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Biomedical subjects

F Yasuma

Publications and source records attributed to F Yasuma.

At least 37 records · Page 2Linked to original sources
PubMed1996

Respiratory sinus arrhythmia. A phenomenon improving pulmonary gas exchange and circulatory efficiency.

BACKGROUND: The primary mechanisms of respiratory sinus arrhythmia (RSA) are understood to be the modulation of cardiac vagal efferent activity by the central respiratory drive and the lung inflation reflex, and the degree of RSA increases with cardiac vagal activity. However, it is unclear whether RSA serves an active physiological role or merely reflects a passive cardiovascular response to respiratory input. We hypothesized that RSA benefits pulmonary gas exchange by matching perfusion to ventilation within each respiratory cycle. METHODS AND RESULTS: In seven anesthetized dogs, a model stimulating RSA was made. After elimination of endogenous autonomic activities, respiration-linked heartbeat fluctuations were generated by electrical stimulation of the right cervical vagus during negative pressure ventilation produced by phrenic nerve stimulation (diaphragm pacing). The vagal stimulation was performed in three conditions; phasic stimulation during expiration (artificial RSA) and during inspiration (inverse RSA) and constant stimulation (control) causing the same number of heartbeats per minute as the phasic stimulations. Although tidal volume, cardiac output, and arterial blood pressure were unchanged, artificial RSA decreased the ratio of physiological dead space to tidal volume (VD/VT) and the fraction of intrapulmonary shunt (Qap/Qt) by 10% and 51%, respectively, and increased O2 consumption by 4% compared with control. Conversely, reverse RSA increased VD/VT and Qap/Qt by 14% and 64%, respectively, and decreased O2 consumption by 14%. CONCLUSIONS: These results support our hypothesis that RSA benefits the pulmonary gas exchange and may improve the energy efficiency of pulmonary circulation by "saving heartbeats."

Animals↗
PubMed1996

Ultra-low-field magnetic resonance imaging in upper airways obstruction in sleep apnea syndrome.

The hypothesis that the sites of upper airways obstruction (UAO) are varied in a patient with obstructive sleep apnea syndrome (OSAS) among different sleep stages is studied. Four patients with OSAS underwent ultra-low-field magnetic resonance imaging (MRI) with a field strength of 0.064 Tesla provided real-time images and generated less noise and necessitated less strict magnetic isolation compared with conventional high-field MRI. After the fixed end-apneic sleep stage was determined, the polysomnogram was switched off and ultra-low-field MRI was commenced. The effects of continuous positive airway pressure (CPAP) on the upper airway patency in the deepest sleep stage obtained for each patient was assessed. Upper airway obstruction was found at the level of the palatopharynx (PP) at sleep onset extended to the glossopharynx (GP) during rapid eye movement (REM) sleep in two cases and during NREM sleep in one case. This combined PP and GP obstruction was observed from sleep onset and remained unchanged in one case. The patent upper airways were observed during treatment with CPAP during REM sleep in two patients and during stage two of NREM sleep in the other two patients. It can be concluded that the sites of UAO vary in a patient with OSAS in different sleep stages. The results also suggest the use of the ultra-low-field MRI in order to visualize the dynamic and real-time behaviors of the upper airways during sleep in patients with OSAS.

Adult↗
PubMed1995

Cardiac hypertrophy in obstructive sleep apnea syndrome.

Fifty-one middle-aged male patients with obstructive sleep apnea syndrome (OSAS) were evaluated using two-dimensional echocardiography, 24-h blood pressure measurements, polysomnography, and plasma norepinephrine (NE) measurements. Among these patients, left ventricular hypertrophy (LVH) (left ventricular posterior wall thickness [LVPWT] or interventricular septal thickness [IVST] > or = 12 mm) and right ventricular hypertrophy (RVH) (right ventricular wall thickness [RVT] > or = 5 mm) were present in 41.2% (21/51) and 11.8% (6/51). LVH was present in 50.0% of group 2 patients (apnea index > or = 20) and in 30.5% of group 1 patients (apnea index < 20). All patients with LVH had hypertension. RVH was present in 21.4% of group 2 patients and none of the group 1 patients. IVST, LVPWT, LV mass, LV mass/body surface area (BSA), and obesity index were significantly greater in group 2 than in group 1. Apnea index and the duration in which nocturnal oxygen saturation was decreased under 90% (duration of SaO2 < 90%), were significantly correlated with LV mass/BSA and 24-h mean blood pressure. Apnea index, number of apneas, duration of nocturnal oxygen saturation less than 90%, weight, and obesity index were significantly greater in patients with both LVH and RVH than in patients without LVH and RVH, or those with only LVH. Plasma NE after waking significantly increased compared with that before sleep (p < 0.05). The ratio of plasma NE levels after waking to those before sleep was significantly correlated with the duration of SaO2 < 90% (r = 0.83, p < 0.05), but not with apnea index. These results suggest that frequent episodes of oxygen desaturation and/or arousal responses caused by apnea may contribute to the complication of LVH and RVH in the long term, and apnea-induced cyclical increases in blood pressure and the resulting sustained elevation in blood pressure associated with the increase in afterload and sympathetic activity may play a role in the development of LVH.

Adult↗
PubMed1995

A case of mitral regurgitation whose nocturnal periodic breathing was improved after mitral valve replacement.

Nocturnal periodic breathing (PB) is often observed in patients with congestive heart failure (CHF). We investigated the sleep architecture polysomnographically in a 54-year-old man with CHF due to mitral regurgitation before and after surgical treatment. We found that the overnight frequency of central dominant sleep apnea decreased from 154 to 56, and the lowest nocturnal oxygen saturation increased from 66% to 85% postoperatively. These improvements in the manifestations of PB might be attributed to the improved hemodynamics after successful valve replacement.

Cheyne-Stokes Respiration↗
PubMed1993

Abdominal muscle activation by respiratory stimuli in conscious dogs.

The responses of the diaphragm, external oblique, and transversus abdominis muscles to hyperoxic hypercapnia and isocapnic hypoxia were studied in four awake dogs to test the hypothesis that central and peripheral chemoreceptor inputs result in different patterns of respiratory muscle activation. The dogs were trained to lie quietly in place, and electromyographic (EMG) discharges of the diaphragm (EMGdi), external oblique (EMGeo), and transversus abdominis (EMGta) were recorded from chronically implanted electrodes. Both hypercapnia and hypoxia recruited EMGeo and EMGta activity, but at comparable levels of minute volume of ventilation the EMG activity of the abdominal muscles was greater during hypercapnia than during hypoxia. However the two chemical stimuli also resulted in different tidal volume (VT) and respiratory frequency responses at any given minute volume of ventilation. When EMG activity was reanalyzed as a function of VT, EMGeo and EMGta were the same for a given VT whether induced by hypercapnia or hypoxia, but EMGdi was consistently greater during hypoxia than during hypercapnia. When the vagus nerves were blocked by cooling exteriorized cervical vagal loops, all abdominal muscle EMG activity was abolished. The findings support the concept that stimulation of the central and peripheral chemoreceptors results in asymmetric activation of the inspiratory and expiratory respiratory muscles. The findings also indicate that afferent vagal stimuli play an important facilitatory role in activation of the abdominal expiratory muscles.

Abdominal Muscles↗
PubMed1993

Effect of inspiratory muscle unloading on arousal responses to CO2 and hypoxia in sleeping dogs.

Chemical respiratory stimuli can induce arousal from sleep, but the specific mechanisms involved have not been established. Therefore, we tested the hypothesis that mechanoreceptor stimuli arising in the ventilatory apparatus have a role in the arousal responses to progressive hypercapnia and hypoxia by comparing arousal responses during spontaneous ventilation with those obtained when the inspiratory muscles were unloaded by mechanical ventilatory assistance. Studies were performed in three trained dogs in which the adequacy of inspiratory muscle unloading was verified by diaphragmatic electromyographic (EMG) recordings. In rapid-eye-movement (REM) sleep the arousal threshold during progressive hypercapnia increased from 68.4 +/- 0.5 (SE) mmHg during spontaneous runs to 72.3 +/- 0.8 mmHg during mechanically assisted runs (P < 0.01). In contrast there were no changes in arousal responses to hypercapnia during non-REM (NREM) sleep or to hypoxia in either NREM or REM sleep. However, during the assisted hypoxic runs, EMG activity of the transversus abdominis muscle was increased compared with the unassisted runs; therefore, the effects on arousal threshold of unloading the inspiratory muscles may have been offset by increased loading of the expiratory muscles. The findings indicate that even in the absence of added mechanical loads, mechanoreceptor stimuli probably arising in the respiratory muscles contribute to the arousal response to hypercapnia during REM sleep.

Animals↗
PubMed1993

24-hour ambulatory blood pressure variability in obstructive sleep apnea syndrome.

The 24-h ambulatory blood pressure (24h-ABP) was examined in 21 men, aged 38 to 65 years (mean 50.6), with obstructive sleep apnea syndrome (OSAS) and in 123 normal male control subjects, aged 40 to 60 years (mean 48.1) who did not have OSAS, obesity, autonomic nervous system abnormality, cardiac disease, or respiratory disease (group C), to assess the role of apneas in the circadian variation of blood pressure (BP). The 24h-ABP patterns in OSAS patients were classified into three types as follow: normotensive OSAS patients with normal BP throughout the 24-h period with nocturnal BP fall (type 1); hypertensive OSAS patients with progressive BP elevation from onset of sleep to early morning (type 2); and hypertensive OSAS patients with elevated BP (systolic BP > or = 140 mm Hg or diastolic BP > or = 90 mm Hg) at any time during a 24-h period (type 3). It was concluded that the circadian BP variation in type 1 was almost identical to the level and pattern of group C; the circadian variations in types 2 and 3 were significantly different from that of group C; and the patients with types 2 and 3 BP patterns had more severe OSAS than type 1 patients. The severity of OSAS was an important factor in nocturnal elevation of BP, hence affecting the circadian variation of BP. Noninvasive 24h-ABP monitoring is a useful procedure for understanding the clinical features of OSAS patients with or without hypertension.

Adult↗
PubMed1991

Interaction of chemical and mechanical respiratory stimuli in the arousal response to hypoxia in sleeping dogs.

The role of respiratory mechanoreceptor stimuli in the arousal response to hypoxia was studied in three trained dogs. The dogs breathed through a cuffed endotracheal tube inserted through a chronic tracheostomy, and resistive loads of 8 to 49 cm H2O/L/s were added to the expiratory circuit. Arterial O2 saturation (SaO2) was measured with an ear oximeter, and isocapnic progressive hypoxia was induced by a rebreathing technique. Arousal from sleep was determined by electroencephalographic and behavioral criteria. SaO2 at arousal from non-rapid eye movement (NREM) sleep increased progressively from 67.5 +/- 4.6% (mean +/- SEM), with no added resistance to 85.2 +/- 0.5% with the highest resistance (p less than 0.01), and from 60.6 +/- 0.6 to 81.6 +/- 0.4% during REM sleep (p less than 0.01). The added resistances also increased the steady-state (normoxic) level of alveolar PCO2 (PACO2). However, when PACO2 was increased to comparable levels by the addition of dead space rather than expiratory resistance to the breathing circuit, SaO2 at arousal from hypoxia was significantly lower than during expiratory resistive loading (p less than 0.05). We therefore conclude that mechanoreceptor stimuli arising from the ventilatory apparatus may contribute substantially to the arousal response to hypoxia.

Animals↗
PubMed1991

Effects of vasodilators on venous tone in vivo in dogs.

The authors investigated, in vivo, the effects of four vasodilators on venous tone in dogs. Baseline venous tone was determined from the pressure: diameter relationships in the inferior vena cava (VSIVC) and femoral vein (VSFV) as measured during several seconds of occlusion of the proximal inferior vena cava. All of the slopes were nearly linear. All vasodilators were administered in dosages sufficient to lower blood pressure by approximately 20%; these dosages also decreased systemic vascular resistance by 15% to 30%. Isosorbide dinitrate reduced VSIVC from 7.17 +/- 0.81 to 5.81 +/- 0.73 mmHg/mm and VSIVC from 59.4 +/- 13.5 to 37.2 +/- 6.6 mmHg/mm. Neither nifedipine nor nisoldipine altered VSIVC or VSFV. However, prazosin decreased VSIVC from 13.2 +/- 3.3 to 10.7 +/- 2.7 mmHg/mm and VSFV from 43.5 +/- 11.3 to 29.9 +/- 8.8 mmHg/mm. These results suggest that isosorbide dinitrate and prazosin decrease venous tone in vivo, whereas nifedipine and nisoldipine do not.

Animals↗
PubMed1990

Respiratory muscle activation by chemical stimuli in awake and sleeping dogs.

The present findings in awake and sleeping dogs confirm the early observations in anesthetized cats (Bainton et al., 1978; Sears et al., 1982), and more recent studies in awake and sleeping humans (Takasaki et al., 1989), that suggest an asymmetry in pattern of respiratory motoneuron and muscle activation by central and peripheral chemoreceptor stimulation, with central chemoreceptor stimulation driving both inspiratory and expiratory mechanisms, and peripheral chemoreceptor stimulation driving inspiratory and inhibiting expiratory mechanisms. Because REM sleep inhibits the nondiaphragmatic muscles, which include the expiratory muscles, there is a reduction in CO2 response during this sleep stage. In contrast because the response to hypoxia is mediated predominantly by the diaphragm, which is not generally inhibited by REM sleep, there is less effect of REM sleep on the overall response to hypoxia. In addition to being of basic importance, these concepts may have important clinical implications.

Afferent Pathways↗
PubMed1990

[Heart rate changes in sleep apnea syndrome].

Sleep apnea syndrome (SAS) is often associated with arrhythmias. The study was performed to clarify the characteristics and mechanisms of the heart rate (HR) changes during and after sleep induced apneas. Thirty-one patients with SAS without definitive heart disease, aged 17-78 years (mean 54.2 years), were examined by electroencephalograms, electrocardiograms, electrooculograms, nasal and oral breathing, thoracic and abdominal respiratory movements and arterial oxygen saturation (SaO2). [Results and Discussion] At the onset of sleep apnea, some showed progressive reductions in HR, followed by abrupt tachycardia on the resumption of breathing. Thirty-one patients with SAS were classified into three Groups (A, B, C). Group A demonstrated that HR changes occurred associated with apnea both in stage REM and in stage non-REM. Group B demonstrated that HR changes occurred associated with apnea only in stage REM. Group C demonstrated that HR changes did not occur associated with apnea. In Group A, apnea frequency and apnea index were higher than those of Group C. In Group A, the lowest SaO2 was lower than that of Group C, total time under 90% of arterial oxygen saturation (SaO2) was longer than that of Group C. There was a good negative correlation between oxygen saturation and HR changes. Further, HR changes were augmented by arousal response. This might be related to the arousal response as well as to the cardiostimulatory effects of hypoxia associated with increased ventilation. The arousability in response to apneas might be important in HR changes. In SAS, the degree of HR changes was related to apnea frequency, apnea index, apnea length and sleep stage.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1989

Breathing abnormalities during sleep in patients with chronic heart failure.

Polysomnography was carried out in 11 adult outpatients with stable chronic heart failure (CHF) due to valvular heart disease in order to investigate respiratory abnormalities during sleep. The subjects consisted of 6 males and 5 females and their ages ranged from 54 to 76 years. A coexisting central dominant sleep apnea syndrome (SAS) was found in 4 males, 3 of whom had evidence of nasal obstruction. A successful mitral valve replacement in one patient with central dominant SAS was associated with a reduction in the frequency of sleep apnea. The results suggest complications caused by respiratory abnormalities during sleep are common and should be considered in the management of patients with CHF.

Aged↗
PubMed1989

Retinal embolism from left atrial myxoma.

Retinal artery embolism that had arisen as a complication of a left atrial myxoma was diagnosed in a young man who had suddenly developed a visual disorder in his left eye. A tumor in the left atrium was surgically excised. Pathologically, retinal embolism secondary to atrial myxoma is rare. To our knowledge, only 15 cases have been documented so far. The present case was only the second case of an isolated retinal embolism that had developed without systemic involvement, and the first case of retinal artery branch embolism that had resulted from a left atrial myxoma.

Adult↗
PubMed1989

[Hemodynamic study of negative pressure ventilation using diaphragm pacing].

A negative pressure ventilation (NPV) by unilateral or bilateral diaphragm pacing (DP) was prepared for canine experiments. A shift from positive pressure ventilation (PPV) to NPV resulted in elevation of mean aortic pressure, increase in stroke volume and depression of mean pulmonary arterial pressure. Examination of the interaction between respiratory cycle and cardiac function during PPV, disclosed a reduction of right ventricular stroke volume and elevation of mean aortic and right ventricular end-diastolic pressure at end inspiration, compared to those at end expiration. During NPV with DP, left ventricular stroke volume, heart rate and mean aortic pressure were increased immediately after DP (immediately after inspiration) compared to those at end expiration. The experimental model of DP, in which respiratory condition could be easily altered, was considered to be useful to evaluate the effect of NPV on cardiac function.

Animals↗
PubMed1989

[Two cases of cardiac tamponade, complicated by malignant, effusive pericarditis and treated by creating a pericardial peritoneal window].

Reported are two cases of a cardiac tamponade complicated by a malignant, effusive pericarditis were treated by a pericardial, peritoneal window. In both cases, a reaccumulation of pericardial fluid was noticed, within a month after percutaneous, continuous pericardial drainage, and a tumor invasion was seen to the anterior mediastinum creating a pericardial, peritoneal window was considered useful for the treatment of the cardiac tamponade, secondary to the malignant, effusive pericarditis.

Adult↗