[#1] Regulação do bombeamento cardíaco: DÉBITO CARDÍACO | MK Fisiologia

Summary

This video discusses the regulation of cardiac output, focusing on the relationship between stroke volume and heart rate in determining cardiac output. It explains how stroke volume is influenced by preload, afterload, and contractility, while heart rate is modulated by the autonomic nervous system. The sympathetic and parasympathetic systems affect heart rate by altering the action potential frequency and conduction speed in the heart. The video emphasizes that both stroke volume and heart rate can be adjusted to regulate cardiac pumping, particularly during physical activity or rest, and introduces the factors that affect stroke volume, which will be explained in future videos.

Takeaways

• 😀 The cardiac output (CO) is calculated by multiplying the stroke volume (SV) by the heart rate (HR), and represents the volume of blood pumped by the heart per minute.
• 😀 Stroke volume (SV) is the volume of blood ejected by the heart per beat and can be calculated by subtracting the final systolic volume from the final diastolic volume.
• 😀 To calculate cardiac output, you can multiply the stroke volume by the heart rate. For example, if the stroke volume is 75 ml and the heart rate is 68 beats per minute, the cardiac output will be 5100 ml per minute.
• 😀 Cardiac output can be regulated by altering either the stroke volume or the heart rate. An increase in stroke volume or heart rate results in higher cardiac output, while a decrease has the opposite effect.
• 😀 The heart rate is influenced by the autonomic nervous system, particularly the sympathetic and parasympathetic branches, which regulate the frequency of action potentials in the sinoatrial node.
• 😀 The parasympathetic nervous system decreases the heart rate during rest by releasing acetylcholine, which hyperpolarizes the membrane of pacemaker cells and delays action potentials.
• 😀 The sympathetic nervous system increases the heart rate during activity by releasing norepinephrine, which depolarizes the pacemaker cells, accelerating the firing of action potentials.
• 😀 The conduction velocity of action potentials between the atria and ventricles is also regulated by the autonomic nervous system, which affects the speed at which electrical signals are transmitted.
• 😀 Stroke volume is determined by three key factors: preload, afterload, and myocardial contractility. Changes in any of these factors will affect the stroke volume and, consequently, the cardiac output.
• 😀 Understanding how the autonomic nervous system and factors like preload, afterload, and contractility influence cardiac output is crucial for understanding how the heart adapts to different physical activities and states of rest.

Q & A

What is cardiac output and how is it calculated?

Cardiac output (CO) is the amount of blood the heart pumps per minute. It is calculated by multiplying stroke volume (SV) by heart rate (HR), i.e., CO = SV × HR.

How can stroke volume (SV) affect cardiac output?

Stroke volume is the volume of blood pumped by the heart with each beat. If the stroke volume increases, cardiac output also increases, and if it decreases, cardiac output decreases.

How does heart rate influence cardiac output?

Heart rate, or the number of heartbeats per minute, directly affects cardiac output. A higher heart rate increases cardiac output, while a lower heart rate reduces it.

What factors can regulate heart rate?

Heart rate is regulated by the autonomic nervous system, particularly through the sympathetic nervous system (which increases heart rate) and the parasympathetic nervous system (which decreases heart rate).

How does the sympathetic nervous system influence heart rate?

The sympathetic nervous system increases heart rate by releasing norepinephrine, which accelerates the depolarization of heart cells, causing the heart to beat faster.

What role does the parasympathetic nervous system play in regulating heart rate?

The parasympathetic nervous system decreases heart rate by releasing acetylcholine, which hyperpolarizes the heart's cells and slows their depolarization, leading to a slower heart rate.

What is stroke volume and how is it related to cardiac output?

Stroke volume is the amount of blood ejected from the heart per beat. It contributes to cardiac output, as CO is the product of stroke volume and heart rate. Changes in stroke volume will directly affect cardiac output.

What is pre-load and how does it affect stroke volume?

Pre-load refers to the initial stretching of the heart muscle before contraction. The greater the pre-load, the more the heart muscle stretches, which can increase stroke volume.

What is after-load and how does it influence stroke volume?

After-load is the resistance the heart must overcome to eject blood. An increase in after-load can decrease stroke volume, as the heart has to work harder to pump against higher resistance.

What is contractility and how does it impact stroke volume?

Contractility refers to the strength of the heart's contraction. Stronger contractions increase stroke volume, while weaker contractions reduce it.