Authored by Phillip J Camp*
Abstract
Background: It is well known that obstructive sleep apnea (OSA) prevalence increases as body mass index (BMI) increases. Patients with OSA experience nocturnal apnea episodes which can result in hypoxemia, transient elevation of right atrial pressures, and a possible increase in right to left shunting. As such, OSA diagnosis and therapy may be tailored to address right-to-left shunting in these patients. Whether the prevalence of PFO in OSA patients is or is not increased, it may be appropriate to include transthoracic echocardiography (TTE) testing as a component of routine evaluation of patients with OSA.
Objectives: We hypothesize that patients with hypoxemia related to OSA are more likely to have a PFO than those patients with OSA without hypoxemia.
Methods: 80 patients with OSA verified by 4 different criteria were referred for TTE by the UNM Sleep Center. All patients underwent saline contrast TTE. The prevalence of PFO in our general echo population was calculated over the last year for comparison.
Results: Of 80 patients with varying degrees of OSA, ten (12.5%) had right to left shunting. PFO was not statistically associated with any AHI (Apnea Hypopnea Index). The only statistically significant association was between OSA and BMI (p<0.001). The prevalence of PFO in the control group was found to be 12.2%.
Conclusions: In contrast to previous studies, there was no association between OSA of any severity and PFO in our study population. There however was a statistically significant association between OSA and BMI.
Abbreviations: PFO: Patent Foramen Ovale; OSA: Obstructive Sleep Apnea; TTE: Transthoracic Echocardiogram; BMI: Body Mass Index; AHI: Apnea Hypopnea Index
Introduction
The epidemic of obesity has been well documented. Over 65 percent of U.S. adults are either overweight or obese [1]. Twenty percent of those overweight with a mean body mass index (BMI) of 25 to 28 have been estimated to have mild obstructive sleep apnea (OSA), and 6 percent of the overweight have been estimated to have at least moderate OSA [2]. Further supporting the link between obesity and OSA is the Wisconsin trial which showed that weight loss decreased the severity of OSA.2 However, not all patients with OSA are obese and it is estimated in the general population that 4% of middle aged men and 2% of middle aged women have OSA [3]. OSA has been demonstrated to produce significant adverse health consequences including development of systemic hypertension; increased risk of myocardial infarction; increased insulin resistance; and particularly relevant for the present study, an increased risk of stroke [4]. Patent foramen ovule (PFO) is a prevalent condition found in approximately 20 percent of adults on autopsy [5]. Shunting of venous blood across a PFO occurs when there is a higher right atrial than left atrial pressure and may result in paradoxical emboli [6,7]. Patients with OSA experience nocturnal apnea episodes which can result in systemic arterial oxyhemoglobin desaturation and transient elevation of right atrial pressures. In the presence of complicating cardiopulmonary conditions, there may be persistent pulmonary hypertension. Transesophageal echocardiography (TEE) is thought to be the gold standard for detection of PFO, however, it is semi-invasive and in the sedated patient makes detecting right-to-left shunting more difficult due to the lack of ability to perform the Valsalva maneuver [9]. A study by Lam, et al. in 2011 showed that there was no significant difference in sensitivities between TEE and TTE in detection of PFO when the Valsalva maneuver was employed [9]. Further supporting TTE in screening for PFO is a study which did not show any significant difference in detection of PFO between TTE and TEE [10]. Our hypothesis is there is a correlation between OSA and PFO and that OSA diagnosis and therapy may be tailored to better address potential right-to-left shunting. We believe that available data support routine TTE evaluation of patients with OSA with high proportional desaturation for PFO.
Methods
Study population
The study was reviewed and approved by the Institutional Review Board at the University Of New Mexico School Of Medicine in Albuquerque New Mexico. The sample included 97 patients (Figure 1). Patients were included if they had documented obstructive sleep apnea by overnight sleep study conducted at the University of New Mexico Sleep Center. Patients then underwent a saline agitated contrast transthoracic echocardiogram to evaluate for the presence of a PFO. Over the last year, 2,686 patients in the general population of patients were referred for TTE with saline bubble study. A random number generator was used (random.org) to select a frequency matched sample (4:1) to serve as the control group. The first 320 patients were selected in order of randomization.
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