GRENOBLE – Suffering from sleep-disordered breathing may affect the heart at a very early stage, French researchers report.

In the study published ahead of print in the European Respiratory Journal, almost one in four patients suffering from obstructive sleep apnoea also showed signs of diastolic dysfunction, reflecting an abnormal relaxation of the heart's left ventricle.

Obstructive sleep apnoea (OSA) is a condition characterised by multiple breathing pauses during sleep resulting in intermittent insufficient oxygen supply to the brain as well as a non-restorative sleep. Clinically, patients (or their partners) complain of marked snoring and excessive daytime sleepiness.

Recently, the disorder has been associated with an increased risk for cardiovascular disease and the development of diabetes. Patients suffering from episodes of OSA are not merely getting too little quality sleep; the intermittent lack of oxygen triggers a chain of biochemical events that puts them at risk for cardiovascular disease and interferes with their glucose metabolism.

As far as the heart is concerned, a disturbance in the so-called diastolic function, leading to heart failure, may correlate directly with the severity of oxygen desaturation, report Prof. Jean-Philippe Baguet, and colleagues of the department of Cardiology, University Hospital Grenoble, France.

The study included 150 newly diagnosed OSA patients without known cardiovascular disease.

OSA was evaluated either by full polysomnography (72%) or ventilation polygraphy, standard examination tools for the diagnosis of nocturnal respiratory arrest. These recordings allowed for the calculation of a respiratory disturbance index (RDI), an indicator of the severity of sleep-disordered breathing, taking into account the number of apnoeas and hypopnoeas per hour. In the study, the diagnosis of OSA syndrome was retained if the RDI > 15 per h.

The patients’ blood pressure, heart rate and oxygen saturation were measured, as well as standard blood chemistry.

Using cardiac ultrasound, the researchers were able to show that almost one-quarter of the patients had an abnormal relaxation of their left ventricle. Thirty-four  (22.7%) out of the 150 patients thus suffered from first-stage left ventricular diastolic dysfunction. Patients with an abnormal diastole tended to be older and 81% were hypertensive. In addition, the prevalence of nocturnal hypertension was higher in patients with impaired left ventricular diastolic function than in those with normal left ventricular function (80 versus 67%; p=0.042).

The only respiratory parameter independently associated with left ventricular diastolic abnormality was mean nocturnal oxygen saturation.
In addition, 13% of the patients had left ventricular hypertrophy which correlated with the systolic blood pressure and mean nocturnal oxygen saturation.
“Our findings demonstrate that left ventricular diastolic dysfunction frequently occurs in patients with OSA and that it is related to the severity of oxygen desaturation,” summarises Prof. Baguet.

Older patients suffering from important intermittent hypoxia during sleep are particularly vulnerable to this mechanism, indicating that age may increase the sensitivity to hypoxic episodes.

These findings have marked clinical relevance because OSA, a potential risk factor for cardiovascular disease, is a highly treatable condition.
“Morbidity and mortality in heart failure patients with preserved LV systolic function (i.e. diastolic dysfunction) is high and almost equals that of patients with a diagnosis of systolic heart failure,” concludes Prof. Baguet.

Reference:
Baguet JP et al. Eur Respir J. 2010 Jun 18. [Epub ahead of print]