Loss of distensibility of the pulmonary vasculature may be a marker that allows earlier detection of impending pulmonary hypertension, based on hemodynamic data from the medical records of 90 patients across the spectrum of pulmonary vascular disease.
Normal pulmonary circulation is distensible, allowing distension and recruitment of the pulmonary vasculature during exertion that in turn reduces pulmonary vascular resistance. Loss of this distensibility increases resistance and thus pulmonary arterial pressure, and is a characteristic of mild pulmonary vascular disease. Such disease is a precursor of full-blown pulmonary hypertension (PH), which “is a relatively late hemodynamic event in the evolution of pulmonary vascular disease,” said Dr. Edmund M. T. Lau of Université Paris-Sud, and his associates.
The percentage change in vascular diameter per mm Hg increase in distending pressure has been proposed for estimating the distensibility of resistive pulmonary vessels. This “distensibility value” has been assessed in animal studies and in healthy human subjects, but has not yet been assessed as a possible marker of mild pulmonary vascular disease or PH.
The researchers assessed this distensibility value in 31 patients with PH, 33 with mild pulmonary vascular disease but no PH as yet, and 26 control subjects with no pulmonary vascular disease. The data were obtained from the medical records of these patients, who had undergone right-sided heart catheterization, both at rest and during exercise, over a 6-year period.
The percentage change in vascular diameter per mm Hg increase in distending pressure was “strikingly reduced” (0.45%/mm Hg) in the mild pulmonary vascular disease group compared with the control group (1.4%/mm Hg). As expected, the group with PH had the lowest distensibility value, at 0.25%/mm Hg.
Using a cutoff value of 0.76%/mm Hg allowed the researchers to distinguish control subjects from patients with mild disease with a sensitivity of 88% and a specificity of 100%. “To our knowledge, this is the first study to validate the fit of [this] model in subjects with pulmonary vascular disease and to demonstrate that [percentage change in vascular diameter per mm Hg increase in distending pressure] is dramatically reduced in patients who have mild pulmonary vascular disease without manifest PH.
“Taken together, our findings suggest that vascular distensibility is markedly attenuated prior to the development of PH and that [this value] may serve as a useful vascular index in the setting of early disease detection,” Dr. Lau and his associates said (CHEST 2016;149:353-61).
The distensibility value calculated for this study’s control group (1.4%/mm Hg) was slightly lower than that reported in the literature for normal, healthy subjects and in vitro animal vessels (2%/mm Hg). That is likely because the control participants were older than the subjects in previous studies, and vascular distensibility is known to decrease with increasing age, the researchers said.
They added that it might be useful to calculate the distensibility value when patients suspected of having pulmonary vascular disease undergo invasive pulmonary hemodynamic evaluations. “It would be of particular interest to assess [it] in populations at a high risk of developing PH, such as carriers of the BMPR2 mutation and patients with systemic sclerosis.”
Obviously, estimating the distensibility value using noninvasive evaluation would be preferable, the researchers noted. Preliminary studies of healthy control subjects and carriers of the BMPR2 mutation undergoing stress ECG testing have shown that calculating the distensibility value is feasible using Doppler echocardiography data, they added.
This study was supported by Fonds de Dotation Recherche en Santé Respiratoire, Fondation du Souffle, and the INSERM–University of Sydney Exchange Grant. Dr. Lau reported having no relevant financial disclosures; his associates reported ties to Actelion, Aires, Bayer, Bristol-Myers Squibb, GlaxoSmithKline, Novartis, Pfizer, and United Therapeutics Corporation.