Heart rate and myocardial substrate preference during normal and hypoxic perfusion of the heart in vivo.

Selective utilization of carbohydrates and FFA by the heart was studied on the open-chest dog preparation. The heart was paced at frequencies from 120-240/min, and arterial and coronary venous blood samples were taken at these frequencies both during normal ventilation and hypoxia (arterial PO2 similar to 55 mmHg). The concentrations of glucose, lactate, pyruvate, and FFA were determined, and substrate utilization was calculated from these values and coronary blood flow. It was found that increased heart rate, particularly during hypoxia, increased utilization of both glucose and FFA. However, the relative amount of the energy produced from glucose utilization was minimal during hypoxia and most glucose underwent glycolysis only. Thus, whereas in control conditions of the relation between carbohydrate and FFA was about 60% to 40% during hyposia and high frequency the relation was reversed and almost 90% of all energy produced was supplied by FFA.     

The transmission ratio distortion of the th2-haplotype in vivo and in vitro

The th2-haplotype is transmitted at low frequencies (less than 0.30) by +/th2 males in normal matings. In the studies described here, the transmission frequency of the th2-haplotype from Rb7/th2 males was determined for normal and delayed matings and in vitro inseminations. The data show the transmission frequency from the two in vivo inseminations to be less than 0.30 and to be statistically equivalent. However, the in vitro transmission frequency (0.80) is significantly greater than either of the in vivo frequencies. The results show that the environment in which fertilization occurs affects the transmission frequency of this specific t-haplotype significantly.     

Losartan corrects abnormal frequency response of renal vasculature in congestive heart failure

In congestive heart failure, renal blood flow is decreased and renal vascular resistance is increased in a setting of increased activity of both the sympathetic nervous and renin-angiotensin systems. The renal vasoconstrictor response to renal nerve stimulation is enhanced. This is associated with an abnormality in the low-pass filter function of the renal vasculature wherein higher frequencies (> or =0.01 Hz) within renal sympathetic nerve activity are not normally attenuated and are passed into the renal blood flow signal. This study tested the hypothesis that excess angiotensin II action mediates the abnormal frequency response characteristics of the renal vasculature in congestive heart failure. In anesthetized rats, the renal vasoconstrictor response to graded frequency renal nerve stimulation was significantly greater in congestive heart failure than in control rats. Losartan attenuated the renal vasoconstrictor response to a significantly greater degree in congestive heart failure than in control rats. In control rats, the frequency response of the renal vasculature was that of a first order (-20 dB/frequency decade) low-pass filter with a corner frequency (-3 dB, 30% attenuation) of 0.002 Hz and 97% attenuation (-30 dB) at > or =0.1 Hz. In congestive heart failure rats, attenuation did not exceed 45% (-5 dB) over the frequency range of 0.001-0.6 Hz. The frequency response of the renal vasculature was not affected by losartan treatment in control rats but was completely restored to normal by losartan treatment in congestive heart failure rats. The enhanced renal vasoconstrictor response to renal nerve stimulation and the associated abnormality in the frequency response characteristics of the renal vasculature seen in congestive heart failure are mediated by the action of angiotensin II on renal angiotensin II AT1 receptors.     

Correspondence of low mean shear and high harmonic content in the porcine iliac arteries

BACKGROUND: Temporal variations in shear stress have been suggested to affect endothelial cell biology. To better quantify the range of dynamic shear forces that occur in vivo, the frequency content of shear variations that occur naturally over a cardiac cycle in the iliac arteries was determined. METHOD OF APPROACH: Computational fluid dynamic calculations were performed in six iliac arteries from three juvenile swine. Fourier analysis of the time-varying shear stress computed at the arterial wall was performed to determine the prevalence of shear forces occurring at higher frequencies in these arteries. RESULTS: While most of each artery experienced shear forces predominantly at the frequency of the heart rate, the frequency spectra at certain regions were dominated by shear forces at higher frequencies. Regions whose frequency spectra were dominated by higher harmonics generally experienced lower mean shear stress. The negative correlation between shear and dominant harmonic was significant (p=0.002). CONCLUSIONS: Since lesion development typically occurs in regions experiencing low time-average shear stress, this result suggests that the frequency content of the shear exposure may also be a contributing factor in lesion development. A better understanding of the vascular response to shear components of different frequencies might help rationalize the notion of "disturbed flow" as a hemodynamic entity.     

Periodicities in respiration and heart rate in newborns

Periodic breathing is common in normal infants, but may be associated with prolonged apnea leading to crib death. The mechanisms of periodic breathing and its relation to normal breathing patterns are unclear. We recorded respiratory and heart rate (HR) patterns of 11 healthy newborn infants during quiet sleep, in both normal and periodic breathing. Spectral analysis of the respiratory pattern revealed a low-frequency (LF) periodicity in normal breathing approximately equal to the frequency of periodic breathing when this occurs. Periodic breathing thus appears to be an exaggeration of an underlying slow amplitude variation which is present in regular breathing. LF periodicity also appeared in the HR pattern in both normal and periodic breathing, suggesting an LF modulation of cardiovascular control as well. The lack of a definite phase relation between HR and ventilation at LF may indicate dominant peripheral, rather than central, interactions between HR and respiration at these frequencies.     

电刺激迷走神经对蟾蜍心率和心率变异的影响

目的:观察不同频率迷走神经刺激对蟾蜍离体心脏的心率及心率变异的影响。方法:将蟾蜍心脏和右侧迷走交感干离体后,以不同频率电刺激神经,记录心电图曲线并作心率变异性(HRV)分析。结果:交感神经阻断后,电刺激迷走交感干,心率(HR)显著下降(P0.01),全部正常心动周期的标准差(SDNN)和相邻正常心动周期差值的均方根(RMSSD)显著升高(P0.01),不同频率刺激组之间没有明显差异;与对照组相比,各指标变化较大;给药组0.2Hz时高频(HF)显著升高(P0.01),低频/高频比值(LF/HF)明显降低(P0.05),0.8Hz时HF和LF/HF接近刺激前水平。结论:一定范围内增加刺激频率,迷走神经降低心率的作用增强;没有交感神经调节条件下的迷走神经对心率和心率变异的调节可能存在不同的机制。     

Frequency-dependent contractile strength in mice over- and underexpressing the sarco(endo)plasmic reticulum calcium-ATPase

One of the prominent markers of end-stage heart failure at the molecular level is a decrease in function and/or expression of the sarcoplasmic reticulum ATPase protein [sarco(endo)plasmic reticulum calcium-ATPase, SERCA]. It has been often postulated that a decrease in SERCA pump activity can contribute in a major way to decreased cardiac function. To establish a functional relationship, we assessed how alterations in SERCA activity level affect basic contractile function in healthy myocardium devoid of other significant molecular changes. We investigated baseline contractile function, frequency-dependent activation, and beta-adrenergic response in ultrathin trabeculae isolated from hearts of mice overexpressing SERCA (transgenic, TG), underexpressing SERCA2a (heterozygous knockout, Het), and their respective wild-type (WT) littermates. At physiological temperature and frequency, compared with their respective WT littermates, SERCA1a mice displayed increased developed force at frequencies of 4-8 Hz ( approximately 90% increase at 4 Hz) and force equal to WT mice at 10-14 Hz. Force development at 4 Hz in presence of 1 muM isoproterenol was similar in TG and WT mice. In Het mice, developed force was nearly identical at the lower end of the frequency range (4-8 Hz) but slightly depressed at higher frequency (P < 0.05 at 14 Hz). In presence of 1 muM isoproterenol, developed force at 4 Hz was equal to that in WT mice. Compared with normal levels, increased SERCA activity enhanced force development only at subphysiological frequencies. A reduction in SERCA activity only showed a depression of force at the higher frequency range. Thus generalizations regarding the correlation between SERCA activity and contractility can be highly ambiguous, because this relationship is critically dependent on other factors including stimulation frequency.     

High frequency characteristics of the arterial system

Pressure, flow and diameter were measured in the abdominal aorta of five anesthetized dogs during normal heart beats and heart beats with a superimposed impulse (generated by rapidly injecting a small volume of saline into the system). From Fourier analysis it was found that the impulse enhanced the amplitudes of the higher harmonics so that frequencies up to 80 Hz could be studied. Both the input impedance and apparent phase velocity above 20 Hz were independent of frequency and their average values were designated as characteristic impedance and true phase velocity. Average characteristic impedance for all five animals was 2.0 +/- 0.1 X 10(8) Nsm-5 and average phase velocity was 8.3 +/- 0.6 ms-1. Phase velocities calculated from characteristic impedance (1.76-2.39 X 10(8) Nsm-5) and from the slope of the pressure-diameter relation (0.102-0.25 X 10(-8) Nm-3) were similar to the true phase velocity as defined above (6.79-9.85 ms-1). It may be concluded that the input impedance converges to characteristic impedance and apparent phase velocity converges to phase velocity for high frequencies.     

Association between level of intelligence and heart rate variability

Earlier we discovered that heart rate variability was associated with the level of intelligence. The purpose of this study is to confirm this association using more reliable method and to define more precisely the frequency band within which the amplitude of the heart rate modulations is related to intelligence. 13 males (aged 14 to 17) were the study subjects. The total score of the computer game Tetris was taken as a general measure of the intelligence level. Heart rate was recorded electrocardiographically both at rest and during playing Tetris. Frequency analysis of heart rate was carried out with digital Fourier transformation. Correlation analysis showed that there was positive association between the level of intelligence and the amplitude of heart rate modulation at the frequencies 0.30 and 0.15 modulations per RR interval. This association is closer for the heart rate at rest than for the heart rate during mental work and for the frequency 0.30 than for the 0.15 modulations per RR interval.     

The Relationship between Gene Polymorphism and CRP Level in a Chinese Han Population

We investigated the relationships among the +1444C/T polymorphism in the C-reactive protein (CRP) gene and the concentration of CRP and the risk of coronary heart disease. Using polymerase chain reaction-restriction fragment length polymorphism, we analyzed the frequency distribution of genotypes and alleles of the +1444C/T polymorphism in samples from 128 patients with coronary heart disease (coronary stenosis more than 50%) and 119 unrelated normal individuals. The plasma levels of CRP and lipids in the subjects were also measured. The frequencies of the genotypes were CC 89.1%, CT 10.9%, and TT 0% in patients and CC 89.9%, CT 10.1%, and TT 0% in controls. The frequency of allele C was 94.5% in patients and 95.0% in controls, and allele T was 5.5% in patients and 5.1% in controls. The distribution of genotypes and alleles in the Chinese Han population was significantly different from that of the Caucasian population. There were no significant differences between frequencies of genotype and allele of controls and those of patients (P>0.05), but in controls the concentrations of CRP in the CC genotype subgroup were significantly higher than those in the CT genotype subgroup (P<0.05). This suggests that the +1444C/T variant in the CRP gene influences the basal CRP level in normal people. These findings imply that there may eventually be a need to establish genotype-specific risk thresholds of the CRP level.     

Integration of autonomic and local mechanisms in regulating cardiovascular responses to heating and cooling in a reptile (<Emphasis Type="Italic">Crocodylus porosus</Emphasis>)

Reptiles change heart rate and blood flow patterns in response to heating and cooling, thereby decreasing the behavioural cost of thermoregulation. We tested the hypothesis that locally produced vasoactive substances, nitric oxide and prostaglandins, mediate the cardiovascular response of reptiles to heat. Heart rate and blood pressure were measured in eight crocodiles (Crocodylus porosus) during heating and cooling and while sequentially inhibiting nitric-oxide synthase and cyclooxygenase enzymes. Heart rate and blood pressure were significantly higher during heating than during cooling in all treatments. Power spectral density of heart rate and blood pressure increased significantly during heating and cooling compared to the preceding period of thermal equilibrium. Spectral density of heart rate in the high frequency band (0.19–0.70 Hz) was significantly greater during cooling in the saline treatment compared to when nitric-oxide synthase and cyclooxygenase enzymes were inhibited. Cross spectral analysis showed that changes in blood pressure preceded heart rate changes at low frequencies (<0.1 Hz) only. We conclude that the autonomic nervous system controls heart rate independently from blood pressure at higher frequencies while blood pressure changes determine heart rate at lower frequencies. Nitric oxide and prostaglandins do not control the characteristic heart rate hysteresis response to heat in C. porosus, although nitric oxide was important in buffering blood pressure against changes in heart rate during cooling, and inhibition caused a compensatory decrease in parasympathetic stimulation of the heart.     

The first heart sound during the isovolumetric contraction

We make the first attempt to construct a qualitative theory covering the whole process of the major part of the first heart sound from an electrical activation to the phonocardiographic observations at the thorax. We calculate the amplitudes and frequencies of the radiated pressures during the isovolumetric contraction period generated by the muscular wall of the left ventricle and by the valves considered as a spherical shell and two-dimensional membranes, respectively. The analysis shows that both the hemodynamic and the valvular theory are able to explain most of the characteristic features of the first heart sound (linear relation between the amplitudes of the radiated pressure and the slope of the left ventricular pressure-time curve; directional polarity of the amplitudes; equidistant frequency peaks with a decline in amplitudes). However, existing magnitudes of the set of physiological parameters involved seems to favour the hemodynamic theory of the first heart sound. The aortic valve can be neglected as a source of sound. The initial conditions (like valve closure velocity), according to our theory, cannot be important. The predicted time-plot and frequency spectrum of the radiated pressure show a general resemblance with the recorded ones. It is essential to have considerably more quantitative acoustic data both for normal and diseased hearts for subsequent theoretical development.     

Effects of walking speed and step frequency on estimation of physical activity using accelerometers

This study evaluated the accuracy of assessing step counts and energy costs under walking conditions altered by step frequency changes at given speeds using uni- (LC) and tri-axial accelerometers (AM, ASP). Healthy young men and women (n=18) volunteered as subjects. Nine tests were designed to manipulate three step frequencies, low (-15% of normal), normal, and high (+15%), at each walking speed (55, 75, and 95 m/min). A facemask connected to a Douglas bag was attached to subjects, who wore accelerometers around their waist. LC underestimated the step counts at normal or high step frequency at 55 m/min and AM also at all step frequencies at 55 m/min, whereas ASP did not in all trials. LC underestimated metabolic equivalents (METs) at low or normal step frequency at all walking speeds. AM underestimated METs at low step frequency at all walking speeds and at high step frequency of 95 m/min. ASP gave underestimates only at low step frequency of 95 m/min. The degree of the percentage error of METs for AM and ASP was affected by step frequency. Significant interaction between step frequency and speed was found that for LC. These results suggest that LC and AM can cause errors in step-count functions at a low walking speed. Furthermore, LC may show low accuracy of the METs measurement during walking altered according to step frequency and speed, whereas AM and ASP, which are tri-axial accelerometers, are more accurate but the degree of the percentage error is affected by step frequency.     

Characteristics of evoked potentials and single neuron responses in the cat sensorimotor cortex to sound stimuli with different frequencies.

The characteristics of the averaged evoked potentials (AEP) (experiments with awake non-paralysed animals), of the evoked potentials (EP) and of the responses of single sensorimotor cortical neurons (acute experiments) of cats to tone-bursts with frequencies within 0.1-6.0 kHz were studied. Response selectivity to the tone-burst frequencies which are energetically pronounced in some biologically significant sounds for the cat was observed. The averaged curve of the dependence of the amplitude of AEP in the somatosensory cortical region (S1) on the tone-burst frequency has reliable maximum values at the frequencies of 0.8, 1.6 and 2.0-3.0 kHz. Most pronounced changes in the heart rhythm were observed within the tone-burst frequency ranges in which the AEP of the highest amplitudes were recorded. The amplitude of the AEP was found to increase during the conditioned reflex elaboration. The curve of the dependence of the probability of the EP occurrence on the frequency at equal sound pressure levels had maximum values at the frequencies of 1.6 and 3.2 kHz. The highest amplitude values of EP were found at frequencies of 0.8, 1.6 and 3.2 kHz. More than half of the recorded neurons revealed the lowest values of the response thresholds and the maximum values of the occurrence probability under suprathreshold stimulation at frequencies close to 0.8, 1.6, and 3.2 kHz. It is supposed that the above mentioned feature of the input frequency organization in sensorimotor cortex is connected with the selectivity as to the biological significance of acoustic stimuli.     

Spectral analysis of heart sounds: Relationships between some physical characteristics and frequency spectra of first and second heart sounds in normals and hypertensives

Frequency analysis of heart sounds has been gaining recognition as a possible indicator of several heart and valve diseases, although a comprehensive study of normal heart sounds has not been published. Relating the frequency content of normal heart sounds to certain physical characteristics surrounding the generation of these sounds could lead to a valuable diagnostic tool and give a better understanding of the mechanism of heart sounds production. In this study, the first and second heart sounds from seventy-four normal, and seven hypertensive volunteers were recorded, digitized and analysed using a Fast Fourier Transform algorithm. Statistical analysis was used to relate physical characteristicss (sex, blood pressure, and body surface area) of the subjects to the frequency content of normal heart sounds and to compare normal and hypertensive heart sounds. Statistical analysis showed that the major concentration of energy, for both first heart sound (S1) and second heart sound (S2), is below 150 Hertz (Hz) which may indicate that both sounds are caused by vibrations within the same structure, possibly the entire heart. However S2 spectra have greater amplitude than S1 spectra above 150 Hz, which may be due to vibrations within the aorta and pulmonary artery. Relationships observed between body surface area, sex, blood pressure, and the frequency content of heart sounds indicate that as heart size increases, the amplitude of the frequency coefficients above 150 Hz decreases. These observations were more identifiable in the S1 spectra than in the S2 spectra, possibly because the S2 higher frequency components may mask subtle changes in the S2 spectra caused by heart size changes. However, when the changes in heart size are significant, as in hypertension or increased body surface area, trends in the S2 spectra can be observed.     

Low frequencies of apparently fragile X chromosomes in normal control cultures: a possible explanation

Low frequencies of apparently fragile X [fra(X)] chromosomes have been reported in normal control, short-term, whole blood cultures, and they have been noted in both amniocyte and fetal blood cultures. However, there is currently no universal agreement on the lowest frequency for fra(X)(q27) that is diagnostic for the fragile X syndrome. Here, we present our observations on low levels of apparently fra(X) chromosomes in normal samples. We observed frequencies of 0.5% in short-term whole blood cultures and 0.9% in amniotic fluid cell cultures. In 1982, Steinbach et al. described nonspecific telomeric structural changes (TSC) and suggested that such low frequencies of apparently fra(X) chromosomes in normal material may be occurring by the same mechanism that is responsible for TSC formation. To determine if TSC formation can explain the significant baseline frequencies of fra(X) in normal controls, 10,457 cells were screened from 178 individuals referred for fra(X) analysis. Our findings indicated that TSC are not randomly distributed across chromosomes but tend to occur at specific sites. Based on our observations, we offer the hypothesis that the low frequency of apparent fra(X) in normal individuals may be due to nonrandom TSC distribution.     

A plausible explanation for heart rates in mammals

We consider a simple model to give a plausible mechanical explanation of what are the actual resting heart rates of mammals optimized for. We study what is the optimal frequency for a viscoelastic fluid circulating in a pulsatile way through a network of tubes and conclude that the heart rate is not optimized to transport blood through the whole net. Rather, actual resting heart rates of mammals happen at frequencies that optimize flow in vessels of radii that correspond to large arteries, which bring oxygenated blood rapidly far away from the heart, towards head and limbs. Our results for the optimal frequencies, obtained using observed radii of femoral arteries in mammals, agree best with the heart rates observed. We find a theoretical allometric relation between optimal flow frequency and radius: ν∼R⁻¹. This one, agrees with the exponent obtained when plotting observed heart rates versus radii of both, femoral arteries and carotids in mammals of different sizes, from mice to horses.     

Effects of variation of inverted-repeat sequences on reactions mediated by the transposase of Tn21.

The frequencies of one-ended transposition and normal transposition of derivatives of Tn21 that contain mutant inverted-repeat sequences (IRs) have been measured. In general, there was a linear relationship between the log of the frequency of one-ended transposition of a mutant IR and the log of the frequency of normal transposition of an element flanked by a wild-type IR at one end and by the mutant IR at the other. This implied that one-ended and normal transposition share the rate-limiting step that determines the frequency of transposition and that both IRs are involved in the rate-limiting step in normal transposition. Surprisingly, it was found that only the outer 18 base pairs of the IR of Tn21 engaged accurately in both one-ended and normal transposition, at about 1% of the frequency of the wild-type IR.     

Dynamic analysis of flutter in disk type mechanical heart valve prostheses

Parametric study of the low frequency oscillations occasionally observed in certain types of disc type prosthetic heart valves (PHV) are carried out using a finite element technique. The analysis is performed to determine the frequencies of the dynamic fluttering with the help of the 'ANSYS' computer program. The results show that the frequencies of the dynamic fluttering for both the circular occluders and the semi-circular occluders are at least two orders of magnitude higher than that observed in vivo. It is thus concluded that the clinically observed leaflet oscillations should not be a dynamic flutter phenomenon. Rather, the vortex shedding has been assumed to be the cause of these oscillations.