Decrease In Cardiac Stroke Volume Research Articles

Uloga dehidratacije u sportskim performansama i preporuke za rehidrataciju

The acute and chronic effects of dehydration on athletes' health are well known, but it is less known about the relationship between dehydration and sports performance. There is an overall consensus in the literature that dehydration ≥ 2% body mass represents a threshold at which endurance, as aerobic performance, becomes impaired. Dehydration degrades aerobic performance by various mechanisms, such as a decrease in VO2 max, a decrease in circulatory volume and consequent decrease in cardiac stroke volume. At higher levels of dehydration, there is an increase in heart rate, body temperature, carbohydrate oxidation and muscle glycogenolysis. The effect of dehydration on anaerobic sports performance, such as muscle strength and power, is less known. The high osmotic stress that usually accompanies high levels of intracellular dehydration can modulate the permeability of the blood-brain barrier, alter the neuronal firing of osmoreceptor cells in the hypothalamus, and potentially affect the excitability of motor output pathways. Studies have shown that acute dehydration impairs muscle strength and endurance and increases the perception of fatigue but without changes in markers of central and peripheral neuromuscular function. In addition to the physical, dehydration also affects the mental performance of athletes. Symptoms of dehydration (dry mouth, thirst, headache, fatigue) affect the athletes' cognitive functions and their cognitive resilience. Therefore, personalized rehydration strategies play a key role in athletes' safety during sporting activities, as well as in optimizing sports performance. In this paper, the role of dehydration on physical and mental athletes' performance will be reviewed, as well as the latest recommendations for adequate rehydration.

NHE-1 participates in isoproterenol-induced downregulation of SERCA2a and development of cardiac remodeling in rat hearts

Impaired Ca(2+) handling is one of the main characteristics in heart failure patients. Recently, we reported abnormal expressions of Ca(2+)-handling proteins in isoproterenol (ISO)-induced hypertrophied rat hearts. On the other hand, Na(+)/H(+) exchanger (NHE)-1 inhibitor has been demonstrated to exert beneficial effects in ischemic-reperfusion injury and in the development of cardiac remodeling. The aims of the present study are to investigate the role of NHE-1 on Ca(2+) handling and development of cardiac hypertrophy in ISO-infused rats. Male Wistar rats were randomly divided into vehicle [control (CTL)] and ISO groups without or with pretreatment with a selective NHE-1 inhibitor, BIIB-723. ISO infusion for 1 wk significantly increased the ratios of heart to body weight and left ventricle (LV) to body weight and collagen accumulation. All of these increases were antagonized by coadministration with BIIB-723. The ISO-induced significant increase in LV wall thickness was suppressed significantly (P < 0.05) by BIIB-723. ISO-induced decreases in cardiac stroke volume and a total mechanical energy per beat index, systolic pressure-volume area at midrange LV volume, were normalized by BIIB-723. The markedly higher expression of NHE-1 protein in the ISO group than that in CTL group was suppressed (P < 0.05) by BIIB-723. Surprisingly, ISO induced downregulation of the important Ca(2+)-handling protein sarcoplasmic reticulum Ca(2+)-ATPase 2a, the expression of which was also normalized by BIIB-723 without changes in phosphorylated phospholamban (PLB)/PLB expression. We conclude that NHE-1 contributes to ISO-induced abnormal Ca(2+) handling associated with cardiac hypertrophy. Inhibition of NHE-1 ameliorates cardiac Ca(2+)-handling impairment and prevents the development of cardiac dysfunction in ISO-infused rats.

Decrease in cardiac stroke volume in humans during inhalations of 8% hypoxic gas mixture

The effect of 15-min inhalation of 8% hypoxic gas mixture on stroke volume was studied in 17 healthy volunteers. The parameter decreased in all volunteers who endured this exposure to the end. At the beginning of exposure the decrease in stroke volume negatively correlated with HR changes, but this correlation disappeared as hypoxia augmented. Physiological significance of stroke volume decrease during severe hypoxia is discussed.

Pneumothorax during positive-pressure mechanical ventilation

The hemodynamic and respiratory effects of unilateral pneumothorax were studied during positive-pressure mechanical ventilation in five sheep. The sheep were anesthetized, intubated, and placed on mechanical ventilation with positive end-expiratory pressure (5 cm H2O). After baseline studies, including chest roentgenograms, were taken, increments of air were injected into the right pleural cavity. Measurements were repeated at pneumothoraces of 500, 1,000, and 1,500 ml. There was a steady fall in cardiac output (p less than 0.02) at pneumothoraces of 1,000 and 1,500 ml. The decrease in cardiac stroke volume paralleled that of cardiac output. Heart rate rose (p less than 0.05) at a pneumothorax of 1,500 ml. There appeared to be a linear relationship between the percent increase in pneumothorax as estimated by roentgenogram and the percent fall in cardiac output (r = 0.991). There was a steady rise in mean pulmonary arterial, pulmonary arterial capillary wedge, superior vena caval, and inferior vena caval pressures, although the changes in inferior vena caval pressure were not statistically different from baseline. Peak airway pressure increased from baseline at pneumothoraces of 1,000 and 1,500 ml. Both right and left end-expiratory intrapleural pressures increased and were statistically different (p less than 0.01) from baseline. However, there was a substantially greater rise in right intrapleural pressure than left. Arterial oxygen tension remained physiological throughout the study. This study indicates that cardiac output decreases as the amount of pneumothorax increases in sheep during mechanical ventilation. This study also demonstrates that, during positive-pressure mechanical ventilation, a relatively benign-appearing pneumothorax by chest roentgenogram may be associated with a significantly depressed cardiac output. In addition, arterial oxygen tension may not be useful in predicting the onset of pneumothorax during mechanical ventilation.

Cardiovascular events associated with spontaneous apnea in the Australian short‐finned eel, Anguilla australis

AbstractHeart output, arterial pressures, and buccal pressure were measured in conscious, unrestrained eels (Anguilla australis). The branchial ventilatory pattern comprised alternating periods of eupnea and apnea. The transition from eupnea to apnea was always associated with significant decreases in ventral aortic blood pressure (−20%), dorsal aortic blood pressure (−16%), ventral aortic blood flow (−39%) and heart rate (−27%), and a significant increase in systemic vascular resistance (+39%). Although there were, significant decreases in cardiac stroke volume in some animals, heart output was primarily determined by heart rate. The rapidity of the transition to apnea and the occasional occurrence of Mayer waves in the circulation of A. australis is considered as evidence in favour of the neural regulation of systemic vascular resistance.

The effectiveness of oxygen transfer during normoxia and hypoxia in the dogfish (Scyliorhinus canicula L.) before and after cardiac vagotomy

1. The effectiveness of oxygen transfer across the gills of dogfish was measured during normoxia and hypoxia, both before and after transection of the cardiac vagus nerves. Direct measurement of ventilation volume (\(\dot Vw\)) agreed with values calculated by the Fick technique. 2. Hypoxia caused a significant reduction in blood oxygen tension and content and in rate of oxygen consumption (\(\dot M_{O_2 }\)). There was a marked bradycardia accompanied by a compensatory increase in cardiac stroke volume (Table 1). The ventilation/perfusion ratio (\(\dot Vw/\dot Vb\)) increased due to an increase in respiratory stroke volume. % Extraction (% Ext) and effectiveness of transfer (Ew) of oxygen from water were maintained during hypoxia, possibly due to an increase in the transfer factor (\(T_{O_2 }\)). 3. Cardiac vagotomised fish showed an increase in normoxic heart rate accompanied by a decrease in cardiac stroke volume. There was no bradycardia during hypoxia. The absence of the bradycardia had no observable effect on the efficacy of oxygen transfer during hypoxia (Table 3). 4. Following cardiac vagotomy, the oxygen tension in the venous blood (\(P\bar v_{O_2 }\)) was reduced both during normoxia and hypoxia, and\(\dot Vw\) did not increase during hypoxia (Table 3). These differences were, however, apparent in sham-operated fish (Table 2). 5. The measured variables and derived values for effectiveness of oxygen transfer are compared with those described for other fish.

Alterations in the coronary circulation of man following ascent to 3,100 m altitude.

Alterations in coronary blood flow associated with adaptation to high altitude were examined. Three normal men native to low altitude were studied, first at sea level, and again after 10 days' sojourn at 3,100 m altitude. During rest at high altitude, a 32% decrease in coronary blood flow was largely offset by a 28% increase in coronary arterial O2 extraction to maintain myocardial O2 delivery. The increase in O2 extraction resulted mainly from a decrease in coronary sinus blood O2 content and saturation. However, coronary sinus O2 tension remained constant, implying a decrease in the affinity of hemoglobin for O2. These observations are consistent with the hypothesis that coronary blood flow is regulated to maintain constant myocardial tissue O2 tension (as reflected here by coronary sinus blood O2 tension). The absence of a decrease in coronary sinus O2 tension or a decrease in myocardial lactate extraction imply that myocardial hypoxia did not develop. Therefore, myocardial hypoxia is not the basis for the decrease in cardiac stroke volume at high altitude reported previously and also observed in the present study.