BIOC33Winter2013 Lab Exam Review.docx

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University of Toronto Scarborough
Biological Sciences
Stephen Reid

BIOC33Winter2013 Lab Exam Review Lab 1: ECG I Introduction o Main function of the heart = pump blood through 2 circuits o Pulmonary circuit = through the lungs to oxygenate the blood and remove carbon dioxide o Systemic circuit = deliver oxygen and nutrients to tissues and remove carbon dioxide o In order to beat the heart needs 3 types of cells  rhythm generators that produce electrical signals (SA node), conductors to spread the signal and contractile cells (myocardium) to mechanically pump the blood o Pacemaker cells start the electrical sequence of depolarization and repolarization o Inherent rhythmicity or automaticity  property of cardiac tissue o Sinoatrial node (SA node) generates electrical signal  spreads through the internodal pathwyas and atrial fibres to the AV node  down the bundle of His, through the right and left bundle branches and up into the Purkinje fibres o o when depolarization reaches the contractile cells they contract and when repolarization signal reaches they relax o SA node depolarization is followed by atrial contraction as the electrical stimulus spreads from the SA node through the atrial muscle o Impulse reaches the AV node through the internodal fibres  electrical signal is delayed in the AV node for approximately 0.20 seconds when then atria contract o Then the signal is relayed to the ventricles through the bundle of His, right and left bundle branches and Purkinje fibres  stimulate the ventricles to contract (ventricular systole) o Repolarization also starts with the SA node and spreads through the atria and then the ventricles (ventricular diastole) o The heart rate and strength of contractions are modified by the sympathetic and parasympathetic dividiosns of the autonomic nervous system o Sympathetic nervous system = accelerator  speeding up and increasing contractile force of the heart (increases HR) o Sympathetic influence increases during inhalation o Parasympathetic nervous system = break  slows down HR o During relaxation, parasympathetic influence becomes dominant and HR slows down o Parasympathetic influence increases during exhalation o By placing electrodes on other parts of the body the echoes of the heart’s electrical activity can be detected  ECG (electrocardiogram) o o interval = one wave and a straight line o segment = period from end of one wave to beginning of next wave COMPONENTS OF THE ECG Segment Measurement points… Represents… P wave begin and end on the (baseline); depolarization of atrial muscle as negativity normally upright in standard limb leadspreads from the SA node toward the ventricles 1 P-R Interval from start of P wave to start of QRS time it takes for the impulse sent from the SA complex node to travel to the ventricles P-R Segment from end of P wave to start of QRS interval between atrial depolarization and complex ventricular polarization QRS complex begin and end on the isoelectric line spread of excitation through ventricular (baseline) from start of Q wave to end of myocardium—results in depolarization of S wave ventricular muscle. Repolarization is also part of this segment, but the electrical signal for atrial repolarization is masked by the larger QRS complex (see Fig 5.2) S-T Segment interval between end of S wave and start period during which ventricles are more or less of T wave uniformly excited T wave begin and end on the isoelectric line beginning of ventricular relaxation (restoration of (baseline) ventricular myocardium to resting or excitable state) Q-T Interval start of QRS complex to end of T wave electrical systole (when ventricular beat is generated) o lead  the arrangement of 2 electrodes (one positive and one negative) with respect to a third electrode (ground) o this experiment = Lead II = positive on left ankle, negative on right wrist and ground on right ankle DURATION AMPLITUDE PHASE (second) (millivolts) P wave 0.06 – 0.11 < 0.25 P-R interval 0.12-0.20 P-R segment 0.08 QRS complex (R) < 0.12 0.8 - 1.2 S-T segment 0.12 Q-T interval 0.36-0.44 T wave 0.16 < 0.5 o there are temporary increases and decreases in HR associated with resting respiratory cycle made by systemic atrial and systemic venous pressure receptors (baroreceptors) reflexes in response to cycling of intrathoracic pressure o inspiratory muscles contract  intrathoracic pressure decreases  thoracic veins expand  venous pressure decreases  venous return decreases  cardiac output decreases  systemic arterial blood pressure decreases  reduced frequency of carotid baroreceptor firing (usually decreases HR in response to high MAP)  HR increases o when inspiratory muscles relax, expiration occurs passively  intrathoracic pressure increases  thoracic veins compress  venous pressure increases  venous return increases  systemic venous baroreceptros increase heart rate  but increase in CO and systemic arterial BP causes the carotid baroreceptor to fire  decreases in HR 2 o o average resting HR is 70  athletes can have heart rates as low as 50 BPM o athletes tend to develop left ventricular hypertrophy  larger and more efficient hearts o in sedentary indiiduals, these changes can be indicatory of failing hearts Experiment right forearm WHITE lead right leg left leg BLACK lead RED lead o (ground) o during calibration check for large baseline drifts  electrodes may not be in good contact 3 o Data Analysis o Seated deep breathing: BPM increased during inspiration and the time for one cardiac cycle decreased o During expiration time for cardiac cycle decreased even more, and heart rate increased even more  why? The temporary increase should be cancelled out by the carotid sinus which decreases HR back to normal o Heart rate increases after exercise o After exercise, ventricular systole increases and ventricular diastole decreases Lab 2: ECG II Introduction o William Einthoven developed string galvanometer  won Nobel Prize in 1924 o The spread of the signal from the SA node through the atria to the AV node causes a negative charge to occur which induces depolarization = P wave o The depolarization of the ventricles is recorded as the QRS complex in the ECG o Then the ventricles start to repolarize which is recorded as the T wave o Because the current spreads along specialized pathways and depolarizes in sequence the electrical activity has a spatial orientation or electrical axis o Amount of signal generated is proportional to amount of tissue being depolarized  since the ventricles make up majoritiy of mas of heart, the largest deflection is the depolarization of the ventricles which occurs during the QRS complex o Body contains fluids with ions that allow for electrical conduction  possible to measure electrical activity from the surface of skin o Measurements in the leg approximate those occurring in the groin and those in the forearms approximate those occuring at the shoulder  electrodes placed on ankle, and wrists o Groud electrode = right leg above the ankle - Lead I ++ Lead II-ead III + + right arm left arm Frontal Sagittal right leg left leg (ground) o o lead = spatial arrangement of 2 electrodes on the body o lead axis = recording direction of the lead (negative  positive) o the ECG recorder computed the difference between the negative and the positive electrodes o Einthoven’s Triangle  configuration of 3 leads with the polarity shown below o Lead I: Right Arm (RA) “–” electrode, Left Arm (LA) “+” electrode o Lead II: Right Arm (RA) “–” electrode, Left Leg (LL) “+” electrode o Lead III: Left Arm (LA) “–” electrode, Left Leg (LL) “+” electrode o This lead configuration (figure above) is called the standard bipolar limb lead o Einthoven’s Law says: Lead I + Lead III = Lead II (measures mean electrical axis in the frontal plane) o The mean electrical axis of the heart = summation of all the vectors occurring in the cardiac cycle  can approximate by looking at QRS interval since represents majority of electrical activity in the heart o Approximation can also be made by using the R peaks  largest magnitude in the cardiac cycle 4 magnitude of R wave from leads 0,0 I + - + - - + + + - + Axisan Electrical Mean Electrical Axis III o o direction of resulting vectors approximates the mean electrical axis of the hear and the length of the vector approximates the mean potential of the heart o to do this more accurately you would add the magnitude of the Q, R and S peaks algebraically and plot that number for Lead I and Lead III and repeat the above process to find the mean electrical axis of the heart Experiment 1 above 2 above right wrist left wrist 2 above 1 above right ankle left ankle o o after calibration there should be no baseline drifts in the ECG trace  subject must remain relaxed because EMG muscle signals will corrupt the ECG signal o record lying down: o o segment 2: breathing in and breathing out  cannot breathe too deeply because muscle EMG would corrupt the ECG trace Data Analysis o o Note: the R waves are always positive, no matter the lead o The amplitude of the QRS (max) was measured for Lead I and Lead III o The QRS complex (in both leads) is lowest when lying down; greater when breathing out in Lead III and greater when breathing in in Lead II o The amplitudes of the R waveswas measured and Einthoven’s Triangle plotted o The mean electrical axis of the heart is greater lying down than sitting up  when lying down, diaphragm and organs are pushing up towards the heart, causing the heart to move up into the chest and causing the MEA to move towards the right (increasing magnitude) 5 o The MEA of the heart is greater when breathing out than when breathing in  when you breathe in, the diaphragm relaxes and the heart is allowed to hang a little bit straighter (downwards) in the cavity, shifting the MEA towards the right (increasing magnitude) o 3 factors that affect the orientation of the mean electrical axis of the heart  anatomical position of the heart, pattern of electrical conduction, and characteristics of the cardiac muscle o during branch bundle block, the electrical axis shifts towards the side with the block because the wave of depolarization will spread faster on the side that is not blocked, making the overall direction of depolarization from te side that spreads faster to the blocked side  so in LBBB, the RBB will depolarize first before the L, so the direction of depolarization will be from R to L and the mean electrical axis will shift towards the Left as a result Lab 3: Blood Pressure Introduction o systolic pressure  the force of blood in your arteries as the heart contracts and pushes it out (highest arterial pressure reached during ventricular systole)  100-139 mm of Hg in resting adult o diastolic pressure  force of blood between heart beats (lowest arterial pressure reached during ventricular diastole)  60-89 mm of Hg o blood flow through the heart and the blood vessels is unidirectional  flows into the heart from the pulmonary and systemic veins and out of the heart into pulmonary and systemic arteries o blood flow is unidirectional because of 4 valves that prevent retrograde or backward flow during the cardiac cycle o Right AV valve (tricuspid) and the left AV valve (bicuspid or mitral) prevent backward flow from the ventricles into the atria o The pulmonary semilunar valve and the aortic semilunar valve prevent backward flow of blood from arteries into the ventricles o During ventricular diastole (relaxation)  the AV vales open and semilunar valves close allowing the ventricles to be filled with blood o During ventricular systole (contraction)  the AV valves close, and the semilunar valves are opened, allowing the ventricles to eject blood into the arteries o So the cardiac cycle consists of ejection and filling so blood flow into the arteries is not continuous  BP and blood flow in the arteries is pulsatile  increases during systole and decreases during ventricular diastole o o PP = SP – DP  PP is directly related to SV and inversely related to HR and TPR o Flow through a closed circuit is determined by the pressure energy causing the flow and the resistance to flow by the blood vessel walls (friction) and internal viscosity of the blood  F = P/R o the pressure refers to Mean Arterial Pressure  converts pulsatile pressure into a continuous pressure that determines the average rate of blood flow from the beginning of the circuit (left ventricle) to the end of the circuit (right atria) o ventricle spends more time in diastole during the cardiac cycle so  MAP = (PP/3) + Diastolic Pressure o or MAP = (SP + 2 DP) /3 o systemic arterial blood pressure is measured indirectly because direct measurements are invasive and not practical nor convenient  indirect methods can only give approximation, may be influenced by person taking the measurement (audio acuity etc.) and quality of calibration of the equipment being used o most common indirect way of measuring BP = ascultatory methods  sthetoscope + sphyngomomanometer 6 o o inflating the rubber cuff causes the underlying artery to collapse  sound is created by turbulent blood flow passing through the compressed vessel  when cuff pressure > systolic arterial pressure, the artery is collapsed, no blood flow, and no sound o as the cuff pressure is reduced, blood flow begins when cuff pressure falls just below the systolic arterial pressure  short tapping sound (first Korotkoff sound) may be heard = systolic pressure o sound increases in intensity as cuff pressure is reduced, then become muffled (second sound of Korotkoff) = diastolic pressure o then the sounds disappear because the vessel is no longer compressed by the cuff and normal non-turbulent flow resumes o o NOTE: the Korotkoff sounds appear at the time of the T wave o If measured at the heart, this sound should appear right after the R peak but there is a delay due to the time it takes the pressure wave to reach the arm so the sounds are shifter in time with respect to the R-wave o If the subject has hypertension, ascultatory gap may occur  hear sound at higher cuff pressure but it fades out as you decrease the pressure and reappears at a still lower pressure  requires alternate method of BP measurement o many factors that influence blood pressure measurement, such as: genetics, age, body weight, state of physical activity, level of salt, caffeine or other drugs in the system, monitor’s hearing, etc BLOOD PRESSURECLASSIFICATIONS for Adults in a resting state Category Systolic mmHg Diastolic mmHg Recommended follow-up Optimal < 120 and < 80 Recheck in 2 years Normal < 130 and < 85 Recheck in 2 years High Normal 130-139 or 85-89 Recheck in 1 year Hypertension: Stage 1 — mild 140-159 or 90-99 Confirm within 2 months Stage 2 — moderate 160-179 or 100-109 Evaluate within 1 month Stage 3 — severe  180 or  110 Evaluate immediately or within 1 week based on clinical situation 7 Basic measurement step Reason 1. Select the proper size cuff for your Subject. if the cuff is too large you may get incorrect low readings, and if it is too small you may get incorrect high readings. 2. Make sure all the air in the sphygmomanometer If air is left in the cuff you may get a false high reading because an cuff is expelled before use. excessive amount of pressure will be required to occlude the brachial artery. 3. Close the valve. 4. Position the Subject’s arm at heart level. You need to minimize the effects of gravity. Arm above heart level can give false low readings, and arm below heart level can give false high readings. 5. Place the cuff so that the “Artery” label is over the The cuff pressure must be applied directly to the artery, which Subject’s brachial artery requires the bladder inside the cuff to be in the proper position. 6. Position the cuff such that the lower edge of the The cuff edge should be high enough to avoid covering any part of cuff is 1.5 to 2 inches above the antecubital fossa the stethoscope diaphragm. This is to minimize any extraneous (inner aspect of elbow). noise cause by the cuff rubbing against the diaphragm. A loose cuff can give a false high reading because of the increased 7. Wrap the cuff evenly and snugly around the Subject’s arm and allow the Velcro to hold it in pressure required to occlude the brachial artery. place. 8. Make sure all the rubber tubing and cables of both Any tubing on the sphygmomanometer that is pinched can cause the sphygmomanometer cuff and stethoscope are false pressure reading and if the stethoscope tubing is pinched, it not tangled or pinched. can greatly reduce the loudness of the Korotkoff sounds. 9. Position the sphygmomanometer pressure dial Reading the dial at an angle can cause inaccurate readings due to indicator such that you can read the face of the parallax error. dial straight on. Notes for the following steps: - an overinflated cuff may produce a vasospasm, which can cause a) It is important to not inflate the cuff higher than incorrect pressure readings. is needed. - occlusion of blood caused by the cuff creates venous congestion b) It is important to not leave the cuff at a high in the forearm. The blood must be allowed to drain or it can lead pressure for an extended period of time. to incorrect pressure readings. For the same reason, it important to wait at least one (1) minute between successive blood pressure measurements. Step we will use: The stethoscope diaphragm needs to be placed over the brachial 10. Palpate the brachial artery between the antecubital fossa and the lower edge of the cuff to artery where the Korotkoff sounds are best heard. find where the pulse is best felt. This procedure can be a bit tricky so take note: The pulse is felt when the artery is compressed over bone or firm tissue. To feel the pulse, compress the artery firmly then ease up on the pressure slightly. After a few tries you should get the hang of it. Step we will use: 11. Inflate the cuff to 160 mmHg. This technique has the advantage of being quick and easy, and for reasons discussed above, it is preferable to minimize the amount of time the cuff is at high pressure. The disadvantage of this technique is that it uses more pressure than most Subjects probably need, and (in rare cases) it may miss the point of diastolic pressure. 12. Place the stethoscope in the correct position. Excessive pressure could distort the artery and give incorrect pressure indications (usually gives a diastolic pressure reading that is too low). Also, excessive pressure can cause the stethoscope to rub on the Subject’s skin, which may generate extraneous noise. 13. Release the pressure at a rate of 2 to 3 Deflating too slowly produces venous congestion, which can give mmHg/second. false high diastolic pressure readings. Deflating too rapidly leads to inaccuracies because the actual point of systolic or diastolic pressure could lie between heartbeats. The slower the heart rate, the more inaccurate the reading. 14. Note the pressure at which the Korotkoff sounds This sound indicates the pressure closest to the systolic first appear (systolic). pressure. 15. Continue to listen and note the pressure when the This pressure is close to the point of diastolic pressure. 8 sounds completely disappear (diastolic). 16. Deflate the cuff as rapidly as possible afterThis will minimize patient discomfort and reduce venous sounds disappear. congestion. Experiment o o Segment 1 and Segment 2: left arm, sitting up o o Segment 3 and Segment 4: Right arm, sitting up  shoud look similar to above o Segment 5 and Segment 6: Right arm, lying down o Segment 7 and Segment 8: Right arm, after exercise Data Analysis o o = corresponds to T wave o 9 o the marker is inserted where the person hears the sound  but the computer actually records the sound before that, which corresponds to the T wave on the ECG trace o to find BPM  select R to R  60/ delta T = BPM o the time between the R wave and the first Korotkoff sound is how long it takes for the pressure wave to reach the arm from the heart o if HR increases then BP (MAP) would increase This increase could however, lead to compensatory changes via the baroreflex leading to a decrease in SV and/or TPR which could prevent any observed increase in BP o Pulse Pressure (PP) = Systolic Pressure (SP) – Diastolic Pressure (DP) o Pulse pressure is directly related to SV and inversely related to HR. o When SV increases, SP increases more than DP. o If HR increases, filling time decreases, EDV decreases, SV decreases and PP decreases. o If HR decreases, filling time increases, EDV increases, SV increases and PP increases. o PP increases during exercise because SP increases to a greater extent than DP when SV increases at the start of exercise Lab 4: ECG and Pulse Introduction o During the cardiac cycle the electrical actibity of the ventricles is represented by the QRS complex, and is preceded by the mechanical event of ventricular muscle contraction (systole)  begins at the time of R wave and ends at the end of T wave o ventricular systole results in a volume of blood (SV) pushed into the arteries  aorta from the L ventricle o aorta and other arteries have muscular walls, which allows the arterial walls to expand slightly to receive the volume of blood during sytole and then eleastic recoil of the arteries helps to continue pushing the blood through the rest of the system  MAP is the driving force of blood flow o pumping action of ventricles also sends a pressure wave that is transmitted via the arterial walls  the stiffer the vessel walls the faster the transmission of the pressure wave but the more work required by the heart to move the same blood volume o when pressure wave is transmited to periphery like the finger tip there is a pulse of increased blood volume o changes in blood volume of organs may be caused by autonomic nervous system, environmental factors (temperature), metabolic activity of organ etc. o the actual blood flow is slower than the transmission of the pressure wave o fastest blood flow is in the aorta  40-50cm/sec  the speed of the pressure wave though is much faster o speed of the pressure wave from the heart to periphery can be affected by the heart’s ability to contract strongly, BP, relative elasticity of arteries (Resistance), diameters of systemic arteries and arterioles o plethysmography : study of blood volume changes within an organ by using volume displacement techniques o transducer operates by convering light energy to electrical energy and this is called a photoelectric transducer  measures amount of light reflected off skin o blood absorbs light in a manner proportional to blood volume  the greater the blood volume, the greater the light absorption o the reflected light is then converted into electrical signlas Experiment rWHITE leadrm BLACK lead left leg (ground) RED lead o 10 o calibration: o o measure 3 different situation  arm relaxed, opposite arm immersed in cold water, and arm up Data Analysis o Fig. 7.11 o Fig. 7.12 o measured delta T and BPM based on R-R interval and then measured pulse interval (delta T) and pulse rate besed on adjacent pulse peakse (above figures) o the pulse rate increases from normal when there is temperature change (colder) o the pulse rate decreases when the arm is help up  speed is decreased because MAP is decreased (less force of gravity, less TPR) and BF = P/R so a decrease is pressure causes a decrease is speed o QRS amplitude remained constant through the segments while the pulse amplitude decreased with temperature decrease, and further decreased when the arm was held up  relative to blood volume o The QRS shows electrical activity through the heart which is always the same even if the HR increases or decreases therefore the amplitude of the QRS does not change with change in temperature or anatomic position o On the other hand the amplitude of the pulse is related to blood volume  amplitude was lowest when the arm is held up because blood volume in the finger decreases, and so the amplitude of the pulse wave will have decreased as well to reflect that Lab 5: Respiratory Cycle I Introduction o 3 functions of the respiratoy system : provide oxygen for energy, provide outlet for carbon dioxide, and help maintain pH of the blood plasma o inspiration: skeletal muscles (diaphragm and external intercostals) contract, increasing volume and decreasing pressure within the thoracic cavity of the lungs o air rushes from high pressure to low pressure so it goes into the lungs o during resting expiration, the muscles relax, decreases volume of thoracic cavity, and increasing pressure, allow air to go back into the atmosphere  expiration is passive at rest o during exercise or forced exhalation, the expiratory muscles pull down the rib cage and compress the lungs 11 o During inspiration, oxygen drawn into the lungs diffuses to the pulmonary capillaries and is transported to cells via erythrocytes (red blood cells) o Some of the carbon dioxide reacts with water in the body to form carbonic acid, which then dissociates to H and bicarbonate o The erythrocytes transport CO2and H back to the lungs. Once in the lungs, the H and HCO3recombine to form water and CO 2 CO 2 Excretion (pulmonary ventilation) Pulmonary - HCO 3 Blood Reaction proceeds to left, pH increase - r Cl edlodcel H CO H + HCO - CO +2H O 2 2 3 3 Chloride Dioxide Water Carbonic Acid HyIongenBicarbonate Shift Ion Cl- Systemic Blood CO 2 Reaction proceeds to right, pH decreaseO - Production 3 (cell metabolism) o o many factors involved in regulation of ventilation  rate and depth of breathing o basic rhythm of breathing is established by inspiratory and expiratory respiratory centers in the medulla o the inspiratory center intitiates inspiration by activation of inspiratory muscles  during rest breathing (eupnea) the average RR is 12-14 cycles/minutes o the expiratory center acts to limit and then inhibit the inspiratory center, thereby producing a passive expiration o the basic breath pattern is affected by higher centers in the brain, feedback from peripheral and central chemoreceptors in the arterial system and medulla, stretch receptors in the lungs, and other sensory receptors in the body o example: cerebral control evident during speech which requires expiratory air to pass over the vocal cords o chemoreceptors sense oxygen,carbon dioxide and H+ levels in blood and in cerebrospinal fluid of medulla o hyperventilation: breathing rate and depth is increased so that the lungs rid body of caron dioxide faster than it is being produced  increase in pH because H+ isused up quickly o this depresses ventilation until normal carbon dioxide and H+ ion levels are restored o apnea vera temporary cessation of breathing after voluntary hyperventilation o hypoventilation  shallow and slow breathing results in the lungs gaining carbondioxide (hypoapnia) because it is not removed as fast as it is formed net gain of H+ ions wich lowers pH in body fluids o the chemoreceptor feedback causes ventilation to increase until carbon dioxide levels and extracellular pH levels return to normal o NOTE: we are more sensitive to changes in carbon dioxide than oxygen in blood  the central medullary chemoreceptors are exposed to unbuffered cerebrospinal fluid so the changes brought about by dissociation of carbon dioxide are more pronounced than in blood o At high altitudes  low levels of O2 stimulate increased ventilation which decreases carbon dioxide and H+  causes increased pH
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