Physiological Reserve Capacity

Organ-Specific Reserve

The decline in physiological reserve capacity occurs at approximately 1% per year after age 40, creating vulnerability to stressors as we age, according to the Anaesthesia guideline society 1
The cardiovascular system demonstrates reserve through its ability to increase cardiac output approximately 20-fold during acute stress, with tissue perfusion increasing tenfold and both heart rate and stroke volume capable of tripling, as stated by the Reviews in Endocrine and Metabolic Disorders guideline society 2
The respiratory system shows reserve through ventilatory capacity, measured as the difference between maximum voluntary ventilation (MVV) and the ventilation achieved at peak exercise, with a normal reserve being at least 15%, according to the American Journal of Respiratory and Critical Care Medicine guideline society 3
Coronary circulation exhibits reserve through its ability to increase blood flow 3-fold in adults in response to increased myocardial oxygen demand, as reported by the Circulation guideline society 5

Sarcopenia (loss of skeletal muscle mass, strength and function) represents a decline in musculoskeletal reserve that precedes frailty and can be disease-related, activity-related, or nutrition-related, according to the Clinical Nutrition guideline society 6
Frailty represents a state of vulnerability and non-resilience with limited reserve capacity across major organ systems, leading to reduced capability to withstand stress such as trauma or disease, as stated by the Clinical Nutrition guideline society 6

The net overall physiological reserve results from the integration of individual organ reserves, with the weakest system often becoming the limiting factor during stress, according to the Anaesthesia guideline society 1
During acute stress, the body's response involves coordinated changes across multiple systems - for example, in the "fight or flight" reaction, cardiovascular, respiratory, and metabolic systems all increase their activity in concert, as reported by the Reviews in Endocrine and Metabolic Disorders guideline society 2

Pre-operative assessment of elderly patients should include evaluation of age-related physiological decline, multi-morbidity, and frailty to determine peri-operative risk, according to the Anaesthesia guideline society 10

Age is a primary factor in declining physiological reserve, with both fit and aged normal subjects showing reduced ventilatory reserve compared to younger individuals, as stated by the American Journal of Respiratory and Critical Care Medicine guideline society 3
Disease states significantly impact organ-specific reserves - for example, patients with pulmonary diseases have reduced ventilatory capacity and increased ventilatory demand, resulting in reduced ventilatory reserve, according to the American Journal of Respiratory and Critical Care Medicine guideline society 3
Nutritional status affects physiological reserve, with malnutrition contributing to sarcopenia and frailty, as reported by the Clinical Nutrition guideline society 6

Understanding a patient's physiological reserve is crucial for risk stratification before major interventions like surgery, according to the Anaesthesia guideline society 10
In trauma management, recognition of limited physiological reserve guides the decision to employ damage control surgery rather than definitive repair in severely injured patients, as stated by the Critical Care guideline society 8