External manifestations of cardiac activity. Regulation

of heart work

ATRIAL SYSTOLE 0,1sec

Ventricle systole 0,33sec

VENTRICLE SYSTOLE 0,33sec

Sponsored

Medical Lecture Notes – All Subjects

USMLE Exam (America) – Practice

VENTRICLE SYSTOLE 0,33sec

COMMON PAUSE 0,37sec

COMMON PAUSE 0,37sec

COMMON PAUSE 0,37sec

External manifestations of cardiac activity

• Mechanical (apex beat, pulse)

• Sound (heart tones)

• Electrical (ECG)

Sphygmogram

1.Anacrote2. Catacrote3. Incisure4. Dicrotic rise

FREQUENCY

MAGNITUDE

VELOCITY

rarus

altus

frequens

tardus

сеler

parvus

PULSUS CHARACTERISTICS

SYSTOLIC TONE

components:1. VALVULAR (A-V valves closure)

2. MUSCULAR asynchronous contraction

3. VASCULAR (aorta vibration )

4. TENDON (chordae tendineae tension)

SYSTOLIC TONE. PLACES OF BEST HEARING

• heart apex projection (IV-V intercostal space on the left, 1,5-2 cm medial from the medioclavicular line)

•the place of junction of sternum body and xyfoid processus

DIASTOLIC TONE

components:1. VALVULAR (semi-lunar

valves closure)

2. VASCULAR (blood rebound )

DIASTOLIC TONE. PLACES OF BEST HEARING

• II right intercostal space along the parasternal line (over aorta).

• II left intercostal space along

the parasternal line (over pulmonary artery).

Right atrium excitation- ascending part of P-wave

Spreading of excitation from SA to AV node – interval PQ

Excitation of left part of intraventricular septum – Q wave

Excitation of ventricles’ apexes – R wave

Spreading of excitation from endocardium to epicardium

- QRS complex

Depoloarization in ventricles completed – ST segment

Quick final repolarization of the ventricles – T wave

MECHANISMS OF HEART REGULATION

•INTRACARDIAC REGULATION

•EXTRACARDIAC REGULATION

INTRACARDIAC REGULATION

1.Myogenic

a)Geterometric (Franc-Starling law)

b)Gomeometric (Boudichi “staircase”)

2.Peripherial heart reflexes

Franc-Starling law

• The more heart chambers are filled with blood during diastole, the greater force of contraction they develop during systole

• This prevents ventricles from dilation allowing them to eject all the blood

Boudichi “staircase”

• At high frequency of stimulation force of contraction increases regardless of the cardiomyocytes length

Peripheral heart reflexes

• Are performed by methasympathetic system in the heart

• They restrict Frank-Starling law so that to readjust cardiac output to the systemic BP

• The most prominent reflex is from right atrium to left ventricle

Peripheral heart reflexes

• In case of high systemic BP high threshold receptors are activated in right atrium and via cholinergic fibers decrease heart rate & stroke volume in the left ventricle

• In case of low systemic BP low threshold receptors are activated in right atrium and via adrenergic fibers increase heart rate & stroke volume in the left ventricle

EXTRACARDIAC REGULATION

•Nervous regulation (SNS, vagus)

•Humoral regulation (Ad, Thyroxin)

HEART INNERVATION

Mechanism of sympathetic stimulation

• Adrenalin opens Na+ channels• Na+ influx depolarises myocardiocyte’s

membrane• Threshold decreases (“+” batmotrophic effect)• Time of SDD decreases (“+” chronotrophic

effect)• Conductivity increases (“+” dromotrophic effect)• Contractility increases (“+” inotrophic effect)

Influence of sympathetic nerve stimulation on AP of the pacemaker ( A – before, B – after stimulation)

ΔV1, Δ V2 – thresholds of depolarization, α1, α2 – angler, showing the steepness of depolarization, t1, t2 – time of slow diastolic

depolarization

Influence of vagus stimulation on AP of the pacemaker ( A – before, B – after stimulation)ΔV1, Δ V2 – thresholds of depolarization, α1, α2 – angler, showing the steepness of depolarization, t1, t2 – time of slow diastolic depolarization

Mechanism of parasympathetic stimulation

• Acetylcholine opens K+ channels• K+ efflux repolarises myocardiocyte’s membrane• Threshold increases (“-” batmotrophic effect)• Time of SDD increases (“-” chronotrophic effect)• Conductivity decreases (“-” dromotrophic effect)• Contractility decreases (“-” inotrophic effect)