Antonio Crisafulli

Muscle metaboreflex-induced increases in stroke volume.

PURPOSE Accumulation of by-products of metabolism within skeletal muscle may stimulate sensory nerves, thus evoking a pressor response named muscle metaboreflex. The aim of this study was to evaluate changes in central hemodynamics occurring during the metaboreflex activation. METHODS In seven healthy subjects, the metaboreflex was studied by postexercise regional circulatory occlusion at the start of the recovery from a mild rhythmic forearm exercise. Central hemodynamics was evaluated by means of impedance cardiography. RESULTS The main findings of this study were that, with respect to rest, the metaboreflex: 1) raised mean blood pressure (+13%; P < 0.01); 2) enhanced myocardial contractility (-12% in preejection period/left ventricular ejection time ratio; P < 0.01); 3) prolonged diastolic time (+11%; P < 0.01); 4) increased stroke volume (+ 10%; P < 0.05); and 5) increased cardiac output (+6%; P < 0.05). These responses were present neither during recovery without circulatory occlusion nor during circulatory occlusion without prior exercise. Moreover, the metaboreflex did not affect systemic vascular resistance and induced bradycardia with respect to recovery without circulatory occlusion. CONCLUSION These results suggest that the blood pressure response during metaboreflex activation after mild rhythmic exercise is strongly dependent on the capacity to increase cardiac output rather than due to increased vascular resistance.

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.

Cardiovascular and ventilatory control during exercise in chronic heart failure: Role of muscle reflexes

During exercise nervous signals are generated by stimulation of mechanically (muscle mechanoreflex) and chemically (muscle metaboreflex) sensitive skeletal muscle receptors. These receptors and their associated afferent fibres are sensitive to muscle work and reflexively adjust the haemodynamic, ventilatory and circulatory responses during physical effort. Thus the muscle reflex is essential in achieving normal responses to exercise in healthy subjects. In chronic heart failure, characterised by exercise intolerance with early occurrence of dyspnea or fatigue, peripheral muscle abnormalities (i.e. muscle atrophy, decreased peripheral blood flow, fibre-type transformation, and reduced oxidative capacity) trigger an exaggerated muscle reflex. This abnormality has recently been implicated in the genesis of the disabling symptoms. We review the role of the muscle reflex in regulating the cardiovascular and the ventilatory systems during exercise in both healthy and diseased conditions.

Physiological responses and energy cost during a simulation of a Muay Thai boxing match

Muay Thai is a martial art that requires complex skills and tactical excellence for success. However, the energy demand during a Muay Thai competition has never been studied. This study was devised to obtain an understanding of the physiological capacities underlying Muay Thai performance. To that end, the aerobic energy expenditure and the recruitment of anaerobic metabolism were assessed in 10 male athletes during a simulation match of Muay Thai. Subjects were studied while wearing a portable gas analyzer, which was able to provide data on oxygen uptake, carbon dioxide production, and heart rate (HR). The excess of CO2 production (CO2 excess) was also measured to obtain an index of anaerobic glycolysis. During the match, group energy expenditure was, on average (mean +/- standard error of the mean), 10.75 +/- 1.58 kcal.min-1, corresponding to 9.39 +/- 1.38 metabolic equivalents. Oxygen uptake and HRs were always above the level of the anaerobic threshold assessed in a preliminary incremental test. CO2 excess showed an abrupt increase in the first round, and reached a value of 636 +/- 66.5 mL.min-1. This parameter then gradually decreased throughout the simulation match. These data suggest that Muay Thai is a physically demanding activity with great involvement of both the aerobic metabolism and anaerobic glycolysis. In particular, it appears that, after an initial burst of anaerobic glycolysis, there was a progressive increase in the aerobic energy supply. Thus, training protocols should include exercises that train both aerobic and anaerobic energetic pathways.

Role of heart rate and stroke volume during muscle metaboreflex-induced cardiac output increase: differences between activation during and after exercise

We hypothesized that the role of stroke volume (SV) in the metaboreflex-induced cardiac output (CO) increase was blunted when the metaboreflex was stimulated by exercise muscle ischemia (EMI) compared with post-exercise muscle ischemia (PEMI), because during EMI heart rate (HR) increases and limits diastolic filling. Twelve healthy volunteers were recruited and their hemodynamic responses to the metaboreflex evoked by EMI, PEMI, and by a control dynamic exercise were assessed. The main finding was that the blood pressure increment was very similar in the EMI and PEMI settings. In both conditions the main mechanism used to raise blood pressure was a CO elevation. However, during the EMI test CO was increased as a result of HR elevation whereas during the PEMI test CO was increased as a result of an increase in SV. These results were explainable on the basis of the different HR behavior between the two settings, which in turn led to different diastolic time and myocardial performance.

Estimating stroke volume from oxygen pulse during exercise.

This investigation aimed at verifying whether it was possible to reliably assess stroke volume (SV) during exercise from oxygen pulse (OP) and from a model of arterio-venous oxygen difference (a-vO(2)D) estimation. The model was tested in 15 amateur male cyclists performing an exercise test on a cycle-ergometer consisting of a linear increase of workload up to exhaustion. Starting from the analysis of previous published data, we constructed a model of a-vO(2)D estimation (a-vO(2)D(est)) which predicted that the a-vO(2)D at rest was 30% of the total arterial O(2) content (CaO(2)) and that it increased linearly during exercise reaching a value of 80% of CaO(2) at the peak workload (W(max)) of cycle exercise. Then, the SV was calculated by applying the following equation, SV = OP/a-vO(2)D(est), where the OP was assessed as the oxygen uptake/heart rate. Data calculated by our model were compared with those obtained by impedance cardiography. The main result was that the limits of agreement between the SV assessed by impedance cardiography and the SV estimated were between 22.4 and -27.9 ml (+18.8 and -24% in terms of per cent difference between the two SV measures). It was concluded that our model for estimating SV during effort may be reasonably applicable, at least in a healthy population.

Pathophysiology of human heart failure: importance of skeletal muscle myopathy and reflexes

What is the topic of this review? This article reviews the role played by reflexes arising from muscle metaboreceptors in the pathophysiology of exercise intolerance in chronic heart failure (CHF). These receptors trigger the metaboreflex, which is likely to play an important role in the genesis of exercise intolerance in CHF. What advances does it highlight? This article highlights that, in CHF, the target blood pressure response during muscle metaboreflex activation is achieved mainly by vasoconstriction, whereas in healthy individuals the main mechanism is an increase in cardiac output.

Quantification of spinning® bike performance during a standard 50-minute class

Abstract Spinning is a type of indoor fitness activity performed on stationary bikes by participants who pedal together to the rhythm of music and the motivating words of an instructor. Despite worldwide popularity of this type of recreational activity, to date there have been few, mainly non-scientific, studies of the impact of spinning on metabolic, respiratory, and cardiovascular functions. The main aim of this study was to evaluate a number of metabolic and cardiovascular variables during a standard 50-min class performed by Spinning® instructors of both sexes: six males (age 30 ± 4.8 years, body mass index 24 ± 2.5 kg · m−2; mean ± s) and six females (age 34 ± 6.3 years, body mass index 21 ± 1.9 kg · m−2). The mean power output, heart rate, and oxygen uptake during the performance were 120 ± 4 W, 136 ± 13 beats · min−1, and 32.8 ± 5.4 ml · kg−1 · min−1 respectively for males, and 73 ± 43 W, 143 ± 25 beats · min−1, and 30 ± 9.9 ml · kg−1 · min−1 respectively for females. Analysis of individual performances showed that they were compatible with physical exercise that ranged from moderate-to-heavy to very heavy, the latter conditions prevailing. The results show that this type of fitness activity has a high impact on cardiovascular function and suggest that it is not suitable for unfit or sedentary individuals, especially the middle aged or elderly, who are willing to begin a recreational physical activity programme.

Hemodynamic during a postexertional asystolia in a healthy athlete : a case study

Hemodynamic events leading to spontaneous postexertional vasovagal syncope are not completely understood because of the lack of beat-to-beat data. We report a case study of a young athlete who undergoes a syncopal episode during the recovery period following a maximal cycle-ergometer test. The episode was monitored by an impedance cardiograph which can gather noninvasively beat-to-beat the flow of heart rate (HR), stroke volume (SV), cardiac output (CO), diastolic filling rate (SV/DT), and myocardial contractility index (PEP/LVET). The most important findings of this report are the dramatic reduction of SV/DT preceding the syncope, the increment of SV together with the reduction of HR preceding and following the syncope, the prompt recovery of CO values after the syncopal episode despite the bradycardia, and the reduction of PEP/LVET after the syncope. This report confirms the importance of active recovery immediately after strenuous exercise and supports the hypothesis that the reduction of SV/DT in the presence of an inotropic stimulation can trigger the vasovagal reaction.

Haemodynamic effect of metaboreflex activation in men after running above and below the velocity of the anaerobic threshold

Previous studies have shown that the muscle metaboreflex, along with its effect on peripheral vasculature, is capable of inducing substantial enhancement in cardiac performance, stroke volume and cardiac output. This study was designed to determine whether the metaboreflex recruited by means of postexercise muscle ischaemia (PEMI) after running at two intensities was capable of eliciting similar enhancement in these cardiovascular parameters. In eight healthy male athletes the metaboreflex was studied with the PEMI method at the start of recovery from running bouts at a velocity of 30% above (PEMI‐AVAT) or below (PEMI‐BVAT) the anaerobic threshold previously assessed. Control exercise recovery tests at the same intensities were also conducted. Haemodynamics were evaluated by means of impedance cardiography. The main results were that: (1) the PEMI‐AVAT test induced an increase in stroke volume, which was not present during the other protocol conditions; (2) the PEMI‐AVAT test also induced a blunted heart rate response compared with the control situation, but this relative bradycardia was fully compensated by the stroke volume increment so that cardiac output was maintained and even increased in comparison with the other protocol sessions; and (3) finally, there was no detectable increase in systemic vascular resistance during PEMI‐AVAT. These results provide evidence that, like what has previously been reported for small muscle mass exercise, metaboreflex activation after running is capable of enhancing cardiac performance and stroke volume. Moreover, this study strengthens the concept that the cardiovascular response to metaboreflex is not merely the consequence of an increase in systemic vascular resistance.