Topographic distribution of pulmonary ventilation and perfusion in the horse.

The study analyzed the distribution of breathing and blood flow in the lungs of healthy Thoroughbred horses, finding uniformity within a particular lung segment and an increase in ventilation rate from non-dependent to dependent lung regions matching a similar blood flow gradient.

Study Purpose and Methodology

• This research investigates the distribution of ventilation to perfusion ratios (VA/Q), where ventilation refers to air movement in and out of the lungs, and perfusion refers to blood flow to the lungs. It is primarily studied in a specific segment (strip) of the lungs in healthy Thoroughbred geldings.
• This study was conducted using a steady-state process involving the inhalation and intravenous infusion of the radioactive gas krypton-81m. Krypton-81m is often used as a tracer in medical imaging to measure regional lung function.

Findings and Observations

• The study found that the ventilation to perfusion ratio is uniformly distributed within a vertical lung strip located over the 9th rib on the horse’s right side. This area is likely chosen due to its central location in the lung, facilitating ease of comparative study.
• The ventilation per unit of alveolar volume (V/VA), which was measured from the clearance of the inhaled radioactive gas in five horses, increases from non-dependent lung zones to the dependent lung zones. Alveolar volume refers to the space in the lungs where gas exchange occurs, and this increase implies a gradient of ventilation in the horse’s lungs.

Concluding Remarks

• From the research, it is evident that a vertical gradient of pulmonary ventilation exists in horses. This gradient matches a similarly observed gradient of blood flow (perfusion). In other words, as the horses breathe more deeply or heavily (ventilation increases), there’s also an increase in the blood flow to the lungs (perfusion increases), thereby providing an efficient gas exchange system.