Respiratory changes in circulation and pulsus paradoxus
THE CONTEXT
Respiration changes blood flow through the right and left sides of the heart, producing normal variations in blood pressure, pulse rate and heart sounds.
Inspiration
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Falling intrathoracic pressure increases venous return to the right heart and increases right ventricular output.
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Increased capacitance of the pulmonary vascular bed sequesters blood in the lungs, reducing blood flow to the left ventricle and causing a slight fall in blood pressure.
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During inspiration, jugular venous pressure falls, blood pressure falls by up to 10 mmHg, and heart rate accelerates.
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The second heart sound splits: inspiration prolongs right ventricular ejection, delaying P2, and shortens left ventricular ejection, bringing A2 forward.
Expiration
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Venous return to the right heart and right ventricular output decrease, while venous return to the left heart and left ventricular output increase.
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Blood pressure and jugular venous pressure rise, heart rate slows, and the second heart sound fuses.
Pulsus paradoxus
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Pulsus paradoxus describes an exaggerated fall in blood pressure during inspiration. It occurs with severe airways obstruction due to asthma or chronic obstructive pulmonary disease and is also characteristic of cardiac tamponade.
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In cardiac tamponade, external pressure constrains cardiac filling. During inspiration, right ventricular compression impedes the normal increase in flow.
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The interventricular septum moves to the left, impairing left ventricular filling and cardiac output and producing an inspiratory blood pressure fall greater than 10 mmHg.
Electrical events identified on the accompanying ECG
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The P wave represents atrial depolarisation, the QRS complex represents ventricular depolarisation, and the T wave represents ventricular repolarisation.