Cardiovascular System Adaptation

ASEN 5016 Lecture 17: Cardiovascular System Adaptation

Guest Lecturer: Dr. Louis Stodieck

OBJECTIVES

1. Describe basic cardiovascular anatomy and physiology

2. Identify factors governing cardiac function and peripheral flow

3. Explain short term response to space flight (post-insertion to days)

4. Explain long term adaptation to space flight (weeks to months)

5. Summarize post-flight effects / recovery

6. Describe countermeasures to Cardiovascular Deconditioning

1. Basic cardiovascular anatomy and physiology

Cardiac anatomy

chambers, valves, arteries and veins
electrical conduction tissues and nerves

Cardiac physiology

cardiac electrical activity
cardiac mechanical activity

2. Factors governing cardiac function and peripheral flow

Cardiac Contractility (CC)

End Diastolic Volume (EDV)

Heart Rate (HR)

Stroke Volume (SV)

Cardiac Output (CO)

Total Peripheral Resistance (TPR)

Blood Pressure (BP) – Systolic and Diastolic

Control of cardiac function – intrinsic and extrinsic

3. Short term response to space flight (post-insertion to days)

Post Insertion (minutes to hours)

Loss of hydrostatic pressure
Cephalic fluid shift
Heart volume increases (~fluid swelling)
Increased EDV causes decreased HR, TPR and contractility
CVP decreases (unexpected response,complex series of physical and physiological mechanisms)
Physiological responses tend to balance the immediate physical reactions induced by microgravity

Short Duration Response to Microgravity (hours to days)

Fluid shift maintained (facial puffiness, engorged veins)
Increased diuresis
Decreased water intake

Loss of blood plasma volume and total body water

EDV decreases lead to increase in HR over time

4. Long term adaptation to space flight (weeks to months)

Continued increase in HR

Presumed decrease in baroreceptor reflex responses

Exaggerated response to LBNP (HR increase)

System tends to stabilize

Heart volume decrease (atrophy)

Heart rhythm disturbances noted

Disproportionate loss of red blood cell mass to plasma (?)

Changes in microvasculature (?)

Increased venules and decreased arterioles

5. Post Flight Effects / Recovery

Orthostatic Intolerance (hours)

Fluids shift to lower extremities
EDV decreases causing increased HR
Control of BP may not be adequate
Syncope potential
Weakened leg muscles results in reduced venous valve blood pumping action

Elevated HR (several days)

Similar to disuse / sedentary effects

Anemic-like conditions after rehydration (RBC dilution)

Duration of the recovery period depends on duration of exposure to reduced-gravity

6. Countermeasures to Cardiovascular Deconditioning

In-flight

Exercise
Lower Body Negative Pressure Device (LBNP)
Russian Chibis (LBNP) and Penguin (elastic load) suits
Neck cuff (positive or negative pressure)
Thigh cuffs

Pre-landing

Saline fluid loading
G-suits (positive pressure, lower torso)
Recumbent seating

Post-mission

Exercise, time