Click on the body part for specific impairments with each system.
During bedrest and inactivity, the brain is not getting the normal feedback for all the homeostasis loops that keep all systems in balance. Joints are not providing positional change information, inner ear is not providing orientation change information, baroreceptors in the blood vessels are not providing stretch and change information. Sleep/wake cycles are disrupted and delirium and disorientation are very common. Anxiety and depression are also common, especially in the elderly.
Weakness and decreased compliance of the diaphragm, and intercostal muscles reduces the effectiveness of the lungs to deliver sufficient oxygen to the bloodstream and remove waste gasses. Weakness of the muscles of inspiration also make it difficult to wean from the ventilator. Decreased movement of secretions increases risk of colonization of bacteria, leading to pneumonia and collapse of the alveoli (or air spaces). This further reduces ventilation, leading to ventilation / perfusion mismatch and shunting, where blood circulates through the lungs without exchanging gasses. These conditions further contribute to hypoxia.
The heart muscle gets weaker, and efficiency of each beat is reduced. Stroke volume is reduced, and therefore, resting heart rate must increase to meet the demand. The cardiac muscle needs calcium and other minerals for normal contraction. Immobility and lack of weight bearing contribute to dysregulation of minerals also contributes to cardiac insufficiency.
Disruption of the normal homeostatic mechanisms and feedback loops is manifested metabolically with increased insulin resistance, hyperglycemia and lipid dysregulation.
Immobility causes the movement of the gut (Peristalsis) to slow down. This leads to fecal impaction. This can increase the risk of intestinal aspiration into the peritoneal cavity, and the toxins released from endothelial breakdown in the lining of the gut are a primary source of tumor necrosis factor – alpha (TNF-α) which is implicated in the SIRS-MODS cascade. Additionally, immobility reduces the effectiveness of nutrient transport from the intestines into the cells. This can contribute to malnutrition and increased risk of delirium and further complicate organ dysfunction.
Immobility and especially non-weight bearing, leads to loss of calcium from the long bones. This is seen in astronauts as well as bed-ridden patients when the bones are not being loaded by gravity. The increased calcium is excreted through the urine and the kidneys. There is increased risk of kidney stones as they filter increasing levels of calcium and other minerals.
Neuromuscular pathology is a major problem with immobility. The term has been coined “Post-ICU Neuromyopathy” since the problem involves the nerves and neuromuscular junction, as well as the muscle tissue itself. Muscle damage can last years after discharge from the hospital, and can result in long-lasting disability. The heart muscle and respiratory muscles are affected as well as the muscles involved with bodily movement and function.
Just 20 minutes of uninterrupted pressure on the skin can begin the process of skin breakdown, through occlusion of the smallest blood vessels, called the arterioles, (ischemic change) and direct compression of the skin cells themselves. Often the damage occurs deep at the bone interface, and by the time redness is seen externally, significant damage has already occurred. In addition to ischemia, immobility also increases the risk of moisture, malnutrition and decreased oxygenation of skin cells through incontinence, changes to the gut and to the lungs, respectively.
Joints and Bones
Joint contraction and stiffness is common from lack of movement, and the feedback loops to the brain about position, muscle-tendon and ligament length and tension are not active. Joint pain is a common side effect of bed rest, even in the absence of joint pathology. Joints require cyclical loading and movement for nutrition. The bones lose calcium and other minerals when there is no weight going through them. Additionally, the joints lose proprioception which is the ability to know their position relative to end of range of the joint, or relative to gravity. This is an important factor for balance, and a risk factor for falling in patients who have been immobile for any length of time.