Cardio Exercise Test May Not Be Needed to Predict PH Outcomes

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by Steve Bryson, PhD |

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A passive leg raise is equally as effective as exercise in measuring pulmonary vascular distensibility, a physiological marker to predict outcomes in people with pulmonary hypertension (PH), a study suggests.

This finding is important for patients who cannot exercise or do not have access to clinical exercise facilities, the scientists noted.

The study, “Pulmonary vascular distensibility with passive leg raise is comparable to exercise and predictive of clinical outcomes in pulmonary hypertension,” was published in the journal Pulmonary Circulation.

Pulmonary vascular distensibility (PVD) is the ability of the blood vessels in the lungs to widen in response to increases in the amount of blood the heart pumps. It protects the right ventricle of the heart, which pumps blood through the lungs, from potentially damaging high blood pressures.

In PH, which is characterized by high blood pressure in the pulmonary arteries, PVD is reduced, impairing exercise ability and putting extra strain on the right ventricle.

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PVD measured during cardiopulmonary exercise testing has been used to predict outcomes in PH and heart failure cases. However, not all patients with PH are willing or able to exercise.

A passive leg raise (PLR) is a simple body motion that shifts blood from the lower extremities back to the heart, increasing pressure.

Researchers at the University of Wisconsin–Madison wondered if PVD could be measured during a passive leg raise rather than exercise to help those unable to exercise or access facilities with exercise testing.

“Here, we sought to determine whether distensibility calculated with a PLR maneuver was comparable to distensibility calculated with exercise,” the team wrote.

Among the 50 people (46% female) PH patients enrolled, 10 were diagnosed with pulmonary arterial hypertension (PAH), caused by the narrowing of the pulmonary arteries (pre-capillary).

Eighteen participants had pulmonary venous hypertension (isolated post-capillary, Ipc-PH) due to the heart being unable to carry blood away from the lungs, triggered by conditions affecting the left side of the heart.

The remaining 15 patients had a combination of pre- and post-capillary features (Cpc-PH). Seven individuals with no significant PH were included as a control group.

Patients presented with shortness of breath upon exertion at the clinic and a median New York Health Association (NYHA) class 3 severity — symptoms occurring with light activity.

The team measured the blood pressure parameters of participants at rest, during a passive leg raise, and a cardiopulmonary exercise test. PAH participants received medicines that dilate blood vessels (vasodilators) after exercise.

As expected, during both the leg raise and exercise, the Ipc-PH and Cpc-PH groups had the highest pulmonary capillary wedge pressure (PCWP), a measure of pressure on the left side of the heart.

In the control group, the cardiac output — the amount of blood the heart pumps per minute — was 2.5-times higher during exercise than at rest. In contrast, the PH patients were unable to double their cardiac output with exercise.

PVD was defined as the percent increase in small pulmonary arteries’ diameter per increase in pressure (mmHg) and calculated from measurements of PCWP, cardiac output, mean pulmonary artery pressure (mPAP), and the total pulmonary resistance (TPR), the ratio of mPAP to cardiac output.

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Overall, there was no significant difference in PVD measured during the passive leg raise or exercise. Moreover, PVD during exercise was correlated linearly with PVD during the passive leg raise across all groups.

According to the researchers, the lack of difference between PVD measured by either method indicated that the response of blood circulation in the small pulmonary arteries to increased blood flow during passive leg raise is the same as more blood flow during exercise.

Consistently, during exercise and passive leg raise, the PVD was reduced significantly in PH patients compared to controls. PVD also was lower in PAH individuals than the Ipc-PH and control groups.

To examine survival from adverse outcomes, such as cardiovascular death or hospitalization, within one year after the exercise study, the team divided the patients into two groups: those with a PVD less than 0.7%, and the rest with a PVD of 0.7% or more. Of note, in healthy individuals, the increase in PVD is 1.5% to 2% per mmHg during exercise.

Survival analysis revealed that individuals with a PVD of 0.7% or higher during the passive leg raise or exercise had reduced cardiovascular death and hospital admissions. The rate of adverse outcomes and the median survival were similar in PVD, whether measured during the leg raise or exercise.

Among patients with a PVD of 0.7% or higher, none died, and one individual was admitted to the hospital due to a cardiovascular symptom. In contrast, two died, and five were hospitalized for cardiovascular indications in the group with a PVD of less than 0.7%.

Finally, the median survival following cardiovascular-related events was longer in those with a high PVD than a low PVD (11.9 vs. 10.2 months).

“In summary, this study shows that pulmonary vascular distensibility can be measured via PLR and may provide prognostic information similar to distensibility with exercise,” the investigators wrote. “This finding is clinically important for subjects who are unable to exercise and/or for clinicians who do not have exercise cardiac catheterization facilities.”

“Future studies are needed to validate these findings on a larger scale and different disease [manifestations] and severity,” they added.