Cardiac muscle histology Electrocardiograms Arrhythmias Blood pressure measurement Drug treatment of hypertension Cardiac Muscle
intercalated discs • mechanical connections between cells • contain gap junctions
Figure 14.5h, p. 442 Cardiac muscle has intercalated discs
Wheater Figure 8.3 Cardiac muscle—arrows indicate intercalated discs
Be able to identify: • type of tissue: cardiac muscle • structure: intercalated disc Wheater, Fig. 6.26: High magnification electron micrograph of an intercalated disc Cardiac muscle is electrically coupled
• gap junctions are channels that allow action potentials to be conducted from cell to cell
Figure 3.8b, p. 74 Wheater, Fig. 6.26: High magnification of an intercalated disc
FA: fascia adherens: site of mechanical linkage N: nexus junction: region where gap junctions are located Electrocardiogram Interpretation of electrocardiograms (ECG)
Figure 14.16f; p.457
From Figure 14.16g; p.457 Patient with arrythmia
A 65-year-old man who had been treated for hypertension for the past 10 years presented with increasing fatigue, dizziness, and palpitations. He did not have chest pain or any other symptoms. An electrocardiogram (ECG) was obtained.
Figure 1 in JAMA (2019) 322(7): 688-689 What might cause fatigue and dizziness?
Are there P waves?
Are there normal QRS waves?
What is the heart rate?
Is the heart rate regular? Atrial fibrillation
• erratic electrical activity in atria causes fibrillatory waves with no P waves • excitation of ventricles is via normal path through AV node so QRS is normal-looking • excitation randomly enters AV node to cause irregularly irregular R-R intervals • can cause tachycardia
Figure 2 in JAMA (2019) 322(7): 688-689 https://jamanetwork.com/journals/jama/fullarticle/2748482 Fibrillation: irregular and uncoordinated contraction of cardiac muscle
atrial fibrillation ECG: no P waves • atria don’t pump blood • treated with anti- clotting drugs
ventricular fibrillation ECG: no QRS waves • ventricles don’t pump blood • rapidly fatal • treated with defibrillator
ECG traces from Figure 14.16g, p. 457 AV node conduction block
Does a QRS wave follow each P wave?
Does the QRS wave look normal?
What is the heart rate? AV node conduction block
Does a QRS wave follow each P wave?
Does the QRS wave look normal
What is the heart rate?
What is acting as the pacemaker of the heart? Premature ventricular contraction
From Becker, D. (2006) Anesth. Prog. 53: 53-64 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1614214/pdf/i0003-3006-53-2-53.pdf
Are there normal QRS waves following P waves?
Are there abnormal QRS waves?
Are all the QRS waves the same shape?
How many ectopic foci are there? Arterial pressure • the blood pressure oscillates between a high systolic pressure and a low diastolic pressure • the mean arterial pressure (MAP) is the average pressure throughout the entire cycle • the pulse pressure is the difference between the systolic pressure and the diastolic pressure • systolic and diastolic pressure measured using a sphygmomanometer
MAP
See this page: https://www.physiologyweb.com/calculators/mean_arterial_pressure_calculator.html Blood pressure measurement
Figure 14.7, p. 483 Blood pressure measurement
systolic pressure
diastolic pressure
Adapted from Figure 3 https://opentextbc.ca/anatomyandphysiology/chapter/20-2-blood-flow-blood-pressure-and-resistance/
What causes the sounds? Turbulent flow through the narrowed artery. Ensuring accurate measurement of blood pressure
1. Cuff should be at the level of the heartàgravity will change the reading if the arm is above or below the heart. What happens to the blood pressure reading if the cuff is above the heart? What happens to the blood pressure reading if the cuff is below the heart?
2. Patient must be positioned properlyàrelaxed, sitting with feet flat on the floor an back supported. Patient should be seated for 3-5 minutes without talking or moving before taking the first BP reading.
3. Cuff must fit properly and be placed on bare skin.
Source: Hypertension (2019) 73: e35-e36 https://www.ahajournals.org/doi/full/10.1161/HYP.0000000000000087 Automated blood pressure monitor
• oscillometric device: measures the waveform of pressure fluctuations in the artery as pressure in the cuff decreases • calculates systolic pressure and diastolic pressure based on changes in the waveform
wrist cuff Calculations
pulse pressure (PP) = systolic pressure (SP) – diastolic pressure (DP) PP = SP - DP mean arterial pressure (MAP) = about a third of the way between DP and SP MAP = DP + 1/3 PP Blood pressure medications
diuretics ACE inhibitors Angiotensin II receptor antagonists Ca++ channel blockers Mean arterial pressure
Figure 15.8a, p. 485 Blood plasma is part of the extracellular fluid
Figure 5.1b, p. 123
Figure 16.1, p. 512 à blood volume is related to extracellular fluid volume The kidneys regulate extracellular fluid volume by regulating the amount of Na+ in the extracellular fluid
sensors detecting regulated changes in ECF volume variable Diuretics decrease ECF volume by inhibiting Na+ reabsorption in the nephron The kidneys regulate extracellular fluid volume by regulating the amount of Na+ in the extracellular fluid
sensors detecting regulated changes in ECF volume variable
increased renin secretion part of kidney response to decreased ECF volume Renin-angiotensin-aldosterone system
angiotensin II causes vasoconstriction
aldosterone promotes Na+ reabsorption in the distal nephron
• ACE inhibitors decrease formation of angiotensin II • angiotensin II receptor antagonists block angiotensin II signaling Ca++ channel blockers decrease peripheral resistance by reducing vascular smooth muscle contraction arterioles
M: smooth muscle
Wheater Figure 8.12a