Carotid Artery PalpationCarotid Artery Palpation

External pressure on carotid artery may External pressure on carotid artery may slow HRslow HR

Due to direct stimulation of barorecptor in Due to direct stimulation of barorecptor in carotid arterycarotid artery

Still appropriate site to measure HR during Still appropriate site to measure HR during ex.ex.

Cortical InputCortical Input

Impulses from cerebral cortex pass via Impulses from cerebral cortex pass via small afferent nerves through CVC in small afferent nerves through CVC in medullamedulla

Allows emotional state to influence CV Allows emotional state to influence CV responseresponse

Impulses cause HR to rise rapidly prior to Impulses cause HR to rise rapidly prior to ex. (anticipatory HR)ex. (anticipatory HR)

Probably due to increase in sympathetic Probably due to increase in sympathetic discharge and a decrease in vagal tonedischarge and a decrease in vagal tone

Magnitude of increase is greatest in short Magnitude of increase is greatest in short sprint events and lower in longer eventssprint events and lower in longer events

Represents a 74% increase of HR during a Represents a 74% increase of HR during a 60 yd sprint60 yd sprint

Large portion of HR adjustment to exercise Large portion of HR adjustment to exercise reflects the cortical input that occurs during reflects the cortical input that occurs during initial stages of activityinitial stages of activity

Receptors in joints and muscles (muscle Receptors in joints and muscles (muscle afferents) probably provide a large amount of afferents) probably provide a large amount of input to increase HR during initial stages as input to increase HR during initial stages as well well

Heart as a pumpHeart as a pumpincrease HR increase HR increase in SV; increase in SV;

limitationslimitationsOnce HR reaches a certain level, Once HR reaches a certain level, strength of contraction decreases, strength of contraction decreases,

may be due to overuse of may be due to overuse of substrates in cardiac musclesubstrates in cardiac muscle

Period of diastole is so short, Period of diastole is so short, cannot fill adequatelycannot fill adequately

with artificial stimulation: peak ability to with artificial stimulation: peak ability to pump blood is 100-150 bpmpump blood is 100-150 bpm

with sympathetic stimulation: increase HR with sympathetic stimulation: increase HR and strength of contraction peak ability: and strength of contraction peak ability: 170-220 bpm170-220 bpm

Cardiac ContractilityCardiac Contractility

ΔΔP/ P/ ΔΔt: rate of change of ventricular t: rate of change of ventricular pressure with respect to timepressure with respect to time

way to assess the strength of the way to assess the strength of the contraction of the heartcontraction of the heart

as ventricular pressure increases at its as ventricular pressure increases at its most rapid rate, the most rapid rate, the ΔΔP/ P/ ΔΔt also peakst also peaks

usually, rate of rise of ventricular pressure usually, rate of rise of ventricular pressure correlates well with strength of ventricular correlates well with strength of ventricular contraction…….. two factors that influence contraction…….. two factors that influence ΔΔP/ P/ ΔΔt which are not related to cardiac t which are not related to cardiac contractility are:contractility are:

1. Increased input pressure to the left 1. Increased input pressure to the left ventricle (EDV, preload)ventricle (EDV, preload)

2. Pressure in the aorta, afterload2. Pressure in the aorta, afterload

Influence of Potassium and Influence of Potassium and Calcium ionsCalcium ions

Excess potassium in extracellular fluids Excess potassium in extracellular fluids causes heart to become dilated, flaccid, causes heart to become dilated, flaccid, and slows HRand slows HR

large quantities can block the cardiac large quantities can block the cardiac impulse from the atria to the ventricles via impulse from the atria to the ventricles via AV bundleAV bundle

elevations of 2-3X normal can weaken elevations of 2-3X normal can weaken heart enough to lead to deathheart enough to lead to death

high extracellular potassium high extracellular potassium concentrations can cause a decrease in concentrations can cause a decrease in the resting membrane potential in the resting membrane potential in cardiac muscle fiberscardiac muscle fibers

lower resting membrane potential lower resting membrane potential decrease in AP potential decrease in AP potential weaker weaker contractioncontraction

Excess calcium causes opposite effectExcess calcium causes opposite effect heart goes into spastic contractionheart goes into spastic contraction due to direct influence of calcium ions in due to direct influence of calcium ions in

exciting the cardiac contractile processexciting the cardiac contractile process deficiency in calcium will cause flaccidity, deficiency in calcium will cause flaccidity,

similar to excess potassiumsimilar to excess potassium changes due to calcium are rare, blood changes due to calcium are rare, blood

levels are tightly controlledlevels are tightly controlled

TemperatureTemperature

increased T will increase HR, sometimes as much increased T will increase HR, sometimes as much as 2Xas 2X

decreased T will cause decreased HR, as low as decreased T will cause decreased HR, as low as few bpm when body temperature is 60-70few bpm when body temperature is 60-70 F, near F, near deathdeath

moderate T increase can enhance the contractile moderate T increase can enhance the contractile strength of the heartstrength of the heart

prolonged elevation in T can cause an exhaustion prolonged elevation in T can cause an exhaustion of the metabolic systems of the heart, causing of the metabolic systems of the heart, causing weaknessweakness

Blood TransportBlood Transport

arteries carry oxygenated blood (except pulmonary arteries carry oxygenated blood (except pulmonary artery)artery)

can withstand high pressurescan withstand high pressures composed of connective tissue and smooth musclecomposed of connective tissue and smooth muscle from aorta (elastic as well as muscular), through from aorta (elastic as well as muscular), through

arteries, arterioles, metarterioles, and finally, arteries, arterioles, metarterioles, and finally, capillariescapillaries

arterioles: smooth muscle; can constrict and dilate arterioles: smooth muscle; can constrict and dilate dependent on peripheral blood needsdependent on peripheral blood needs

metarterioles are less muscularmetarterioles are less muscular

capillaries are microscopic blood capillaries are microscopic blood vessels which contain ~5% of the total vessels which contain ~5% of the total blood volumeblood volume– single layer of endothelial cells, may abut single layer of endothelial cells, may abut

the membranes of surrounding cellsthe membranes of surrounding cells– density may be 2-3,000/ mmdensity may be 2-3,000/ mm22

– capillary density is higher in cardiac musclecapillary density is higher in cardiac muscle– precapillary spinchter controls the mouth of precapillary spinchter controls the mouth of

the capillary, local control of BF in the the capillary, local control of BF in the capillaries of specific tissuescapillaries of specific tissues

– ~1.5 seconds to pass a blood cell through ~1.5 seconds to pass a blood cell through an average capillary (effective way to an average capillary (effective way to exchange)exchange)

Blood pressureBlood pressure

surge of blood enters the aorta every time surge of blood enters the aorta every time the L ventricle contractsthe L ventricle contracts

portion is stored in aorta, arteries and portion is stored in aorta, arteries and arterioles cannot handle the rapid run off arterioles cannot handle the rapid run off of blood equal to ejectionof blood equal to ejection

causes a pressure wave through the causes a pressure wave through the arterial system (pulse)arterial system (pulse)

Mean arterial pressure (MAP): average Mean arterial pressure (MAP): average pressure in the arterial system during the pressure in the arterial system during the cardiac cyclecardiac cycle– spend more time in diastole, it is a little less spend more time in diastole, it is a little less

than the average of systole and diastolethan the average of systole and diastole

VeinsVeins

blood flows from capillaries into venules to blood flows from capillaries into venules to veinsveins

blood from lower body enters heart via blood from lower body enters heart via inferior vena cavainferior vena cava

blood from the head and shoulders blood from the head and shoulders empties into the superior vena cavaempties into the superior vena cava

when blood enters venules, the impetus when blood enters venules, the impetus for flow is minimal (low pressure)for flow is minimal (low pressure)

blood returns viablood returns via

1. Flap-like valves (one-way) at short intervals 1. Flap-like valves (one-way) at short intervals in the veinsin the veins

2. Valves are easily compressed by neighboring 2. Valves are easily compressed by neighboring musclesmuscles

couple the one-way valves with the couple the one-way valves with the compression, milking action returns bloodcompression, milking action returns blood

65% of blood volume is in the veins at rest65% of blood volume is in the veins at rest veins are considered capacitance vessels veins are considered capacitance vessels

and reservoirs for bloodand reservoirs for blood