Cardio_Chapter 002

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Chapter 2: Physiology of the Cardiovascular and Pulmonary Systems:

Chapter 2: Physiology of the Cardiovascular and Pulmonary Systems

The Pulmonary System:

The Pulmonary System Functions Exchange oxygen and carbon dioxide between environment, blood, and tissue Oxygen is necessary for energy production Physiology includes three components Ventilation Gas exchange or respiration Transport of gases to peripheral tissue

The Pulmonary System:

The Pulmonary System Ventilation Mechanical movement of gases into and out of the lungs At rest normal respiratory rate = 10 to 15 bpm Tidal volume – 350 to 500 ml of air Minute ventilation = ventilatory rate × tidal volume Additional lung volumes

The Pulmonary System:

The Pulmonary System Fig. 2-1. Lung volumes and capacities as displayed by a time versus volume spirogram. Values are approximate. The tidal volume is measured under resting conditions.

The Pulmonary System:

The Pulmonary System Control of breathing Requires repetitive stimulation from the brain Neurons in brainstem – medulla oblongata/pons Afferent connections to the brainstem Hypothalamic and limbic influence – sensations of pain or alterations in emotion Chemoreceptors – sense alterations in blood pH, carbon dioxide, and oxygen levels Lung receptors – irritant, stretch, J receptor Joint and muscle receptors

The Pulmonary System:

The Pulmonary System Fig. 2-2. Neurochemical respiratory control system.

The Pulmonary System:

The Pulmonary System Mechanics of Breathing Movement of air in and out of lungs results from pressure differences Affected by lung compliance, elasticity, surface tension Intrapulmonary and atmospheric pressures Inspiration is always active Boyle’s law – pressure of given quantity of gas is inversely proportional to its volume Inspiration – negative intrapulmonary pressure Expiration – intrapulmonary pressure exceeds atmospheric pressure

The Pulmonary System:

The Pulmonary System Intrapleural and Transmural Pressures Two layers separated by intrapleural space containing viscous fluid Transmural pressure is difference between intrapulmonary and intrapleural pressures and maintains lung near chest wall Physical Properties of Lungs Compliance – tendency to collapse or recoil while inflated Elasticity – tendency of structure to return to its initial size after being distended Surface tension – surface active agent is surfactant Resistance to airflow – affected by pressure differences, diameter, and length of airway

The Pulmonary System:

The Pulmonary System Fig. 2-6. Two pairs of unequally filled alveoli arranged in parallel illustrate the effect of a surface-active agent. One pair of alveoli is shown without surfactant ( A ) and the other is shown with surfactant ( B ). In the alveoli without surfactant, if Tsml were the same as Tbig, Psml would have to be many times greater than Pbig; otherwise, the smaller alveolus would empty into the larger one. In the alveoli with surfactant, Tsml is reduced in proportion to the radius of the alveolus, which permits Psml to equal Pbig. Thus, alveoli of different radii can coexist. Refer to the text for details.

The Pulmonary System:

The Pulmonary System Partial Pressures of Gases Atmospheric air = 79.04% nitrogen, 20.93% oxygen, 0.03% carbon dioxide Diffusion – differences in partial pressure of each gas within alveoli and pulmonary capillary create a pressure gradient; gas moves from high to low pressures Perfusion – refers to blood flow to the lungs

The Pulmonary System:

The Pulmonary System Ventilation and Perfusion Matching Optimal respiration or gas exchange occurs if distribution of gas (ventilation) and blood (perfusion) match at level of alveolar capillary interface Affected by body positions

The Pulmonary System:

The Pulmonary System Transport of oxygen and carbon dioxide Transport of oxygen – 98% is transported by hemoglobin Hemoglobin – ability to carry 4 molecules of O 2 Oxyhemoglobin dissociation curve Carbon dioxide transport Dissolved in plasma Bound to protein component of hemoglobin (carbaminohemoglobin) Bicarbonate ion

The Pulmonary System:

The Pulmonary System Fig. 2-11. The oxyhemoglobin dissociation curve. Note that in the “flat” portion of the curve (80 mm Hg and above), a change in the partial pressure of arterial oxygen (PaO 2 ) of as much as 20 mm Hg does not appreciably alter the hemoglobin saturation. However, in the “steep” portion of the curve (below 60 mm Hg), relatively small changes in saturation result in large changes in the PaO 2 . pH, The logarithm of the reciprocal of hydrogen ion concentration; DPG, diphosphoglycerate.

The Pulmonary System:

The Pulmonary System Acid-Base balance Metabolically produced acids largely eliminated from body via lungs Other acids are regulated by kidneys and liver Arterial blood gases (ABGs) provide information on pH, PaCO 2 , PaO 2 , HCO 3 -

The Cardiovascular System:

The Cardiovascular System Primary function - transportation and distribution of essential substances to tissues of body and removal of by-products from cellular metabolism The Cardiac Cycle Period from beginning of heartbeat to beginning of next heartbeat Divided into two periods – systole and diastole

The Cardiovascular System:

The Cardiovascular System Fig. 2-14. The mechanical events of the cardiac cycle shown in relation to the electrical events of the electrocardiogram. In late diastole, just prior to the P wave, the ventricles fill passively. At about the time that the P wave ends, the atria contract to eject up to 30% of the end-diastolic ventricular volume. A period of isovolumic ventricular contraction begins very shortly after the onset of the QRS complex. Ventricular ejection coincides with the early portion of the ST segment.

The Cardiovascular System:

The Cardiovascular System Fig. 2-15. Events of the cardiac cycle for left ventricular function, showing changes in left atrial pressure, left ventricular pressure, aortic pressure, ventricular volume, the electrocardiogram, and the phonocardiogram.

The Cardiovascular System:

The Cardiovascular System Physiology of Cardiac Output Reflects the volume of blood ejected out of left ventricle into systemic vasculature per minute Cardiac Output = Heart Rate × Stroke Volume Regulation of Heart Rate Heart beats automatically between 60 and 100 bpm Sympathetic and parasympathetic nerve fibers to heart when activated alter intrinsic pacing rate Sympathetic – increase heart rate via SA node Parasympathetic – slows heart rate via SA node

The Cardiovascular System:

The Cardiovascular System Sympathetic nerve endings (beta-adrenergic receptors) in myocardial wall when stimulated vasodilates coronary arteries Parasympathetic influence vasoconstricts coronary arteries

The Cardiovascular System:

The Cardiovascular System Regulation of Stroke Volume Preload – blood returning to heart or end diastolic volume (EDV) Frank-Starling mechanism Contractility – influenced by intrinsic (myocardial stretch) and extrinsic (activity of sympathoadrenal system) Afterload – blood ejected out of heart is influenced by pressure generated in ventricle compared to pressure in systemic vasculature

The Cardiovascular System:

The Cardiovascular System Ejection Fraction Best indicator of cardiac function Ratio of volume of blood ejected out of ventricles relative to volume of blood received by ventricles Normal = 60% to 70% Venous Return Affected by two factors – total blood volume and pressure within the venous vasculature

The Cardiovascular System:

The Cardiovascular System Coronary Blood Flow Squeezed during systole, but perfuse myocardium during diastole Regulated by autonomic nervous system

The Cardiovascular System:

The Cardiovascular System Blood flow to muscles during exercise Blood flow patterns change as a result of sympathetic nervous system action During exercise release of norepinephrine vasoconstricts blood to digestive organs/kidneys, thus redirecting to skeletal muscle Determinants of myocardium’s metabolic rate is rate pressure product = HR × systolic BP

The Cardiovascular System:

The Cardiovascular System Aging and cardiovascular physiology Normal aging alters functioning of CV system Chronic illnesses and comorbidities further affect functioning Left ventricular wall thickness increases Increased vascular thickness Maximal oxygen uptake and cardiac output reduce

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