Flow of air into and out of the lungs occurs by bulk flow along pressure gradients created in between the external environment and the alveoli. During quite breathing, these pressure gradients are created by contraction of the diaphragm and the external intercostal muscles during inspiration and the elastic recoil of the lungs during expiration. The alterations in pressure in the pleural space — intra-pleural pressure P pl and the alveoli - intra-alveolar pressure P alv can be studied separately and become important in studying the volume changes with the changes in pressure.
The intra-pleural pressure at the commencement of inspiration is approximately This is achieved by the elastic recoil forces of the lungs acting inwards and the recoil forces of the chest wall acting outwards. With the onset of inspiration, the diaphragm contracts and pulls the attached parietal pleura downwards while contraction of the external intercostal muscles pulls the ribcage and the attached parietal pleura outwards.
This causes the negativity of the intra-pleural pressure to increase. Therefore, the pressure inside the alveoli relative to the atmospheric pressure is 0 cmH 2 O. The increased negativity of intra-pleural pressure during inspiration pulls the visceral pleura and the attached lungs outwards counteracting the elastic recoil forces of the lungs creating a negative pressure within the alveoli and thereby creating a pressure gradient between the environment which is at the atmospheric pressure and the lungs.
Airflows through this pressure gradient, and as the air enters the alveoli, the negativity in pressure decreases and with the cessation of the inspiratory muscle contraction, the intra-alveolar pressure returns to the atmospheric pressure.
During expiration, the elastic recoil of the lungs exerts a force acting inwards. The chest wall also recoils in response and the negativity of the intra-pleural pressure decreases and returns to the The pressure does not rise further as the chest wall exerts a force acting outwards at total lung volumes of less than 4 L.
With the cessation of inspiratory muscle activity, the outward force exerted by the negative intra-pleural pressure is over-ridden by the elastic recoil forces of the lungs acting inwards. This causes a positive pressure inside the alveoli in relation to the atmospheric pressure. The air filling the alveoli flows out along the so formed pressure gradient.
This flow of air decreases the positive pressure inside the alveoli and at a point the intra-alveolar pressure equalizes with the atmospheric pressure, ceasing the flow of air.
In addition to studying the pressure and volume changes that occur within the alveoli, the pressure across the lung, across the chest wall and across the whole respiratory system can be studied against volume changes of the lungs. Thus, three transmural pressures Pin — Pout can be defined:.
The volume change that occurs in a system per unit pressure change is defined as the compliance of the system. This is the ease at which a structure can be stretched.
The compliance of the lungs, chest wall and the respiratory system can be studied separately by studying the volume changes in the respiratory system against the pressure changes across the respective structure. The pressure-volume curves of the lungs, chest wall and the respiratory system shows that the steepest relationship between the volume and the pressure exists in volumes closer to FRC.
This means the compliance becomes highest closer to FRC. The curves tend to flatten as the volume reaches the TLC, i. The chest wall and the lungs lie in series, forming the respiratory system. Therefore, the compliance of the respiratory system C rs has the following relationship to the compliance of the chest wall C w and that of the lungs C l :. The compliance of healthy lungs is approximately 0.
The compliance of the chest wall is also closer to 0. Thus, the compliance of the respiratory system becomes less 0. Therefore, it is evident that the respiratory system as a whole is less stretchable compared to the lungs or the chest wall when considered alone.
Sign in or sign up and post using a HubPages Network account.Also Visit CVpharmacology. Klabunde A single cycle of cardiac activity can be divided into two basic phases - diastole and systole. Diastole represents the period of time when the ventricles are relaxed not contracting. Throughout most of this period, blood is passively flowing from the left atrium LA and right atrium RA into the left ventricle LV and right ventricle RVrespectively see figure at right.
The blood flows through atrioventricular valves mitral and tricuspid that separate the atria from the ventricles.
1-5 Baseline Vital Signs and SAMPLE History
The LA receives oxygenated blood from lungs through four pulmonary veins that enter the LA. At the end of diastole, both atria contract, which propels an additional amount of blood into the ventricles.
Systole represents the time during which the left and right ventricles contract and eject blood into the aorta and pulmonary artery, respectively. During systole, the aortic and pulmonic valves open to permit ejection into the aorta and pulmonary artery. The atrioventricular valves are closed during systole, therefore no blood is entering the ventricles; however, blood continues to enter the atria though the vena cavae and pulmonary veins.
The cardiac cycle diagram shown to the right depicts changes in aortic pressure APleft ventricular pressure LVPleft atrial pressure LAPleft ventricular volume LV Voland heart sounds during a single cycle of cardiac contraction and relaxation.
These changes are related in time to the electrocardiogram. An online video and tutorial of the cardiac cycle from the Health Education Assets Library is available: cardiac cycle video. Aortic pressure is measured by inserting a pressure-measuring catheter into the aorta from a peripheral artery, and the left ventricular pressure is obtained by placing a catheter inside the left ventricle and measuring changes in intraventricular pressure as the heart beats.
Left atrial pressure is not usually measured directly, except in investigational procedures; however, left atrial pressure can be estimated by recording the pulmonary capillary wedge pressure. Ventricular volume changes can be assessed in real time using echocardiography or radionuclide imaging, or by using a special volume conductance catheter placed within the ventricle. To analyze systole and diastole in more detail, the cardiac cycle is usually divided into seven phases.
The first phase begins with the P wave of the electrocardiogramwhich represents atrial depolarization, and is the last phase of diastole. Phases represent systole, and phases represent early and mid-diastole.
The last phase of the cardiac cycle ends with the appearance of the next P wave, which begins a new cycle. Detailed descriptions of each phase can be obtained by clicking on each of the seven phases listed below. Cardiovascular Physiology Concepts Richard E. Klabunde, PhD.These two numbers reflect different aspects of the pressure being exerted by your blood as it pulses through your arteries.
When your heart pumps blood into your arteries, it pushes the blood along under a head of pressure. Doctors measure your blood pressure as a way of quantifying the force being exerted by this moving blood against the walls of your arteries. Because the heart beats, the blood flow through the arteries is not steady as with a fire hosebut pulsatile, and the flow of blood, and the pressure it exerts, fluctuate from moment to moment.
Both the systolic and diastolic pressures are important. If the readings are too high, hypertension may be present. The pressure exerted by your blood flowing through your arteries is not constant but is dynamic, and constantly reflects what the heart is doing at a given moment. This dynamic ejection of blood into the arteries causes the pressure within the arteries to rise. The peak blood pressure reached during active cardiac contraction is called the systolic blood pressure.
When a person is exercisingduring periods of emotional stress, or at any other time when the heart is stimulated to beat more strongly than at rest, the force of cardiac contraction increases—and the systolic pressure goes up. The increase in systolic blood pressure that occurs during these conditions of cardiac stress is entirely normal.
If the systolic blood pressure is lower than normal, systolic hypotension is said to be present. If systolic hypotension is severe enough, it can cause lightheadednessdizzinesssyncopeor if it lasts long enoughorgan failure. The diastolic blood pressure is the pressure the blood exerts within the arteries in between heartbeats, that is, when the heart is not actively ejecting blood into the arteries.
After the heart is finished contracting, the cardiac ventricles relax momentarily so that they can be refilled with blood, in preparation for the next contraction.
Blood pressure is a very dynamic thing.What is the Pressure Volume Loop Curve? Explained in 6 minutes!!!
The level of your blood pressure depends on the activity of your heart and the elasticity of your arteries. As we have seen, the blood pressure is actively changing from moment to moment as the heart cycles between systole and diastole.
In addition, your systolic and diastolic blood pressure the highest and the lowest blood pressure reached during any given cardiac cycle can change substantially from minute to minute depending on your state of activity, your state of stress, your state of hydration, and several other factors.
The standard recommended by experts requires the blood pressure to be taken in a calm, warm environment after you have been resting quietly for at least five minutes. This is why most experts today recommend recording the blood pressure over an extended period of time, with ambulatory monitoring, before making the diagnosis of hypertension. Systolic and diastolic blood pressures represent the pressures within the blood vessels during different parts of the cardiac cycle.
Accurately measuring both of these values is important in diagnosing and managing hypertension.Want to keep track of your blood pressure? Microsoft Excel can help you automatically generate charts from recorded data to determine the state of your health or that of a loved one.
The Blood Pressure Tracker Template for Excel provides sections for adding daily blood pressure and heart rate information, which is automatically presented in the form of a blood pressure chart. This template provides two worksheets, one for adding data and the other for displaying a chart for your data. Once done, your chart will automatically be updated the moment you enter information about the Systolic and Diastolic Blood Pressure and the heart rate.
Having a visual representation at your disposal can make it that much easier for you to determine the closeness of the blood pressure and heart rate to normal levels; to identify any worrying trends in due course of time. It takes me to the same page. Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Sign up to our newsletter. Record Daily Blood Pressure And Generate Trends This template provides two worksheets, one for adding data and the other for displaying a chart for your data.
Leave a Comment Cancel reply Your email address will not be published.Also Visit CVpharmacology. Klabunde Left ventricular pressure-volume PV loops are derived from pressure and volume information found in the cardiac cycle diagram upper panel of figure. When this is done, a PV loop is generated bottom panel of figure and linked YouTube video.
Therefore, changes in ventricular compliance alter the slope of the passive filling curve. For example, in ventricular hypertrophy the ventricle is less compliant i. Another example of how the EDPVR can be altered is when a ventricle chronically dilates remodels as occurs in dilated cardiomyopathy or in valve disease.
A dilated ventricle has a higher passive compliance and therefore the slope of the filling curve is reduced. This results in lower ventricular pressures during filling at any given ventricular volume.
The maximal pressure that can be developed by the ventricle at any given left ventricular volume is defined by the end-systolic pressure-volume relationship ESPVRwhich represents the inotropic state of the ventricle. Peak systolic pressure loop height also decreases because arterial pressure falls as the cardiac output declines during IVC occlusion.
Therefore, afterload is decreased along with the preload. A linear relationship generally occurs within a narrow range of pressures and volumes several beats. After several seconds the ESPVR becomes non-linear with a steeper slope as baroreflexes increase ventricular inotropy.
The end-diastolic and end-systolic pressure-volume relationships are analogous to the passive and total tension curves used to analyze muscle function.
The PV loop changes when the preload, afterload and inotropic state of the heart change. Cardiovascular Physiology Concepts Richard E. Klabunde, PhD. To illustrate the pressure-volume relationship for a single cardiac cycle, the cycle can be divided into four basic phases: ventricular filling phase a; diastoleisovolumetric contraction phase b; systoleejection phase c; systoleand isovolumetric relaxation phase d; diastole.
Point 1 on the PV loop is the pressure and volume at the end of ventricular filling diastoleand therefore represents the end-diastolic pressure and end-diastolic volume EDV for the ventricle.
As the ventricle begins to contract isovolumetrically phase bthe mitral valve closes and the LVP increases, but the LV volume remains the same, therefore resulting in a vertical line all valves are closed. Once LVP exceeds aortic diastolic pressure, the aortic valve opens point 2 and ejection phase c begins.
During this phase the LV volume decreases as LVP increases to a peak value peak systolic pressure and then decreases as the ventricle begins to relax. When the aortic valve closes point 3ejection ceases and the ventricle relaxes isovolumetrically - that is, the LVP falls but the LV volume remains unchanged, therefore the line is vertical all valves are closed.The heart is an organ responsible for pumping blood through the blood vessels using rhythmic contractions of cardiac muscle.
The human heart is the pump for the circulatory system, and along with the circulatory system is considered to be an organ of the cardiovascular system. It consists of four chambers and pumps blood through both systemic and pulmonary circulation to enable gas exchange and tissue oxygenation. The heart is located in the thoracic cavity between the lungs and protected by the rib cage. The heart consists of four chambers separated into two sides.
Each side contains an atria which receives blood into the heart and flows it into a ventricle, which pumps the blood out of the heart. The atria and ventricle on each side of the heart are linked together by valves that prevent backflow of blood. The wall that separates the left and right side of the heart is called the septum. The left heart deals with systemic circulation, while the right heart deals with pulmonary circulation.
The left side of the heart receives oxygenated blood from the pulmonary vein and pumps it into the aorta, while the right side of the heart receives deoxygenated blood from the vena cava and pumps it into the pulmonary vein. The pulmonary vein and aorta also have valves connecting them to their respective ventricle. The sinoatrial SA and atrioventricular AV nodes are bundles of nerve fibers that form this conduction system. They are located in the left atrial wall of the heart and send nerve impulses to a large, highly specialized set of nerves called the Purkinje fibers, which in turn send those nerve impulses to the cardiac muscle tissue.
These nodes can send impulses to the heart without central nervous system stimulation, but may be influenced by nervous stimulation to alter heart rate. The heart also has its own blood supply, the cardiac arteries that provide tissue oxygenation to the heart as the blood within the heart is not used for oxygenation by the heart. The heart is enclosed in a double-walled protective membrane called the pericardium, which is a mesothelium tissue of the thoracic cavity.
The double membrane of pericardium contains pericardial fluid which nourishes the heart and prevents shock. This composite sac protects the heart, anchors it to surrounding structures, and prevents the heart from overfilling with blood. The wall of the heart is composed of three layers of different tissues. The outer layer is called the epicardium, or visceral pericardium, since it is also the inner wall of the pericardium.
The middle layer of the heart, the myocardium, and contains specialized cardiac muscle tissue responsible for contraction. Cardiac muscle tissue is distinct from skeletal or smooth muscle because it pumps involuntarily based on conduction from the AV and SA nodes. The inner layer is called the endocardium and is in contact with the blood that the heart pumps. It also merges with the inner lining of blood vessels and covers heart valves.
Cardiac tissue is permanent tissue that does not heal or regenerate when damaged. As a result, is prone to scarring and enlargement due to mechanical stress and injury.
The Mammalian Heart : The position of valves ensures proper directional flow of blood through the cardiac interior. Note the difference in the thickness of the muscled walls of the atrium and the left and right ventricle. The pericardium is a thick, membranous, fluid-filled sac which encloses, protects, and nourishes the heart. The pericardium is the thick, membranous, fluid-filled sac that surrounds the heart and the roots of the vessels that enter and leave this vital organ, functioning as a protective membrane.
The pericardium is one of the mesothelium tissues of the thoracic cavity, along with the pleura which cover the lungs. The pericardium is composed of two layers, an outer fibrous pericardium and an inner serous pericardium. Membranes of the Thoracic Cavity : A transverse section of the thorax, showing the contents of the middle and the posterior mediastinum.
The pleural and pericardial cavities are exaggerated since normally there is no space between parietal and visceral pleura and between pericardium and heart. The fibrous pericardium is the outer layer of the pericardium.The first step in solving problems in public health and making evidence-based decisions is to collect accurate data and to describe, summarize, and present it in such a way that it can be used to address problems.
Information consists of data elements or data points which represent the variables of interest. When dealing with public health problems the units of measurement are most often individual people, although if we were studying differences in medical practice across the US, the subjects, or units of measurement, might be hospitals. A population consists of all subjects of interest, in contrast to a samplewhich is a subset of the population of interest.
It is generally not possible to gather information on all members of a population of interest. Instead, we select a sample from the population of interest, and generalizations about the population are based on the assumption that the sample is representative of the population from which it was drawn. Procedures to summarize data and to perform subsequent analysis differ depending on the type of data or variables that are available.
As a result, it is important to have a clear understanding of how variables are classified.
Pressure versus Time Graph
Discrete variables may be further subdivided into:. For example, total serum cholesterol level, height, weight and systolic blood pressure are examples of continuous variables. Frequency distribution tables are a common and useful way of summarizing discrete variables. Representative examples are shown below. In the offspring cohort of the Framingham Heart Study 3, subjects completed the 7th examination between andwhich included an extensive physical examination.
One of the variables recorded was sex as summarized below in a frequency distribution table. Note that the third column contains the relative frequencies, which are computed by dividing the frequency in each response category by the sample size e. With dichotomous variables the relative frequencies are often expressed as percentages by multiplying by The investigators also recorded whether or not the subjects were being treated with antihypertensive medication, as shown below.
This indicates that seven individuals had missing data on this particular question. Missing data occurs in studies for a variety of reasons. If there is extensive missing data or if there is a systematic pattern of missing responses, the results of the analysis may be biased see the module on Bias for EP for more detail.
There are techniques for handling missing data, but these are beyond the scope of this course. Sometimes it is of interest to compare two or more groups on the basis of a dichotomous outcome variable. For example, suppose we wish to compare the extent of treatment with antihypertensive medication in men and women, as summarized in the table below. Here, both sex and treatment status are dichotomous variables. Because the numbers of men and women are unequal, the relative frequency of treatment for each sex must be calculated by dividing the number on treatment by the sample size for the sex.
The numbers of men and women being treated frequencies are almost identical, but the relative frequencies indicate that a higher percentage of men are being treated than women.
Note also that the sum of the rightmost column is not