Cardiopulmonary response to exercise in patients with intrapulmonary vascular shunts.
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.
Department of Medicine, Royal Postgraduate Medical School, Hammersmith Hospital, London, United Kingdom.
M K
MK
Whyte
J M
JM
Hughes
J E
JE
Jackson
A M
AM
Peters
S C
SC
Hempleman
D P
DP
Moore
H A
HA
Jones
D000293:Adolescent; D000328:Adult; D001165:Arteriovenous Malformations / Q000503:physiopathology*; D002245:Carbon Dioxide / Q000097:blood; D002302:Cardiac Output / Q000502:physiology; D015444:Exercise / Q000502:physiology*; D005260:Female; D006321:Heart / Q000503:physiopathology*; D006439:Hemodynamics / Q000502:physiology; D006801:Humans; D008168:Lung / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology; D011652:Pulmonary Circulation / Q000502:physiology*; D011659:Pulmonary Gas Exchange / Q000502:physiology; D015656:Respiratory Mechanics / Q000502:physiology; D014655:Vascular Resistance / Q000502:physiology
D002245:Carbon Dioxide