Does blood pressure normally decrease during expiration in a healthy adult?

Blood Pressure Changes During Normal Respiration

No, blood pressure does not normally drop with expiration in healthy adults—it actually drops slightly during inspiration. In spontaneously breathing individuals, systolic blood pressure decreases by a small amount (typically <10 mmHg) during inspiration and returns to baseline or slightly increases during expiration 1, 2.

Normal Respiratory Physiology

During spontaneous inspiration:

• Pleural pressure becomes more negative (decreases), which increases the pressure gradient for venous return to the right ventricle 3
• Left ventricular afterload increases because intracavitary cardiac pressures are lowered relative to atmospheric pressure, requiring more force to maintain normal arterial pressure 3
• Systolic blood pressure decreases slightly (typically 3-10 mmHg) due to these combined effects 1, 2

During spontaneous expiration:

• Pleural pressure rises (becomes less negative or returns toward atmospheric pressure) 3
• The release of inspiratory effort produces a small expiratory rise in arterial pressure 3
• Systolic blood pressure returns to baseline or increases slightly 1

Clinical Context: Pulsus Paradoxus

The normal inspiratory drop in systolic blood pressure becomes pathological when it exceeds 10 mmHg, a condition called pulsus paradoxus 3, 2. This is defined as a drop in systolic blood pressure >10 mmHg during inspiration while diastolic blood pressure remains unchanged 3.

Key measurement technique:

• During sphygmomanometry, if pulsus paradoxus is present, the first Korotkoff sound is heard only during expiration 3
• As the cuff deflates, there is a point where sounds are audible during expiration but disappear during inspiration 3
• Further deflation reaches a point where sounds are audible throughout the respiratory cycle 3
• The difference between these two points quantifies the magnitude of pulsus paradoxus 3

Pathological conditions causing pulsus paradoxus:

• Cardiac tamponade (most important clinical application) 3, 2
• Severe acute asthma or COPD exacerbations where intrathoracic pressure swings are exaggerated 2
• Conditions with right ventricular distension 2

Mechanical Ventilation Reverses the Pattern

Important caveat: In mechanically ventilated patients, the pattern is reversed 1. During positive pressure ventilation:

• Systolic blood pressure is higher during inspiration than expiration 1
• This occurs because positive airway pressure increases pleural pressure during inspiration, which decreases left ventricular afterload but simultaneously decreases venous return 3
• The falling pleural pressure during expiration tends to decrease systemic arterial pressure 3

Hemodynamic Mechanisms

The inspiratory decrease in blood pressure during spontaneous breathing results from:

• Increased left ventricular outflow impedance as more negative intrathoracic pressure increases the pressure gradient the left ventricle must overcome 4
• Biventricular interdependence, where increased right ventricular filling during inspiration can decrease left ventricular diastolic distensibility through septal shift 2, 5
• Transient reduction in left ventricular stroke volume that occurs despite increased left atrial filling pressure 4

During expiration, blood pressure rises because:

• Left ventricular afterload decreases as pleural pressure becomes less negative 3
• The mechanical advantage for left ventricular ejection improves 3