From the Guidelines
Cardiac reserve is the heart's ability to increase its output beyond resting levels during periods of increased demand, and its normal value allows the heart to increase its output by about 4-5 times above the resting cardiac output, with a maximum heart rate typically achieved at around 220 minus the person's age in years 1.
Definition and Normal Value
Cardiac reserve refers to the heart's ability to increase its output beyond resting levels during periods of increased demand, such as during exercise or stress. The normal cardiac reserve allows the heart to increase its output by about 4-5 times above the resting cardiac output. At rest, a typical adult has a cardiac output of approximately 5 liters per minute, which can increase to 20-25 liters per minute during maximal exercise in a healthy individual.
Key Components
This reserve capacity is achieved through increases in both heart rate and stroke volume.
- Heart rate can typically increase from a resting rate of 60-80 beats per minute to a maximum of about 220 minus the person's age in years, as estimated by the equation 220 - age 1.
- Stroke volume can increase by 50-60% above resting values through enhanced ventricular filling and more forceful contractions.
Clinical Significance
Cardiac reserve decreases with age and various cardiovascular conditions like heart failure, where the heart cannot adequately increase output to meet metabolic demands. Regular aerobic exercise can improve cardiac reserve by increasing maximum cardiac output and making the heart more efficient at rest. This reserve capacity is essential for maintaining adequate tissue perfusion during physical activity and represents an important measure of cardiovascular health and functional capacity.
Assessment
The assessment of cardiac reserve can be done through various methods, including exercise stress testing and stress echocardiography, which can provide valuable information on the heart's ability to increase its output in response to increased demand 1.
- A normal response to stress testing involves the augmentation of function in all LV segments and increases in LVEF and cardiac output.
- The presence of a new or worsening wall motion abnormality identifies ischemia, while the improvement of regional wall motion by ≥1 grade in dysfunctioning segments characterizes recruitable viable myocardium. In clinical practice, the most recent and highest quality study recommends using a cut-off value of ≥5% increase in LVEF to define global contractile reserve in patients with no regional resting dysfunction 1.
From the Research
Definition of Cardiac Reserve
- Cardiac reserve is defined as the difference between basal and maximal cardiac performance 2
- It is an integrative measure of overall cardiac function, accounting for both flow- and pressure-generating capacities of the heart 3
Measurement of Cardiac Reserve
- Cardiac power output (CPO) is a measure of cardiac reserve, calculated as the product of cardiac output and mean arterial pressure, expressed in watts 3, 4
- CPO can be measured non-invasively using techniques such as rebreathing inert gases, impedance cardiology, thoracic bioreactance, estimated continuous cardiac output technology, and transthoracic echocardiography coupled to cardiopulmonary exercise testing 5
Normal Value of Cardiac Reserve
- The normal value of cardiac reserve can vary depending on the population and method of measurement 4
- In one study, cardiac reserve ranged from 0.27 to 5.65 W, indicating a 20-fold difference between the most impaired cardiac function and that of the fittest subject 4
- In another study, peak CPO was higher in athletes (5.87 ± 0.75 W) than in non-athletes (5.4 ± 0.69 W), and cardiac reserve was also higher in athletes (4.92 ± 0.66 W) than in non-athletes (4.26 ± 0.61 W) 3
Clinical Significance of Cardiac Reserve
- Cardiac reserve is a major determinant of exercise capacity in a population of normal subjects and patients with heart disease 4
- A lower cardiac power output reserve is associated with impaired cardiovascular reserve, exercise intolerance, and adverse outcomes in heart failure with preserved ejection fraction 6
- Cardiac power index, a measure of cardiac reserve, can be used to stage heart failure patients and determine the optimal time for implantation of mechanical circulatory support 2