Cardiopulmonary response to exercise in patients with intrapulmonary vascular shunts

J Appl Physiol (1985). 1993 Jul;75(1):321-8. doi: 10.1152/jappl.1993.75.1.321.

Abstract

The majority of patients with intrapulmonary right-to-left shunting due to pulmonary arteriovenous malformations-exhibit good maximum exercise capacity (> 70% predicted) despite profound arterial oxygen desaturation. We studied seven such patients to assess tissue oxygen delivery during steady-state exercise. From rest to exercise [50 +/- 7 (SE) W] arterial saturation fell from 80 +/- 3 to 74 +/- 3%, and mean right-to-left shunt increased slightly from 31 +/- 4 to 34 +/- 5% (P = NS). Minute ventilation was high for oxygen uptake, and the ventilatory equivalent was raised (174 +/- 19% predicted) and was correlated with shunt size (r = 0.93). The majority of the patients maintained pulmonary alveolar blood flow within the predicted range for their power output, but total cardiac output was increased to 142 +/- 11% predicted due to flow through the shunt. Consequently, on exercise, oxygen delivery per unit oxygen consumption [2.3-3.3 (normal range 1.6-2.4)] and calculated mixed venous oxygen tension (27.0 +/- 0.8 Torr) were preserved. Arterial PCO2 rose on exercise by 2.8 +/- 1.2 Torr, in proportion to the ratio of flow through the shunt to total cardiac output (r = 0.73), but remained low (33.1 +/- 1.4 Torr) in absolute terms. The high cardiac output on exercise may be facilitated by a low pulmonary vascular resistance (0.33 +/- 0.08 mmHg.1-1.min, measured at rest), which may explain why exercise performance is better in these patients than in patients with equivalent hypoxemia from other causes.

MeSH terms

  • Adolescent
  • Adult
  • Arteriovenous Malformations / physiopathology*
  • Carbon Dioxide / blood
  • Cardiac Output / physiology
  • Exercise / physiology*
  • Female
  • Heart / physiopathology*
  • Hemodynamics / physiology
  • Humans
  • Lung / physiopathology*
  • Male
  • Middle Aged
  • Oxygen Consumption / physiology
  • Pulmonary Circulation / physiology*
  • Pulmonary Gas Exchange / physiology
  • Respiratory Mechanics / physiology
  • Vascular Resistance / physiology

Substances

  • Carbon Dioxide