L6: Physiologic Changes of Bedrest

What are potential conditions that may require bedrest?

• Respiratory Failure (e.g., Acute Respiratory Distress)

• Spinal Cord Injury

• Burns

• Sepsis / Multi-Organ Failure

• Multi-Trauma

T/F: Bedrest has an effect on every major organ system

True

With bedrest there is an initial fluid shift from the ________ to the ________

Extremities, Trunk

Considering patients on bedrest, what does the initial fluid shift cause in relation to the heart?

Increased venous return to the right atrium

Increased venous return to the right atrium causes stimulation of _________ which is a _________

Atrial Naturetic Peptide (ANP), Vasodilator

What occurs as a result of Atrial Naturetic Peptide?

• Dilates afferent glomerular arteriole which causes increased GFR 

• Increased GFR causes increased urine output & renal secretion of Na+ 

• Consequently… increased urine output and secretion of Na+ causes low circulating plasma volume

Increased Venous Return also causes decreased expression of ________ occurs from the activation of ________ and ________

Anti-Diuretic Hormone (ADH), Aortic arch, Carotid sinus baroreceptors
This also leads to diuresis (which can cause hypovolemia)

With the fluid shift that occurs with patients on bedrest, what occurs for these patients who have Type 2 Diabetes?

• Increased Insulin Resistance occurs in individuals with Type 2 Diabetes
  

• This is due to decreased expression of the Glut 4 Transporter  

  • Glut 4 Transporter is a protein that moves sugar from the blood to the muscle

Decreased Glut 4 Transporter can be seen in as little as ________ of bedrest

3 days

If someone has diuresis this can increase the risk for ________

[Hint -- impact of bed rest on hematology]

Hypovolemia

What hematological changes occur as a result of hypovolemia?

• Greater loss of plasma (relative to RBC) causes increased hematocrit 

• Increased Hematocrit leads to:

  • Increased viscosity of blood

  • Increased resistance to blood flow (which stresses the CV system)

  • Increased risk for DVT

Skeletal muscle ________ occurs as a result of bed rest

Atrophy

What hematological changes occurs as a result of skeletal muscle atrophy (due to bed rest)?

• Decreased O₂ Carrying Capacity 

  • With skeletal muscle atrophy there is a lesser demand for O₂

• There is an insufficient stimulus (because there is ""sufficient"" circulating O2 d/t lack of demand) → kidneys do not secrete erythropoietin 

• Decreased erythropoietin leads to..

  • Decreased erythropoiesis in red bone marrow

  • Decreased RBC production
    

Hypovolemia (↓ blood volume) is indicative of ________ circulating blood plasma and ________ central venous pressure

↓, ↓

What effect can hypovolemia have on blood pressure?

• Decreased blood volume can cause low BP which can cause orthostatic hypotension

  • So low BP would be the initial cause of O.H. 

• Over time (so if a patient is on bedrest for a long period of time), baroreceptor sensitivity decreases due to lack of adequate stimulation

• This decreased sensitivity causes an an impaired baroreceptor reflex in response to standing → orthostatic hypotension 

  • Impaired baroreceptor reflex would be a secondary cause of O.H.
    

What effect does hypovolemia on the cardiovascular system (e.g., SV, VO2 max, Q, etc.)?

• Decreased Stroke Volume

  • This is due to ↓ ventricular filling and ↓ end diastolic volume (EDV)

• Dec stroke volume also leads to

  • ↓ VO2 Max 

  • ↓ Cardiac Output (Q) if chronic OR NO CHANGE if acute 

How does cardiac output (Q) change with ↓ Stroke Volume?

• Acutely -- NO CHANGE 

  • ↑ Resting HR to compensate and attempt to maintain Q

  • Resting HR ↑ by 10 bpm after 4 weeks of bed rest

• Chronc -- ↓ Cardiac Output
  

How does a patient's aerobic power change with bedrest? Why?

• ↓ Aerobic Power 

  • This is due to cardiac muscle atrophy

  • Which therefore leads to decreased exercise tolerance

What respiratory system changes occur due to hypovolemia (that occurs with bedrest)?

• Impaired Mucocilliary Escalator 

  • Occurs d/t decreased blood volume, dehydration, and hypovolemia

  • MCE depends heavily on fluid / adequate volume

  • Causes mucus pooling in the lower airways

• Dehydration = Thicker Mucus, ↓ Expectoration

What other respiratory system changes occur from bedrest?

• Narrowed Airways (fewer deeper breaths)

  • ↓ Compliance (stiffness in lungs and chest wall)
    

• Stiffness causes...

  • ↓ Lung Volume & Capacities

  • ↓ Airflow rates

  • ↓ Respiratory muscle strength

  • Alterations in gas exchange

  • ↓ Vital Capacity

  • ↓ Residual Volume

• Increased Respiratory Rate to Compensate
  

Less exercusion of the chest can lead to what other impairments?

• Decreased Cough -- increases risk of infection 

• Contractures of the costo-vertebral joints

• Atelectasis

What changes to the musculoskeletal system occurs with bedrest?

• ↓ Weight Bearing

• ↓ Number / Magnitude of Contractions in Postural Muscles

  • Leads to muscle atrophy 

• Antigravity muscles atrophy more than antagonistic muscle groups

  • Greater weakness of the Quads and PFs vs Hamstrings and DFs

What skeletal adaptations occur as a result of bedrest?

• Disuse Osteopenia (loss of bone mass)

  • ↑ Osteoclastive Activity (& ↓ Osteoblastic Activity)
    

• Bony sites in WB bones are most susceptible for disuse osteopenia

  • e.g., calcaneus, femoral neck, and spine

What thermoregulatory changes occur as a result of bed rest?

• ↑ Resting Core Body Temperature

• ↑ Body Temperature with Exercise → Increased HR

  • Because if pt has inc. resting core body temp, then exercise will only increase body temperature further 
    

• ↓ Regulation of Body Heat

  • Altered Sweating Responses

    • Can lead to fatigue, cramping, syncope (dizziness), & heat stroke

    • Also causes limited exercise tolerance

What is the key takeaway regarding the implications of bedrest?

Bedrest (by itself) has major implications for our patients and their ability to maintain and sustain function. 

We need to consider the length of time a patient has been on bedrest and how this might impact the patients ability to function (along w/ other co-morbid conditions)