Heart Rate And Central Aortic Pressure
When the heart rate is relatively slow, reflected waves may reach the root of the aorta in systole even if the elastic properties of the aorta are normal. This may result in an increase in the central aortic pressure . Thus, when the heart rate slows sufficiently, the central aortic pressure will increase, assuming that the aortic function remains unchanged. When the aortic function improves and the heart rate decreases, as with regular aerobic exercise, the central aortic pressure may stay the same, despite a slower heart rate. In contrast, when the heart rate decreases with pharmacologic agents that do not alter aortic function, as with -adrenergic blocking agents, central aortic pressure may increase. This is not related to an increase in the duration of systole, as previous investigators suggested, but mostly to an increase in the duration of diastole. The effect of a slow heart rate on the central aortic pressure may be enhanced when a slow heart rate is associated with an increase in peripheral resistance .
Fig.;4
Metabolic Rate And Size Of A Species
If thermolysis as we know it in Mammals and Birds is an answer to such limitation, it is only partial since an increase in size must always be accompanied by a decrease in the rate of metabolism. Consequently the maximum size attainable by an organism is limited since below a certain level of metabolism a cell cannot perform its activity. Since the increase in surface area that parallels the increase in size is not sufficent to dissipate the heat produced, it is obvious that heat production, i.e. metabolic rate, must be controlled .
And here we have to reduce what seems at first sight contradictory. Indeed why should some multicellular organisms resort to new mechanisms of extra heat production instead of keeping the primitive rate of metabolism as exemplified by the monocellular. An answer to the question can only be incomplete for lack of knowledge. But without going into a detailed argumentation it is certainly reasonable to assume that homeothermy did appear late in evolution well after the metabolic pattern of large size organism was already acquired. The selective advantage conferred by homeothermy over poekilothermy is obvious and need not be discussed here.
Parameter Estimation And Parametric Images In Molecular Imaging
Fig.;15.5 shows a flowchart for estimating cerebral metabolic rate of glucose , which is the parameter of interest in FDG studies with PET. The time course of FDG uptake in the brain is followed by a dynamic PET study that collects a series of images over predetermined time intervals. A region of interest is defined to generate a tissue time activity curve of the average activity concentration within the ROI, which represents the sum of FDG and the phosphorylated FDG-6-PO4 in the tissue. Arterial blood samples are measured to obtain a plasma time activity curve over the whole scan period, which is used as input function to the kinetic model. The microparameters of K1, k2, k3 and k4 of the kinetic model are estimated from the model equations based on the measured TTAC and PTAC. CMRGlc can then be estimated as shown in Fig.;15.5 based on the rate constants, the endogenous glucose concentration Cglu and the lump constant LC which accounts for differences between endogenous glucose and FDG.
Figure;15.5. Flowchart of estimating cerebral metabolic rate of glucose from ROI-derived tissue time activity curve.
Figure;15.6. Flowchart of generating parametric image of cerebral metabolic rate of glucose.
I. Allaman, P.J. Magistretti, in, 2015
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Concluding Remarks And Therapeutic Considerations
MHN N
Temple of Apollo at Delphi
Heart rate is related to survival in apparently healthy individuals and in patients with different underlying cardiovascular diseases . A decrease in heart rate due to therapeutic interventions may result in an increase in survival. The heart rate of individuals with sinus rhythm is regulated by the sinus node. Sinus node function is controlled by several mechanisms. Potassium and calcium channels are the primary loci of the control of spontaneous diastolic depolarization and thus, of intrinsic heart rate in the sinoatrial node. Although If is quantitatively a relatively small current, it is a primary modulator of the slope of diastolic depolarization and thus, exerts an important influence over heart rate . However, there are many other factors that directly or indirectly affect sinus node rate, such as autonomic nervous system activity, metabolic rate and inflammatory processes. Since many factors regulate heart rate, it may indeed be these factors, rather than the heart rate itself, that determine survival . However, heart rate has multiple direct effects on the cardiovascular system, regardless of the regulatory mechanisms. These effects directly affect the cardiovascular system in multiple ways that, in turn, may affect survival .
Fig.;12
Table;2
Heart Rate And Endothelial Function
LV systole results in a generation of pressure that travels from the root of the aorta into the peripheral arterial circulation as a pulse wave . The pressure waves with each ventricular systole produce a stress on the arterial endothelial cells. Intrinsic repair mechanisms maintain normal endothelial function when the applied stress is within physiologic limits. When the stress is pathologic the intrinsic repair mechanisms are inadequate to maintain normal endothelium, and thus endothelial damage may occur. This may result in arterial aging and cardiovascular disease. The faster the heart rate, the greater the effect on the endothelium. In fact, endothelial damage and repair starts in utero with the first heart beat .
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Oxygen And The Myocardium
Oxygen is essential for the production of energy that permits all body functions. The amount of oxygen available for production of this energy is termed the tissue oxygen content. The myocardial oxygen content is a balance between how much oxygen is delivered to the heart minus how much oxygen is consumed by the heart.
The amount of oxygen delivered to the heart depends on how well the lungs function, how much Hgb is present to carry the oxygen, and how much blood carrying the Hgb flows through the heart muscle via the coronary arteries. If pulmonary function is normal and there is sufficient Hgb, coronary blood flow will determine how much oxygen is delivered to the myocardium. Coronary blood flow is determined by the difference in mean pressure between the aorta and the right atrium , into which coronary blood empties. Because coronary flow is greatest during diastole, slower heart rates are associated with improved myocardial oxygen delivery.
Increases in heart rate result in increasing myocardial oxygen consumption while decreasing time for diastole when coronary blood flow is greatest. The combination can set the stage for an imbalance in myocardial oxygen demand and supply, leading to myocardial ischemia. Cardiac failure is characterized by an increase in sympathetic tone and relative increases in heart rate; the ultimate impact is an inefficient myocardium that can result in deleterious remodeling.
Extreme Bradycardia And Tachycardia In The Worlds Largest Animal
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Edited by Nancy Knowlton, Smithsonian Institution, Washington, DC, and approved October 25, 2019
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A Simple And Novel Method To Monitor Breathing And Heart Rate In Awake And Urethane
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Affiliation Institute of Physiology and Pathophysiology, University Medical Center of the Johannes Gutenberg-University, Mainz, Germany
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Affiliation Institute of Physiology and Pathophysiology, University Medical Center of the Johannes Gutenberg-University, Mainz, Germany
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Affiliation Institute of Physiology and Pathophysiology, University Medical Center of the Johannes Gutenberg-University, Mainz, Germany
Bradycardia Varies With Depth And Exercise In Diving Mammals
Behaviourally linked ECGs of freely diving Antarctic seals and trained dolphins revealed a complex dive response that was altered by several integrative factors. Instead of a single level of bradycardia, HR while submerged varied with both depth and exercise intensity . The change in HR with depth was nonlinear, following patterns for gas volume changes that occur with increasing hydrostatic pressure at depth . Indeed, the greatest change in HR during a dive occurred between the water surface and depths typically associated with rapid lung compression or expansion ,,. HR declined asymptotically with instantaneous dive depth , reaching a minimum as the animals descended to the dive bottom . Both species showed a negative correlation between minimum HR and maximum dive depth .
Table 1 Morphometrics, study location and instrumentation used on bottlenose dolphins and Weddell seals in this study.
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How Should We Measure Our Heart Rate
Surprisingly, there are over twelve places you can feel your pulse. But there are two that are the easiest and most reliable the radial artery, which runs along the inside of the forearm from the base of the thumb; and the carotid artery, which runs up the front of the neck two fingers to the side of the Adams apple.
The best way to measure heart rate is to sit down for a few minutes and relax, then use two fingers to gently compress the artery and count the beats over 15 seconds. Multiplying this by four will give your heart rate in beats per minute.
If youre using the carotid, its important to only check one side at a time, and not to massage the artery this is an area that senses blood pressure flowing through the artery and signals to the heart to keep it in a tight range; stimulating this area can trick it into dropping the heart rate and blood pressure, leading to a blackout.
Your heart runs on electricity in fact, every single heartbeat is the result of a tiny electrical impulse travelling through your heart muscle. These impulses can be measured using an an electrocardiogram , which is the most reliable and informative measure of your heart rate. The test is non-invasive, painless, and you can get it at most GP practices and pathology services.
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Heart Rate Arterial And Aortic Function
Faster heart rates also result in arterial stiffening. Increasing the rate by pacing from 60 to 90 bpm in humans results in a decrease in carotid and radial artery distensibility. In experimental animals, an increase in heart rate results in stiffening of the aorta. A fast heart rate is also a major determinant of accelerated progression of aortic stiffness in treated patients with arterial hypertension . A stiff aorta will increase the aortic pulse wave velocity . Increased PWV results in rapid expansion of the arterioles and damage to organs, especially the kidneys and the brain . A stiff aorta will also increase reflected wave velocity. Normally reflected waves arrive in the root of the aorta early in diastole and form the diastolic wave, which facilitates coronary blood flow. When reflected wave velocity is increased, reflected waves arrive in the root of the aorta late in systole. The result is the disappearance of the diastolic wave and an increase in the systolic pressure, producing an increase in LV work, MVO2 and reduced coronary blood flow .
Fig.;3
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Hindrance To Blood Flow
Blood flow from the heart, termed cardiac output, is via both the left and right ventricles. Cardiac output is determined by the heart rate and ventricular stroke volume. Blood flows through the systemic arterial or pulmonary arterial trees and is critical to satisfactory function of the heart and consequent perfusion of organs with adequate quantities of blood and the oxygen it contains. Normal cardiac output for dogs and cats is 100200 mL/kg/min and 120 mL/kg/min, respectively.
Most of the hindrance to blood flow is from the degree of constriction of the arterioles, termed vascular resistance; however, some interference is from the stiffness of the portion of the great arteries closest to the ventricles, termed impedance. Impedance is the sum of external factors opposing left ventricular ejection and is closely related to afterload. The ventricles eject a stroke volume into the proximal portion of the great arteries, which expand to accommodate the stroke volume; when the ventricles are relaxed, the distended great arteries recoil and keep blood moving through the arterioles into the capillaries. The aortic and pulmonic valves close and prevent the stroke volume from returning to the ventricle that ejected it.
Systemic vascular resistance is the opposing blood flow that must be overcome to push blood through the peripheral circulation and is calculated by:
/cardiac output
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Can I Change My Heart Rate
More important than trying to reach a lower heart rate is just trying to do more of the things we know keep us healthy. Plenty of exercise , relaxation, a healthy diet, and keeping a careful eye on your blood pressure and waistline will all help.
Wearable devices are great at providing you with heart rates, but be aware theyre not always accurate, and if youre getting abnormal readings, particularly if you have symptoms, then you should see your doctor.
General Principles That Can Be Taught With This Laboratory Exercise
Transferable general principles are arguably the most valuable, and best remembered, content of any laboratory exercise. Instructors are encouraged to draw attention to the following general principles, demonstrated by the diving bradycardia exercise, and to remind students when they recur in later lectures or laboratory exercises.
A physiological response is the product of both ultimate and proximate factors. Ultimate factors are those that lead to positive natural selection for a trait, whereas proximate factors refer to the mechanism by which the response is brought about within an individual. The difference between these two kinds of causation represents a central concept in biological thought, articulated by an unidentified author when he posed the question Why is a house? and recognized that there are two classes of answers: 1) because man needs shelter and 2) because man laid brick on brick .
Biological data are inherently messy, even when measurement is precise. Individuals vary in their responses to any given perturbation, as may be shown by asking students to plot the data from individuals in the class . Statistical analysis was invented so that we can see beyond this individual variation to significant population trends. It is worth noting that this variation, if heritable, is the variation on which natural selection acts; without it, there would be no evolution.
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Horse Health: How Common Are Heart Attacks In Horses
Sarah Andrew
By Jen Roytz
In horses, humans and all other mammals, the heart is responsible for delivering oxygenated and nutrient-rich blood throughout the body and removing metabolic waste through a vast network of blood vessels, therefore any disruption in this process can have detrimental effects.
In horse racing, and most other equestrian sports, the term heart attack has become a catch-all phrase for suspected fatal cardiac events, as was the case recently with the passing of G1 Dubai Golden Shaheen winner XY Jet , who died of an apparent cardiac event the morning of Jan. 8.
While in humans a heart attack, or myocardial infarction, is commonly the result of a loss of blood flow which damages part of the heart muscle, in the equine the scenario is much different. As such, it is exceedingly rare for a horse to suffer a heart attack in the truest sense of the term, however horses can still be at risk for other heart-related maladies.
While sudden death due to a cardiac event is rare, especially in horses of racing age, it is not out of the realm of possibility. The types of heart disease most often associated with equine deaths include electrical irregularities , heart valve defects , congenital defects, aortic rupture and inflammation or degradation due to illness or toxins.
General Considerations For Conducting Maximally Effective Experiments
The basic testing procedure and the additional recommendations below maximize the success of the exercise by controlling for 1) individual variation in basal heart rate, 2) learning or habituation during the exercise, and 3) other changes that might take place in an individuals heart rate over the course of several hours .
The exercise should consist of a series of experiments, each comprising two test conditions . Identical tests in different experiments may yield variable results, even within the same individual. Several studies have shown that the response of heart rate to simulated diving can change over time as the subject becomes habituated to the procedure . This is one of the reasons that pairs of tests, conducted close to each other in time and in randomized order, are the best controls and yield the strongest and most easily interpreted results. Although comparing several test conditions with a single control may appear to save time in the classroom, this approach would require a more complex statistical tool and would require that the order of all tests, including the control, be randomized among subjects to control for time-dependent effects such as habituation.
P< 0.005;
§P 0.0001. Only tests with statistically significant results are shown.
To make use of paired t-tests, each student must complete both test conditions in each experiment, and data must be compiled so that pairs of results from each student are kept together .
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