Cardiac cycle-synchronized electrical muscle stimulator for lower limb training with the potential to reduce the heart's pumping workload.

BACKGROUND: The lower limb muscle may play an important role in decreasing the heart's pumping workload. Aging and inactivity cause atrophy and weakness of the muscle, leading to a loss of the heart-assisting role. An electrical lower limb muscle stimulator can prevent atrophy and weakness more effectively than conventional resistance training; however, it has been reported to increase the heart's pumping workload in some situations. Therefore, more effective tools should be developed. METHODS: We newly developed a cardiac cycle-synchronized electrical lower limb muscle stimulator by combining a commercially available electrocardiogram monitor and belt electrode skeletal muscle electrical stimulator, making it possible to achieve strong and wide but not painful muscle contractions. Then, we tested the stimulator in 11 healthy volunteers to determine whether the special equipment enabled lower limb muscle training without harming the hemodynamics using plethysmography and a percutaneous cardiac output analyzer. RESULTS: In 9 of 11 subjects, the stimulator generated diastolic augmentation waves on the dicrotic notches and end-diastolic pressure reduction waves on the plethysmogram waveforms of the brachial artery, showing analogous waveforms in the intra-aortic balloon pumping heart-assisting therapy. The heart rate, stroke volume, and cardiac output significantly increased during the stimulation. There was no change in the systolic or diastolic blood pressure during the stimulation. CONCLUSION: Cardiac cycle-synchronized electrical muscle stimulation for the lower limbs may enable muscle training without harmfully influencing the hemodynamics and with a potential to reduce the heart's pumping workload, suggesting a promising tool for effectively treating both locomotor and cardiovascular disorders.

Comparison of cardiovascular response to sinusoidal and constant lower body negative pressure with reference to very mild whole-body heating.

BACKGROUND: The purpose of the present study was to compare sinusoidal versus constant lower body negative pressure (LBNP) with reference to very mild whole-body heating. Sinusoidal LBNP has a periodic load component (PLC) and a constant load component (CLC) of orthostatic stress, whereas constant LBNP has only a CLC. We tested two sinusoidal patterns (30-s and 180-s periods with 25 mmHg amplitude) of LBNP and a constant LBNP with -25 mmHg in 12 adult male subjects. RESULTS: Although the CLC of all three LBNP conditions were configured with -25 mmHg, the mean arterial pressure (MAP) results showed a significantly large decrease from baseline in the 30-s period condition (P <0.01). In contrast, the other cardiovascular indices (heart rate (HR), stroke volume (SV), cardiac output (CO), basal thoracic impedance (Z(0)), total peripheral resistance (TPR), the natural logarithmic of the HF component (lnHF), and LF/HF (ln(LF/HF))) of heart rate variability (HRV) showed relatively small variations from baseline in the 30-s period condition (P <0.01). The result of the gain and phase of transfer function at the sinusoidal period of LBNP showed that the very mild whole-body heating augmented the orthostatic responses. CONCLUSION: These results revealed that the effect of the CLC of LBNP on cardiovascular adjustability was attenuated by the addition of the PLC to LBNP. Based on the results of suppressed HRV response from baseline in the 30-s period condition, we suggest that the attenuation may be caused by the suppression of the vagal responsiveness to LBNP.

Acute effects of warm footbath on arterial stiffness in healthy young and older women.

Acute systemic thermal therapy can improve arterial stiffness in both animals and humans. We examined and compared the effects of acute local thermal therapy (footbath) on an indicator of human arterial stiffness, cardio-ankle vascular index (CAVI), in 16 healthy young (29.4 ± 0.4 years) and 16 older (59.8 ± 1.7 years) women. Measurements were made at baseline (BL) and at 0 and 30 min after footbath in footbath trial, and at corresponding time points without footbath in control trial. In the footbath trial, subjects immersed their lower legs and feet in water for 30 min, with water temperature ranging from 41 to 43°C. The results showed that footbath elicited significant reductions in CAVI at 0 min compared to the same trial's baseline in both young and older groups (0.55 ± 0.07, P = 0.01 for young; 0.42 ± 0.15, P = 0.03 for older, respectively) with no changes found in the control trials. The percentage of CAVI change at 0 min was significantly greater in young women (91.9 ± 1.1%) compared to older women (96.5 ± 1.8%, P < 0.05). This study indicated that acute warm footbath results in transient improvement of systemic arterial stiffness in both healthy young and older women. Despite similar intervention, the percentage response of arterial stiffness to footbath was attenuated in older women.

Correlation of the Time Interval from the Peak of Mitral E Wave to the Peak of Pulmonary Venous D Wave with Mitral Doppler Indexes

BACKGROUND: Pulmonary venous diastolic flow follows the pattern of mitral flow and is dependent on the pressure difference between the pulmonary vein and the left atrium (LA). The magnitude of the decrease in LA pressure in early diastole depends on both the volume of the blood leaving the LA and the stiffness of the left ventricle (LV) and the LA. Relaxation process is known to govern early diastolic compliance. We hypothesized that in patients with decreased early diastolic compliance due to LV relaxation abnormality, there may be rapid rise in LV and LA pressure, resulting in early peak of pulmonary venous D wave as early LV diastolic filling progress. This study was undertaken to define this hypothesis and to examine the relation of the time interval between E wave peak and D wave peak to mitral doppler indexes. METHOD: Patients with significant mitral or aortic valvular disease, or patients with LV ejection fraction below 60%, or patients who have pseudonormal or restrictive LV filling pattern on mitral and pulmonary venous Doppler, were excluded from this study. Mitral Doppler indexes including peak E velocity, peak A velocity, E wave acceleration time (EAT) and deceleration time (EDT) were measured. E/A ratio was calculated. The isovolumic relaxation time from aortic valve closure (Ac) to the onset of E wave , the time interval from Ac to the peak of E wave (AcE), the time interval from Ac to the peak of D wave, and the diastolic time from Ac to R of electrocardiogram (AcR) were measured by the pulsed wave Doppler and phonocardiography. The time interval from the peak of E wave to the peak of D wave (ED) was calculated by the subtraction of AcE from AcD. RESULTS: 1) ED is significantly shorter in patients with E/A or =1 (58.9+/-27.4 msec versus 74.7+/-17.2 msec, p<0.05). 2) ED correlated with IVRT (r=-0.400, p<0.01), AcR (r=0.414, p<0.01), but not with E/A ratio, EDT, or EAT. 3) Multivariate linear regression analysis with all the previously mentioned variables showed that IVRT, AcR, and EAT were independent determinants of the ED. CONCLUSION: This study demonstrates that the ED is shortened in patients who are regarded as having LV relaxation abnormality and that ED is affected by IVRT, AcR, and EAT.

The age-related advancement of arterial disease measured by Doppler ultrasound diastolic flow analysis.

OBJECTIVE: To quantify by A-mode Doppler sonography the age-related progression of arterial disease so that age dependent normal values may be established for the screening Doppler peripheral arterial exam. Arterial distensibility was assessed by A-mode Doppler diastolic flow analysis as a measure of atherogenesis. These values will increase the sensitivity and decrease the incidence of false-positive results when the Doppler exam is utilized to differentially diagnosis vascular and sciatic neurogenic claudication. The relationship between age and results from the standard ankle/arm index ultrasound pneumatic cuff examination was also analyzed. DESIGN: A two by three analysis of variance with orthogonal Helmert contrast codes and simple linear regression analysis was utilized for this cross-sectionally designed investigation. The dependent measures of diastolic flow analysis and ankle/arm pressure index were obtained within three nested successively increasing age groups. SETTING: Chiropractic office. SUBJECTS: Studied were a total of 90 sedentary nonsmoking subjects, aged 23-79 yr, all of whom had normally accepted levels of serum glucose, cholesterol and blood pressure. Subjects were screened for evidence of aortic coarctation, myocardial infarction, tachyarrhythmia, aortic valve stenosis, mitral prolapse, hypertension, hypercholesterolemia, diabetes and peripheral occlusive arterial disease. Anthropometric measurements and percent body fat were obtained. A predictive oxygen consumption bike ergometer test was performed to obtain aerobic capacity. The commonly utilized standard ankle/arm index ultrasound pneumatic cuff examination and arterial diastolic flow analysis were performed with A-mode Doppler ultrasound on all subjects. RESULTS: These results demonstrate that a significant inverse linear relationship exists between aging and arterial compliance (p < .0001) in our population. Diastolic flow analysis had a greater sensitivity to arterial disease than the standard ankle/arm index ultrasound pneumatic cuff procedure. CONCLUSION: When utilizing A-mode Doppler ultrasound diastolic flow analysis as an indicator of early peripheral atherosclerotic arterial disease, increased sensitivity may be obtained when the age-related elevation in atherogenesis is taken into account.

[Clinical survey of 126 cases with mitral valve prolapse detected at the annual health check-up].

Clinical and echocardiographic survey of mitral valve prolapse (MVP) was performed in 616 cases, which were selected from about 6,000 health check-up. An echocardiographic study revealed MVP in 126 cases. The prevalence of MVP was about 2% (health check-up survey) and 20.5% (echo study). The male and female ratio was 102/24. Frequent premature contractions, isolated atrial fibrillation and an apical systolic murmur were more frequently associated with MVP. Among 13 cases of isolated atrial fibrillation, seven with MVP were permanent, while other six without MVP were transient. Most cases (77%) were asymptomatic. Mild mitral regurgitation proved by auscultation and phonocardiography was observed in only two cases (1.6%), and most of the cases (81%) had no mitral regurgitant signals by a Doppler study.

[Effect of stimulation of the hypothalamic paraventricular nucleus on the electrical and contractile characteristics of the myocardium in dogs]. / Influence de l'excitation du noyau paraventriculaire hypothalamique sur les caractéristiques électriques et contractiles du myocarde chez le chien.

Electrical stimulation of the hypothalamic paraventricular nucleus results in bradycardia and hypotension. A direct transtemporal approach was used to implant an insulated electrode in the site of the third ventricle. The bradycardia and hypotension have been studied previously and have been shown to be due to inhibition of the alpha and beta vascular and myocardiac adrenergic receptors. The effects of this inhibition on the electrical appearances and the mechanical and phonocardiographic parameters of myocardial contractility were observed in this present study. The force and velocity of LV isometric contraction were reduced as shown by reduction in dP/dT, the delay in its peak and the reduction of the angle between the upstroke of ventricular contraction with the base line. The onset of left ventricular ejection was delayed. The high frequency (60 and 140 Hz) components of the first heart sound disappeared, confirming their contribution to the intensity of this sound. The ECG rapid QRS phase and AV conduction time were unchanged, but the slow phase of the T wave became more negative as the depressant effect on the myocardium increased.

Effect of myocardial shortening velocity on duration of electrical and mechanical systole. S2T interval as measure of shortening rate.

To determine the effect of myocardial shortening velocity on the duration of electrical and mechanical systole, five healthy men, ages 32 to 41, were studied. Carotid message and atropine were used to define the effects of changes in heart rate without changes in shortening rate. The effects of amyl nitrite, which produced approximately the same degree of tachycardia as atropine but a significantly higher maximum shortening rate, were compared with those of atropine to assess the effects of faster shortening velocities. The increased heart rate produced by both agents caused a substantial decrease in both the QT and the S1S2 intervals, but the QT interval was longer and the S1S2 interval shorter with the amyl nitrite. Thus, the S2T interval was substantially longer after amyl nitrite. The results are in keeping with the finding in isolated cardiac muscle that active shortening increases action potential duration and decreases the duration of mechanical activation. These observations raise the possibility that longer QT intervals and shorter S1S2 intervals would also be seen in patients with hypokinetic ventricular segments when the healthy muscle contracts more vigorously to compensate for the weaker segments.