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Pulmonary Circulation at Exercise

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Abstract

The pulmonary circulation is a high‐flow and low‐pressure circuit, with an average resistance of 1 mmHg/min/L in young adults, increasing to 2.5 mmHg/min/L over four to six decades of life. Pulmonary vascular mechanics at exercise are best described by distensible models. Exercise does not appear to affect the time constant of the pulmonary circulation or the longitudinal distribution of resistances. Very high flows are associated with high capillary pressures, up to a 20 to 25 mmHg threshold associated with interstitial lung edema and altered ventilation/perfusion relationships. Pulmonary artery pressures of 40 to 50 mmHg, which can be achieved at maximal exercise, may correspond to the extreme of tolerable right ventricular afterload. Distension of capillaries that decrease resistance may be of adaptative value during exercise, but this is limited by hypoxemia from altered diffusion/perfusion relationships. Exercise in hypoxia is associated with higher pulmonary vascular pressures and lower maximal cardiac output, with increased likelihood of right ventricular function limitation and altered gas exchange by interstitial lung edema. Pharmacological interventions aimed at the reduction of pulmonary vascular tone have little effect on pulmonary vascular pressure‐flow relationships in normoxia, but may decrease resistance in hypoxia, unloading the right ventricle and thereby improving exercise capacity. Exercise in patients with pulmonary hypertension is associated with sharp increases in pulmonary artery pressure and a right ventricular limitation of aerobic capacity. Exercise stress testing to determine multipoint pulmonary vascular pressures‐flow relationships may uncover early stage pulmonary vascular disease. © 2012 American Physiological Society. Compr Physiol 2:711‐741, 2012.

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Figure 1. Figure 1.

Starling resistor model to explain the concept of closing pressure within a circulatory system. Flow (Q) is determined by the gradient between an inflow pressure, or mean pulmonary artery pressure (Ppa), and an outflow pressure which is either closing pressure (Pc) or left atrial pressure (Pla). When Pla > Pc, the (Ppa–Pla)/Q relationship crosses the origin (A curve) and PVR is constant. When Pc > Pla, the (Ppa–Pla)/Q relationship has a positive pressure intercept (B and C curves), and PVR decreases curvilinearly with increasing Q. The B and C curves are curvilinear a low flow representing recruitment. Also shown are possible misleading PVR calculations: PVR, the slope of (Ppa–Pla)/Q may remain unchanged in the presence of a vasoconstriction (from 1 to 2) or decrease (from 1 to 3) with no change in the functional state of the pulmonary circulation (unchanged pressure/flow line). Adapted from reference . Permission pending.

Figure 2. Figure 2.

Mean pulmonary artery pressure (Ppa) as a function of cardiac output (Q) at constant left atrial pressure (Pla), left panel, and Ppa as a function of Pla at constant Q in an anesthetized dog before (stippled line) and after (full line) injection of oleic acid (OA) to produce an acute lung injury. Lung injury was associated with a shift of linear Ppa‐Q relationships to higher pressures, with increased extrapolated pressure intercept (small stipple line). Pla was transmitted to Ppa in a close to 1:1 relationship before oleic acid, but only at a pressure equal to the extrapolated pressure intercept of Ppa‐Q after oleic acid, which is compatible with an increased closing pressure becoming the effective downstream pressure of the pulmonary circulation. Adapted, with permission, from reference .

Figure 3. Figure 3.

Pressure‐flow relationships of an isolated perfused mouse lung before (empty sqares) and after (full squares) embolization. The shape of the multipoint pressure‐flow relationship is increasingly curvilinear at decreasing flow. Extrapolated pressure intercept from best adjustments on “physiological” values for pressure and flow leads to spurious estimations of increased closing pressures. Adapted, with permission, from reference .

Figure 4. Figure 4.

Pulmonary vascular impedance spectra in a dog, at rest and running. Running was associated with a decrease in 0 Hz impedance, but an increase in the ratio of pressure and flow moduli (in dyne/s/cm5) at all frequencies, and a decrease in low‐frequency phase angle, suggestive of decreased proximal compliance of the pulmonary arterial tree. Drawn, with permission, after reference .

Figure 5. Figure 5.

Effects of exercise (shaded columns) on pulmonary vascular resistance (PVR), characteristic impedance (Zc), and arterial compliance (Ca) in healthy human subjects. Exercise decreased PVR and increased Ca, while there was no significant change in Zc. Drawn, with permission, from data in reference .

Figure 6. Figure 6.

Effects of increasing levels of exercise in the supine and in the sitting position on mean ± SD (vertical bars) pulmonary vascular resistance (PVR, Wood units or mmHg/L) in healthy volunteers. Initial PVR was higher in the sitting position, but otherwise PVR decreased slightly with increasing levels of workload, and this was similar in the supine and in the sitting positions. Redrawn, with permission, after reference .

Figure 7. Figure 7.

Rapid recovery of mean pulmonary artery pressure (mPpa) and cardiac output (Q) after maximal exercise. Values are reported as mean ± SD (vertical bars). *P< 0.05 compared to resting baseline. After 20 min, Q is still higher than resting baseline. Drawn from reference , permission pending.

Figure 8. Figure 8.

Linear relationship between mean pulmonary artery pressure (Ppam) and cardiac output (Q) in 25 healthy subjects during progressively severe exercise until maximum tolerated. The slope of PpamQ was 1.37 mmHg/L/min. Adapted from reference . Permission pending.

Figure 9. Figure 9.

Mean ± SD (vertical bars) values of mean pulmonary artery wedge pressure (Ppw) and right atrial pressure (Pra) as a function of cardiac output (Q) during progressive exercise in normal volunteers, left panel, and Ppw versus Pra of the same subjects, right panel. Both Ppw and Pra increase with Q, but the gradient between the pressures tended to increase. The right panel shows that Ppw is correlated to Pra, but is higher than Pra by 5 mmHg at rest, and this increases with a slope of 1.49 mmHg increase in Ppw for every mmHg increase of Pra at exercise. Adapted, with permission, from references and .

Figure 10. Figure 10.

Mean ± SD (vertical bars) values of mean pulmonary artery pressure (Ppa) and wedged Ppa (Ppw) as a function of cardiac output (Q) during progressive exercise in normal volunteers, left panel, and Ppa versus Prw of the same subjects, right panel. Both Ppa and Ppw increase with Q, but the gradient between the pressures tends to remain unchanged. The left panel shows that Ppa is correlated to Prw, but is higher than Ppw by 9 mmHg at rest, and this increases with a slope of 1.1 mmHg increase in Ppa for every mmHg increase of Ppw at exercise. Adapted, with permission, from references and .

Figure 11. Figure 11.

Individual mean ± SE values of pulmonary artery wedge pressure (Ppw) as a function of cardiac output (Q) in subjects with a low (untrained) versus a high exercise capacity (trained). The increase in Ppw was delayed until higher Q in the fittest subjects, suggesting improved ventricular compliance. Adapted, with permission, from reference .

Figure 12. Figure 12.

Predicted minus measured mean pulmonary artery pressure (Ppa) as a function of mean Ppa in healthy exercising volunteers. The stippled line shows 2 SD, which is equal to 1.7 mmHg. This presentation is suggestive of a good agreement. The prediction of Ppa was obtained using the distensibility model of Linehan. Adapted, with permission, from reference .

Figure 13. Figure 13.

Mean values for pulmonary artery pressure (Ppa) and pulmonary artery wedge pressure (Ppw) as a function of cardiac output (Q) in exercising horses. Exercise in horses is associated with marked increases in pulmonary vascular pressures. Adapted, with permission, from reference .

Figure 14. Figure 14.

Relation of pulmonary carbon monoxide diffusion capacity (DLCO) to pulmonary blood flow (Q) at increasing levels of exercise. DLCO increases in proportion of Q, even in Olympic cyclists with very high Q. Adapted, with permission, from references and .

Figure 15. Figure 15.

Echocardiographic apical 4 chamber views at rest (left panel) and at exercise (middle and right panels) after the injection of agitated contrast, showing appearance in the left heart chambers after 4 to 5 beats at moderate exercise, and more so at intense exercise. Courtesy of A La Gerche.

Figure 16. Figure 16.

Curvilinear relationships between mean pulmonary artery pressure (PPA) and arterial oxygen saturation (SaO2) in healthy highlanders (empty symbols) and highlanders with chronic mountain sickness (full symbols), left palel, and between mean pulmonary artery pressure (PPA) and altitude of locations (right panel). Extremes are observed in Lhasa and in Leadville. Hypoxia is a major determinant of Ppa, but there is ethnic variability. Adapted from reference . Permission pending.

Figure 17. Figure 17.

Mean pulmonary artery pressure (Ppa) as a function of cardiac output (Q) at exercise in healthy subjects at sea level, barometric pressure (Pb) 760 mmHg, and after acclimatization at two levels of simulated altitudes. Baseline Ppa and the slope of Ppa‐Q increase with altitude. Adapted, with permission, from reference .

Figure 18. Figure 18.

Averaged mean pulmonary artery pressures (Ppa) versus indexed cardiac output (Q) plots measured invasively (cardiac cath, full lines) or noninvasively (echo‐Doppler, stippled lines) in highlanders exercising at high altitude and in lowlanders exercising at sea leve. From references , with indications of names of first authors in the figure. With the exception of Tibetans in lhasa, highlanders present with higher resting Ppa and increased slopes of Ppa‐Q. Slopes of Ppa‐Q are particularly steep on patients with chronic mountain sickness (CMS). Courtesy of Dante Penaloza.

Figure 19. Figure 19.

Correlation between hypoxia‐induced increase in mean pulmonary artery pressure (Ppam) and decrease maximal oxygen uptake ( o2 max) in healthy volunteers in either acute normobaric or more chronic hypobaric hypoxic conditions. Adapted from reference . Permission pending.

Figure 20. Figure 20.

Two‐point mean pulmonary artery pressure (Ppa) cardiac output (Q) plots in normal subjects (N), or patients with mitral stenosis (MS), acute respiratory distress syndrome (ARDS), chronic obstructive pulmonary disease (COPD), left ventricular failure (LVF), and pulmonary arterial hypertension (PAH). All Ppa‐Q plots are shifted upward to higher pressure with an increased extrapolated pressure intercept (stippled lines). Left atrial pressure was equal to the extrapolated pressure intercept in LVF. Constructed, with permission, with mean data reported in references .

Figure 21. Figure 21.

Plots of mean pulmonary artery pressure (Ppa) as a function cardiac output (Q) in patients with idiopathic pulmonary arterial pressure, with Q increased at exercise or by an infusion of low‐dose dobutamine. The slope of Ppa‐Q was higher with exercise. Adapted from reference . Permission pending.



Figure 1.

Starling resistor model to explain the concept of closing pressure within a circulatory system. Flow (Q) is determined by the gradient between an inflow pressure, or mean pulmonary artery pressure (Ppa), and an outflow pressure which is either closing pressure (Pc) or left atrial pressure (Pla). When Pla > Pc, the (Ppa–Pla)/Q relationship crosses the origin (A curve) and PVR is constant. When Pc > Pla, the (Ppa–Pla)/Q relationship has a positive pressure intercept (B and C curves), and PVR decreases curvilinearly with increasing Q. The B and C curves are curvilinear a low flow representing recruitment. Also shown are possible misleading PVR calculations: PVR, the slope of (Ppa–Pla)/Q may remain unchanged in the presence of a vasoconstriction (from 1 to 2) or decrease (from 1 to 3) with no change in the functional state of the pulmonary circulation (unchanged pressure/flow line). Adapted from reference . Permission pending.



Figure 2.

Mean pulmonary artery pressure (Ppa) as a function of cardiac output (Q) at constant left atrial pressure (Pla), left panel, and Ppa as a function of Pla at constant Q in an anesthetized dog before (stippled line) and after (full line) injection of oleic acid (OA) to produce an acute lung injury. Lung injury was associated with a shift of linear Ppa‐Q relationships to higher pressures, with increased extrapolated pressure intercept (small stipple line). Pla was transmitted to Ppa in a close to 1:1 relationship before oleic acid, but only at a pressure equal to the extrapolated pressure intercept of Ppa‐Q after oleic acid, which is compatible with an increased closing pressure becoming the effective downstream pressure of the pulmonary circulation. Adapted, with permission, from reference .



Figure 3.

Pressure‐flow relationships of an isolated perfused mouse lung before (empty sqares) and after (full squares) embolization. The shape of the multipoint pressure‐flow relationship is increasingly curvilinear at decreasing flow. Extrapolated pressure intercept from best adjustments on “physiological” values for pressure and flow leads to spurious estimations of increased closing pressures. Adapted, with permission, from reference .



Figure 4.

Pulmonary vascular impedance spectra in a dog, at rest and running. Running was associated with a decrease in 0 Hz impedance, but an increase in the ratio of pressure and flow moduli (in dyne/s/cm5) at all frequencies, and a decrease in low‐frequency phase angle, suggestive of decreased proximal compliance of the pulmonary arterial tree. Drawn, with permission, after reference .



Figure 5.

Effects of exercise (shaded columns) on pulmonary vascular resistance (PVR), characteristic impedance (Zc), and arterial compliance (Ca) in healthy human subjects. Exercise decreased PVR and increased Ca, while there was no significant change in Zc. Drawn, with permission, from data in reference .



Figure 6.

Effects of increasing levels of exercise in the supine and in the sitting position on mean ± SD (vertical bars) pulmonary vascular resistance (PVR, Wood units or mmHg/L) in healthy volunteers. Initial PVR was higher in the sitting position, but otherwise PVR decreased slightly with increasing levels of workload, and this was similar in the supine and in the sitting positions. Redrawn, with permission, after reference .



Figure 7.

Rapid recovery of mean pulmonary artery pressure (mPpa) and cardiac output (Q) after maximal exercise. Values are reported as mean ± SD (vertical bars). *P< 0.05 compared to resting baseline. After 20 min, Q is still higher than resting baseline. Drawn from reference , permission pending.



Figure 8.

Linear relationship between mean pulmonary artery pressure (Ppam) and cardiac output (Q) in 25 healthy subjects during progressively severe exercise until maximum tolerated. The slope of PpamQ was 1.37 mmHg/L/min. Adapted from reference . Permission pending.



Figure 9.

Mean ± SD (vertical bars) values of mean pulmonary artery wedge pressure (Ppw) and right atrial pressure (Pra) as a function of cardiac output (Q) during progressive exercise in normal volunteers, left panel, and Ppw versus Pra of the same subjects, right panel. Both Ppw and Pra increase with Q, but the gradient between the pressures tended to increase. The right panel shows that Ppw is correlated to Pra, but is higher than Pra by 5 mmHg at rest, and this increases with a slope of 1.49 mmHg increase in Ppw for every mmHg increase of Pra at exercise. Adapted, with permission, from references and .



Figure 10.

Mean ± SD (vertical bars) values of mean pulmonary artery pressure (Ppa) and wedged Ppa (Ppw) as a function of cardiac output (Q) during progressive exercise in normal volunteers, left panel, and Ppa versus Prw of the same subjects, right panel. Both Ppa and Ppw increase with Q, but the gradient between the pressures tends to remain unchanged. The left panel shows that Ppa is correlated to Prw, but is higher than Ppw by 9 mmHg at rest, and this increases with a slope of 1.1 mmHg increase in Ppa for every mmHg increase of Ppw at exercise. Adapted, with permission, from references and .



Figure 11.

Individual mean ± SE values of pulmonary artery wedge pressure (Ppw) as a function of cardiac output (Q) in subjects with a low (untrained) versus a high exercise capacity (trained). The increase in Ppw was delayed until higher Q in the fittest subjects, suggesting improved ventricular compliance. Adapted, with permission, from reference .



Figure 12.

Predicted minus measured mean pulmonary artery pressure (Ppa) as a function of mean Ppa in healthy exercising volunteers. The stippled line shows 2 SD, which is equal to 1.7 mmHg. This presentation is suggestive of a good agreement. The prediction of Ppa was obtained using the distensibility model of Linehan. Adapted, with permission, from reference .



Figure 13.

Mean values for pulmonary artery pressure (Ppa) and pulmonary artery wedge pressure (Ppw) as a function of cardiac output (Q) in exercising horses. Exercise in horses is associated with marked increases in pulmonary vascular pressures. Adapted, with permission, from reference .



Figure 14.

Relation of pulmonary carbon monoxide diffusion capacity (DLCO) to pulmonary blood flow (Q) at increasing levels of exercise. DLCO increases in proportion of Q, even in Olympic cyclists with very high Q. Adapted, with permission, from references and .



Figure 15.

Echocardiographic apical 4 chamber views at rest (left panel) and at exercise (middle and right panels) after the injection of agitated contrast, showing appearance in the left heart chambers after 4 to 5 beats at moderate exercise, and more so at intense exercise. Courtesy of A La Gerche.



Figure 16.

Curvilinear relationships between mean pulmonary artery pressure (PPA) and arterial oxygen saturation (SaO2) in healthy highlanders (empty symbols) and highlanders with chronic mountain sickness (full symbols), left palel, and between mean pulmonary artery pressure (PPA) and altitude of locations (right panel). Extremes are observed in Lhasa and in Leadville. Hypoxia is a major determinant of Ppa, but there is ethnic variability. Adapted from reference . Permission pending.



Figure 17.

Mean pulmonary artery pressure (Ppa) as a function of cardiac output (Q) at exercise in healthy subjects at sea level, barometric pressure (Pb) 760 mmHg, and after acclimatization at two levels of simulated altitudes. Baseline Ppa and the slope of Ppa‐Q increase with altitude. Adapted, with permission, from reference .



Figure 18.

Averaged mean pulmonary artery pressures (Ppa) versus indexed cardiac output (Q) plots measured invasively (cardiac cath, full lines) or noninvasively (echo‐Doppler, stippled lines) in highlanders exercising at high altitude and in lowlanders exercising at sea leve. From references , with indications of names of first authors in the figure. With the exception of Tibetans in lhasa, highlanders present with higher resting Ppa and increased slopes of Ppa‐Q. Slopes of Ppa‐Q are particularly steep on patients with chronic mountain sickness (CMS). Courtesy of Dante Penaloza.



Figure 19.

Correlation between hypoxia‐induced increase in mean pulmonary artery pressure (Ppam) and decrease maximal oxygen uptake ( o2 max) in healthy volunteers in either acute normobaric or more chronic hypobaric hypoxic conditions. Adapted from reference . Permission pending.



Figure 20.

Two‐point mean pulmonary artery pressure (Ppa) cardiac output (Q) plots in normal subjects (N), or patients with mitral stenosis (MS), acute respiratory distress syndrome (ARDS), chronic obstructive pulmonary disease (COPD), left ventricular failure (LVF), and pulmonary arterial hypertension (PAH). All Ppa‐Q plots are shifted upward to higher pressure with an increased extrapolated pressure intercept (stippled lines). Left atrial pressure was equal to the extrapolated pressure intercept in LVF. Constructed, with permission, with mean data reported in references .



Figure 21.

Plots of mean pulmonary artery pressure (Ppa) as a function cardiac output (Q) in patients with idiopathic pulmonary arterial pressure, with Q increased at exercise or by an infusion of low‐dose dobutamine. The slope of Ppa‐Q was higher with exercise. Adapted from reference . Permission pending.

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Robert Naeije, N. Chesler. Pulmonary Circulation at Exercise. Compr Physiol 2012, 2: 711-741. doi: 10.1002/cphy.c100091