Lab 5

Objectives of Laboratory #5

Investigate heart sounds and their correlation to cardiac cycle events:

• Understand the significance of heart sounds in diagnosing cardiac conditions and how they change during different cardiac phases.

Determine blood pressure under resting and exercising conditions:

• Measure blood pressure metrics both at rest and during physical activity to assess cardiovascular health and response to exertion.

Observe an electrocardiogram (ECG) under resting and exercising conditions:

• Analyze the changes in the ECG patterns to understand heart electrical activity variations during differing physiological states.

Investigate the induction of bradycardia by facial immersion:

• Explore how the diving reflex affects heart rate and discuss its implications for understanding heart rate regulation in response to environmental stressors.

Study some aspects of circulation:

• Examine the functioning of veins and arteries, including how blood flow is regulated and the physiological differences between active and passive hyperemia.

Heart Sounds

Heart Sounds: Heard with a stethoscope, typically described as "lub-dub".

• "Lub": Produced by the closure of the atrioventricular (AV) valves (tricuspid and mitral valves) at the onset of ventricular systole (contraction), marking the beginning of the heartbeat.

• "Dub": Associated with the closure of the semilunar valves (aortic and pulmonary valves) following ventricular systole, indicating the end of one cardiac cycle and the start of the next.

Recording Heart Sounds: Procedure

1. Use a stethoscope in a quiet setting to minimize background noise.

2. Position the stethoscope in the fifth left intercostal space (tricuspid area) to hear heart sounds clearly, focusing on the apex beat for the best sound transmission.

3. Take note of the pitch, duration, quality (e.g., sharp, dull), and timing related to the pulse felt at the wrist and carotid artery.

4. Record all observations during listening, including any variations with breathing or physical exertion to further understand physiological changes.

Blood Pressure Determination

Auscultatory Method: An indirect method to measure blood pressure, using a sphygmomanometer (blood pressure cuff) and stethoscope.

• Korotkoff Sounds: Sounds used to determine systolic and diastolic pressures through the process of occluding and releasing blood flow in the brachial artery.

• The first sound (systolic pressure) occurs when blood starts to flow through the artery, indicating the maximum pressure during contraction, and the last sound (diastolic pressure) indicates the return to laminar flow (absence of sound), reflecting the lowest pressure in the circulatory system.

Procedure:

1. Subject positioned comfortably, ensuring the arm is at heart level for accurate readings.

2. Cuff applied 2-3 cm above the inside elbow, properly aligned with the brachial artery to ensure the most accurate placement.

3. Inflate the cuff to a pressure higher than anticipated systolic pressure, then gradually release pressure while listening for Korotkoff sounds to note the systolic and diastolic pressures.

4. Conduct measurements in both upright and recumbent positions following periods of rest to observe variations in blood pressure and assess orthostatic changes.

Electrocardiogram (ECG) & Cardiac Output

Cardiac Output (Q): Represents the amount of blood the heart pumps per minute; calculated as:
Q = HR \times SV

• where HR is heart rate (beats per minute) and SV is stroke volume (the volume of blood pumped with each beat).

Stroke Volume (SV): Defined as the difference between end diastolic volume (EDV) and end systolic volume (ESV):
SV = EDV - ESV

• Changes in SV can indicate various cardiac conditions; understanding these metrics is crucial for assessing heart health.

Cardiac output can vary based on individual fitness levels. Generally, it increases in healthy individuals during exercise due to significant heart rate increases as the body demands more oxygen.

• Cardiac output is also regulated by physiological factors, including metabolic demands and changes in vessel diameter, supported by autonomic nervous system activity (sympathetic and parasympathetic regulation).

Methods of Measuring Cardiac Output

Techniques may include MRI, Doppler ultrasound, thermodilution, or employing a pulse transducer in conjunction with blood pressure measurements to estimate cardiac output accurately under varying conditions.

Reflex Bradycardia: Diving Reflex

Diving Reflex: A physiological response observed in mammals that optimizes oxygen usage while submerged; characterized by bradycardia (decrease in heart rate) and selective peripheral vasoconstriction, which prioritizes blood flow to essential organs like the brain and heart while reducing it in peripheral areas.

• Reflex studied by having students perform controlled breath-holding and face immersion in varying water temperatures to observe heart rate changes and physiological responses, providing insights into autonomic regulation and stress response mechanisms.

Circulation

Veins: Contain valves ensuring one-way blood flow despite gravitational forces, playing a crucial role in venous return against gravity, especially in the extremities.

• Types of Hyperemia:

  • Active Hyperemia: Increased blood flow in response to enhanced metabolic needs and activities (e.g., during heat exposure or physical exercise).

  • Passive Hyperemia: Accumulation of blood due to obstructed venous return, which can be illustrated by applying pressure or occlusion to limbs and observing the effects on blood flow.

• Explore circulatory dynamics through simple exercises tracking venous pressure and capacity changes with varied physical actions (e.g., lifting arms, applying tourniquets, etc.) to better understand circulation regulation in real-time activities.