Three-dimensional simulations of peripheral, deep venous flow during muscular exercise in limbs of healthy subjects and in those with venous dysfunction were carried out by a computational ...fluid-dynamics (CFD) approach using the STAR CCM + platform. The aim was to assess the effects of valvular incompetence on the venous calf pump efficiency. The model idealizes the lower limb circulation by a single artery, a capillary bed represented by a porous region and a single vein. The focus is on a segment of the circuit which mimics a typical deep vein at the level of the calf muscle, such as the right posterior tibial vein. Valves are idealized as ball valves, and periodic muscle contractions are given by imposing time-dependent boundary conditions to the calf segment wall. Flow measurements were performed in two cross-sections downstream and upstream of the calf pump. Model results demonstrate a reduced venous return for incompetent valves during calf exercise. Two different degrees of valvular incompetence are considered, by restricting the motion of one or both valves. Model results showed that only the proximal valve is critical, with a 30% reduction of venous return during calf exercise in case of valvular incompetence: the net flow volume ejected by the calf in central direction was 0.14 mL per working cycle, against 0.2 mL for simulated healthy limbs. This finding appeared to be consistent with a 25% reduction of the calf ejection fraction, experimentally observed in chronic venous disease limbs compared with healthy limbs.
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.
The aim of the present study was to test the contribution of stroke volume (SV) in hemodynamic response to muscle metaboreflex activation in healthy individuals. We hypothesized that an acute ...decrease in cardiac afterload and preload due to the administration of a vasodilating agent could reduce postexercise muscle ischemia (PEMI)-induced SV response. Ten healthy males (age 33.6 ± 1.3 yr) were enrolled and randomly assigned to the following study protocol: 1) PEMI session, 2) control exercise recovery (CER) session, 3) PEMI after sublingual administration of 5 mg of isosorbide dinitrate (ISDN), and 4) CER after ISDN. Central hemodynamics were evaluated by means of impedance cardiography. The main findings were a blunted SV response during metaboreflex following acute arterial and venous vasodilation, associated with a reduction in cardiac diastolic time and filling, and a decrement of systemic vascular resistance. These hemodynamic changes restrain blood pressure response during metaboreflex activation. Our results indicate that hemodynamic response to metaboreflex activation is a highly integrated phenomenon encompassing complex interplay between heart rate, cardiac performance, preload, and afterload and that impairment of one or more of these parameters leads to altered hemodynamic response to metaboreflex.
A reduction in catecholamine levels during exercise has been described in young subjects with type 1 diabetes mellitus (DM1). It has been suggested that type 1 diabetes per se is associated with the ...loss of sympathetic response before any clinical evidence. Considering that an increase in sympathetic drive is required for normal cardiovascular response to muscle metaboreflex, the aim of this study was to assess the hemodynamics during metaboreflex in DM1 patients. Impedance cardiography was used to measure hemodynamics during metaboreflex activation, obtained through postexercise ischemia in 14 DM1 patients and in 11 healthy controls (CTL). Principal results were: 1) blunted blood pressure response during metaboreflex was observed in DM1 patients compared with the CTL; 2) reduced capacity to increase systemic vascular resistance was also witnessed in DM1 subjects; 3) DM1 subjects reported higher stroke volumes as a consequence of reduced cardiac afterload compared with the CTL, which led to a more evident cardiac output response, which partially compensated for the lack of vasoconstriction. These facts suggest that cardiovascular regulation was altered in DM1 patients and that there was a reduced capacity to increase sympathetic tone, even in the absence of any overt clinical sign. The metaboreflex test appears to be a valid tool to detect early signs of this cardiovascular dysregulation.
The diving response is the sequence of cardiovascular, respiratory and metabolic adjustments produced by apnoea and further strengthened by cooling of the facial area and/or hypoxia. This study aimed ...at comparing the cardiovascular response to diving of trained divers with that of a control group. In this order, 14 trained divers were compared with 14 non-divers. By means of impedance cardiography and continuous monitoring of arterial pressure, hemodynamic data were collected during three different experimental sessions. Each session included a cycle-ergometer exercise against a workload of 0.5 W kg
−1
of body mass, pedalling in a steady-state condition. During exercise, each subject randomly accomplished 40 s of breath-hold exercise with face immersion (test A) or in air (test B). A control exercise test with normal breathing (test C) was also performed. Divers showed a faster onset of bradycardic response (ANOVA,
P
< 0.01) and a faster adjustment in systemic vascular resistance (
P
< 0.001 for divers vs. controls) than did non-divers. Moreover, cardiac output decreased only in divers during the first phase of test A (
P
< 0.01 for divers vs. controls). The most striking findings were that divers showed a more rapid cardiovascular adjustment with respect to controls, in particular in heart rate and systemic vascular resistance; moreover, with continued apnoea, a delayed increase in myocardial performance and stroke volume occurred and obscured the cardiovascular effects of the diving response.
Individuals with walking disability, as a result of pathological conditions or traumas, show a reduction in left ventricle end diastolic volume (EDV). In fact EDV is closely related to the blood ...pressure gradient between the postcaval vein and the right atrium which, during locomotion, is partially due to the calf veins squeezing caused by the rhythmic contraction of the triceps surae and the crushing of the sole of the foot’s veins. In this study, a mechatronic device was applied to nineteen healthy voluntary participants’ lower limbs to test cardiodynamic response to a mechanical intermittent stimulation. The device consisted of inflatable bladders embedded in two shells and acting on the skin of the calf and foot of both legs. The pressure trend on the legs was regulated by a portable programmable logic controller. During the compression protocol to the legs, which involved some sequences of activation-deactivation following a peristaltic compression having a caudal-rostral trend, EDV, assessed by the impedance cardiography technique, increased of about 10% up the pre-test value. The legs compression protocol imposed by means of our pneumatic device might be useful to avoid the negative consequences for cardiovascular performance caused by de-conditioning status linked to walking disabilities.
The muscle metaboreflex is enhanced in chronic heart failure (CHF) patients, and this fact has been associated with the early fatigue shown by these patients in response to exercise. In animal ...studies of CHF, it was found that the limited capacity to enhance ventricular performance is responsible for a functional shift from a cardiac output to a systemic vascular resistance (SVR) increase in the mechanism by which the cardiovascular system raises blood pressure in response to the metaboreflex. However, the existence of this functional shift is still unknown in humans. The present study was undertaken to test the hypothesis that a similar hemodynamic response was also present in humans with CHF. The hemodynamic response to metaboreflex activation obtained through postexercise ischemia was assessed in nine patients with CHF and nine healthy controls (CTL) by means of impedance cardiography. The main results were that 1) the blood pressure rise due to the metaboreflex was similar in the two groups; 2) the CTL group achieved the blood pressure response via cardiac output increase, and the CHF group, via SVR increase; and 3) stroke volume was enhanced in the CTL group and decreased in the CHF group. This study demonstrates that in CHF patients, metaboreflex recruitment causes a functional shift from flow increase to peripheral vasoconstriction in the mechanism through which blood pressure is increased. The incapacity to enhance cardiac performance and stroke volume is probably the primary cause of this cardiovascular alteration.
The beneficial effects of beetroot juice supplementation (BJS) have been tested during cycling, walking, and running. The purpose of the present study was to investigate whether BJS can also improve ...performance in swimmers. Fourteen moderately trained male master swimmers were recruited and underwent two incremental swimming tests randomly assigned in a pool during which workload, oxygen uptake (VO₂), carbon dioxide production (VCO₂), pulmonary ventilation (VE), and aerobic energy cost (AEC) of swimming were measured. One was a control swimming test (CSW) and the other a swimming test after six days of BJS (0.5 l/day organic beetroot juice containing about 5.5 mmol of NO₃⁻). Results show that workload at anaerobic threshold was significantly increased by BJS as compared to the CSW test (6.3 ± 1 and 6.7 ± 1.1 kg during the CSW and the BJS test respectively). Moreover, AEC was significantly reduced during the BJS test (1.9 ± 0.5 during the SW test vs. 1.7 ± 0.3 kcal·kg⁻¹1·h⁻¹ during the BJS test). The other variables lacked a statistically significant effect with BJS. The present investigation provides evidence that BJS positively affects performance of swimmers as it reduces the AEC and increases the workload at anaerobic threshold.
Accumulation of metabolic end products within skeletal muscle stimulates sensory nerves, thus evoking a pressor response termed "metaboreflex." The aim of this study was to evaluate changes in ...hemodynamics occurring during metaboreflex activation obtained by postexercise muscle ischemia (PEMI) after two different exercise intensities. In twelve healthy subjects, the metaboreflex was studied with the PEMI method at the start of recovery from one leg-dynamic knee extension performed at intensities of 30% (PEMI 30%) and 70% (PEMI 70%) of the maximum workload achieved in a preliminary test. Control exercise recovery tests at the same intensities were also conducted. Central hemodynamics were evaluated by means of impedance cardiography. The main findings were that 1) during metaboreflex, exercise conducted against the higher workload caused a more pronounced blood pressure increase than the strain conducted against the lower workload; and 2) during PEMI 70%, this blood pressure response was mainly achieved through enhancement of myocardial contractility that increased stroke volume and, in turn, cardiac output, whereas during PEMI 30%, the blood pressure response was reached predominantly by means of vasoconstriction. Thus a substantial enhancement of myocardial contractility was reached only in the PEMI 70% test. These results suggest that hemodynamic regulation during metaboreflex engagement caused by PEMI in humans is dependent on the intensity of the previous effort. Moreover, the cardiovascular response during metaboreflex is not merely achieved by vasoconstriction alone, but it appears that there is a complex interplay between peripheral vasoconstriction and heart contractility recruitment.
Spinal cord injured (SCI) individuals show an altered hemodynamic response to metaboreflex activation due to a reduced capacity to vasoconstrict the venous and arterial vessels below the level of the ...lesion. Exercise training was found to enhance circulating catecholamines and to improve cardiac preload and venous tone in response to exercise in SCI subjects. Therefore, training would result in enhanced diastolic function and capacity to vasoconstrict circulation. The aim of this study was to test the hypothesis that one year of training improves hemodynamic response to metaboreflex activation in these subjects. Nine SCI individuals were enrolled and underwent a metaboreflex activation test at the beginning of the study (T0) and after one year of training (T1). Hemodynamics were assessed by impedance cardiography and echocardiography at both T0 and T1. Results show that there was an increment in cardiac output response due to metaboreflex activity at T1 as compared to T0 (545.4±683.9 mL·min−1 versus 220.5±745.4 mL·min−1, P<0.05). Moreover, ventricular filling rate response was higher at T1 than at T0. Similarly, end-diastolic volume response was increased after training. We concluded that a period of training can successfully improve hemodynamic response to muscle metaboreflex activation in SCI subjects.
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