Relationship of carbon dioxide tension in arterial blood to pulmonary wedge pressure in heart failure

Hypocapnia contributes to the genesis of Cheyne-Stokes respiration and central sleep apnoea in patients with congestive heart failure (CHF) and is associated with increased mortality. However, the cause of hypocapnia in patients with chronic stable CHF is unknown. Since pulmonary congestion can induce hyperventilation via stimulation of pulmonary vagal afferents, the present study tested the hypothesis that in patients with CHF (carbon dioxide tension in arterial blood (Pa,CO2)) is inversely related to pulmonary capillary wedge pressure (PCWP), and that alterations in PCWP would cause inverse changes in Pa,CO2. In 11 CHF patients undergoing diagnostic cardiac catheterization, haemodynamic variables and arterial blood gas tensions were measured simultaneously at baseline. In three patients, these measurements were repeated after coronary angiographic dye infusion and nitroglycerine infusion. At baseline, Pa,CO2 correlated inversely with PCWP (r=-0.80, p=0.003). In the three patients in whom multiple measurements were made, acute alterations in PCWP caused inversely proportional changes in Pa,CO2. The present study concludes that in patients with congestive heart failure, pulmonary capillary wedge pressure is an important determinant of carbon dioxide tension in arterial blood. These findings imply that hypocapnia in patients with chronic stable congestive heart failure is a respiratory manifestation of elevated left ventricular filling pressures.