Rate In Normal Subjects Research Articles

Glomerular Filtration Rate Decline and increased Serum Creatinine Concentration in Abia State University Teaching Hospital Aba

Glomerular filtration Rate (GFR) is essentially the most reliable index of kidney function in health. A decrease in GFR is a pointer to decline in Kidney function and persistent or progressive GFR decline is a specific diagnostic criterion for chronic kidney disease (CKD). In defining CKD, we consider GFR of less than 60ml/min/1.73m 2 for three months or more. Markers of Kidney function test assess the normal function of kidneys. These markers may be biochemical or even radioactive. They assist in measuring GFR, as well as the concentrating and diluting property (tubular function) of kidneys. One of such biochemical markers is Serum Creatinine. An increase or decrease in the serum level of these biomarkers can be of help in determining the efficiency of kidney function. Endogenously produced creatinine is an accepted biomarker of kidney function. It is produced from the metabolism of skeletal muscle creatine. It is released into the plasma in a stable rate in normal subjects, and freely filtered at the glomerulus. However, creatinine is secreted into the urine in the proximal tubule which can occasionally overestimate GFR by 10- 20 %.A number of GFR estimating equations have been developed to overcome some of the limitations of estimating GFR from serum creatinine. The CG equation (Cockcroft Gault) was developed in 1973 and is used widely. A new equation Modification of diet in renal disease (MDRD) study equation was developed in 1999 and has since been validated in a number of populations. The MDRD equation was used in estimating GFR in this study.

Evaluation of the Reaction Time and Accuracy Rate in Normal Subjects, MCI, and Dementia Using Serious Games

The main purpose of this research is to evaluate the differences in the reaction time and accuracy rate of three categories of subjects using our serious games. Thirty-seven subjects were divided into three groups: normal (n1 = 16), MCI (Mild Cognitive Impairment) (n2 = 10), and dementia—moderate-to-severe (n3 = 11) groups based on the MMSE (Mini Mental State Examination). Two serious games were designed: (1) whack-a-mole and (2) hit-the-ball. Two dependent variables, reaction time and accuracy rate, were statistically analyzed to compare elders’ performances in the games among the three groups for three levels of speed: slow, medium, and fast. There were significance differences between the normal group, the MCI group, and the moderate-to-severe dementia group in both the reaction-time and accuracy-rate analyses. We determined that the reaction times of the MCI and dementia groups were shorter compared to those of the normal group, with poorer results also observed in accuracy rate. Therefore, we conclude that our serious games have the feasibility to evaluate reaction performance and could be used in the daily lives of elders followed by clinical treatment in the future.

Echocardiographic Assessment of Left Ventricular Twisting and Untwisting Rate in Normal Subjects by Tissue Doppler and Velocity Vector Imaging: Comparison of Two Methods

I have read Echocardiographic Assessment of Left Ventricular Twisting and Untwisting Rate in Normal Subjects by Tissue Doppler and Velocity Vector Imaging: Comparison of Two Methods with great interest and congratulate the authors on their comprehensive and very balanced overview of recent studies on the left ventricular (LV) deformation analysis (1). However, there are three incorrect aspects that in my opinion needs clarification. Frist, the authors calculated the LV rotation by integrating the rotational velocity, determined from the DTI velocities of the septal and lateral regions, and correcting [R (t)] for the LV radius over time. R (t) is incorrect in Equation 1; it should be improved to:

Echocardiographic Assessment of Left Ventricular Twisting and Untwisting Rate in Normal Subjects by Tissue Doppler and Velocity Vector Imaging: Comparison of Two Methods

Echocardiographic Assessment of Left Ventricular Twisting and Untwisting Rate in Normal Subjects by Tissue Doppler and Velocity Vector Imaging: Comparison of Two Methods

Echocardiographic Assessment of Left Ventricular Twisting and Untwisting Rate in Normal Subjects by Tissue Doppler and Velocity Vector Imaging: Comparison of Two Methods

Background: The torsional parameters of the left ventricle (LV) are sensitive indicators of the cardiac performance. The torsion/twist of the LV is the wringing motion of the heart around its long axis created by oppositely directed apical and basal rotations and is determined by contracting myofibers in the LV wall which are arranged in opposite directions between the subendocardial and subepicardial layers. This motion is essential for regulating the LV systolic and diastolic functions. Objectives: Recent advances in echocardiography techniques have allowed for quantification of LV mechanics. The aim of the present study was to compare various LV twisting and untwisting parameters in healthy human subjects determined by velocity vector imaging (VVI) and tissue Doppler imaging (TDI) at rest. Patients and Methods: All volunteers (47 healthy subjects in two groups: 24 subjects in VVI group and 23 subjects in TDI group) underwent complete echocardiographic study, and LV torsional parameters were assessed by VVI or TDI methods. In addition, LV torsion and LV twisting/untwisting rate profiles were calculated throughout cardiac cycle. Results: Twist degree was significantly lower in the VVI group than in the TDI group (P = 0.008, r = 0.56). LV torsion was lower in the VVI group but was not significant. (P = 0.13, r = 0.38). Twisting rate (P = 0.004, r = 0.66) and untwisting rate (P = 0.0001, r = 0.61) were lower in the VVI group, but when timing of untwisting rate was normalized by systolic duration, there was no significant difference between the two groups (P = 0.41, r = 0.59). Similarly, when peak untwisting rate was normalized by LV length, there was a significant decline in normalized peak untwisting rate in the VVI group (P = 0.004, r = 0.62), but not in peak twisting rate normalized by LV length (P = 0.12, r = 0.42). Peak untwisting rate normalized by LV torsion was not statistically different between the two groups (P = 0.05, r = 0.53). Conclusions: Results suggest that these methods cannot be interchanged, and VVI showed significantly lower LV peak twist, peak twisting rate and peak untwisting rate. However, when LV twist and LV twisting rates were normalized to LV length, values were comparable for both imaging techniques.

Assessment of Functional Capacity in Clinical and Research Settings

The assessment of functional capacity reflects the ability to perform activities of daily living that require sustained aerobic metabolism. The integrated efforts and health of the pulmonary, cardiovascular, and skeletal muscle systems dictate an individual’s functional capacity. Numerous investigations have demonstrated that the assessment of functional capacity provides important diagnostic and prognostic information in a wide variety of clinical and research settings. This scientific statement, an update of the previously published American Heart Association (AHA) document,1 highlights the major clinical and research applications of functional capacity assessment. For a comprehensive review of exercise testing, the reader is referred to the American College of Cardiology (ACC)/AHA Guidelines for Exercise Testing.2,3 Functional capacity is the ability of an individual to perform aerobic work as defined by the maximal oxygen uptake (Vo2max), that is, the product of cardiac output and arteriovenous oxygen (a−Vo2) difference at physical exhaustion, as shown in the following equation: ![Formula][1] Where HR indicates heart rate and SV indicates stroke volume. Because Vo2max typically is achieved by exercise that involves only about half of the total body musculature, it is generally believed that Vo2max is limited by maximal cardiac output rather than peripheral factors.4 Although Vo2max is measured in liters of oxygen per minute, it usually is expressed in milliliters of oxygen per kilogram of body weight per minute to facilitate intersubject comparisons. In addition, functional capacity, particularly when estimated from the work rate achieved rather than directly measured Vo, is frequently expressed in metabolic equivalents (METs), with 1 MET representing the resting energy expenditure (≈3.5 mL O2 · kg−1 · min−1). In this instance, functional capacity is commonly expressed clinically as a multiple of the resting metabolic rate. Vo2max … [1]: /embed/graphic-1.gif

Sympathetic Neural Outflow and Chemoreflex Sensitivity Are Related to Spontaneous Breathing Rate in Normal Men

Respiration contributes importantly to short-term modulation of sympathetic nerve activity. However, the relationship between spontaneous breathing rate, chemoreflex function, and direct measures of sympathetic traffic in healthy humans has not been studied previously. We tested the hypothesis that muscle sympathetic nerve activity and chemoreflex sensitivity are linked independently to respiratory rate in normal subjects. We studied 69 normal male subjects aged 29.6+/-8.1 years. Subjects were subdivided according to the tertiles of respiratory rate distributions. Mean respiration rate was 10.6 breaths/min in the first tertile, 14.8 breaths/min in the second tertile, and 18.0 breaths/min in the third tertile. Subjects from the third tertile (faster respiratory rate) had greater sympathetic activity than subjects from the first tertile (slower respiratory rate; 29+/-3 versus 17+/-2 bursts/min; P<0.001). Stepwise multiple linear regression analysis revealed that only respiratory rate was linked independently to sympathetic activity (r=0.42; P<0.001). In comparison to subjects with slow respiratory rate, subjects with fast respiratory rate had greater increases in minute ventilation during both hypercapnia (7.3+/-0.8 versus 3.2+/-1.0 L/min; P=0.005) and hypoxia (5.7+/-0.8 versus 2.4+/-0.7 L/min; P=0.007). Muscle sympathetic nerve activity and chemoreflex sensitivity are linked to spontaneous respiratory rate in normal humans. Faster respiratory rate is associated with higher levels of sympathetic traffic and potentiated responses to hypoxia and hypercapnia. Spontaneous breathing frequency, central sympathetic outflow, and chemoreflex sensitivity exhibit significant and hitherto unrecognized interactions in the modulation of neural circulatory control.

Why is the management of glucocorticoid deficiency still controversial: a review of the literature

All endocrinologists would like to make glucocorticoid replacement therapy for their hypoadrenal patients as physiological as possible. Many would like the reassurance of a method of monitoring such treatment to confirm that they are achieving this aim. Advances in our knowledge of the normal physiology are relevant to our attempts to do this. The cortisol production rate in normal subjects is lower than was previously believed. The normal pattern of glucocorticoid secretion includes both a diurnal rhythm and a pulsatile ultradian rhythm. Glucocorticoid access to nuclear receptors is 'gated' by the 11-beta-hydroxysteroid dehydrogenase enzymes, which interconvert active cortisol and inactive cortisone. Such complexities make the target of physiological glucocorticoid replacement therapy hard to achieve. The available evidence suggests that conventional treatment of hypoadrenal patients may result in adverse effects on some surrogate markers of disease risk, such as a lower bone mineral density than age-sex matched controls, and increases in postprandial glucose and insulin concentrations. Although the quality of life of hypoadrenal patients may be impaired, there is no evidence of an improvement on higher doses of steroids, although quality of life is better if the hydrocortisone dose is split up, with the highest dose taken in the morning. Thus the evidence suggests that most patients may safely be treated with a low dose of glucocorticoid (e.g. 15 mg hydrocortisone daily) in two or three divided doses, with education about the appropriate action to take in the event of intercurrent illnesses.

Breathing frequency and use of expiratory muscles do influence the dynamic positive end-expiratory pressure

End-expiratory air trapping due to obstructive airway disease can be estimated through the measurement of intrinsic positive end-expiratory pressure PEEP i. The influence of breathing-frequency and use of expiratory muscles on PEEP i were measured in 10 normal and 10 chronic bronchitic patients (COPD). Insignificant control values of PEEP i increased to measurable values at high breathing rate in normal subjects. Control values were higher in COPD patients and increased at fast breathing rate. When corrected for the use of expiratory muscles according to simultaneous gastric pressure drop, PEEP i decreased in COPD, but still increased at high rate. We conclude that modifying the respiratory rate can increase PEEP i values independently of the severity of airway obstruction and the use of expiratory muscles. Before estimating the pathological value of a PEEP i measurement or evaluating the effects of a treatment, we always need to know the simultaneous breathing frequency.

Acute effect of water on blood pressure. What do we know?

Water drinking elicits a large, acute, pressor response in patients with autonomic failure who experience severe orthostatic hypotension. This essentially cost-free intervention has been successfully employed therapeutically in these patients to attenuate orthostatic and postprandial hypotension. In orthostatic intolerance patients, water drinking blunts the orthostatic tachycardia but has only a modest effect on blood pressure. Water drinking also has effects on blood pressure and heart rate in normal subjects, although the actions are more subtle. The cardiovascular effects seem to be in part mediated through sympathetic activation. The exact mechanism that causes the sympathetic activation is not known.

The Ability of Frequency Doubling Technology to Detect Abnormality of Visual Function in Early Glaucoma

To evaluate the ability of the Frequency Doubling Technology(FDT) threshold test in detecting abnormality of visual function in early glaucoma patients. The C-20 full threshold test of FDT was performed on 34 normal-tension glaucoma(NTG) patients and 39 primary open-angle glaucoma(POAG) patients with visual field defects limited to the upper or lower hemi-field as detected by Humphrey Field Analyzer(HFA) and on 79 normal control subjects. Optic disk findings and FDT results corresponding to the intact hemi-field were evaluated. FDT abnormalities in normal subjects were calculated as false positive rates in FDT. The sensitivity and specificity of FDT, calculated based on optic disk findings, were 75.0% and 61.1% in POAG, and 61.1% and 66.7% in NTG, respectively, while the false positive rate in normal subjects was 11.4%. FDT can detect glaucomatous functional abnormality earlier than HFA.

Coronary blood flow velocity in normal infants and young adults assessed by transthoracic echocardiography

The present study has demonstrated that it is possible to measure blood flow of the coronary artery in children using transthoracic 2-dimensional Doppler echocardiography. This is the first study on the relations between coronary flow velocity and age and heart rate in normal subjects.

Left Ventricular Hypertrophy in Hypertensive Patients Is Associated With Abnormal Rate Adaptation of QT Interval

Objectives. This study sought to examine whether the responses of the QT interval to changes in the heart rate were altered in left ventricular hypertrophy (LVH).Background. The QT interval has been shown to have a delayed adaptation to sudden changes in heart rate in normal subjects. Abnormalities in the adaptation of the QT interval to changes in the RR interval may facilitate the development of ventricular arrhythmias.Methods. Consecutive newly diagnosed hypertensive subjects, not taking any medications, were age and gender matched for LVH (n = 21) versus no LVH (n = 16). QT interval dynamics were analyzed under visual control using a validated algorithm with automatic QT measurements at the end of the T wave. A computerized Holter system was developed to study the QT interval response to changes in the RR interval. The adaptive response of the QT interval was measured as the ratio of the slope from 10% to 90% of the QT change relative to the RR interval change (dQT/dRR10–90). Steady state adaptation was also studied as the percent shortening and lengthening of the QT interval during acceleration and deceleration of heart rate.Results. The adaptive response of the QT interval measured as dQT/dRR10–90was increased in the LVH group compared with that in the control subjects during both acceleration (0.33 ± 0.06 vs. 0.18 ± 0.02, p = 0.02) and deceleration phases (0.23 ± 0.04 vs. 0.16 ± 0.02, p = 0.03). In the LVH group, the percent lengthening of the QT interval was greater (7.6 ± 0.7 vs. 5.1 ± 0.2, p = 0.03), whereas the percent shortening was not significantly different (5.71 ± 0.5 vs. 4.6 ± 0.3, p = 0.43), than that in control subjects.Conclusions. The QT interval response to changes in the RR interval is rapid and exaggerated in LVH. These abnormalities of the QT interval response demonstrate that there are altered repolarization dynamics in patients with LVH that may make them vulnerable to serious ventricular arrhythmias.(J Am Coll Cardiol 1997;29:778–84)

Diurnal variation of urinary leukotriene E 4 and histamine excretion rates in normal subjects and patients with mild-to-moderate asthma

Background: Leukotriene E 4 (LTE 4) and histamine excreted into the urine reflect the in vivo synthesis and release of cysteinyl leukotrienes and histamine, respectively. We examined the diurnal variation of the excretion rate of these mediators over 4 consecutive days in normal subjects ( n = 5) and patients with stable mild-to-moderate asthma ( n = 8). Methods: Sixteen consecutive 6-hour urine samples were collected over 4 days. Urinary LTE 4 concentrations were determined by reverse-phase high-pressure liquid chromatography, followed by ELISA. Urinary histamine concentrations were measured by ELISA. The excretion rates of these compounds were normalized relative to urinary creatinine content. Results: The mean urinary LTE 4 excretion rate was 83.8 ± 38.2 pg/mg creatinine (mean ± SD) in normal subjects; in patients with asthma, the urinary LTE 4 excretion rate (110.0 ± 59.2 pg/mg creatinine) was significantly higher than that in normal subjects ( p < 0.05). The urinary histamine excretion rate was not different between normal subjects (24.0 ± 12.5 ng/mg creatinine) and patients with asthma (31.5 ± 25.8 ng/mg creatinine). A robust and systematic within-day variation ( p < 0.01), but no day-to-day variation, was observed in histamine excretion rate. Although the magnitude of variation in LTE 4 excretion within a day was significantly greater in patients with asthma than in normal subjects ( p < 0.05), we could not identify any specific diurnal variation pattern in either the normal or the asthma group. No significant correlation was observed between urinary LTE 4 and histamine excretion rate within any subject. Conclusions: Patients with asthma excrete LTE 4 in the urine at a greater rate than normal subjects. Although no systematic variation in urinary LTE 4 excretion rates over the course of a day was observed in either normal subjects or patients with stable asthma, the presence of a systematic diurnal variation of urinary histamine excretion exists in both groups. (J A LLERGY C LIN I MMUNOL 1995;96:643-51.)

Exercise-induced changes in R wave amplitude and heart rate in normal subjects

An intermittent exercise protocol on a treadmill was used to examine six healthy subjects, and a steady protocol was applied to three of the subjects before and after short-term training. The peak blood velocity in the common carotid artery increased by 73.1% during the intermittent protocol and recovered to resting level within 3 minutes, while the heart rate (HR) remained high even 5 minutes after exercise. R wave amplitude (RWA) increased significantly from 1.40 ± 0.39 mV at rest to 1.59 ± 0.33 mV ( P < .05) immediately after the start of walking, and decreased gradually to 1.46 ± 0.36 mV ( P < .05) during 3 minutes of walking. Thus, it decreased significantly to 1.31 ± 0.40 mV ( P < .01) during the interphase from exercise to rest, and increased again during recovery or rest periods in the intermittent protocol. The results suggest that an increase in the venous return per heart beat at the start of walking induces the increase in RWA, and that its abrupt decrease at the end of walking induces the decrease in RWA. Subjects with a higher HR response and recovery slopes have smaller abrupt changes in RWA at the interphases between rest and walking. The gradual decrease in RWA during walking may be related to a gradual increase in HR and a gradual decrease in systemic peripheral resistance, and the gradual increase in RWA after walking may be related to a gradual decrease in HR and a gradual increase in systemic peripheral resistance.

Electrocardiographic repolarization measurements at rest and during exercise in normal subjects and in patients with coronary artery disease

Normal values for simple and rate-corrected measures of the duration and dispersion of electrocardiographic (ECG) repolarization during treadmill exercise were obtained in 94 clinically normal men, and the behavior of these measures during ischemia was examined in 79 men with catheterization-proven disease or with stable angina, all of whom had normal resting ECGs. Temporal measures of repolarization, exemplified by QTc, were found to be moderately sensitive for disease only when highly specific criteria were derived from data at peak exercise heart rates that were significantly higher in normal subjects than in patients; sensitivities of rate-corrected measures declined markedly when criteria were derived from matched heart rate data in normal subjects. In contrast, the standard deviation of the mean measured J-point to T-wave peaks across the V1 to V6 precordial leads (SD-SoTm), a measure of precordial dispersion of repolarization, was unrelated to exercise heart rate in normal subjects; SD-SoTm exceeding the 95% value at matched intraexercise heart rates in normal subjects was found at peak exercise in 38% of men with coronary disease, including some patients with otherwise false-negative standard exercise test responses.

Left Ventricular volumes during exercise in normal subjects and patients with dilated cardiomyopathy assessed by first-pass radionuclide angiography

During isotonic exercise, left ventricular (LV) suction and the Frank-Starling law of the heart may have important roles in the enhancement of early LV diastolic filling and in the increase of myocardial contractility, respectively. It remains controversial whether these mechanisms operate in normal subjects or patients with dilated cardiomyopathy. Ten healthy subjects and 10 patients with idiopathic dilated cardiomyopathy who underwent maximal upright bicycle exercise testing were studied. First-pass radionuclide angiography was performed at both rest and peak exercise using a multicrystal gamma camera. In normal subjects, LV end-systolic volume at peak exercise was smaller than during baseline (17 ± 7 vs 30 ± 15 ml/m 2; p < 0.05), whereas rapid filling volume was greater (52 ± 16 vs 38 ± 8 ml/m 2; p < 0.01). In patients with dilated cardiomyopathy, both end-systolic (108 ± 34 to 123 ± 53 ml/m 2; p = NS) and rapid filling (24 ± 6 to 28 ± 9 ml/m 2; p = NS) volumes did not change from rest to peak exercise. A significant correlation was found between the changes in end-systolic volume at peak exercise and in peak rapid filling rate in normal subjects (r = 0.6; p < 0.05), but not in patients with dilated cardiomyopathy (r = 0.3; p = NS). In normal subjects, end-diastolic volume at peak exercise was similar to that during baseline (78 ± 14 and 85 ± 15 ml/m 2, respectively; p = NS), whereas in patients with dilated cardiomyopathy, it was greater (164 ± 50 vs 146 ± 33 ml/m 2; p < 0.05). This study shows that during exercise, cardiac suction may have a role in the enhancement of early diastolic filling in normal subjects, as indicated by a significant correlation between the changes in end-systolic volume and peak rapid filling rate, but not in patients with dilated cardiomyopathy. Conversely, the Frank-Starling law of the heart operates in patients with dilated cardiomyopathy, as suggested by the increase in LV end-diastolic volume, but not in normal subjects.

Effects of the cold pressor test on short-term fluctuations of finger arterial blood pressure and heart rate in normal subjects.

The effect of the cold pressor test on autonomic cardiovascular control was studied non-invasively by means of spectrum analysis of periodic heart rate and blood pressure fluctuations in ten normal subjects. Fast Fourier Transform algorithm based on a 256-point time series (sampling rate 2 Hz, i.e. 2-min and 8-s) was used to estimate the amplitude spectra of heart rate and blood pressure rhythmicity at the low frequency (70-140 mHz) and respiration related frequency (230-270 mHz) band. Respiration rate was controlled at 250 mHz. Auto- and cross-spectral techniques were used to determine the complex relationship between systolic blood pressure and heart rate fluctuations in the frequency domain. The spectral pattern of systolic and diastolic blood pressure showed a marked increment of the absolute and relative (100 multiplied with absolute value/total area under the curve of the amplitude spectrum from 15-500 mHz) low frequency component: control vs. cold pressor test--systolic blood pressure--absolute values (in [mmHg/Hz1/2]): 634.4 +/- 48.9 vs. 827.4 +/- 69.9*; relative values (in [%]): 26 +/- 2 vs. 32 +/- 2*; diastolic blood pressure--absolute values: 433.2 +/- 42.3 vs. 537.2 +/- 45.8*; relative values: 35 +/- 3 vs. 40 +/- 2*, (average +/- SEM, *P < 0.05). The cold pressor test induced no change in average heart rate; the absolute low frequency component in heart rate spectra increased clearly during the test: low frequency component (in [bpm/Hz1/2]): 586.9 +/- 89.9 vs. 712.0 +/- 91.4*, while the relative low frequency component did not change: 29 +/- 3 vs. 30 +/- 3.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of QT interval during postural transitory changes in heart rate in normal subjects

A lack of homogeneity, and the presence of intrinsic abnormalities in ventricular myocardial repolarization are thought to be important mechanisms underlying the development of malignant ventricular arrhythmias. 1–4 These abnormalities are believed to be reflected, at least in part, in the finding of a relative elongation in the QT interval to the preceding RR interval. 5,6 Although the QT-RR relation has been examined clinically as a static relation (QTc), 7 it appeared important to evaluate it in the framework of the dynamic QT response to transitory changes in heart rate, because it is possible in some cases that the abnormalities in the ventricular repolarization process that could precipitate malignant ventricular arrhythmias emerge only in its dynamic response, and not in a static relation. Although some studies have reported the response of the QT interval to the sudden and sustained changes in heart rate produced by strenuous exercise, 5,6,8 this method appears impractical, particularly for evaluating patients with malignant ventricular arrhythmias. In this study, we developed a microcomputer-based, automated technique for assessing the beat-to-beat QT-RR relation to examine the dynamic response of the QT interval to transitory changes in the heart rate during the head-up tilt test.

Effects of baroceptor and cardiopulmonary reflexes on neural control of heart rate in normal man, as assessed by power spectral analysis.

This study was designed to establish the neurally-mediated effects of baroceptor and cardiopulmonary reflexes on heart rate in normal subjects. We therefore studied the effects of various interventions, able to modify the activity of arterial baroreceptors and cardiopulmonary receptors, on the power spectrum of the R-R interval in nine healthy men. To confirm the efficacy of these interventions left ventricular volume was monitored using a portable radionuclide probe. Isosorbide dinitrate (5 mgm sublingually) while sitting unloads both baroreceptors and the cardiopulmonary receptors; it decreased left ventricular end-diastolic volume (p < 0.01) and the mean R-R interval (p < 0.005), increased the power of the low-frequency (LF) component of the R-R interval (p < 0.01), decreased the power of the high-frequency (HF) component (p < 0.005) and increased the LF/HF ratio (p < 0.05). The application of cuffs around the thighs in the supine position, which unloads only cardiopulmonary receptors, decreased left ventricular end-diastolic volume (p < 0.05) but did not affect mean R-R interval, LF component, HF component and LF/HF ratio (p > or = 0.10). Leg raising, which loads only cardiopulmonary receptors, increased left ventricular end-diastolic volume (p < 0.05) and did not affect the mean R-R interval, LF component, HF component and LF/HF ratio (p > or = 0.10). In conclusion, our data suggest that, in normal man, baroreceptor unloading increased sympathetic and decreased parasympathetic neural control of heart rate; cardiopulmonary reflexes do not appear to have a direct neurally mediated effect on heart rate.