Blood Shift During Cough: Negligible or Significant?

Area of Science:

• Cardiovascular Physiology
• Respiratory Mechanics
• Emergency Medicine

Background:

• Rhythmic coughing can generate blood flow during ventricular fibrillation, acting as a form of cardiac massage via intrathoracic and intra-abdominal pressure changes.
• Previous research demonstrated significant blood shifts (BS) from the thorax to extremities during expulsive maneuvers, with abdominal pressure regulating splanchnic blood outflow (abdominal circulatory pump).

Purpose of the Study:

• To investigate if coughing activates the abdominal circulatory pump, providing additional circulatory output to maintain consciousness in individuals with a non-beating heart.
• To quantify blood shifts during voluntary coughs at varying lung volumes.

Main Methods:

• Seven healthy subjects performed voluntary coughs at three lung volumes: tidal, intermediate, and total lung capacity (TLC).
• Blood shifts (BS) from thorax to extremities were measured using double body plethysmography (DBP) during quiet breathing and coughing.
• Comparisons were made between BS during quiet breathing and coughing at different operating lung volumes.

Main Results:

• Blood shifts during coughing were significantly higher than during quiet breathing (p < 0.05).
• During the expulsive phase, BS increased with operating lung volume, reaching nearly 700 ml at TLC and approximately 400 ml at lower volumes.
• The compressive phase showed an outflow of around 200 ml.

Conclusions:

• Deep, vigorous coughing activates both thoracic and abdominal pump mechanisms, influencing cardiopulmonary interactions.
• The thoracic pump facilitates pulmonary vein emptying into the left heart.
• The abdominal pump generates circulatory output from the splanchnic reservoir, potentially maintaining consciousness during unstable cardiac rhythms.