What is the effect of inspiration on preload (ventricular filling)?

From the Guidelines

Inspiration increases preload to the right ventricle while decreasing preload to the left ventricle due to changes in intrathoracic pressure and venous return.

Key Points

• During inspiration, the decrease in pleural pressure (Ppl) increases the gradient for venous return to the right ventricle (RV), thereby increasing RV filling and preload 1.
• This decrease in Ppl also expands the pulmonary vessels, temporarily holding more blood in the lungs and reducing the amount returning to the left ventricle (LV), thus decreasing LV preload 1.
• The changes in Ppl and transpulmonary pressure (TP) during inspiration have significant effects on cardiac function, particularly in patients with conditions like ARDS, where lung compliance and vascular resistance are altered 1.
• Understanding these physiological changes is crucial for interpreting cardiovascular measurements and distinguishing normal respiratory variations from pathological conditions 1.

Mechanism of Inspiration on Preload

The mechanism by which inspiration affects preload is complex and involves changes in Ppl, TP, and venous return.

• The decrease in Ppl during inspiration increases venous return to the RV, enhancing RV filling and preload 1.
• However, the expanded lungs during inspiration can compress the heart, particularly affecting the thin-walled right ventricle, which can slightly impede right ventricular filling despite the overall increase in venous return 1.
• The effects of inspiration on LV preload are opposite, with the decreased venous return reducing LV filling and preload 1.

Clinical Implications

The effects of inspiration on preload have significant clinical implications, particularly in patients with cardiovascular or respiratory diseases.

• Understanding these effects is essential for correctly interpreting cardiovascular measurements and distinguishing normal respiratory variations from pathological conditions 1.
• In patients with conditions like ARDS, the altered lung compliance and vascular resistance can lead to significant changes in preload and cardiac function during inspiration 1.

From the FDA Drug Label

The principal pharmacological action of Nitroglycerin Injection is relaxation of vascular smooth muscle and consequent dilatation of peripheral arteries and veins, especially the latter Dilatation of the veins promotes peripheral pooling of blood and decreases venous return to the heart, thereby reducing left ventricular end-diastolic pressure and pulmonary capillary wedge pressure (preload).

The effect of inspiration on preload (ventricular filling) is not directly addressed in the provided drug label.

• The label discusses the effects of nitroglycerin on preload, but does not mention inspiration.
• Therefore, no conclusion can be drawn about the effect of inspiration on preload based on this information 2.

From the Research

Effect of Inspiration on Preload

The effect of inspiration on preload, specifically ventricular filling, can be understood through various studies.

• Inspiration increases right ventricular (RV) preload and left ventricular (LV) afterload during spontaneous breathing 3.
• Mechanical ventilation with positive pressure reduces LV preload and afterload 3.
• The right ventricle is highly sensitive to small loading changes during inspiration, and both RV preload and afterload are altered during inspiration 4.
• Venous return, a contributor to RV preload, may change in opposite directions according to the type of ventilation (spontaneous or assisted) 4.

Mechanisms of Inspiration

The mechanisms of inspiration that modulate cardiovascular control are complex.

• Large reductions in intrathoracic pressure (>20 cmH2O) caused by some inspiration maneuvers or pathophysiology can result in adverse hemodynamic effects 5.
• However, the respiratory pump can improve cardiovascular functions when a "sweet spot" for generation of negative intrathoracic pressure during inspiration can be maintained at or less than 10 cmH2O below normal inspiration 5.
• This can result in greater cardiac filling and output, lower intracranial pressure, cardiac baroreflex resetting, and greater cerebral blood flow oscillatory patterns 5.

Clinical Implications

Understanding the effects of inspiration on preload has important clinical implications.

• In patients with heart failure, preload augmentation may precipitate heart failure decompensation 6.
• Preload reduction therapies, including splanchnic nerve modulation and pharmacological interventions, may be used to prevent heart failure decompensation 6.
• The goal of treatment is to optimize hemodynamic status, decrease biventricular filling pressures, and improve morbidity and reduce risk for readmission 7.