controls. There were no significant differences in the expression of b-FGF and PDGF receptors in the myocyte and non-myocyte populations and the vascular regions between the HCM and control groups. Our study revealed that the expression of PDGF-B protein was up-regulated in HCM, suggesting the contribution of this molecule to the development of intramyocardial vasculopathy.

Adolescent↗
PubMedDate not supplied

Reduced response of cardiac norepinephrine release to isometric handgrip exercise in heart failure.

In order to evaluate the relation of cardiac norepinephrine (NE) release to left ventricular function, blood was taken simultaneously from the coronary sinus (CS) and the aorta (A) in 19 patients with heart diseases, at rest and during isometric handgrip exercise (IHG) at 30% of their maximal contraction. Plasma NE was analyzed by Renzini's THI method. The concentrations of plasma NE at rest were 397 +/- 66 (S.E.M.) ng/liter in CS and 292 +/- 50 in A. IHG significantly increased NE to 578 +/- 88 in CS and to 462 +/- 85 in A (p less than 0.001). Estimated NE release from the heart (deltaNE = NECS - NEA) correlated inversely to left ventricular end-diastolic pressure at rest (r = -0.520, p less than 0.05) and during IHG (r= -0.689, p less than 0.01). The changes in deltaNE induced by IHG correlated to the slope of the left ventricular function curve (r=0.618, p less than 0.01). It is concluded that the response of cardiac NE release to exercise is reduced in patients with depressed cardiac function.

Blood Pressure↗