Cardiovascular Function
Adequate exchange of respiratory gases and metabolic substances depends on the efficiency of the cardiovascular system, including the heart, arteris, venous channels, and lymph vessels. Physical immobility produces three critical changes in the adaptive ability of this system to carry blood to and from capillaries: (1) vasomotor control, (2) blood return to the heart, and (3) venous statis.
Orthostatic hypotension is the inability of the autonomic nervous system to adapt readily to a sudded change from a recumbent to an upright position. Equalization of the blood supply throughout the body is affected adversely during prolonged bedrest. The valves within the veins require muscle action to assist them in opening to permit venous return of blood to the heart. Without adequate muscle contraction, tone is lost, muscles lose strength, and venous blood tends to pool in the lower extremities. The decrease in neurovascular reflex control of blood vessels during bedrest may be caused by the lower pressure, higher flow, and increased diameter of vessels in the supine position.
Though rest in considered an essential factor in the treatment of disease, a second major change in cardiovascular performance resulting from immobility has been identified. The heart suffers an increased work load in the resting supine position resulting from the altered distribution of blood throughout the body. Gravity provides downward pressure in the erect position. When this is relieved by lying down, the circulating blood volume is increased, placing an additional load on the right side of the heart as more blood returns from the periphery to the heart.
Periodically, the patient on bedrest is required to exert strain on his heart in what is known as the Valsava maneuver. This is the act of fixing the thorax, holding one`s breath, and thereby forcing pressure against the closed glottis-the action one takes when straining to defecate. Intrathoracic pressure occurs, resulting in a rush of blood to the heart. This maneuver may be used by a bedfast patient as often as 20 to 30 times per hours as he uses his arms and the muscles of the upper trunk to change position in bed.
Thrombus formation is the third hazard associated with cardiovascular functions during immobility. Venous stasis occurs, leading to hypercoagulability of the blood. External pressure is exerted by the patient`s which contributes to an increased viscosity of the blood and may in turn lead to clotting. Also, the blood level of calcium is increased during rest. The calcium may combine with material from platelets to from thrombin (a percursor for the conversion of fibrinogen to fibrin), producing hypercoagulability.
The intima of blood vessels may be easily damaged by maintaining one position for a prolonged time, especially if one extremity rests on the other. Platelets will then form a matrix over the damaged area and may form a clot.
Range-of-motion exercises to assist in venous flow and the restoration or maintenance of muscle tone will be important to your care of any patient on bedrest. Consult a nursing fundamentals text for specific information on doing range-of-motion exercises. Self-care should be encouraged as much as possible within the limits set by the medical regimen. Frequent changes in position should be required, especially for providing a change from horizontal to vertical whenever possible. Patient teaching should help the patient learn how to move in bed with a minimum of effort; an overbed trapeze can be provided for this purpose.
One of the best examples of nursing support for adaptation is that of preventing constipation. Positioning the patient in a well-supported position on the bedpan or commode helps to relieve the strain that might otherwise put too much work load on the heart.
References :
Browse, N.L., Physiology and Pathology of Bedrest. Springfield, III.: Charles C. Thomas, Publisher, 1965.
Olson, Edith V., “The Hazards of Immobility”, American Journal of Nursing, 67: No.4, 1971.
Murray, RB and Zentner JP., Nursing Concepts for Health Promotion, Second Edtion, Prentice-Hall, Inc, Englewood Cliffs, N.J, 1979.
