Cardiovascular, metabolic and plasma catecholamine responses to passive and active exercises.
Eight healthy male volunteers (aged 19.6+/-3.0 years) were submitted to the unloaded active (AE) and passive (PE) cycling exercise-tests performed on an adapted cycle ergometer at a pedalling rate of 50 rpm. Intensity of active exercise was about 10% of VO2 max. In the PE exercise test the ergometer was moved electrically. During both tests the systolic time intervals (STI), stroke volume (SV), heart rate (HR), blood pressure (BP), oxygen uptake (VO2), rating of perceived exertion (RPE), electrical muscle activity (EMG), plasma adrenaline (A), noradrenaline (NE) and blood lactate (LA) concentrations were measured. Exercise induced changes in VO2, RPE and EMG were significantly higher during AE than PE. Shortening of the pre-ejection period (PEP) and diminishing of the PEP to ejection time (ET) ratio were similar in both types of exercise, whereas HR increased only during AE. A significant increase in cardiac output (p<0.01) resulted from increased SV (p<0.01) during PE and from increased HR (p <0.01) during AE. MAP increased only during PE and it was higher than at rest and during AE (p<0.01). Absence of changes in SV and MAP during AE may be considered as a secondary effect of the decrease in TPR. Plasma catecholamines did not increase above resting values in either type of exercise. Blood LA concentration increased during both PE and AE but it reached higher values (p<0.01) after the latter test. The present data suggest that the inotropic state depends on the mechanoreflexes originated in skeletal muscles. However, contribution of changes in preload to shortening of PEP can not be excluded. (+info)
Analysis of organ physiology in transgenic mice.
The increasing availability of transgenic mouse models of gene deletion and human disease has mandated the development of creative approaches to characterize mouse phenotype. The mouse presents unique challenges to phenotype analysis because of its small size, habits, and inability to verbalize clinical symptoms. This review describes strategies to study mouse organ physiology, focusing on the cardiovascular, pulmonary, renal, gastrointestinal, and neurobehavioral systems. General concerns about evaluating mouse phenotype studies are discussed. Monitoring and anesthesia methods are reviewed, with emphasis on the feasibility and limitations of noninvasive and invasive procedures to monitor physiological parameters, do cannulations, and perform surgical procedures. Examples of phenotype studies are cited to demonstrate the practical applications and limitations of the measurement methods. The repertoire of phenotype analysis methods reviewed here should be useful to investigators involved in or contemplating the use of mouse models. (+info)
Acute cardiovascular response to isocapnic hypoxia. I. A mathematical model.
A mathematical model of the acute cardiovascular response to isocapnic hypoxia is presented. It includes a pulsating heart, the systemic and pulmonary circulation, a separate description of the vascular bed in organs with the higher metabolic need, and the local effect of O(2) on these organs. Moreover, the model also includes the action of several reflex regulatory mechanisms: the peripheral chemoreceptors, the lung stretch receptors, the arterial baroreceptors, and the hypoxic response of the central nervous system. All parameters in the model are given in accordance with the physiological literature. The simulated overall response to a deep hypoxia (28 mmHg) agrees with the experimental data quite well, showing a biphasic pattern. The early phase (8-10 s), caused by activation of peripheral chemoreceptors, exhibits a moderate increase in mean systemic arterial pressure, a decrease in heart rate, a quite constant cardiac output, and a redistribution of blood flow to the organs with higher metabolic need at the expense of other organs. The later phase (20 s) is characterized by the activation of lung stretch receptors and by the central nervous system hypoxic response. During this phase, cardiac output and heart rate increase together, and blood flow is restored to normal levels also in organs with lower metabolic need. The model may be used to gain a deeper understanding of the role of each mechanism in the overall cardiovascular response to hypoxia. (+info)
Acute cardiovascular response to isocapnic hypoxia. II. Model validation.
The role of the different mechanisms involved in the cardiovascular response to hypoxia [chemoreceptors, baroreceptors, lung stretch receptors, and central nervous system (CNS) hypoxic response] is analyzed in different physiological conditions by means of a mathematical model. The results reveal the following: 1) The model is able to reproduce the cardiovascular response to hypoxia very well between 100 and 28 mmHg PO(2). 2) Sensitivity analysis of the impact of each individual mechanism underlines the role of the baroreflex in avoiding excessive derangement of systemic arterial pressure and cardiac output during severe hypoxia and suggests the existence of significant redundancy among the other regulatory factors. 3) Simulation of chronic sinoaortic denervation (i.e., simultaneous exclusion of baroreceptors, chemoreceptors, and lung stretch receptors) shows that the CNS hypoxic response alone is able to maintain quite normal cardiovascular adjustments to hypoxia; however, suppression of the CNS hypoxic response, as might occur during anesthesia, led to a significant arterial hypotension. 4) Simulations of experiments with controlled ventilation show a significant decrease in heart rate that can only partly be ascribed to inactivation of lung stretch receptors. 5) Simulations performed by maintaining constant cardiac output suggest that during severe hypoxia the chemoreflex can produce a significant decrease in systemic blood volume. In all the previous cases, model predictions exhibit a satisfactory agreement with physiological data. (+info)
Renal response to volume expansion: learning the experimental approach in the context of integrative physiology.
We describe a laboratory experience for upper-level science students that provides a hands-on approach to understanding the basics of experimental physiology. A pre-lab, interactive tutorial develops the rationale for this experiment by reviewing the renal and cardiovascular mechanisms involved in the response to extracellular fluid volume expansion. After a hypothesis is stated, an experiment is designed to determine the relative importance of dilution of plasma proteins to the overall renal excretory response following volume expansion with intravenous saline. In the lab, students collect data from two groups of anesthetized rats. The protocol involves continuous monitoring of arterial pressure and periodic collection of urine and blood samples after volume expansion with either isotonic NaCl or isotonic NaCl plus 5% albumin. A post-lab tutorial is used to analyze, interpret, and discuss the data. Students next prepare an oral presentation, practice it, and finally present their results and answer questions before peers and instructors. This overall experience involves all of the components of doing a "real" experiment, starting with a question that is not answered in general textbooks of physiology and finishing with an oral presentation of the results. Along the way, students gain a better understanding of a complex homeostatic response and learn the care and value of using animals in research and teaching. (+info)
Comparison of naive and experienced students of elementary physiology on performance in an advanced course.
The purpose of this study was to determine whether, in comparison with naive students, experienced students who have completed an elementary physiology course 1) have a greater knowledge level of physiology and 2) perform better in an upper division physiology course. The educational setting for this study was the cardiovascular block of an advanced undergraduate level course entitled Principles of Human Physiology (PGY 412). The study employed students who had completed elementary physiology (PGY 206) at the University of Kentucky (group 1), students who had completed elementary physiology in another academic program (group 2), and naive students with no prior physiology experience (group 3). A cardiovascular pretest was presented during the opening session of the cardiovascular block in PGY 412. Respective scores for the three groups were 29.4%, 31.7%, and 24.1%, and there were no significant between-group differences. Respective scores on the same pretest items given as a posttest at the end of the cardiovascular block were 90.4%, 91.4%, and 90.4%, and, again, there were no significant between-group differences. Respective scores on other cardiovascular test items given at the end of the block were 78.9%, 78.7%, and 81.1%. Interestingly, the highest score here was achieved by the naive students (group 3), but, once again, between-group differences were not significant. In summary, on the basis of pretest/posttest examination of cardiovascular physiology between naive and experienced students, the results of this study indicate 1) that the common assumption that students entering advanced level physiology courses have a significant retention of knowledge from elementary physiology is not valid and 2) that completion of an elementary physiology course does not offer an advantage in learning advanced material. (+info)
How to help students understand physiology? Emphasize general models.
Students generally approach topics in physiology as a series of unrelated phenomena that share few underlying principles. In many students' view, the Fick equation for cardiac output is fundamentally different from a renal clearance equation. If, however, students recognize that these apparently different situations can be viewed as examples of the same general conceptual model (e.g., conservation of mass), they may gain a more unified understanding of physiological systems. An understanding of as few as seven general models can provide students with an initial conceptual framework for analyzing most physiological systems. The general models deal with control systems, conservation of mass, mass and heat flow, elastic properties of tissues, transport across membranes, cell-to-cell communication, and molecular interaction. (+info)
Patterns of cardiovascular and ventilatory response to elevated metabolic states in the lizard Varanus exanthematicus.
The principal function of the cardiopulmonary system is the precise matching of O(2) and CO(2) transport to the metabolic requirements of different tissues. In some ecothermic vertebrates (amphibians and reptiles), vdot (O2) increases dramatically following feeding. Factorial increments in vdot (O2) range from 1.7 to 44 times above resting rates, and in some cases vdot (O2) approaches or even exceeds values measured during physical activity. There is virtually no information on the cardiopulmonary response during the postprandial period in these animals or how the pattern of cardiopulmonary support compares with that during activity. In our experiments, pulmonary ventilation ( vdot e), heart rate (fh), systemic blood flow ( qdot (sys)), rate of oxygen consumption ( vdot (O2)) and rate of carbon dioxide production ( vdot (CO2)) were measured at 35 degrees C in the lizard Varanus exanthematicus for 24 h prior to the ingestion of meals of various sizes and measured continuously for up to 72 h during the postprandial period. The results of this study were compared with previously published values for treadmill exercise in the same experimental animals. The change in fh and stroke volume (V(S)) for a given increment in vdot (O2) did not differ during exercise and digestion. In contrast, the ventilatory response was very dependent on the nature of the elevated metabolic state. During digestion, an increase in vdot (O2) resulted in a relative hypoventilation in comparison with resting values, whereas hyperventilation characterized the response during activity. During exercise, breathing frequency (f) increased 10- to 40-fold above resting values accompanied by large reductions in tidal volume (V(T)). In contrast, postprandial increases in vdot (O2) resulted in relatively minor changes in f and V(T) almost doubled. These results indicate that, in these lizards, the cardiac response to elevated vdot (O2) is stereotyped, the response being predictable irrespective of the source of the metabolic increment. In contrast, the ventilatory response is flexible and state-dependent, not only in pattern but also in its frequency and volume components. (+info)