Patients with hypertension have elevated VE/VCO2 slope compared with age-matched normotensive controls, indicating ventilatory inefficiency during exercise. VE/VCO2 slopes may help identify increased cardiac risk in patients with hypertension, say the authors.
Ventilatory efficiency is assessed using the relationship between ventilation and carbon dioxide production (minute ventilation/volume of expired CO2 or VE/VCO2).
The VE/VCO2 slope is elevated in people with heart failure with preserved ejection, but it’s unclear whether it’s also elevated in people with primary hypertension.
The study included 55 patients with primary hypertension without heart failure and 24 participants with normal blood pressure who were matched for age, sex, body mass index, and cardiovascular fitness.
Participants completed ramped cardiovascular pulmonary exercise tests to peak oxygen consumption on a bike ergometer. VE/VCO2 slope was calculated throughout, and blood pressure was measured every 1 to 2 minutes.
When grouped by a suggested slope classification, only 27.3% of participants with hypertension had a normal value (VE/VCO2 slope of 20–30), compared with 70.8% of normotensive individuals.
The VE/VCO2 slope was higher in the hypertensive group compared with the control group (31.8 vs 28.4; P = .002).
Peak breathing frequency was elevated in individuals with hypertension (34 vs 31 breaths/min; P = .048), but peak end tidal carbon dioxide was lower in patients with hypertension than in normotensive individuals, with no difference in peak end tidal oxygen.
As for subgroups, the VE/VCO2 slope was higher in untreated and treated-controlled hypertensive individuals than in normotensive individuals; in the treated-uncontrolled group, there was no difference.
Adding this noninvasive measure might be useful in the future for risk stratification and for making treatment decisions, the authors conclude.
The study was conducted by Katrina Hope, BMedSci, BMBS, Bristol Heart Institute CardioNomics Research Group, University of Bristol, United Kingdom, and colleagues. It was published online June 22 in the Journal of the American Heart Association.
Further work is needed to understand the underlying cause of the elevated slope ― for example, whether ventilation/perfusion mismatching is attributable to elevated pulmonary pressure, cardiac dysfunction, or ventilatory limitation.
The study was supported by the British Heart Foundation, the National Institute for Health and Care Research Biomedical Research Centre, the James Tudor Foundation, the Health Research Council of New Zealand, and the Sidney Taylor Trust. The authors have disclosed no relevant conflicts of interest.
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