Define Blood Pressure
= force created by the blood as it pushes against the arterial vessel wall
Describe Blood Pressure
- the blood pressure in the arteries varies with the cardiac cycle
- the highest pressure in the arteries is the systolic pressure, which coincides with the ejection of a stroke volume into the arteries during ventricular systole
- the lowest pressure is called the diastolic pressure, which occurs when the ventricles are relaxed during diastole
- average blood pressure is 120 (systolic pressure)/80 (diastolic pressure) mmHg
Describe the principles of sphygmomanometry
- sphygmomanometers work by partially occluding blood flow through the artery, which produces Korotkoff sounds
- the highest pressure in the cuff at which sounds are heard represents the systolic pressure, and the pressure at which the last sound is heard will be the diastolic pressure
Describe the pressure in the cuff when the pulse disappears
When the pulse disappears the pressure in the cuff is higher than the systolic pressure
= if pulse cannot be felt, the radial artery is completely occluded. This means that the cuff pressure must be higher than systolic pressure
When are Korotkoff sounds heard?
= when the cuff pressure is between the systolic and diastolic pressures, because blood flow is turbulent
When is stroke volume most likely to be high: in reclining or standing?
In reclining
Because gravity effects the blood vessels uniformly and when reclining the blood doesn’t have to work against gravity
Based on an understanding of Frank-Starling Law of the Heart, what will happen when sometimes stands up from lying down?
= the venous return decreases, which reduces the stretch in the ventricle and decreases the next stroke volume
If stroke volume decreases on standing, how is the cardiac output maintained with homeostatic range?
= heart rate increases
Describe how blood pressure and pulse rate changes during a stressor
- pulse rate increases in response to a stressor
- blood pressure (systolic/diastolic) also increases in response to a stressor
Describe the Baroreceptor Reflex
- responds to a mechanical change
- monitors blood flow to heart and sympathetic nervous system
- if too low, baroreceptors fire to brain which increases sympathetic activity to heart and blood vessel, decreasing parasympathetic activity
- works via constricting arterioles and veins by increasing total peripheral pressure
- also works by increasing heart rate, venous return and stroke volume
- baroreceptors are located in carotid sinus and aortic arch
- baroreceptors maintain homeostasis and keep blood pressure constant via constriction of arterioles and veins, it also increases heart rate and stroke volume
Describe central venous pressure
= the blood pressure in the thoracic vena cava - near the right atrium
- is usually about 0-6 mmHg in a healthy individual
Describe venous return
- venous return is the volume of blood returning back to the heart each minute. It depends on the difference in blood pressure at the beginning and end of the venous circulation (the pressure gradient)
- venous return is affected by:
- cardiac suction
- skeletal muscle pump
- venous valves
- respiratory pump
- sympathetic nervous system
Why does blood volume drop in the jugular vein during inspiration?
= the blood in the jugular vein decreases during inspiration because there is a greater pressure gradient so there is greater venous return and not as much blood pooling in the vein
Describe spirometry
Spirometry allows determination of 3 lung volumes
- tidal volume
- inspiratory reserve volume
- expiratory reserve volume
Describe a Vitalograph
= a vitalograph measures the amount of air that can be forcefully exhaled over a period of time
- of particular interest is how much air is exhaled in the first second, the FEV1
- the completed trace can also be used to measure the subject’s forced vital capacity (FVC) and then the ratio of FEV1 to FVC can be calculated
Why do our lungs not fully empty during a maximum expiration
- after forced maximum expiration, air remains in the lungs; this air is called the residual volume. This is due to the transmural pressure gradient
- also due to dynamic small airway closure
Describe FEV1/FVC
a FEV1/FVC less than 75% suggests an obstructive disease such as asthma or emphysema
Describe the Flow-Volume Loop
- the flow volume loop measure airflow rate during forced expiration and forced inspiration
Give definitions for the Flow-Volume loop
Flow 0= beginning of expiration (0 L/sec)
PEF = Peak Expiratory Flow, should be achieved before 15% of vital capacity has been exhaled
100% vital capacity= the end of the forced expiration when all air has been exhaled (when flow is 0 L/sec)
PIF = Peak Inspiratory Flow, should be achieved at about 50% of volume inhaled
Why does the PEF occur early in exhalation?
= elastic recoil contributes most to flow early in expiration
- forceful expiration occurs through muscular effort and elastic recoil of lungs. With fully expanded lungs, elastic recoil is high, so this contributes most to flow early in expiration
What factors are most likely to affect FVC, FEV1 and Flow in a healthy population?
age, height, gender and anatomical build
Define Large Airway Obstruction
- the large airways include the trachea and bronchi
- cartilage is found in the large airways
Draw a ‘NORMAL’ vitalograph and flow-volume loop
see folder for diagram
Draw a vitalograph and flow-volume loop of an individual with LARGE AIRWAY OBSTRUCTION
see folder for diagram
