Cardiovascular system II

Muscle Contraction and Heart Rate

Process of Muscle Contraction:
- Relaxation occurs after contraction, all within less than a second.
- Normal heart rate is approximately 60 beats per minute (bpm), specifically around 68 for the SA node.
Heart Rate Dynamics:
- If the heart rate is 60 bpm:
  - Heart contracts once per second.
- At 20 bpm:
  - Heart beats slower at about 1 every 3 seconds.
- At 80 bpm:
  - Heart contracts three times per second.

Calcium Dynamics:
- Involve calcium entering cells, binding troponin, allowing myosin to bind, and the power stroke to occur.
- ATP allows myosin to release and pump out calcium.

Common Assessment Methods:
- Besides EKGs, monitoring heart rate and checking for chest pains are critical.
- Respiratory rate and blood pressure also provide insights into heart function.
Types of Monitoring:
- Electrocardiogram (ECG/EKG):
  - Non-invasive technique using electrodes to monitor electrical signals of the heart.
  - Smartwatches can provide basic heart monitoring but may lack detailed insights.

Leads and Placement:
- Standard 3-lead setup includes one on each wrist and one on the ankle.
- A 12-lead EKG offers more comprehensive mapping of electrical activity in the heart.

Key Components and Functions:
- SA Node: initiates the heartbeat with action potentials.
- AV Node: receives signals from the SA node.
- Bundle of His: transmits impulses down to the Purkinje fibers.
Action Potentials:
- Electrical signals facilitate contractions of different heart sections.
- Need to minimize patient movement during an EKG for accurate readings due to interference from muscle movement.

Waves and Depolarization:
- P Wave: Represents atrial depolarization.
- QRS Complex: Indicates ventricular depolarization.
- T Wave: Marks ventricular repolarization.
  - Atrial repolarization occurs simultaneously but is overshadowed by ventricular depolarization.
Segments:
- PQ Segment: Duration of time between atrial contraction and ventricular contraction (AV delay).
- QT Interval: Duration for the ventricles to contract and repolarize.

Heart Attack Indicators:
- ST elevated myocardial infarction shows distinct patterns in EKG readings.
Heart Rate Calculation:
- Counting the number of R waves in a set period (e.g., 6 seconds) shows beats per minute.

Tachycardia: Elevated heart rate (above 100 bpm).
Bradycardia: Slower heart rate (below 60 bpm).
Heart Block Variations:
- First Degree: Slowed conduction with longer PQ interval.
- Second Degree: Increased P wave count for each QRS complex.
- Third Degree: Complete disconnection between atrial and ventricular contractions.
Fibrillation Types:
- Atrial and ventricular fibrillation, resulting in ineffective pumping of blood.

Blood Pressure Basics:
- Normal range is generally around 120/80 mmHg (systolic/diastolic).
- Systolic represents contraction pressure, while diastolic is at rest.
Blood Flow Dynamics:
- Unidirectional flow maintained by heart valves: tricuspid, bicuspid (mitral).
- Chordae tendineae and papillary muscles support valve function during ventricular contraction.

Contractile Phases:
- Isovolumetric Contraction: No volume change; pressure builds before ventricle ejects blood.
- Ventricular Ejection: Blood is forcefully exited from ventricles.
Stroke Volume Calculation:
- Determined by end diastolic volume minus end systolic volume.
- Average stroke volume: Approximately 70 ml per heartbeat.

Ejection Fraction:
- Key measure of heart performance; the percentage of blood pumped out from the ventricles.
- Heart failure may reduce ejection fraction to below 35%.