Circulatory responses to exercise: are we misreading Fick?

Investigation of left atrial mechanical function and left ventricular systolic and diastolic parameters in athletes performing resistance exercise and combined exercise

Some individuals who go to fitness centers for various purposes perform resistance exercise (RE) alone, while others engage in combined exercise (CE) by including cardio exercises along with RE. Studying the effects of these two different training methods on left ventricular (LV) systolic and diastolic parameters and left atrial mechanical function is an important step toward understanding the effects of different types of exercise on cardiac function. This knowledge has significant implications for public health, as it can inform the development of targeted and effective exercise programs that prioritize cardiovascular health and reduce the risk of adverse outcomes. Therefore, the primary aim of this study is to comprehensively investigate the LV systolic and diastolic parameters of athletes who engage in RE and CE using ECHO, to contribute to the growing body of literature on the cardiovascular effects of different types of exercise. Forty-two amateur athletes aged between 17 and 52 were included in our study. The participants consisted of the RE (n = 26) group who did only resistance exercise during the weekly exercise period, and the CE group (n = 16) who also did cardio exercise with resistance exercises. After determining sports age (year), weekly exercise frequency (day), and training volume (min) in addition to demographic information of RE and CE groups, left ventricular systolic and diastolic parameters and left atrial functions were determined by ECHO. Findings from our study revealed that parameters including the left ventricular end-diastolic diameter (LVEDD) (p = .008), left ventricular end-diastolic volume (LVEDV) (p = .020), stroke volume index (SV-I) (p = .048), conduit volume (CV-I) (p = .001), and aortic strain (AS) (p = .017) were notably higher in the RE group compared to the CE group. Also left atrial active emptying volüme (LAAEV) of CE was higher than the RE group (p = .031). In conclusion, the cardiac parameters of the RE group showed more athlete's heart characteristics than the CE group. These results may help to optimize the cardiovascular benefits of exercise routines while minimizing the potential risks associated with improper training.

Baroreflex responses to activity at different temperatures in the South American rattlesnake, Crotalus durissus

In humans, physical exercise imposes narrower limits for the heart rate (f_H) response of the baroreflex, and vascular modulation becomes largely responsible for arterial pressure regulation. In undisturbed reptiles, the baroreflex-related f_H alterations at the operating point (G_op) decreases at elevated body temperatures (T_b) and the vascular regulation changes accordingly. We investigated how the baroreflex of rattlesnakes, Crotalus durissus, is regulated during an activity at different T_b, expecting that activity would reduce the capacity of the cardiac baroreflex neural pathway to buffer arterial pressure fluctuations while being compensated by the vascular neural pathway regulation. Snakes were catheterized for blood pressure assessment at three different T_b: 15, 20 and 30 °C. Data were collected before and after activity at each T_b. Baroreflex gain (G_op) was assessed with the sequence method; the vascular limb, with the time constant of pressure decay (τ), using the two-element Windkessel equation. Both G_op and τ reduced when T_b increased. Activity also reduced G_op and τ in all T_b. The relationship between τ and pulse interval (τ/PI) was unaffected by the temperature at resting snakes, albeit it reduced after activity at 20 °C and 30 °C. The unchanged τ/PI and normalized G_op at different T_b indicated those variables are actively adjusted to work at different f_H and pressure conditions at rest. Our data suggest that during activity, the baroreflex-related f_H response is attenuated and hypertension is buffered by a disproportional increase in the rate which pressure decays during diastole. This compensation seems especially important at higher T_b where G_op is already low.

Effect of Exercise-Induced Reductions in Blood Volume on Cardiac Output and Oxygen Transport Capacity

We wanted to demonstrate the relationship between blood volume, cardiac size, cardiac output and maximum oxygen uptake (V.O_2max) and to quantify blood volume shifts during exercise and their impact on oxygen transport. Twenty-four healthy, non-smoking, heterogeneously trained male participants (27 ± 4.6 years) performed incremental cycle ergometer tests to determine V.O_2max and changes in blood volume and cardiac output. Cardiac output was determined by an inert gas rebreathing procedure. Heart dimensions were determined by 3D echocardiography. Blood volume and hemoglobin mass were determined by using the optimized CO-rebreathing method. The V.O_2max ranged between 47.5 and 74.1 mL⋅kg^–1⋅min^–1. Heart volume ranged between 7.7 and 17.9 mL⋅kg^–1 and maximum cardiac output ranged between 252 and 434 mL⋅kg^–1⋅min^–1. The mean blood volume decreased by 8% (567 ± 187 mL, p = 0.001) until maximum exercise, leading to an increase in [Hb] by 1.3 ± 0.4 g⋅dL^–1 while peripheral oxygen saturation decreased by 6.1 ± 2.4%. There were close correlations between resting blood volume and heart volume (r = 0.73, p = 0.002), maximum blood volume and maximum cardiac output (r = 0.68, p = 0.001), and maximum cardiac output and V.O_2max (r = 0.76, p < 0.001). An increase in maximum blood volume by 1,000 mL was associated with an increase in maximum stroke volume by 25 mL and in maximum cardiac output by 3.5 L⋅min^–1. In conclusion, blood volume markedly decreased until maximal exhaustion, potentially affecting the stroke volume response during exercise. Simultaneously, hemoconcentrations maintained the arterial oxygen content and compensated for the potential loss in maximum cardiac output. Therefore, a large blood volume at rest is an important factor for achieving a high cardiac output during exercise and blood volume shifts compensate for the decrease in peripheral oxygen saturation, thereby maintaining a high arteriovenous oxygen difference.

Ventricular myocardial response to exercise in patients with Fontan circulation

BACKGROUND

Exercise stress echocardiography has been used to assess myocardial reserve in various heart diseases. This study examined the ventricular myocardial response to exercise in Fontan patients using exercise stress echocardiography.

METHODS

Twenty-five Fontan patients and 19 control subjects underwent semi-supine bicycle exercise stress echocardiography in this prospective, single-center, cross-sectional study. Pulsed-wave Doppler tissue imaging peak systolic (s') and diastolic (e') velocities, longitudinal strain and systolic strain rate, and early diastolic strain rate data at rest and at peak exercise were obtained for the systemic ventricle. The myocardial reserve of functional parameters was calculated as the difference between peak exercise and rest.

RESULTS

Inter- and intra-observer reliability were both high for exercise stress echocardiography measurements. Compared with controls, Fontan patients had significantly lower s', e', longitudinal systolic strain and strain rate, and early diastolic longitudinal strain rate at rest and at peak exercise as well as reduced myocardial reserve.

CONCLUSIONS

Fontan patients have markedly reduced myocardial reserve during exercise. The use of exercise stress echocardiography assessment may improve the clinical management of Fontan patients.

What determines systemic blood flow in vertebrates?

In the 1950s, Arthur C. Guyton removed the heart from its pedestal in cardiovascular physiology by arguing that cardiac output is primarily regulated by the peripheral vasculature. This is counterintuitive, as modulating heart rate would appear to be the most obvious means of regulating cardiac output. In this Review, we visit recent and classic advances in comparative physiology in light of this concept. Although most vertebrates increase heart rate when oxygen demands rise (e.g. during activity or warming), experimental evidence suggests that this tachycardia is neither necessary nor sufficient to drive a change in cardiac output (i.e. systemic blood flow, Q̇ _sys) under most circumstances. Instead, Q̇ _sys is determined by the interplay between vascular conductance (resistance) and capacitance (which is mainly determined by the venous circulation), with a limited and variable contribution from heart function (myocardial inotropy). This pattern prevails across vertebrates; however, we also highlight the unique adaptations that have evolved in certain vertebrate groups to regulate venous return during diving bradycardia (i.e. inferior caval sphincters in diving mammals and atrial smooth muscle in turtles). Going forward, future investigation of cardiovascular responses to altered metabolic rate should pay equal consideration to the factors influencing venous return and cardiac filling as to the factors dictating cardiac function and heart rate.

Exercise intolerance and fatigue in chronic heart failure: is there a role for group III/IV afferent feedback?

Exercise intolerance and early fatiguability are hallmark symptoms of chronic heart failure. While the malfunction of the heart is certainly the leading cause of chronic heart failure, the patho-physiological mechanisms of exercise intolerance in these patients are more complex, multifactorial and only partially understood. Some evidence points towards a potential role of an exaggerated afferent feedback from group III/IV muscle afferents in the genesis of these symptoms. Overactivity of feedback from these muscle afferents may cause exercise intolerance with a double action: by inducing cardiovascular dysregulation, by reducing motor output and by facilitating the development of central and peripheral fatigue during exercise. Importantly, physical inactivity appears to affect the progression of the syndrome negatively, while physical training can partially counteract this condition. In the present review, the role played by group III/IV afferent feedback in cardiovascular regulation during exercise and exercise-induced muscle fatigue of healthy people and their potential role in inducing exercise intolerance in chronic heart failure patients will be summarised.

Mass Transport: Circulatory System with Emphasis on Nonendothermic Species

Mass transport can be generally defined as movement of material matter. The circulatory system then is a biological example given its role in the movement in transporting gases, nutrients, wastes, and chemical signals. Comparative physiology has a long history of providing new insights and advancing our understanding of circulatory mass transport across a wide array of circulatory systems. Here we focus on circulatory function of nonmodel species. Invertebrates possess diverse convection systems; that at the most complex generate pressures and perform at a level comparable to vertebrates. Many invertebrates actively modulate cardiovascular function using neuronal, neurohormonal, and skeletal muscle activity. In vertebrates, our understanding of cardiac morphology, cardiomyocyte function, and contractile protein regulation by Ca2+ highlights a high degree of conservation, but differences between species exist and are coupled to variable environments and body temperatures. Key regulators of vertebrate cardiac function and systemic blood pressure include the autonomic nervous system, hormones, and ventricular filling. Further chemical factors regulating cardiovascular function include adenosine, natriuretic peptides, arginine vasotocin, endothelin 1, bradykinin, histamine, nitric oxide, and hydrogen sulfide, to name but a few. Diverse vascular morphologies and the regulation of blood flow in the coronary and cerebral circulations are also apparent in nonmammalian species. Dynamic adjustments of cardiovascular function are associated with exercise on land, flying at high altitude, prolonged dives by marine mammals, and unique morphology, such as the giraffe. Future studies should address limits of gas exchange and convective transport, the evolution of high arterial pressure across diverse taxa, and the importance of the cardiovascular system adaptations to extreme environments. © 2017 American Physiological Society. Compr Physiol 7:17-66, 2017.

Causes of exercise intolerance in heart failure with preserved ejection fraction: searching for consensus

Exercise intolerance is one of the cardinal symptoms of heart failure with preserved ejection fraction (HFpEF). We review its mechanistic basis using evidence from exercise studies. One barrier to a consensus understanding of the pathophysiology is heterogeneity of the patient population. Therefore, we pay special attention to varying study definitions of the disease and their possible impact on the causal factors that are implicated. We then discuss the role of exercise testing and its potential to subtype HFpEF in to more homogeneous mechanism-based subclasses.

Near infrared spectroscopy (NIRS) as a new non-invasive tool to detect oxidative skeletal muscle impairment in children survived to acute lymphoblastic leukaemia

BACKGROUND

Separating out the effects of cancer and treatment between central and peripheral components of the O2 delivery chain should be of interest to clinicians for longitudinal evaluation of potential functional impairment in order to set appropriate individually tailored training/rehabilitation programmes. We propose a non-invasive method (NIRS, near infrared spectroscopy) to be used in routine clinical practice to evaluate a potential impairment of skeletal muscle oxidative capacity during exercise in children previously diagnosed with acute lymphoblastic leukaemia (ALL). The purpose of this study was to evaluate the capacity of skeletal muscle to extract O2 in 10 children diagnosed with ALL, 1 year after the end of malignancy treatment, compared to a control group matched for gender and age (mean±SD = 7.8±1.5 and 7.3±1.4 years, respectively).

METHODS AND FINDINGS

Participants underwent an incremental exercise test on a treadmill until exhaustion. Oxygen uptake ([Formula: see text]), heart rate (HR), and tissue oxygenation status (Δ[HHb]) of the vastus lateralis muscle evaluated by NIRS, were measured. The results showed that, in children with ALL, a significant linear regression was found by plotting [Formula: see text] vs Δ[HHb] both measured at peak of exercise. In children with ALL, the slope of the HR vs [Formula: see text] linear response (during sub-maximal and peak work rates) was negatively correlated with the peak value of Δ[HHb].

CONCLUSIONS

The present study proves that the NIRS technique allows us to identify large inter-individual differences in levels of impairment in muscle O2 extraction in children with ALL. The outcome of these findings is variable and may reflect either muscle atrophy due to lack of use or, in the most severe cases, an undiagnosed myopathy.

Neural regulation of cardiovascular response to exercise: role of central command and peripheral afferents

During dynamic exercise, mechanisms controlling the cardiovascular apparatus operate to provide adequate oxygen to fulfill metabolic demand of exercising muscles and to guarantee metabolic end-products washout. Moreover, arterial blood pressure is regulated to maintain adequate perfusion of the vital organs without excessive pressure variations. The autonomic nervous system adjustments are characterized by a parasympathetic withdrawal and a sympathetic activation. In this review, we briefly summarize neural reflexes operating during dynamic exercise. The main focus of the present review will be on the central command, the arterial baroreflex and chemoreflex, and the exercise pressure reflex. The regulation and integration of these reflexes operating during dynamic exercise and their possible role in the pathophysiology of some cardiovascular diseases are also discussed.

Myocardial function and aerobic fitness in adolescent females

A recent report indicated that variations in myocardial functional (systolic and diastolic) responses to exercise do not contribute to inter-individual differences in aerobic fitness (peak VO(2)) among young males. This study was designed to investigate the same question among adolescent females. Thirteen highly fit adolescent football (soccer) players (peak VO(2) 43.5 ± 3.4 ml kg(-1) min(-1)) and nine untrained girls (peak VO(2) 36.0 ± 5.1 ml kg(-1) min(-1)) matched for age underwent a progressive cycle exercise test to exhaustion. Cardiac variables were measured by standard echocardiographic techniques. Maximal stroke index was greater in the high-fit group (50 ± 5 vs. 41 ± 4 ml m(-2)), but no significant group differences were observed in maximal heart rate or arterial venous oxygen difference. Increases in markers of both systolic (ejection rate, tissue Doppler S') and diastolic (tissue Doppler E', mitral E velocity) myocardial functions at rest and during the acute bout of exercise were similar in the two groups. This study suggests that among healthy adolescent females, like young males, myocardial systolic and diastolic functional capacities do not contribute to inter-individual variability in physiologic aerobic fitness.

Sex influence on myocardial function with exercise in adolescents

OBJECTIVES

Ventricular systolic functional response to exercise has been reported to be superior in adult men compared to women. This study explored myocardial responses to maximal upright progressive exercise in late pubertal males and females.

METHODS

Doppler echocardiographic techniques were utilized to estimate myocardial function response to a bout of progressive cycle exercise.

RESULTS

Systolic functional capacity, as indicated by ejection rate (12.5 +/- 2.8 and 13.1 +/- 1.0 [x10(-2)] ml s(-1) cm(-2) for boys and girls, respectively) and peak aortic velocity (208 +/- 45 and 196 +/- 12 cm s(-1), respectively) at maximal exercise, did not differ between the two groups. Similarly, peak values as well as increases in transmitral pressure gradient (mitral E flow velocity), ventricular relaxation (tissue Doppler imaging E'), and left ventricular filling pressure (E/E' ratio) as estimates of diastolic function were similar in males and females.

CONCLUSIONS

This study failed to reveal qualitative or quantitative differences between adolescent boys and girls in ventricular systolic or diastolic functional responses to maximal cycle exercise.

Reproducibility of Doppler measures of ventricular function during maximal upright cycling

Echocardiographic measures of ventricular function during exercise may prove useful in assessing myocardial health. This study examined test-retest reproducibility of measurements of Doppler mitral flow velocity (E-wave) and myocardial tissue Doppler imaging (E'-, S-waves) during a progressive maximal upright cycle test in 12 healthy lean adolescent males. Measurements were taken as subjects pedalled to exhaustion with 35 watt work increments in two separate trials. We observed no significant differences in mean values at rest, submaximal (70 watts) exercise, or maximal exercise for all three variables. Coefficients of variation at maximal exercise were 5.3%, 7.4%, and 8.1% for mitral E, tissue Doppler-S, and tissue Doppler-E', respectively. These findings indicated acceptable levels of reproducibility of Doppler ultrasound techniques for assessing ventricular systolic and diastolic functional response to maximal exercise in young lean male subjects.

What Limits Cardiac Performance during Exercise in Normal Subjects and in Healthy Fontan Patients?

Exercise is an important determinant of health but is significantly reduced in the patient with a univentricular circulation. Normal exercise physiology mandates an increase in pulmonary artery pressures which places an increased work demand on the right ventricle (RV). In a biventricular circulation with pathological increases in pulmonary vascular resistance and/or reductions in RV function, exercise-induced augmentation of cardiac output is limited. Left ventricular preload reserve is dependent upon flow through the pulmonary circulation and this requires adequate RV performance. In the Fontan patient, the reasons for exercise intolerance are complex. In those patients with myocardial dysfunction or other pathologies of the circulatory components, it is likely that these abnormalities serve as a limitation to cardiac performance during exercise. However, in the healthy Fontan patient, it may be the absence of a sub-pulmonary pump which limits normal increases in pulmonary pressures, trans-pulmonary flow requirements and cardiac output. If so, performance will be exquisitely dependent on pulmonary vascular resistance. This provides a potential explanation as to why pulmonary vasodilators may improve exercise tolerance. As has recently been demonstrated, these agents may offer an important new treatment strategy which directly addresses the physiological limitations in the Fontan patient.

Cardiovascular drift in euhydrated prepubertal boys

"Classic" cardiovascular drift is characterized by findings of decreasing stroke volume and mean arterial pressure, rising heart rate, and stable cardiac output during sustained constant-load exercise. Recent studies in adults indicate that when dehydration is prevented by fluid intake, this pattern is altered, with no change in stroke volume and progressive rise in cardiac output. This study was designed to examine this influence of hydration in prepubertal subjects and assess the relationship between cardiovascular drift and aerobic drift (changes in VO2). Eight boys (Tanner stage 1, mean age 11.7 +/- 0.4 y) cycled at an average of 62.9% +/- 3.9% VO2 peak to exhaustion (41.38 +/- 6.30 min) in a thermoneutral environment. Rectal temperature rose from 37.6 +/- 0.1 degrees C at rest to 38.1 +/- 0.2 degrees C at end exercise. Between 5 min and end exercise, average heart rate rose by 13.2% and cardiac output rose by 14.9%, systemic vascular resistance fell by 10.5%, and stroke volume remained stable. Increases in cardiac output paralleled those of VO2, with no change in arterial venous oxygen difference. These findings are consistent with the conclusion that cardiovascular drift is a reflection of aerobic drift, a relationship obscured by the superimposed physiological effects of dehydration during sustained constant load. This study also suggests that such patterns are no different in prepubertal boys and young adult men.

Haemodynamic responses to exercise, ATP infusion and thigh compression in humans: insight into the role of muscle mechanisms on cardiovascular function

The muscle pump and muscle vasodilatory mechanism are thought to play important roles in increasing and maintaining muscle perfusion and cardiac output ((.)Q) during exercise, but their actual contributions remain uncertain. To evaluate the role of the skeletal muscle pump and vasodilatation on cardiovascular function during exercise, we determined leg and systemic haemodynamic responses in healthy men during (1) incremental one-legged knee-extensor exercise, (2) step-wise femoral artery ATP infusion at rest, (3) passive exercise (n=10), (4)femoral vein or artery ATP infusion (n=6), and (5) cyclic thigh compressions at rest and during passive and voluntary exercise (n=7). Incremental exercise resulted in progressive increases in leg blood flow (DeltaLBF 7.4 +/- 0.7 l min(-1)), cardiac output (Delta (.)Q 8.7 +/- 0.7 l min(-1)), mean arterial pressure (DeltaMAP 51 +/- 5 mmHg), and leg and systemic oxygen delivery and (.)VO2 . Arterial ATP infusion resulted in similar increases in (.)Q , LBF, and systemic and leg oxygen delivery, but central venous pressure and muscle metabolism remained unchanged and MAP was reduced. In contrast,femoral vein ATP infusion did not alter LBF, (.)Q or MAP. Passive exercise also increased blood flow (DeltaLBF 0.7 +/- 0.1 l min(-1)), yet the increase in muscle and systemic perfusion, unrelated to elevations in aerobic metabolism, accounted only for approximately 5% of peak exercise hyperaemia.Likewise, thigh compressions alone or in combination with passive exercise increased blood flow (DeltaLBF 0.5-0.7 l min(-1)) without altering (.)Q, MAP or (.)VO2. These findings suggest that the skeletal muscle pump is not obligatory for sustaining venous return, central venous pressure,stroke volume and (.)Q or maintaining muscle blood flow during one-legged exercise in humans.Further, its contribution to muscle and systemic peak exercise hyperaemia appears to be minimal in comparison to the effects of muscle vasodilatation.

Cardiac responses to swim bench exercise in age-group swimmers and non-athletic children

The effect of body posture (e.g., gravity) on circulatory responses to exercise remains to be clarified. This study was designed to examine cardiovascular dynamics during prone swim bench exercise in age-group swimmers and to compare these responses to those of matched non-athletic children. Fourteen trained swimmers (mean age 11.3+/-0.5 years) performed progressive exercise to exhaustion during simulated butterfly stroke exercise on a swim bench. Stroke volume was assessed by the Doppler ultrasound technique. Standard echocardiographic measures of left ventricular dimensions and function were recorded at rest prior to exercise. Swimmers were compared to a group of 11 non-athletic children matched for age, gender, and anthropometric measures. Compared to the nonathletes, the swimmers demonstrated larger resting left ventricular diastolic dimension and mass (adjusted for body size) but no differences in systolic or diastolic function. Mean peak VO(2) was 23.2+/-4.1mlkg(-1)min(-1) and 17.8+/-4.4mlkg(-1)min(-1) in the swimmers and nonathletes, respectively (p<0.05). No significant changes were seen in stroke index with increasing work in either group, with values consistently greater in the swimmers (peak 37+/-6mlm(-2) versus 31+/-5mlm(-2) in the untrained subjects). Failure of stroke volume to rise during a progressive simulated swim test is consistent with a model of peripheral facilitation of circulatory responses to exercise.

Circulatory “Efficacy” during progressive aerobic exercise in children: insights from the Q: VO2 relationship

The relationship between circulatory flow (Q) and oxygen uptake (VO2) may provide insights into performance of peripheral mechanisms which govern blood flow during exercise (circulatory efficacy). This study evaluated the response of Q relative to VO2 during progressive upright cycle exercise in a group of 39 preadolescent boys (mean age 12.2 +/- SD 0.5 years). The Q-VO2 relationship was curvilinear, best described by the cubic equation Q = 3.60(VO2)(3) + 5.24(VO2)(2) + 2.40(VO2) - 0.94. Circulatory efficacy, defined as the %DeltaQ/%DeltaVO2 x 100, fell from 70.4% between the first two workloads to 49.7% at peak exercise. This decline in circulatory efficacy is consistent with other published data suggesting a decline in skeletal muscle pump function at high intensity workloads. The pattern of change in relationship of Q and VO2 during progressive exercise in these children is similar to that observed in studies of adults. This implies that performance of peripheral determinants of circulatory responses to exercise is not affected by biological maturation.

Improvement in serial cardiopulmonary exercise testing following enzyme replacement therapy in Fabry disease

BACKGROUND

Fabry disease is an X-linked genetic disorder resulting in the accumulation of glycosphingolipids in various organs, leading to exercise intolerance and early mortality. Enzyme replacement therapy (ERT) has recently been approved for use in Fabry patients. GOALS OF STUDY: To assess baseline cardiopulmonary exercise characteristics in both invasive and noninvasive tests and to study the impact of ERT on exercise.

METHODS

A total of 15 patients with Fabry disease underwent baseline cardiopulmonary exercise tests. Six patients were randomized 2:1 to receive either ERT or placebo. We performed serial cardiopulmonary exercise tests at baseline and every 3 months over a period of at least 18 months. The baseline test was compared to the last two exercise tests for each patient.

RESULTS

Mean age was 32 years. Mean VO2max was 1.680 +/- 0.67 L/min and increased by 0.459 +/- 0.64 L/min in the patients receiving ERT. Mean VO2max was 1.462 +/- 0.25 L/min and decreased by 0.116 +/- 0.44 L/min in patients on placebo. Mean oxygen pulse (VO2/HR) increased by 1.71 with enzyme, but increased only 0.025 in patients taking placebo. Estimated stroke volume (SV) increased by 10 ml in patients on ERT.

CONCLUSIONS

In this small cohort, exercise tolerance increased in patients receiving enzyme replacement therapy. Cardiopulmonary exercise testing is a useful test in measuring the response to therapy in Fabry disease patients.

Tissue Doppler Assessment of Ventricular Function during Cycling in 7- to 12-yr-old Boys

PURPOSE

Studies utilizing submaximal supine exercise have indicated that tissue Doppler imaging (TDI) may be useful for assessing ventricular systolic and diastolic function during exercise and might offer a means of detecting patients with early myocardial dysfunction. This investigation of 14 healthy boys ages 7-12 yr was designed to assess measures of inotropic and lusitropic function during maximal upright cycle exercise.

METHODS

Color tissue Doppler imaging (S and E' waves, indicative of systolic and diastolic function, respectively), stroke volume, and mitral peak inflow velocity (E wave) were recorded at rest and during a progressive upright cycle test to exhaustion.

RESULTS

Values of TDI-S and TDI-E' were obtained at exhaustive exercise in all but one subject. Mean value of S rose 163% (3.8+/-1.2 to 10.0+/-2.5 cm.s), and average E' increased by 92% (-6.3+/-2.2 to -12.1+/-3.2 cm.s). No significant changes were observed in the ratio of E' to mitral peak flow velocity (E), suggesting that left ventricular end-diastolic pressure remained stable.

CONCLUSIONS

These data indicate that measurement of TDI is feasible during maximal upright exercise, and velocities obtained may provide insights into ventricular systolic and diastolic functional capacity.

Cardiovascular responses to static exercise in boys: insights from tissue Doppler imaging

Ventricular functional changes and mechanisms of the cardiovascular responses during static exercise have not been well delineated in children. In this study, Doppler echocardiographic techniques were utilized to assess cardiovascular adaptations to bilateral isometric leg extension at 30% maximal voluntary contraction for three minutes in a group of 14 healthy boys (mean age 10.2 +/- 1.5 years). Mean heart rate rose from 77 +/- 9 to 106 +/- 11 bpm, stroke volume fell from 59 +/- 9 to 52 +/- 7 ml, and cardiac output increased from 4.58 +/- 0.58 to 5.62 +/- 0.81 l min(-1) (P < 0.05). Mean arterial pressure rose from 86 +/- 7 to 109 +/- 9 mm Hg, with no significant change in peripheral vascular resistance. By tissue Doppler imaging markers, inotropic function improved by 59%, while lusitropic function increased 38%. These findings suggest that (1) cardiovascular responses to static leg extension in boys are similar to those in adult men, and (2) isometric leg extension triggers modest increases in both systolic and diastolic function.

Respiratory muscle energetics during exercise in healthy subjects and patients with COPD

The energy expenditure required by the respiratory muscles during exercise is a function of their work rate, cost of breathing, and efficiency. During exercise, ventilatory requirements increase further exacerbating the potential imbalance between inspiratory muscle load and capacity. High level of exercise intensity in conjunction with contracting respiratory muscles is the reason for respiratory muscle fatigue in healthy subjects. Available evidence would suggest that fatigue of the diaphragm and other respiratory muscles is an important mechanism involved in redistribution of blood flow. Reflex mechanisms of sympathoexcitation are triggered in fatigued diaphragm during heavy exercise when cardiac output is not sufficient to adequately meet the high metabolic requirements of both respiratory and limb musculature. It is very likely that local changes in locomotor muscle blood flow may occur during exhaustive endurance exercise and that changes may have important effect on O2 transport to the working locomotor muscles and, therefore, on their fatigability. In a condition when the respiratory muscles receive their share of blood flow at the expense of limb locomotor muscles, minimizing mechanical work of breathing and therefore its metabolic cost allows a greater amount of cardiac output to be available to be delivered to working limb muscles. Malfunction in any of the multiple components responsible for circulatory flow and O2 delivery will limit the blood supply therefore inhibiting the supply of O2 and the energy substrate to the contracting muscles. Studies are needed to overcome these limitations.