Cardiopulmonary response to exercise in patients with intrapulmonary vascular shunts

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.

Cardiopulmonary Exercise Testing Demonstrates Maintenance of Exercise Capacity in Patients With Hypoxemia and Pulmonary Arteriovenous Malformations

“…Insights into why PAVM patients differ to other hypoxemic respiratory patients are provided by exercise studies performed over 20 years ago. 3,6,7 While concepts are recognised in highly specialised circles, they do not seem to have been incorporated into general pulmonary practice. For example, currently, none of the 2,700 records retrieved through PubMed searches using "oxygen" and "guidelines" is retrieved adding "pulmonary arteriovenous malformation" or equivalent terms.…”

“…[14][15][16] In contrast, for PAVM patients, the absence of alveolar hypoxia/hypoxic pulmonary vasoconstriction, and PAVM-related structural alterations in the pulmonary vessels, mean that pulmonary vascular resistance at rest is low in severely hypoxemic patients. 3,6,7 The majority of PAVM patients have underlying hereditary hemorrhagic telangiectasia(HHT), 11,17,18 but overall, pulmonary hypertension is uncommon in PAVM/HHT patients. 12 When pulmonary hypertension does occur, 19,20 this results not from hypoxia, but from other pathophysiological processes, particularly pulmonary arterial hypertension, 12,[21][22][23][24] and pulmonary venous hypertension associated with hepatic AVMs and high outputs states.…”

Clinical and Molecular Genetic Features of Pulmonary Hypertension in Patients with Hereditary Hemorrhagic Telangiectasia

“…14,30 In contrast, primary pulmonary hypertension is characterized by obliteration of small pulmonary arteries, leading to increased pulmonary vascular resistance, marked elevation of pulmonary arterial pressure, and ultimately, a reduction in cardiac output. 1 We identified a total of 10 subjects with pulmonary hypertension from 5 families with hereditary hemorrhagic telangiectasia and 1 subject with no available family history.…”

Embolisation of pulmonary arteriovenous malformations: no consistent effect on pulmonary artery pressure

“…The reason this question is important is that for individuals with pulmonary AVMs, embolisation is an effective means of reducing lifetime risks of paradoxical embolic stroke and brain abscess [1,2], improving oxygenation [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and treating pulmonary AVM-related haemoptysis [18,19]. Conversely, embolisation may be expected to elevate pulmonary artery pressure (Ppa), since pulmonary AVMs are abnormal dilated vessels between pulmonary arteries and veins that provide low resistance pathways for pulmonary blood flow [20].The question of whether pulmonary AVM embolisation increases Ppa is particularly pertinent, since most individuals with pulmonary AVMs have underlying hereditary haemorrhagic telangiectasia (HHT). Typically recognised by nosebleeds, mucocutaneous telangiectasia and visceral AVMs [21], HHT may be associated with PH [9,[22][23][24][25][26][27][28][29][30].…”