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Biomedical subjects

Y Nakazono

Publications and source records attributed to Y Nakazono.

34 records · Page 2Linked to original sources
PubMed1988

Neuronal origin of parallel suppression of postural tone and respiration elicited by stimulation of midpontine dorsal tegmentum in the decerebrate cat.

This paper describes the possibility that rostal pontine neuronal structures cause the parallel suppression of postural tone and respiration evoked by stimulation of the dorsal tegmental field (DTF) of the pons in decerebrate cats. Stimulation of the DTF along the midline decreased both diaphragmatic activity and the bilateral tone of the hind-limb extensor muscles. Pontine neuronal structures located rostrally to the DTF, from which antidromically activated units could be recorded on stimulation of the DTF, were studied. Antidromic spikes were recorded in and near the nucleus reticularis pontis oralis. Tonic electrical stimulation of these sites caused parallel suppression of postural tone and respiration. These suppressive effects were almost similar to those elicited by the DTF stimulation.

Action Potentials↗
PubMed1988

Parallel suppression of extensor muscle tone and respiration by stimulation of pontine dorsal tegmentum in decerebrate cat.

This paper describes the pontine brainstem area responsible for the suppression of postural muscle tone as well as of respiration in acute precollicular-postmammillary decerebrate (mesencephalic) cats. Stimulation of the dorsal part of the pontine tegmentum (DTF) along the midline (P4-P7, H-5 to H-6) decreased the bilateral tone of the hindlimb extensor muscles and the diaphragmatic activity. Tonic discharges of the extensor muscles were suppressed by DTF stimulation and the suppression of muscle activity continued for more than 5 min after termination of the stimulation. In contrast, the suppression of the diaphragmatic activity, which resulted in apnea in some of the animals tested, resumed in spite of the continuation of the stimulation. However, the rebound augmentation of the diaphragmatic activity appeared immediately after the termination of the stimulation. The existence of such a rebound phenomenon suggested that the suppressive effects on the diaphragmatic activity persisted during the entire period of the stimulation. The recovery of respiratory movements during the stimulation led us to suggest that the strong respiratory drives emerge to overcome the exerted DTF-elicited suppressive effects on respiration. In the paralyzed and vagotomized animal, the DTF-elicited suppressive effects on phrenic neural discharges were minimal when the end-tidal pCO2 was set at a higher level than during spontaneous breathing.

Animals↗
PubMed1988

Relationship between cardiorespiratory dynamics and maximal aerobic capacity in exercising men.

Cardiorespiratory dynamics was tested in 10 men exercising with a relative intensity of 50% VO2max for 10 min. Time constants for cardiac response (SV 21.7 sec, HR 45.8 sec, Q 21.7 sec) were shorter than those for the ventilatory response (of 27.4 sec, VT 70 sec, VE 69.5 sec). Respiratory dynamics was significantly related to the level of VO2max exhibited by the subjects: (f) r = 0.79, p less than 0.02; (VT) r = 0.63, p less than 0.05; (VE) r = 0.78, p less than 0.01. It is concluded that in man the dynamics of the ventilatory response to exercise depend on the actual level of VO2max in the individual.

Adult↗
PubMed1988

Analysis of entrainment of respiratory rhythm by somatic afferent stimulation in cats using phase response curves.

To elucidate how peripheral somatic afferents synchronize the respiratory rhythm to the exercise rhythm, the phrenic nerve activity in the vagotomized, paralyzed, and artificially ventilated cats anesthetized with chloralose-urethane was recorded during electrical stimulation of the superficial radial nerve afferents. At first, a single pulse train was given at various times of the respiratory cycle to obtain a phase-response curve (PRC). The stimulation given at mid to late expiration produced a phase advance, but the stimulation during inspiration produced no measurable phase shifts in most animals (8/10). The maximum phase advance changed depending on the stimulus intensity. The stronger the stimulus intensity, the greater became the maximum phase advance. Repetitive somatic afferent stimulation produced 1:1 entrainment of the respiratory frequency to the repetitive stimulation. Theoretical predictions on the stable entrainment phase and on the entrainment frequency range from the obtained PRC were close to the experimental results. The present study demonstrated the presence of a neuronal circuit synchronizing the respiratory rhythm to the periodic somatic afferents and the manner of how such entrainment occurs.

Afferent Pathways↗
PubMed1988

The origin of the initial abrupt increase in ventilation at the onset of muscular exercise (phase 1) in man.

Ventilation and cardiac output in response to four different exercises, namely, volitional pedalling using a bicycle ergometer with a very mild (7 Watt) load, passive pedalling, electrically-induced isometric twitches of one leg, and voluntary twitches simulating the previous electrical twitches, were measured simultaneously during the transient phase from rest. Cardiac output was determined by automated impedance cardiography. A sudden increase in ventilation was observed immediately after the onset of the volitional and passive pedalling whereas cardiac output increased only gradually. Only a slight difference was observed between the cardio-ventilatory responses to volitional and passive exercises. Neither ventilation nor cardiac output changed significantly in response to volitional and electrical twitches of one leg. Conclusions were then drawn that the cardio-dynamic process could be ruled out as the origin of the initial ventilatory response, and instead, other neurogenic mechanisms mediated either centrally or peripherally, should be considered.

Adult↗
PubMed1988

Respiratory and cardiac responses to dynamic exercise in man.

Ventilation (VE), cardiac output (Q), oxygen consumption (VO2), carbon dioxide production (VCO2), and end tidal gas tensions (PETO2 and PETCO2) were measured in four healthy men during stepwise, steady state increases in work rate on a bicycle ergometer (25, 50, 75, 100, 125, and 150 W). Both the ventilation equivalent (VE/VCO2) and the cardiac equivalent (Q/VCO2) for carbon dioxide, fell during a steady state exercise at 150 W to 2/3 and to 1/3 of the initial levels, respectively. This stepwise reduction in the carbon dioxide production with increasing work rate was compatible with a non-chemical stimulus increasing in proportion to work rate, and governing both ventilation and circulation. These observations do not support the cardio-dynamic hypothesis.

Adult↗
PubMed1987

Neurogenic factors affecting ventilatory and circulatory responses to static and dynamic exercise in man.

The possible influence of neurogenic factors on respiratory and circulatory responses to continuous static (CSE), rhythmic static (RSE), and dynamic (DE) exercises was studied in 15 healthy young men. Ventilation (VE), oxygen uptake (VO2), cardiac output (Q), and blood pressure (BP) were measured during the steady-state of the exercise. For a given VO2, VE, and respiratory frequency (f) enhanced significantly with increasing frequency of RSE, and for the same frequency, the responses of these variables to RSE were significantly higher than those for DE. Although a similar trend was observed in heart rate (HR) and Q responses to exercises, it was not as strong as for ventilatory responses. These results lead to the conclusion that ventilation and circulation during exercise may be influenced by some neurogenic factors mediated either centrally or peripherally.

Adolescent↗
PubMed1987

Effect of hypoxia and hyperoxia on cardiorespiratory responses during exercise in man.

To clarify the role of the carotid body in the mechanism governing exercise hyperpnea, the effect of hypoxia and hyperoxia on ventilation and cardiac output was studied in four healthy men. The VE increased 10.7% in hypoxia and decreased 10.1% in hyperoxia from normoxia as judged from the steady-state values during exercise. On the contrary, Q showed only a slight reduction of -3.2% in hyperoxia. The hypoxic hyperpnea and hyperoxic hypopnea led to a concomitant alteration in PETCO2. An overshoot following the onset of exercise was observed during the first 30s of VE response in hypoxia, which damped progressively in normoxia and hyperoxia. No remarkable difference was observed in the early transient responses of Q between hypoxia and hyperoxia. The discrepancy in the dynamics between VE and Q led to a phasic deviation in PETCO2; an isocapnic transition from the control to stimulus period in normoxia, hypocapnic in hypoxia and hypercapnic in hyperoxia. The time constant representing the kinetics of VE and that for VCO2 prolonged significantly in hyperoxia. These results support the cardiodynamic consequence of exercise hyperpnea, i.e., the carotid body is the first to respond to the increase in CO2 flow into the lungs.

Adult↗
PubMed1986

Degradation of [125I]iodoglucagon by normal rat plasma in radioimmunoassay mixture containing aprotinin and its prevention by p-chloromercuriphenyl sulfonate and leupeptin.

Degradation of [125I]iodoglucagon during RIA of glucagon would result in erroneously high values for immunoreactive glucagon (IRG). Normal rat plasma was found to have high activity for glucagon degradation that was not suppressed by the aprotinin and EDTA routinely added to the RIA system. About 30% of the added radioactive glucagon was degraded during RIA in assay mixture at pH 7.4 containing 0.2 ml normal rat plasma, and the IRG value was calculated to be 150-180 pg/ml plasma. The degradation was completely inhibited by addition of 2 mM p-chloromercuriphenyl sulfonate (PCMS) plus 0.25 mM leupeptin as protease inhibitors, and in their presence the IRG value was about 80 pg/ml. The glucagon-degrading activity was about half as much in assay mixture at pH 8.8 as in that at pH 7.4, but the degradation still affected the accuracy of IRG values. When rat plasma was incubated with [125I]iodoglucagon in the assay conditions used for RIA and then subjected to Bio-Gel P-6 filtration, three new peaks of radioactivity were found in low mol wt fractions, with decrease in the peak corresponding to [125I]iodoglucagon, whereas on similar treatment in the presence of PCMS and leupeptin all the radioactivity was recovered in the glucagon fraction. The average recoveries of authentic glucagon as IRG in the absence and presence of the inhibitors were less than 60% and more than 90%, respectively. These findings indicate that determination of plasma IRG in rats by RIA with assay mixture containing aprotinin gives spuriously high values owing to degradation of the radiotracer, and that PCMS and leupeptin should be added to the sample and assay mixture to prevent this degradation.

4-Chloromercuribenzenesulfonate↗
PubMed1985

Noninvasive pulsed Doppler echocardiographic detection of the direction of shunt flow in patients with atrial septal defect: usefulness of the right parasternal approach.

Noninvasive pulsed Doppler echocardiography combined with two-dimensional echocardiography by the right parasternal approach was performed to detect the shunt flow through the defect in 31 patients with suspected secundum atrial septal defect (ASD). A defect of the interatrial septum was seen on the two-dimensional echocardiograms of 30 of 31 patients. In all the 30 patients, Doppler signals of shunt flow could be recorded by placing the sample volume in the center of the defect on the two-dimensional echocardiogram. Neither a defect nor Doppler signal indicating shunt flow were demonstrated in any of 15 normal control subjects. Cardiac catheterization indicated significant shunt flow in all the 31 patients with suspected ASD. Doppler signals obtained from the center of the defect showed left-to-right and/or right-to-left shunt flow patterns. The direction of the shunt flow was mainly left to right, with its peak in late systole and atrial systole in 28 of 30 patients; mainly right-to-left flow was present in the remaining two patients, who had Eisenmenger's syndrome. The direction of flow as predicted by the Doppler signal was confirmed by the coincidence of direction of flow as seen on the contrast two-dimensional echocardiogram. In 22 patients for whom the measurement of the pulmonary-to-systemic flow ratio by oximetry was believed to be reasonably accurate, the ratio was fairly well correlated with Doppler-determined left-to-right shunt flow velocity (r = .71, SEE = 6.7 cm/sec).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1985

Cardiorespiratory dynamics in men in response to passive work.

Dynamic characteristics of ventilation, cardiac output, and gas exchange in response to passive limb movements were studied in four healthy men in an upright position. Passive exercise was performed on a motor-driven bicycle ergometer, of which pedaling rate was varied from control (30 rpm) to stimulus (90 rpm) level in a stepwise fashion. Stroke volume (SV), heart rate (HR), and cardiac output (Q) were determined continuously during the exercise by using an automated impedance cardiograph. Minute ventilation (VE), respiratory frequency (f), tidal volume (VT), oxygen consumption (VO2), carbon dioxide output (VCO2), end-tidal pressure of oxygen and carbon dioxide (PETO2 and PETCO2), and the gas exchange ratio (R) were also determined at each breath. When the pedaling rate was increased, Q and VE rose in excess of metabolic need with a half response time of about 10 sec, and remained elevated for the duration of the stimulus. VO2 and VCO2 rose transiently, then recovered to the initial control level after a few min. PETCO2 remained at the control level for about one min, then decreased by 1 Torr. PETO2 and R rose transiently. These results suggest that hyperpnea during passive exercise is not induced by chemical stimuli to known chemoreceptors, but is due to reflexes mediated either by moving limbs or the right heart.

Adult↗
PubMed1984

[Detection of a shunt flow through a defect in secundum atrial septal defect by right parasternal approach using pulsed Doppler echocardiography].

Pulsed Doppler echocardiography combined with two-dimensional echocardiographic (2-DE) system was performed to detect a shunt flow through a defect in the interatrial septum (IAS) in patients with secundum atrial septal defect (ASD) utilizing right parasternal approach (RPA). RPA is a method which provides an accurate evaluation of a defect in the IAS on a 2-DE image by placing a transducer on the right of the sternum because the ultrasonic beam passes in a plane almost perpendicular to the IAS. The subjects consisted of 20 patients with ASD (25 +/- 22 yrs) diagnosed by cardiac catheterization or 2-DE with peripheral contrast material injection, and 10 cases of healthy subjects (34 +/- 18 yrs). Defects in the IAS were clearly visible in 19 patients with ASD on 2-DE images by RPA. By placing the sample volume in the center of the defect, Doppler flows could be obtained in 17 of them. In 13 with sinus rhythm, except a case of Eisenmenger syndrome, Doppler signals showed mainly a laminar flow toward the transducer (positive flow), but a transient flow of low velocity away from the transducer (negative flow) was also observed. The positive flow had its peaks in late systole and atrial systole and occasionally in mid-systole, early diastole and mid-diastole. The negative flow occurred in early systole, mid-diastole and late diastole. In a patient with Eisenmenger syndrome and tricuspid regurgitation (TR), a negative turbulent flow was observed from early systole to mid-diastole. In three patients with atrial fibrillation, Doppler signals were variable. The Doppler echogram of a patient with atrial fibrillation but no complication showed a laminar positive flow with its peaks in late systole and mid-diastole, and a negative flow in early systole. One patient with atrial fibrillation and TR had a systolic negative turbulent flow and a mid-diastolic laminar positive flow. In a patient with TR and mitral regurgitation, the Doppler echocardiogram showed a laminar positive flow throughout the entire cardiac cycle with its peaks in early diastole and mid-diastole. Doppler signals from the left atrium (LA) to the right atrium (RA) through a defect coincided in timing with the appearance of negative contrast echo from the defect to the RA on 2-DE image and signals from the RA to the LA coincided with the appearance of the contrast echo into the LA from the RA through the defect. Doppler signals disappeared after the closure of the defect in all six patients examined.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1984

[An experimental study on the relationship between interventricular septal echograms and interventricular pressure gradient].

To evaluate the correlation between the configuration and motion of the interventricular septum (IVS) and the interventricular pressure gradient, six closed-chest dogs were studied. M-mode and two-dimensional echograms, the left (LVP) and right ventricular pressures (RVP), the interventricular pressure gradient (LVP-RVP), phonocardiograms in the left and right ventricles and electrocardiograms were simultaneously recorded. The RVP was gradually elevated by injecting Lycopodium in a peripheral vein. In all six dogs, there were good correlations between the curvature of the IVS and the interventricular pressure gradient in end-systole and in end-diastole. In M-mode echograms of the IVS, three dips were recognized in early diastole (isovolumetric relaxation period, D1 dip), in late diastole (atrial kick, D2 dip) and in early systole (isovolumetric contraction, S1 dip) when the RVP was elevated. Three negative dips on interventricular pressure gradient curves were observed to occur simultaneously with D1, D2, and S1 dips, respectively. A D1 dip was demonstrated in all six dogs, a D2 dip in four dogs, and an S1 dip in six dogs. In conclusion, the curvature of the IVS reflects the change in the interventricular pressure gradients in diastole as well as in systole. D1, D2 and S1 dips in the IVS echogram also reflect changes in the interventricular pressure gradients.

Animals↗
PubMed1983

Dynamics of cardiac output and systolic time intervals in supine and upright exercise.

Transient and steady-state responses of stroke volume (SV), heart rate (HR), cardiac output (Q), left ventricular ejection time (LVET), preejection period (PEP), and the ratio of LVET to PEP during bicycle exercises of 50 and 100 W were studied in four healthy male subjects in supine and upright postures. A computer-based system in which impedance cardiography was incorporated served to determine the above parameters on a 10-s interval basis. SV remained almost unchanged in response to exercises in a supine posture, whereas it increased significantly in an upright posture, although the individual differences among subjects were found to be large. The half-response times of variables to a step work load were determined. An approximate accordance was observed among the response times for HR, Q, and LVET/PEP. There was an inverse relationship between LVET and HR, the slope of which was found to be steeper in the supine posture than in the upright posture, reflecting the difference between the SV responses in both postures. LVET fell shortly after the cessation of exercise despite the decreasing HR. Inasmuch as the paradoxical reduction of LVET was also found in the case where SV remained unchanged in response to exercise, no changes in SV can be the cause thereof. Thus, a transient increase in ejection rate, which is due to either the increased myocardial contractility or decreased peripheral vascular resistance, may be responsible for the phenomenon.

Adult↗
PubMed1983

Cardiorespiratory dynamics during sinusoidal and impulse exercise in man.

Dynamic characteristics of ventilation, cardiac output, and gas exchange during sinusoidally varying work rates for the periods from 1 to 12 min and impulse work rate with a duration of 10 sec were studied on five healthy men in an upright position. Changes in work rate were given by controlling externally the electromagnetic braking system of a bicycle ergometer. Stroke volume, heart rate, and cardiac output during exercise were determined continuously by using an automated impedance cardiograph. Breath by breath determination in minute ventilation, respiratory frequency, tidal volume, oxygen consumption, carbon dioxide output, end-tidal pressures of oxygen and carbon dioxide, and gas exchange ratio were conducted. From these and steady-state response data amplitude and phase relations between each variable and the input work loads were obtained utilizing the frequency analysis techniques. The response characteristics to sinusoidal stimuli were well represented by first-order models with time constants for VE, VCO2, VO2, and Q averaging 75, 67, 52, and 36 sec, respectively. The kinetics of HR closely resembled that of Q. There was a close link between both the dynamics of VE and VCO2. On the other hand, the responses to impulse stimuli were better described by second-order models in which fast and slow response components were connected in parallel. However, the contribution of the fast component to total response was small. Although this response may support in its form the neuro-humoral concept to explain exercise hyperpnea, a tight linkage was observed between VE and VCO2 responses to impulse stimuli. Thus, hyperpnea during the unsteady-state of exercise may be explained by the cardiodynamic hypothesis.

Adult↗