The main error in figure 1 in the article¹ is that the authors have the ventilation triangle upside down.

They use triangles to represent the vertical gradients for ventilation and for perfusion in the erect lung. They correctly indicate that perfusion is higher at the base than at the apex in the erect lung. However, their ventilation triangle indicates that ventilation is higher at the apex than at the base. This is wrong as the reverse is the true situation: ventilation is higher at the base. 

This is a point that is commonly misunderstood. What is higher at the apex is the ventilation:perfusion ratio because the perfusion gradient decreases more rapidly than the ventilation gradient as you move up the erect lung.

The authors have since stated that what they meant to indicate was the gradient for alveolar size which is a conveniently correct post-hoc justification.

Congratulations to Leo O'Shea (Qld) responded with a correct response to this problem. Part of his email: 

"The consequence of perfusion increasing from apex to base at a greater rate than ventilation increases from apex to base, is a decreasing V/Q ratio. Typically ~3.3 at apex to 0.6 at base." 

1. Wahba RW & Tessler MJ Misleading end-tidal CO2 tensions. Canadian Journal of Anaesthesia. 1996; 43(8):862-866.